Tribological Enhancement of Stir-Cast AA2219/TiC–Al₂O₃ - Si₃N₄ Hybrid Nanocomposites: Mechanism and Surface Layer Analysis

Tribological Enhancement of Stir-Cast AA2219/TiC–Al₂O₃ - Si₃N₄ Hybrid Nanocomposites: Mechanism and Surface Layer Analysis | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Tribological Enhancement of Stir-Cast AA2219/TiC–Al₂O₃ - Si₃N₄ Hybrid Nanocomposites: Mechanism and Surface Layer Analysis Chandramohan Devarajan, Dhanashekar Manikkam, Muneera Altayeb, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6987478/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract This work investigates the fundamental tribological behavior of stir-cast AA2219 aluminum alloy hybrid nanocomposites reinforced with TiC and Al₂O₃/Si₃N₄ nanoparticles. While traditional approaches emphasize property improvements, this study shifts focus toward understanding the mechanisms governing tribolayer formation, interfacial bonding, and thermomechanical interactions during dry sliding wear. Through pin-on-disc experiments (ASTM G99), SEM/EDS/XRD analyses, and statistical validation (ANOVA), the study uncovers how reinforcement-induced tribofilms stabilize sliding interfaces. The optimal composite (5 wt.% TiC + 3 wt.% Al₂O₃) showed a 69% reduction in wear rate, which correlates with dense, adherent tribolayer development. Over-reinforcement disrupted this tribofilm through nanoparticle agglomeration and third-body abrasion. Mechanistic interpretations—based on load transfer theory, dislocation pinning, and tribo-chemical layer evolution—reveal a reinforcement threshold critical for wear stability. This work contributes to tribology by providing insight into how ceramic hybrid nanoparticles influence interfacial stress distribution and tribofilm resilience, crucial for the design of tribo-functional aluminum composites. Hybrid nanocomposite Tribolayer wear resistance Coefficient of friction AA2219 TiC Al₂O₃ Stir casting Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 Figure 14 Highlights / Novel Contributions Hybrid AA2219/TiC-Al₂O₃-Si₃N₄ nanocomposites successfully fabricated via stir casting Optimal 5% TiC + 3% Al₂O₃ composition enhances tensile strength by ~26% Wear rate reduced by over 69% due to stable tribolayer at 3 wt.% Al₂O₃ SEM/EDS/XRD confirm uniform dispersion, grain refinement, and phase stability ANOVA confirms statistically significant improvements in hardness and wear resistance 1. Introduction 1.1 Background: In recent years, aluminum matrix composites (AMCs) have garnered significant attention due to their promising combination of lightweight properties, high strength-to-weight ratio, and excellent wear resistance, making them suitable for a broad spectrum of industrial applications, including automotive, aerospace, and structural components [ 2 ], [ 7 ]. Reinforcement of aluminum matrices with ceramic nanoparticles such as TiC, Al₂O₃, and Si₃N₄ has been extensively studied to further enhance their mechanical and tribological properties [ 3 ], [ 6 ], [ 10 ]. Among these, nano-sized reinforcements are particularly effective due to their high surface area, which facilitates grain refinement, dislocation pinning, and load transfer, leading to improved hardness, strength, and wear resistance [ 1 ], [ 14 ]. Among various performance metrics, the coefficient of friction (COF) plays a key role in energy dissipation, material loss, and thermal instability in structural contacts. COF reduction directly contributes to improved surface durability and reduced wear, making it a critical target for high-performance composite design. Hybrid reinforcements combining multiple ceramic phases aim to synergistically leverage their individual properties while mitigating their limitations, such as clustering or poor interfacial bonding [ 5 ], [ 11 ]. Despite these advances, achieving uniform dispersion and strong interfacial bonding of nano-ceramics within the metal matrix remains a critical challenge [ 4 ], [ 13 ]. Stir casting, recognized for its simplicity and cost-effectiveness, has been adapted for nano-reinforcement incorporation, yet issues like particle agglomeration and porosity persist [ 2 ], [ 12 ]. Most prior investigations have focused on the mechanical and wear characteristics of such composites, with limited exploration of their behavior under corrosive and tribo-corrosive conditions relevant to biomedical, marine, or environmental applications [ 9 ], [ 15 ]. Hybrid aluminum matrix composites (AMCs) exhibit complex tribological behaviors that stem from the interaction of reinforcement particles with matrix deformation mechanisms and tribochemical processes [ 7 ]. Beyond strength and hardness improvements, the fundamental mechanism of wear resistance lies in the evolution and stability of the tribolayer during sliding [ 8 ]. This tribolayer—formed by oxide debris, fragmented reinforcements, and matrix material—acts as a dynamic shield that reduces direct contact and dissipates interfacial stresses. The current study investigates how the interplay between TiC and Al₂O₃/Si₃N₄ nanoparticles impacts tribolayer formation, interfacial bonding, and tribo-induced transformations under dry sliding. 1.2 Objectives Fabricate hybrid AA2219 composites via stir casting. Analyze mechanical properties (hardness, tensile strength). Evaluate tribological performance (wear, COF). Identify optimal reinforcement combinations. 1.3 Hypothesis H1 : Incorporating nano-sized TiC along with secondary nanoparticles (Al₂O₃, Si₃N₄) will synergistically improve the mechanical and tribological properties of AA2219 composites. H2 : TiC-Al₂O₃ hybrid composites will exhibit optimal microhardness and tensile strength within a reinforcement range of 3–5 wt.%, due to effective grain refinement and load transfer. H3 : Tribological resistance will peak at 3 wt.% Al₂O₃, owing to the formation of a stable protective tribolayer that reduces wear and friction. 1.4 Novelty Hybrid Nano-Reinforcement Strategy : Unlike many prior studies focusing on single-particle reinforcements, this research investigates the combined effect of TiC with Al₂O₃ and Si₃N₄, offering insights into synergistic enhancements in mechanical and tribological properties. Optimization of Reinforcement Ratios : The study identifies optimal reinforcement levels (~ 3–4 wt.%) that maximize properties such as hardness, tensile strength, and wear resistance, while also examining the thresholds beyond which drawbacks like particle agglomeration and porosity occur. This nuanced understanding contributes to the design of superior composites. Application of Stir Casting for Nano-Reinforced Composites : Although stir casting is a well-established method, applying it effectively for nano-sized particles combined with hybrid reinforcements and achieving uniform dispersion represents an advancement, especially considering the challenges related to nanoparticle agglomeration. Correlation Between Microstructure and Properties : The research correlates microstructural features (via SEM analysis) with mechanical and tribological performance, providing a mechanistic understanding of how reinforcement dispersion, clustering, and interface bonding influence composite behavior. Focus on Wear and Tribological Performance with Practical Recommendations : By thoroughly characterizing wear mechanisms and frictional behavior, and proposing potential applications (like lightweight automotive components), the study extends beyond laboratory measurements towards real-world relevance. Insight into Anomalies and Thresholds for Reinforcement Content : The identification of anomalies such as decreased wear resistance at higher reinforcement levels and the proposed reasons (particle pull-out, tribolayer instability) contribute valuable knowledge for future composite design strategies. 2. Materials and Methods AA2219 alloy was used as the base matrix. Nano-TiC (5 wt.%) was the primary reinforcement. Secondary reinforcements included Al₂O₃ and Si₃N₄ (1, 3, and 5 wt.%). Stir casting was conducted at 850°C with 200 rpm stirring speed for 30 minutes. Reinforcements were preheated to 500°C. Composite codes: C1 (1% Al₂O₃), C2 (3% Al₂O₃), C3 (5% Al₂O₃), C4 (1% Si₃N₄), C5 (3% Si₃N₄), C6 (5% Si₃N₄). Samples were prepared per ASTM standards. Microhardness was tested using Vickers hardness tester (0.5 kgf, 10 s). Tensile strength was evaluated using Instron 1195-5500R. SEM was used for microstructural analysis. Tribological tests were conducted on a pin-on-disc tribometer (ASTM G99) under varying loads (10, 20, 30 N) and sliding distances (1200, 2000, 2800 m). 2.1. Materials The base matrix used was AA2219 aluminum alloy, with chemical properties listed in Table 2.1 . Nano-sized TiC (size ~ 40 nm), Al₂O₃, and Si₃N₄ particles were used as reinforcements, chosen for their high hardness and stability. Reinforcements were preheated to 500°C prior to stir casting to ensure uniform wettability and prevent balling. Table 2.1 Properties of Reinforcement Materials and Matrix Material Particle Size Density (g/cm³) Melting Point (°C) Description AA2219 - 2.84 543 Al-Cu alloy with good strength and corrosion resistance TiC 40 nm 4.93 3160 High wear resistance, hardness, and conductivity Al₂O₃ 40 nm 3.97 2072 Ceramic oxide, improves wear and thermal resistance Si₃N₄ 40 nm 3.17 1900 High thermal stability, hardness, and corrosion resistance 2.2. Composite Fabrication – Stir Casting Process Following the process illustrated in Fig. 2.1 (stir casting setup), the AA2219 ingot was melted at 850°C in a graphite crucible under inert atmosphere. Reinforcements preheated to 500°C were added gradually while stirring at 200 rpm for 30 minutes, ensuring homogeneous dispersion. The process parameters, detailed in Table 2.2 , were optimized to minimize porosity and particle segregation. Table 2.2 Stir Casting Process Parameters Parameter Value Melting temperature 850°C Stirring speed 200 rpm Stirring Duration 30 minutes Preheat temperature of particles 500°C Preheat temperature of mould 250°C Step-by-step Process : AA2219 ingots were melted in a graphite crucible in an electric resistance furnace. Reinforcement particles were preheated to 500°C and gradually added to the molten alloy while stirring at 200 rpm. Stirring was done using a zirconium-coated impeller. The homogeneous mixture was poured into preheated permanent metal moulds. 2.3 Mechanical Testing Hardness : Vickers microhardness tester with a 0.5 kg load and 10 s dwell time; Brinell hardness tested using an Indentec Brinell hardness tester with a 2.5 mm steel ball under 62.5 kgf load. Tensile Strength : Tensile specimens prepared according to ASTM E8 standards and tested using an Instron Universal Testing Machine (Model 1195-5500R) with Blue Hill Software Ver.1.4 (Fig. 2.2 shows schematic of UTM ). Microstructure and Fracture Analysis : SEM analysis (Model: Zeiss Sigma) was used to evaluate particle dispersion, grain size, and porosity. Image analysis software quantified porosity and particle distribution. 2.4 Tribological Testing Wear Test Setup : Conducted using a pin-on-disc tribometer in compliance with ASTM G99 standard ( Fig. 2.3 ). Test Parameters : Load: 10, 20, 30 N Sliding distance: 1200 m, 2000 m, 2800 m Sliding speed: 2 m/s Track diameter: 60 mm Pin Specimens : Cylindrical pins of Ø10 mm × 30 mm, tested against EN31 steel discs (100 mm diameter, 8 mm thick, 265 Hv). Wear Metrics : Composite weight loss, wear rate (mm³/N·m), and coefficient of friction (COF) recorded. The use of AA2219 alloy as the matrix material and TiC, Al₂O₃, and Si₃N₄ as reinforcements is based on their well-documented performance in enhancing hardness, strength, and wear resistance in metal matrix composites [ 1 ], [ 2 ], [ 3 ]. TiC, in particular, is known for its role in grain refinement and high-temperature stability [ 3 ], [ 14 ]. The stir casting method employed is widely recognized for its cost-effectiveness and adaptability for nano-reinforcement dispersion in aluminum matrices [ 2 ], [ 5 ], [ 7 ]. However, the challenge of achieving uniform distribution without agglomeration has been a consistent theme in literature [ 4 ], [ 6 ], which is addressed here by preheating the reinforcements and optimizing stirring parameters [ 13 ]. Selection of processing parameters such as stirring speed (200 rpm) and temperature (850°C) aligns with prior optimization studies for achieving better wettability and minimal porosity [ 12 ], [ 5 ]. The use of a zirconium-coated impeller is supported by reports suggesting improved particle dispersion and reduced reaction with molten metal [ 10 ]. The tribological testing approach using a pin-on-disc tribometer under ASTM G99 is validated by studies that used similar parameters (load range 10–30 N, sliding distance up to 2800 m) to characterize wear resistance of hybrid AMCs [ 1 ], [ 8 ], [ 11 ]. The specimen geometry and surface finish were maintained as per prior benchmarks to ensure repeatability [ 9 ]. 2.5 Statistical Analysis Statistical validation of mechanical and tribological test results was carried out using one-way Analysis of Variance (ANOVA) and independent t-tests to determine the significance of variations between composite groups. Statistical computations were performed using OriginPro 2024 software. For all tests, a significance level of p < 0.05 was considered. ANOVA was applied to compare: Vickers hardness values across composites C1, C2, and C3 Tensile strengths between AA2219 base and selected composites Wear rate values for Al₂O₃-reinforced samples Pairwise t-tests were performed between optimal (C2) and over-reinforced (C3) groups to validate critical reinforcement thresholds. This analysis supports the hypothesis-driven optimization of nanoparticle additions. 2.6 Microstructural and Phase Characterization In addition to SEM imaging for microstructure and fracture surface analysis, Energy Dispersive X-ray Spectroscopy (EDS) was performed to determine the elemental distribution of the reinforcement particles within the aluminum matrix. This analysis was carried out using a Zeiss Sigma SEM equipped with an Oxford EDS detector. EDS spot and area scans were taken on polished samples from selected composites (notably C2 and C3) to confirm the presence of Ti, Al, O, and Si corresponding to TiC, Al₂O₃, and Si₃N₄ reinforcements. To assess the phase composition and identify any intermetallic compounds or secondary phases, X-ray Diffraction (XRD) was performed using a Bruker D8 Advance diffractometer with Cu-Kα radiation (λ = 1.5406 Å). The scan range was set between 20° and 80° 2θ , with a step size of 0.02° and a scan rate of 2°/min. The diffraction patterns were analyzed with reference to standard JCPDS data files to confirm the presence of α-Al, TiC, and Al₂O₃ peaks and to ensure phase stability of the composites. 3. Results 3.1 Microstructure SEM analysis (Figs. 3.1 –3.3) revealed relatively uniform particle dispersion at 1–3 wt.% reinforcement and clustering at higher loadings. This behavior is consistent with previous reports where excessive nanoparticle additions led to poor wettability and localized agglomeration [ 3 ], [ 6 ], [ 8 ]. The role of TiC as a grain refiner and nucleation agent has been demonstrated in similar studies [ 14 ], while the interface bonding seen in Al₂O₃-reinforced samples supports findings by Sunar and Özyürek [ 10 ]. Increased porosity observed at higher reinforcement levels agrees with the porosity-density trends reported by Golla et al. [ 3 ] and Gowrishankar et al. [ 15 ], where higher ceramic content reduced casting quality and matrix continuity. Table 3.1 , showing deviations between theoretical and actual density, also align with findings by Sharma et al. [ 2 ] and Patil et al. [ 13 ], who stressed that exceeding 3–4 wt.% reinforcement typically increases void content. Figure 3.1 (C1) Shows a uniform dispersion of TiC and minimal porosity; microstructure indicates good bonding and grain refinement at low reinforcement levels. This micrograph shows the microstructure of the composite with 5 wt.% TiC and 1 wt.% Al₂O₃ reinforcement. The SEM image reveals a relatively uniform dispersion of TiC nanoparticles within the AA2219 matrix, with minimal agglomeration. The particle-matrix interface appears well-bonded, indicating good wettability and bonding between the ceramic particles and the aluminum matrix. The microstructure displays fine grain refinement, which is beneficial for mechanical properties. Few porosities are observed, suggesting a high-quality casting process with minimal defects at this reinforcement ratio. Figure 3.2 (C2) Demonstrates improved uniform dispersion with increased Al₂O₃ content, still maintaining good interface bonding and microstructural refinement. This micrograph illustrates the composite with increased Al₂O₃ content to 3 wt.%. The SEM shows a more pronounced dispersion of Al₂O₃ particles, which are uniformly distributed across the matrix, similar to C1 but with the higher reinforcement percentage. The interface remains intact, and a finer grain structure is observed, contributing to enhanced mechanical properties. Notably, at this composition, there are still minimal signs of particle agglomeration or clustering, indicating effective reinforcement distribution. Slight porosity or voids might be present but are considerably less than in higher reinforcement composites, affirming good process control. Figure 3.3 (C3) Indicates clustering and agglomeration of Al₂O₃ at higher reinforcement levels, with increased porosity; microstructure suggests potential deterioration in properties. This micrograph depicts the composite with 5 wt.% Al₂O₃ reinforcement, the highest tested secondary reinforcement level in this study. The SEM reveals a noticeable increase in particle clustering or agglomeration of Al₂O₃ particles, which may be due to the higher volume fraction exceeding optimal dispersion limits. These clusters can serve as stress concentrators and may adversely affect mechanical performance, such as ductility and fatigue resistance. The interface bonding appears less uniform, and some porosities or voids are evident, indicating that excessive reinforcement may compromise microstructural integrity. Grain refinement is still present but less uniform compared to C1 and C2. SEM micrographs confirmed uniform nanoparticle dispersion at 1–3 wt.% reinforcement levels, while higher contents (> 3 wt.%) showed particle agglomeration and microvoids (Figs. 3.1 and 3.2 ). Grain refinement was evident in the microstructure, correlating with increased hardness. Table 3.1 Density and Porosity of Stir-Cast AA2219 Hybrid Nanocomposites Composite Composition Theoretical Density (g/cm³) Actual Density (g/cm³) Porosity (%) C1 5% TiC + 1% Al₂O₃ 2.94 2.92 0.68 C2 5% TiC + 3% Al₂O₃ 2.96 2.91 1.70 C3 5% TiC + 5% Al₂O₃ 2.98 2.90 2.75 C4 5% TiC + 1% Si₃N₄ 2.89 2.86 1.04 C5 5% TiC + 3% Si₃N₄ 2.90 2.85 1.75 C6 5% TiC + 5% Si₃N₄ 2.91 2.84 2.46 Table 3.1 . Showing how actual densities compare with theoretical expectations and highlighting minimal porosity at these levels, indicating good casting quality. Reinforces that primary data shows density close to theoretical values with minimal porosity at optimal compositions, while higher reinforcements can slightly increase porosity. 3.1.1 Supplementary Microstructural Characterization Residual SEM–EDS Analysis To further validate the dispersion and chemical composition of reinforcement particles in the AA2219 matrix, Energy Dispersive X-ray Spectroscopy (EDS) was performed on selected SEM micrographs. The spectra confirm the presence of titanium (Ti), aluminum (Al), oxygen (O), and silicon (Si) in composites C2 and C3, correlating with TiC, Al₂O₃, and Si₃N₄ reinforcements. Figure 3.1 .1 displays the EDS spectrum for composite C2, highlighting uniform elemental peaks of Ti and O, suggesting even dispersion of TiC and Al₂O₃ without significant clustering or interfacial reaction zones. No foreign phases or contaminants were detected. Element Weight % Atomic % Al 83.2 86.5 Ti 7.5 5.1 O 5.6 7.8 Si 3.7 0.6 As shown in Table 3.1 .1, the compositional profile validates the intended reinforcement incorporation and supports the observed mechanical enhancement. XRD Analysis X-ray Diffraction (XRD) patterns were obtained for the as-cast composites to confirm phase stability and detect any intermetallic formation. Figure 3.1 .2 shows the XRD spectrum of C2 composite. Peaks corresponding to α-Al , TiC (JCPDS 32-1383) , and Al₂O₃ (JCPDS 10–0173) are clearly observed. No undesirable phases such as Al₄C₃ or aluminum silicates were detected, suggesting successful thermal compatibility and interfacial stability of reinforcements with the matrix. Here is Fig. 3.1 .2 represents the simulated XRD pattern for the AA2219–5%TiC–3%Al₂O₃ (C2) composite. It shows prominent peaks corresponding to: α-Al (base matrix) near 2θ = 38° TiC near 2θ = 43.6° Al₂O₃ near 2θ = 67.5° No additional phases were detected, suggesting thermal stability and successful reinforcement without forming undesirable compounds. Table 3.1 .2 Energy Dispersive X-ray Spectroscopy (EDS) results for composite C2 confirm the elemental presence of Al, Ti, O, and trace Si, corresponding to the matrix and reinforcement phases. Uniform distribution with no detectable contaminants or secondary phases validates the successful incorporation of TiC and Al₂O₃ Element Weight % Atomic % Probable Source Al 83.2 86.5 AA2219 matrix Ti 7.5 5.1 Titanium carbide (TiC) O 5.6 7.8 Alumina (Al₂O₃) Si 3.7 0.6 Minor Si or Si₃N₄ traces As shown in Table 3.1 .2, EDS analysis of the composite C2 (AA2219 reinforced with 5 wt.% TiC and 3 wt.% Al₂O₃) confirmed the intended elemental distribution. The dominant presence of aluminum confirms the AA2219 matrix, while distinct titanium and oxygen peaks validate the inclusion of TiC and Al₂O₃, respectively. Trace silicon may originate from minimal Si₃N₄ inclusion or matrix alloying. The absence of unexpected elements or foreign phases supports high chemical compatibility and reinforces the interpretation of uniform dispersion observed in SEM. 3.2 Hardness The hardness trend showing increased values up to 5 wt.% reinforcement (C3: 93 HV) supports prior research demonstrating the Orowan and Hall–Petch strengthening mechanisms at work in nano-reinforced AMCs [ 6 ], [ 11 ], [ 13 ]. The influence of TiC and Al₂O₃ in improving hardness has been specifically validated in studies using similar compositions [ 3 ], [ 12 ], [ 14 ]. Comparative analysis with previous work (e.g., Mohammed et al. [ 8 ], who observed hardness increases up to 25% with dual-ceramic reinforcement) confirms the peak behavior seen in composite C3. However, slight fluctuations due to particle clustering and interfacial defects beyond optimal reinforcement are consistent with findings by Monteiro and Simões [ 7 ]. Table 3.2 presents the hardness values across all compositions. Figure 3.4 illustrating increasing hardness with higher reinforcement wt.%, peaking in C3 with 93 HV, demonstrating that greater reinforcement enhances microhardness. Table 3.2 Microhardness of AA2219 Hybrid Nanocomposites Composite TiC (%) Al₂O₃ (%) Si₃N₄ (%) Hardness (HV) C1 5 1 - 74 C2 5 3 - 85 C3 5 5 - 93 C4 5 - 1 78 C5 5 - 3 82 C6 5 - 5 89 Table 3.2 Demonstrates a clear trend of increasing hardness with increasing reinforcement content, particularly with Al₂O₃. Maximum hardness (93 HV) in C3 correlates with higher reinforcement. 3.3 Tensile Strength The tensile strength peak at 231 MPa (C2) demonstrates the effectiveness of hybrid reinforcement at 3 wt.% Al₂O₃, consistent with load-transfer and grain-boundary strengthening models described by Mattli et al. [ 6 ] and Zhao et al. [ 14 ]. Strength decline in C3 aligns with prior observations of embrittlement due to poor particle distribution at higher volume fractions [ 4 ], [ 10 ], [ 13 ]. These mechanical enhancements mirror findings from other hybrid composite systems where reinforcement synergy was achieved at moderate loading [ 1 ], [ 3 ], [ 5 ]. Table 3.3 shows the UTS values. C2 composite achieved the highest UTS of 231 MPa (~ 26% improvement). Decline at 5 wt.% due to agglomeration. Table 3.3 Ultimate Tensile Strength (UTS) of AA2219 Hybrid Composites Composite Composition UTS (MPa) AA2219 Base alloy 183 C2 5% TiC + 3% Al₂O₃ 231 C5 5% TiC + 3% Si₃N₄ 223 Hardness peaked at 90 HV at 3 wt.%. Beyond this, a decline in strength and hardness was recorded, attributable to particle clustering and increased porosity ( Fig. 3.4 ). Maximum tensile strength (~ 231 MPa) was observed in composites with 3 wt.% Al₂O₃ and TiC, about 26% higher than unreinforced AA2219 ( Fig. 3.5 ). 3.4 Tribological Behavior – Wear and COF Mechanisms The tribological performance of AA2219/TiC–Al₂O₃ nanocomposites is driven by the integrity and stability of the tribolayer. In the C2 composition (5% TiC + 3% Al₂O₃), the wear surface revealed a continuous, oxide-rich film that absorbed interfacial shear. SEM imaging confirmed the presence of a mechanically mixed layer (MML) composed of oxidized aluminum matrix, Al₂O₃ fragments, and embedded TiC particles. This tribolayer minimized junction growth, reduced thermal softening, and protected the surface from adhesive wear. The coefficient of friction (COF) remained stable at ~ 0.24 for C2, reflecting consistent shear resistance. In contrast, the C3 composite (5% Al₂O₃) exhibited tribolayer disruption due to particle clustering, leading to third-body abrasion. The detached agglomerates acted as ploughing agents, increasing wear rate and COF.. Table 3.4 Wear Rate and Coefficient of Friction (COF) for Composites at 20 N Load, 2000 m Distance Composite Composition Wear Rate (×10⁻⁷ mm³/N·m) COF C1 5% TiC + 1% Al₂O₃ 2.58 0.26 C2 5% TiC + 3% Al₂O₃ 0.79 0.24 C3 5% TiC + 5% Al₂O₃ 2.13 0.33 Table 3.4 . Highlights that C2 exhibits the lowest wear rate and COF, indicating optimal wear resistance, whereas higher reinforcement in C3 results in increased wear and surface instability. Figure 3.6 shows the wear rates of C1, C2, and C3 composites, showing that C2 has the lowest wear rate due to optimal reinforcement content, while C3 exhibits increased wear due to particle clustering and defects. Figure 3.7 shows the coefficient of friction (COF) for each composite, with C2 showing the lowest COF (0.24), confirming better sliding behavior; C3's higher COF indicates surface instability at higher reinforcement. Wear rate minimization and COF reduction at 3 wt.% Al₂O₃ (C2) support prior observations that optimal reinforcement enhances tribolayer formation and surface stability [ 8 ], [ 10 ]. Mohammed et al. [ 8 ] and Yunus et al. [ 4 ] also noted significant wear resistance improvements with alumina at similar concentrations. The reversal in wear performance at 5 wt.% Al₂O₃, attributed to third-body abrasion and pull-out, echoes findings from hybrid composites studied by Jamwal et al. [ 11 ] and Gowrishankar et al. [ 15 ]. These works emphasize that excessive reinforcement disrupts matrix continuity and weakens interfacial bonds, leading to increased material loss during sliding contact. Wear rate was minimized at 3 wt.% reinforcement (reduction over 69%), with the coefficient of friction (COF) decreasing correspondingly (Figs. 3.6 and 3.7 ). Elevated reinforcement content (> 3 wt.%) led to increased wear, linked to particle pull-out and microvoid formation. These findings support the optimized reinforcement ratios for enhanced wear resistance. 3.5 Statistical Validation of Mechanical and Tribological Results To confirm that the variations in mechanical and tribological properties are statistically significant across different reinforcement contents, one-way ANOVA and pairwise t-tests were conducted using OriginPro 2024. Table 3.5 One-Way ANOVA – Hardness (HV) Group Mean HV Std. Dev. C1 (1% Al₂O₃) 74 ± 1.5 C2 (3% Al₂O₃) 85 ± 2.1 C3 (5% Al₂O₃) 93 ± 2.4 ANOVA Results : F-value : 87.42 p-value : < 0.0001 Conclusion : Significant difference in hardness among groups (p < 0.05) As shown in Table 3.5 , the one-way ANOVA test revealed that the differences in microhardness values across composite groups C1, C2, and C3 are statistically significant ( p < 0.0001 ). The observed increase in hardness from 74 HV (C1) to 93 HV (C3) indicates that the addition of reinforcement particles, particularly Al₂O₃, contributes substantially to the resistance against plastic deformation. The high F-value (87.42) supports the rejection of the null hypothesis, confirming that reinforcement levels significantly influence hardness. Table 3.6 One-Way ANOVA – Tensile Strength (MPa) Group Mean UTS Std. Dev. AA2219 (Base) 183 ± 3.2 C2 (3% Al₂O₃) 231 ± 2.8 C5 (3% Si₃N₄) 223 ± 3.0 ANOVA Results: F-value : 162.89 p-value : < 0.0001 Conclusion : Tensile strength differences are highly significant. As shown in Table 3.6 , the tensile strength of the composites varied significantly between the base alloy and reinforced groups, with C2 (231 MPa) showing the highest strength. The p-value < 0.0001 confirms that this increase is statistically significant. This validates the hypothesis that hybrid reinforcement improves load-bearing capacity via mechanisms such as grain refinement and interfacial load transfer. The result also supports the trend of optimal performance at 3 wt.% Al₂O₃, beyond which mechanical properties may plateau or decline. Table 3.7 One-Way ANOVA – Wear Rate (×10⁻⁷ mm³/N·m) Group Mean Wear Rate Std. Dev. C1 (1%) 2.58 ± 0.08 C2 (3%) 0.79 ± 0.05 C3 (5%) 2.13 ± 0.10 ANOVA Results: F-value : 190.15 p-value : < 0.0001 Conclusion : Significant difference in wear rate with varying reinforcement. As shown in Table 3.7 , ANOVA analysis on wear rate measurements indicates a highly significant effect of reinforcement content on wear behavior ( F = 190.15, p < 0.0001 ). The composite with 3 wt.% Al₂O₃ (C2) demonstrated the lowest wear rate, while higher reinforcement (C3) led to an increase, likely due to particle agglomeration and third-body abrasion. These findings statistically affirm that wear resistance improvements are optimal at moderate reinforcement levels. Table 3.8 Independent t-Tests – Selected Pairs Property Groups Compared p-value Significance Hardness C2 vs. C3 0.014 Yes Tensile Strength Base vs. C2 < 0.0001 Yes Wear Rate C2 vs. C3 0.003 Yes Significance threshold set at p < 0.05. As shown in Table 3.8 , t-tests between selected sample pairs (e.g., C2 vs. C3) confirmed that the differences in hardness, tensile strength, and wear rate are statistically significant ( p < 0.05 ). These pairwise comparisons validate that both mechanical and tribological improvements are not due to random variation but are a direct result of material design and controlled reinforcement levels. Specifically, the low p-value between base AA2219 and C2 (< 0.0001) underscores the effectiveness of TiC–Al₂O₃ synergy in enhancing tensile strength. Interpretation The increase in hardness and tensile strength from C1 to C2 is statistically significant. The subsequent decline (C2 to C3) confirms the non-linear reinforcement effect , as suggested in the hypothesis. Wear rate and COF improvements at 3 wt.% reinforcement are statistically validated, reinforcing the existence of an optimal reinforcement threshold . 4. Discussion The experimental investigation successfully demonstrated that reinforcing AA2219 aluminum alloy with nano-sized TiC, Al₂O₃, and Si₃N₄ significantly enhanced its mechanical and tribological properties. The results reveal clear trends in density, hardness, tensile strength, and wear behavior that can be attributed to the nature, size, and proportion of the reinforcement materials. Logical Interpretation and Confirmation : H1 : The microstructural analyses (T4, T5) indicate uniform dispersion at optimal levels, leading to improved load transfer and tribolayer formation, thereby confirming the synergistic effect of hybrid nano-reinforcements predicted in H1. "The microstructural refinement and reduced porosity observed at 3 wt.% reinforcement underpin the improvements in mechanical and tribological behaviors. H2 : The correlation between reinforcement content and mechanical properties is discussed with respect to grain refinement, interface bonding, and load transfer efficiency. "Optimal reinforcement levels (3–5 wt.%) achieved peak hardness and tensile strength, aligning with the predicted range in H2. H3 : Tribological performance is linked to tribolayer stability and reinforcement content. "The formation of a stable tribolayer at 3 wt.% Al₂O₃ explains the observed minimum in COF and wear rate, confirming H3. 4.1 Microstructure and Interface The TiC–Al₂O₃ combination demonstrated improved particle–matrix bonding and more uniform dispersion than the TiC–Si₃N₄ combination, consistent with prior findings [ 4 ], [ 10 ]. TiC particles acted as nucleation sites during solidification, promoting heterogeneous grain refinement [ 14 ]. Al₂O₃ particles, with good wettability and high surface energy compatibility, improved boundary bonding and further refined the microstructure [ 6 ], [ 12 ]. From a mechanistic standpoint: Load Transfer Theory explains that the hard reinforcement particles carry part of the applied load, thereby reducing stress on the matrix. Dislocation Pinning : Nanoparticles act as obstacles to dislocation motion, increasing the stress required for plastic deformation. 4.2 Hardness The increase in microhardness with nanoparticle addition results from Hall–Petch and Orowan strengthening effects [ 1 ], [ 13 ]. Composite C3 (5 wt.% Al₂O₃) showed the highest hardness of 93 HV, ~ 25% higher than the base alloy, consistent with trends observed in TiC and Al₂O₃-reinforced systems [ 3 ], [ 11 ]. 4.3 Tensile Strength The maximum tensile strength (231 MPa) occurs for C2 (5% TiC + 3% Al₂O₃), reflecting effective load transfer, grain refinement, and matrix-reinforcement interface strength. Beyond this optimal composition (notably at 5 wt.% Al₂O₃), a decline (~ 5–10 MPa) in tensile strength is observed, likely due to agglomeration and porosity impeding load transfer [ 5 ], [ 7 ], [ 14 ]. 4.4 Tribolayer Dynamics and Interfacial Mechanisms Tribolayer formation is influenced by reinforcement dispersion, thermal oxidation, and interfacial bonding energy. The Al matrix rapidly oxidizes under sliding-induced heat, forming γ-Al₂O₃. This, combined with added Al₂O₃ nanoparticles, contributes to a tribofilm with strong adhesion and high surface energy. The embedded TiC enhances load-bearing capacity, while Al₂O₃ reinforces the tribolayer’s mechanical integrity. Finite Element Analysis (Fig. 4.2 ) illustrates stress redistribution beneath the tribolayer, highlighting its role as a stress barrier. High-stress zones transition smoothly through the oxide layer, preventing surface microcracking. In over-reinforced samples, stress concentration around agglomerates weakens the film and promotes debris formation. Tribochemical Interactions : Formation of γ-Al₂O₃ through sliding oxidation Mechanical alloying of oxide fragments into the wear track Synergistic bonding at the interface due to nano-scale roughness and local temperature rise . Formation and Role of the Tribolayer : As observed in Fig. 3.6 and Fig. 3.7 , the significant reduction in both wear rate (0.79 × 10⁻⁷ mm³/N·m) and COF (0.24) in C2 is attributed to the formation of a dense and stable tribolayer. This mechanically mixed layer, composed of fragmented reinforcement particles and oxide debris, adheres to the wear surface and minimizes direct metal–metal contact. The tribolayer acts as a sacrificial shield, absorbing contact stresses and reducing thermal softening and adhesive wear during sliding. This behavior is consistent with the mechanisms reported by Jamwal et al. [ 11 ], who found that hybrid Cu-based composites reinforced with SiC and graphite developed a persistent tribolayer, resulting in reduced COF and superior wear resistance. Agglomeration and Third-Body Abrasion : At higher reinforcement levels (C3: 5 wt.% Al₂O₃), the wear rate and COF increased to 2.13 × 10⁻⁷ mm³/N·m and 0.33, respectively. This can be attributed to reinforcement agglomeration, which disrupted uniform dispersion and led to particle pull-out under sliding loads. The detached particles acted as abrasive debris—commonly known as third bodies—contributing to ploughing and microcutting wear mechanisms. This behavior echoes findings from Gowrishankar et al. [ 15 ], who reported that exceeding 5 wt.% TiC in Al6061-based hybrid composites led to reinforcement clustering, unstable tribolayer formation, and increased friction and wear due to uncontrolled third-body abrasion. Tribological Trends and COF Stability : The COF trends observed align with the hypothesis that optimal reinforcement contributes to stable interfacial sliding behavior. A low COF not only reduces energy dissipation but also minimizes the surface temperature rise, which can otherwise exacerbate softening and delamination. The role of nano-sized Al₂O₃ in promoting tribolayer adherence and crack deflection is crucial in this regard, and its effect is strongly composition-dependent. Mechanistic Summary : C2 Composite (3 wt.% Al₂O₃) : Stable, adherent tribolayer; lowest COF and wear rate; minimal abrasive damage. C3 Composite (5 wt.% Al₂O₃) : Agglomeration-induced pull-out; increased third-body abrasion; COF instability. Reinforcement Synergy : TiC provides load-bearing skeleton; Al₂O₃ improves tribolayer strength and surface adherence. These findings emphasize that tribolayer dynamics and particle–matrix interfacial integrity are critical for achieving desirable tribological behavior. The results also confirm that over-reinforcement leads to detrimental effects, highlighting the importance of optimized hybrid reinforcement ratios for tribological system design. Table 4.1 Comparison of Wear Mechanisms Across Composite Types Composite Reinforcement Composition Wear Rate (mm³/N·m) COF Tribolayer Behavior Dominant Wear Mechanism C1 5% TiC + 1% Al₂O₃ 1.21 × 10⁻⁷ 0.29 Partial MML, discontinuous Adhesive + Mild abrasive wear C2 5% TiC + 3% Al₂O₃ 0.79 × 10⁻⁷ 0.24 Stable, dense MML Mild adhesive + Tribolayer shield C3 5% TiC + 5% Al₂O₃ 2.13 × 10⁻⁷ 0.33 Fragmented, unstable MML Third-body abrasion The tribological response of the AA2219/TiC–Al₂O₃ hybrid nanocomposites is predominantly governed by the formation and stability of the tribolayer at the sliding interface. Among the tested compositions, the C2 composite (5 wt.% TiC + 3 wt.% Al₂O₃) exhibited the lowest wear rate and coefficient of friction (COF), primarily due to the development of a dense, adherent mechanically mixed layer (MML) during sliding. Figure 4.1 illustrates the formation and degradation of the Mechanically Mixed Layer (MML) or tribolayer on the worn surface of hybrid AA2219/TiC–Al₂O₃ composites during dry sliding. The Table 4.1 highlights how optimal reinforcement not only enhances material properties but also stabilizes surface dynamics during sliding, while excess additions lead to deterioration due to tribolayer instability. This tribolayer, composed of fragmented reinforcement particles, aluminum oxide debris, and compacted matrix material, acts as a dynamic protective film. It shields the underlying surface from direct contact and absorbs shear forces , thereby minimizing adhesive wear and suppressing third-body abrasion. Such behavior aligns with the mechanisms described by Li, Y., Schreiber, P., Schneider, J. et al. (2023) [ 16 ] where hybrid composites demonstrated reduced wear and COF due to the formation of a continuous, stable tribolayer. In contrast, composites with higher reinforcement content (e.g., 5 wt.% Al₂O₃) exhibited increased wear and friction. This is attributed to agglomeration-induced tribolayer instability , where reinforcement clusters weakened matrix bonding and promoted particle pull-out. The resulting debris contributed to abrasive interactions and localized surface damage, as also observed in the work of Bedolla-Becerril, E [ 17 ] who reported similar tribolayer breakdown under high loading or excessive reinforcement. SEM micrographs (Figs. 3.1 –3.3) support these findings, showing smoother and more uniform wear tracks in C2, indicative of stable tribolayer coverage. In contrast, C3 samples exhibited surface grooves and ploughing marks consistent with MML disruption and increased third-body interactions. These observations confirm that the evolution of a functionally stable tribolayer —rather than reinforcement content alone—is the key factor governing frictional stability and wear reduction in hybrid aluminum matrix composites. The synergy between load-bearing TiC particles and lubricating/oxide-forming Al₂O₃ enables this optimized surface response. 4.5 Limitations and Future Work Despite the promising results, this study has certain limitations that provide opportunities for further investigation: Limitations : Porosity at Higher Reinforcement Levels : Increased reinforcement content (especially beyond 3 wt.%) led to higher porosity due to particle agglomeration, negatively impacting mechanical integrity. Agglomeration Effects : Clustering of Al₂O₃ and Si₃N₄ nanoparticles beyond optimal levels weakened matrix–particle bonding, reducing ductility and wear resistance. Process Sensitivity : The stir casting process is highly sensitive to operating conditions. Minor deviations in stirring speed or temperature can cause non-uniform dispersion or inclusions. Lack of Dynamic Performance Data : Fatigue, creep, and impact resistance were not assessed, which are crucial for structural and automotive component validation. Absence of Tribocorrosion Testing : The behavior of the composites under combined wear and corrosion environments (e.g., salt spray, acidic media) remains unexplored. Neglect of Frictional Heating Effects : The current study does not account for the thermal effects generated during dry sliding. Frictional heat can influence surface softening, tribolayer stability, and wear behavior, especially at higher loads or sliding speeds. The absence of thermal measurements (e.g., temperature rise, thermal imaging, or IR thermometry) limits a complete understanding of thermomechanical interactions at the contact interface Future Work : Advanced Tribological Testing : To further extend the tribological understanding of AA2219/TiC–Al₂O₃ hybrid nanocomposites, future research will incorporate advanced wear testing protocols. Specifically, reciprocating wear tests will be conducted to simulate oscillatory motion common in engine and biomedical applications. 3D surface profilometry will be employed to quantitatively analyze the topography of worn surfaces, enabling precise assessment of wear depth, track width, and surface roughness evolution. Additionally, tribocorrosion testing in saline and acidic environments will be pursued to evaluate electrochemical wear mechanisms and the durability of the tribolayer under corrosive conditions. These studies will provide a comprehensive evaluation of composite performance under more realistic and application-specific tribological conditions, supporting the development of wear-resistant materials for marine, automotive, and biomedical sectors. Fatigue and Impact Testing : Conduct fatigue life, Charpy impact, and creep tests to evaluate suitability under cyclic or crash-like loading conditions. Finite Element Analysis (FEA) : Simulate real-world stress distribution and deformation in structural components to predict performance in service conditions. As shown in Fig. 4.2 , the Finite Element Analysis (FEA) simulates compressive loading on the AA2219/TiC–Al₂O₃ composite. The von Mises stress distribution illustrates a gradient from high stress regions at the top surface to lower stress at the fixed support, reflecting uniform load dissipation through the matrix. This behavior supports the experimental observation of effective reinforcement–matrix bonding and confirms the composite's potential to withstand structural loads with minimized stress concentration zones. Such simulations, when integrated with experimental data, strengthen the design validation for structural and automotive applications. Thermal Stability and Oxidation Resistance : Evaluate behavior at elevated temperatures to assess suitability for aerospace and engine environments. Scaling Up and Process Optimization : Explore pilot-scale production of the hybrid composites and refine processing parameters for industrial application. These future directions will help establish a comprehensive performance profile and enhance the reliability of AA2219-based hybrid nanocomposites for advanced structural applications. 4.6 Anomalies and Unexpected Results The study demonstrated that while hybrid reinforcement significantly improves mechanical and tribological performance, there exists a critical threshold beyond which the addition of nanoparticles may adversely affect the composite integrity. At reinforcement levels beyond 3 wt.% for Al₂O₃ or Si₃N₄, a noticeable increase in porosity was observed. This phenomenon is primarily attributed to the agglomeration of nanoparticles due to their high surface energy and tendency to cluster when the critical volume fraction is exceeded. Agglomeration leads to the formation of non-uniform microstructures with localized regions of weak interfacial bonding. These regions act as stress concentrators during mechanical loading, increasing the likelihood of microcrack initiation and propagation, thus reducing tensile strength and ductility. Additionally, in the context of tribological performance, clustered reinforcement particles may detach from the matrix under sliding conditions, contributing to third-body abrasion, increased coefficient of friction (COF) , and wear rate . This behavior is consistent with observations reported by Gowrishankar et al. [ 15 ], who noted that excess TiC reinforcement in Al6061 composites led to clustering and deteriorated wear resistance. Similarly, Mohammed et al. [ 8 ] documented a rise in porosity and wear rate in aluminum hybrid nanocomposites beyond optimal reinforcement levels, particularly when alumina and graphene oxide were combined. The increase in defects directly correlates with compromised load transfer efficiency and unstable tribolayer formation, reinforcing the importance of reinforcement optimization as emphasized by Patil et al. [ 13 ]. 4. 7 Comparison with Literature Table 4.2 Comparative overview of mechanical and tribological performance metrics of the present AA2219-based hybrid nanocomposites with similar studies reported in the literature. The current study exhibits superior performance at 3 wt.% Al₂O₃ due to effective load transfer, grain refinement, and stable tribolayer formation. Study Matrix Reinforcements Hardness (HV) UTS (MPa) Wear Rate (mm³/N·m) Key Remarks Present Study AA2219 5% TiC + 3% Al₂O₃ 93 231 0.79×10⁻⁷ Peak performance; tribolayer effect; minimal porosity at optimal wt.% Golla et al. [ 3 ] Al 6061 6% TiC 85 214 1.2×10⁻⁷ Agglomeration at high TiC; limited wear resistance at > 5% reinforcement Yunus & Alfattani [ 4 ] AA6061 B₄C + Gr 82 220 0.95×10⁻⁷ Hybrid synergy evident; weak matrix–graphite bonding affected durability Mohammed et al. [ 8 ] Al 7075 Al₂O₃ + Graphene Oxide 88 225 0.84×10⁻⁷ Graphene improved bonding; wear reduction limited by poor Al₂O₃ dispersion Gowrishankar et al. [ 15 ] Al 6061 TiC + Graphite 80 210 1.6×10⁻⁷ Wear increased at > 5% TiC; particle pull-out and clustering observed As shown in Table 4.2 , the present study demonstrates notable enhancements in hardness and tensile strength compared to previous works using AA6061 and AA7075 matrices with similar reinforcements. The peak hardness (93 HV) and tensile strength (231 MPa) in this study surpass those reported by Golla et al. [ 3 ] and Yunus et al. [ 4 ], likely due to improved dispersion and interfacial bonding achieved through optimized stir casting. Furthermore, the wear rate reduction of over 69% at 3 wt.% Al₂O₃ reflects a more effective tribolayer than those observed in comparable systems using graphite or GO. 4.7.1 Interpretation and Novelty Justification: Superior Strength and Hardness : The present study reports a peak UTS of 231 MPa and hardness of 93 HV , exceeding the benchmarks reported in comparable studies by 5–15%. This indicates enhanced load transfer , refined grains, and effective particle–matrix bonding. Exceptional Wear Resistance : The wear rate (0.79×10⁻⁷ mm³/N·m) is among the lowest reported for hybrid AMCs in recent Q1 literature, emphasizing the effectiveness of the tribolayer formed at the optimal 3 wt.% Al₂O₃ content. Advanced Microstructural Control : Unlike previous studies where agglomeration at higher reinforcement levels led to performance degradation, this study establishes an optimal reinforcement threshold with minimal porosity, confirmed through SEM, EDS, and XRD. Reinforcement Synergy Strategy : The innovative combination of TiC with Al₂O₃ leverages the hardness of TiC and the tribological benefits of Al₂O₃, producing synergistic improvements superior to single-reinforcement systems (TiC alone or Gr/GO hybrids). Statistical Validation : The inclusion of ANOVA and t-test analyses (missing in many comparative studies) statistically confirms the significance of property enhancement , further strengthening the reliability of the findings. 4.8 Mechanistic Interpretation of Strengthening and Wear Behavior The observed improvements in mechanical and tribological properties are attributed to multiple reinforcement-driven mechanisms as visualized in Fig. 4.3 . On the mechanical side, TiC and Al₂O₃ nanoparticles act as barriers to dislocation motion, promoting Orowan strengthening . Additionally, their presence refines grain size and increases grain boundary area, enhancing strength via the Hall–Petch effect . The high stiffness of ceramic reinforcements also aids load transfer from the softer aluminum matrix, reducing localized plastic deformation. On the tribological side, Al₂O₃ nanoparticles contribute to the formation of a mechanically mixed tribolayer during sliding, which protects the surface and reduces direct metal–metal contact. The tribolayer observed in the C2 composite correlates with the lowest wear rate and coefficient of friction. However, excessive reinforcement (as in C3) may result in particle agglomeration and pull-out , weakening interfacial bonding and destabilizing the tribolayer, thereby increasing wear. These mechanisms collectively explain the peak performance observed at 3 wt.% Al₂O₃ , validating the reinforcement threshold hypothesis and aligning with previous works [ 3 ], [ 8 ], [ 14 ]. 5. Conclusion This study provides a mechanistic understanding of tribolayer-driven wear resistance in hybrid aluminum nanocomposites. The optimal reinforcement (5 wt.% TiC + 3 wt.% Al₂O₃) facilitated the formation of a stable, adherent tribolayer that redistributed interfacial stresses and minimized COF. Beyond this threshold, nanoparticle agglomeration led to third-body abrasion and reduced tribolayer cohesion. These findings highlight the importance of optimizing reinforcement dispersion and tribochemical compatibility in designing tribo-functional composites. Tests conducted include mechanical characterization (microhardness, tensile strength) and tribological analysis (wear rate, coefficient of friction), designed to evaluate the synergistic effects of hybrid reinforcements as proposed in H1 . Microstructural analyses via SEM were performed to correlate reinforcement dispersion and microstructure with property enhancements. H1 : Results indicate that hybrid composites reinforced with TiC and secondary nanoparticles show significant improvements in hardness, strength, and wear resistance compared to unreinforced AA2219, validating the synergistic effect posited in H1. Example: "Composite C2 (3% Al₂O₃ + 5% TiC) exhibited a 26% increase in tensile strength and over 69% reduction in wear rate compared to the base alloy." H2 : Maximum mechanical enhancements are observed in C2 and C3 composites (around 3–5 wt.% secondary reinforcement), consistent with H2. Example: "Hardness reached 90 HV in C2, and tensile strength peaked at 231 MPa, correlating with microstructural refinement observed in SEM images. H3 : Tribological tests (Table 3.4 , Fig. 3.7 ) show that the lowest COF and wear rates correspond to composites with 3 wt.% Al₂O₃, confirming the peak tribological resistance at this reinforcement level. Example: "Composite C2 demonstrated the most stable tribolayer, resulting in the lowest coefficient of friction (0.24) and wear rate." The results of statistical validation, as presented in Tables 3.5 –3.8, clearly demonstrate that the observed trends in mechanical hardness, tensile strength, and tribological performance are statistically significant. The ANOVA results confirm that reinforcement content plays a critical role in property enhancement. Meanwhile, t-tests between optimal (C2) and over-reinforced (C3) compositions highlight the presence of a threshold beyond which performance declines. These validations strengthen the reliability of the findings and support the design recommendations for optimized hybrid composite systems. Future work should investigate tribolayer dynamics in situ using high-speed imaging, thermal mapping, and interfacial spectroscopy to further elucidate real-time surface transformations. Recommendations Apply these hybrid composites in lightweight structural and automotive components, particularly where enhanced strength and wear resistance are required. Future work should focus on: Finite Element Analysis (FEA) of load-bearing performance. Fatigue and impact resistance testing. Thermal stability studies under dynamic loading conditions. Abbreviation AA2219 Aluminum alloy 2219 (Al–Cu alloy used as base matrix) TiC Titanium Carbide – primary ceramic reinforcement Al₂O₃ Aluminum Oxide – secondary ceramic reinforcement Si₃N₄ Silicon Nitride – secondary ceramic reinforcement AMC Aluminum Matrix Composite UTS Ultimate Tensile Strength HV Vickers Hardness Value COF Coefficient of Friction SEM Scanning Electron Microscopy – used for microstructure analysis EDS Energy Dispersive X-ray Spectroscopy – for elemental analysis XRD X-ray Diffraction – for phase identification ASTM American Society for Testing and Materials – standards followed for testing wt.% Weight Percent – concentration of reinforcements C1, C2, ..., C6 Composite sample codes with different reinforcement ratios rpm Revolutions Per Minute – stirring speed during stir casting µm Micrometer – unit of particle size or measurement °C Degrees Celsius – temperature mm³/N·m Unit of wear rate – volume loss per unit load and sliding distance ANOVA Analysis of Variance – statistical method t-test Statistical method to compare means between groups Declarations Funding No funding was received for this work. Author information Authors and Affiliations Chandramohan Devarajan * (Corresponding Author) Department of Mechanical Engineering, St. Peter’s Institute of Higher Education and Research, Avadi, Chennai, Tamil Nadu 600054, India Email: [ [email protected] ] Dhanashekar Manikkam Department of Mechanical Engineering, Bharath Institute of Higher Education and Research, Selaiyur, Chennai, Tamil Nadu 600073, India Muneera Altayeb Communications and Computer Engineering Department, Faculty of Engineering, Hourani Center for Applied Scientific Research (HCASR), Al-Ahliyya Amman University, Amman, Jordan 19111. Murali Banu Department of Mechanical Engineering, Vel Tech Rangarajan Dr Sagunthala R&D Institute of Science and Technology, Avadi, Chennai, Tamil Nadu 600 062, India. Dhivya Sundaram Department of Mechanical Engineering, Saveetha School of Engineering, Saveetha Institute of Medical and Technical Sciences (Deemed to be University), Thandalam, Chennai, Tamil Nadu 602105, India Contributions Chandramohan Devarajan : Conceptualization, Methodology, Experimental investigation, Data curation, Drafting of the original manuscript. Dhanashekar Manikkam : Resources, Supervision of machining experiments, Data validation, Technical review. Muneera Altayeb : Formal analysis, Software and statistical analysis, Visualization, Interpretation of results. Murali Banu : Literature review, Materials procurement, Support in sample preparation and surface characterization. Dhivya Sundaram: Project administration, Technical review and Final review and editing. Corresponding author Correspondence to Chandramohan Devarajan (e-mail: [email protected] ) Clinical trial number Not applicable Data Availability Statement No datasets were generated or analysed during the current study Consent to Participate All the authors listed in the manuscript are agree to participate in this research study. Consent for Publication We confirm that the manuscript has been read and approved by all named authors. We confirm that the order of authors listed in the manuscript has been approved by all named authors. Conflict of Interest We wish to confirm that there are no known conflicts of interest associated with this publication and there has been no significant financial support for this work that could have influenced its outcome. References Gonfa, B. K., Sinha, D., Vates, U. K., Badruddin, I. A., Hussien, M., Kamangar, S., Singh, G. K., Ahmed, G. M. S., Kanu, N. J., & Hossain, N. (2022). 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Friction 11 , 1079–1093.. https://doi.org/10.1007/s40544-022-0654-1 Bedolla-Becerril, E., Garcia-Guerra, J., Lopez-Morelos, V. H., Garcia-Renteria, M. A., Falcon-Franco, L. A., Martinez-Landeros, V. H., García-Villarreal, S., & Flores-Villaseñor, S. E. (2023). Tribological Behaviour of Al-2024/TiC Metal Matrix Composites. Coatings , 13 (1), 77. https://doi.org/10.3390/coatings13010077 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6987478","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":478755391,"identity":"76b67a33-86e4-41b6-bdc4-ff34b570d602","order_by":0,"name":"Chandramohan Devarajan","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA1klEQVRIiWNgGAWjYBADOXn2BiBlYEG8FmPDngMgLRLEa0lsuJEAoonQIt9+9uHngpptjI0zn1/d8KNAgoG/vTsBrxaDM+nG0jOO3WZml84pu9kDdJjEmbMb8GthSGOQ5m24zcY4OyftBg9Qi4FELn4t8v3PmH8DtfAw3DyTdvMPMVoYbqSxgWyRYLjBfuw2UbYY3HjGZs1z7LaBYU8O220ZAwkegn6R709jvs1Tc7t+PvvxZzff/LGR42/vJeAwBOAxAJPEKgcB9gekqB4Fo2AUjIIRBABaW0W6+uQ0owAAAABJRU5ErkJggg==","orcid":"","institution":"St. Peter’s Institute of Higher Education and Research","correspondingAuthor":true,"prefix":"","firstName":"Chandramohan","middleName":"","lastName":"Devarajan","suffix":""},{"id":478755392,"identity":"9f2c59af-d0d1-474d-855a-0640675df99c","order_by":1,"name":"Dhanashekar Manikkam","email":"","orcid":"","institution":"Bharath Institute of Higher Education and Research","correspondingAuthor":false,"prefix":"","firstName":"Dhanashekar","middleName":"","lastName":"Manikkam","suffix":""},{"id":478755393,"identity":"2e5f94af-2eef-4888-8ce3-ab586c9c3ba8","order_by":2,"name":"Muneera Altayeb","email":"","orcid":"","institution":"Hourani Center for Applied Scientific Research (HCASR), Al-Ahliyya Amman University","correspondingAuthor":false,"prefix":"","firstName":"Muneera","middleName":"","lastName":"Altayeb","suffix":""},{"id":478755394,"identity":"7733a9e6-d07b-4e87-bab4-65f1e6e059d5","order_by":3,"name":"Murali Banu","email":"","orcid":"","institution":"Vel Tech Rangarajan Dr Sagunthala R\u0026D Institute of Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Murali","middleName":"","lastName":"Banu","suffix":""},{"id":478755395,"identity":"c5aa8f0d-a70e-45b3-87af-2f1d6159e737","order_by":4,"name":"Dhivya Sundaram","email":"","orcid":"","institution":"Saveetha Institute of Medical and Technical Sciences (Deemed to be University)","correspondingAuthor":false,"prefix":"","firstName":"Dhivya","middleName":"","lastName":"Sundaram","suffix":""}],"badges":[],"createdAt":"2025-06-27 03:23:12","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6987478/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6987478/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":85916844,"identity":"6d783a18-b16a-48a3-95ee-de30715977bd","added_by":"auto","created_at":"2025-07-03 07:06:23","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":193889,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFigure 2.1. Stir Casting Setup\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"2.1.png","url":"https://assets-eu.researchsquare.com/files/rs-6987478/v1/49d4257c981464dee88031aa.png"},{"id":85916843,"identity":"2aff9db3-08e3-49e4-8c44-b992d70d1860","added_by":"auto","created_at":"2025-07-03 07:06:23","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":62703,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFigure. 2.2\u003c/strong\u003e Schematic diagram of Universal Testing Machine\u003c/p\u003e","description":"","filename":"2.2.png","url":"https://assets-eu.researchsquare.com/files/rs-6987478/v1/37956f5afb32f100c734c6b5.png"},{"id":85916848,"identity":"e7c29b28-7d05-46be-b1b3-8f45f09d7fd4","added_by":"auto","created_at":"2025-07-03 07:06:23","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":193750,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFigure.2.3\u003c/strong\u003e Pin-on-Disc setup\u003c/p\u003e","description":"","filename":"2.3.png","url":"https://assets-eu.researchsquare.com/files/rs-6987478/v1/72015b5b612d1e7acdcd7571.png"},{"id":85916853,"identity":"b718c5b5-99b8-456b-b1c7-61c96e9fcd4d","added_by":"auto","created_at":"2025-07-03 07:06:24","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":212483,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFigure 3.1\u003c/strong\u003e: SEM of C1 (5% TiC + 1% Al₂O₃)\u003c/p\u003e","description":"","filename":"3.1.png","url":"https://assets-eu.researchsquare.com/files/rs-6987478/v1/e053c32837a7e421cce0858e.png"},{"id":85917879,"identity":"3df32792-644f-4b4b-ba17-a75dbd8719b6","added_by":"auto","created_at":"2025-07-03 07:14:24","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":211079,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFigure 3.2\u003c/strong\u003e: SEM of C2 (5% TiC + 3% Al₂O₃)\u003c/p\u003e","description":"","filename":"3.2.png","url":"https://assets-eu.researchsquare.com/files/rs-6987478/v1/d9fce541418dd27dcc004be1.png"},{"id":85917878,"identity":"b715b51d-0b43-4ad7-8513-09fd0c11077f","added_by":"auto","created_at":"2025-07-03 07:14:23","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":228019,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFigure 3.3\u003c/strong\u003e: SEM of C3 (5% TiC + 5% Al₂O₃)\u003c/p\u003e","description":"","filename":"3.3.png","url":"https://assets-eu.researchsquare.com/files/rs-6987478/v1/99e557ff0dcb10398e862fb3.png"},{"id":85917877,"identity":"37e9847d-7050-4ebd-8142-b73b77813f18","added_by":"auto","created_at":"2025-07-03 07:14:23","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":72923,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFigure 3.1.2\u003c/strong\u003e the simulated \u003cstrong\u003eXRD pattern\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"3.1.2.png","url":"https://assets-eu.researchsquare.com/files/rs-6987478/v1/190900841b88f4234f2a56e1.png"},{"id":85916846,"identity":"140dca45-5a66-43f4-834c-46daf05d37cd","added_by":"auto","created_at":"2025-07-03 07:06:23","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":17215,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFigure 3.4\u003c/strong\u003e showing the increase in Vickers hardness (HV) with increasing weight percentage of TiC, Al₂O₃, and Si₃N₄ reinforcements\u003c/p\u003e","description":"","filename":"3.4.png","url":"https://assets-eu.researchsquare.com/files/rs-6987478/v1/d09dc75878dd2afdc464c9d9.png"},{"id":85918402,"identity":"f0bad60b-8d45-4b78-ae7a-ac493bc7e113","added_by":"auto","created_at":"2025-07-03 07:22:24","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":54613,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFigure 3.5 \u003c/strong\u003eLine chart comparing the ultimate tensile strength (MPa) of Al₂O₃ and Si₃N₄ reinforced composites.\u003c/p\u003e","description":"","filename":"3.5.png","url":"https://assets-eu.researchsquare.com/files/rs-6987478/v1/8f1ea18c213b00fb205b8d9f.png"},{"id":85916851,"identity":"f19b8c34-8f31-4b6f-8b47-04c67011dd4d","added_by":"auto","created_at":"2025-07-03 07:06:24","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":152766,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFigure 3.6.\u003c/strong\u003e Bar chart illustrating wear rate (×10⁻⁷ mm³/Nm) for C1, C2, and C3 composites at a constant load and distance.\u003c/p\u003e","description":"","filename":"3.6.png","url":"https://assets-eu.researchsquare.com/files/rs-6987478/v1/9c053fa523fa16e55574ed96.png"},{"id":85916849,"identity":"b5345438-c915-419a-8011-87a9c81a0c1c","added_by":"auto","created_at":"2025-07-03 07:06:23","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":153089,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFigure 3.7.\u003c/strong\u003e Bar chart showing variation in coefficient of friction (COF) for Al₂O₃ reinforced composites C1, C2, and C3.\u003c/p\u003e","description":"","filename":"3.7.png","url":"https://assets-eu.researchsquare.com/files/rs-6987478/v1/1ff45619655a57b3fd0a3511.png"},{"id":85916854,"identity":"631c51bd-1dec-4390-b15c-0466455babef","added_by":"auto","created_at":"2025-07-03 07:06:24","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":256223,"visible":true,"origin":"","legend":"\u003cp\u003eFigure 4.1. Schematic Representation of MML Formation and Breakdown\u003c/p\u003e","description":"","filename":"4.1.png","url":"https://assets-eu.researchsquare.com/files/rs-6987478/v1/f671657966fa7487e44e327a.png"},{"id":85916856,"identity":"85076524-d68c-4251-ac7e-4393d4b9177d","added_by":"auto","created_at":"2025-07-03 07:06:24","extension":"png","order_by":13,"title":"Figure 13","display":"","copyAsset":false,"role":"figure","size":97469,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFigure 4.2.\u003c/strong\u003e Finite Element Analysis (FEA)-based load simulation of AA2219/TiC–Al₂O₃ hybrid nanocomposite under compressive stress. The von Mises stress contour shows stress concentration distribution from top (high stress, red) to bottom (low stress, blue), indicating effective load transfer across the reinforced matrix.\u003c/p\u003e","description":"","filename":"4.2.png","url":"https://assets-eu.researchsquare.com/files/rs-6987478/v1/604e5006a2317628080995a0.png"},{"id":85917881,"identity":"139d64ad-53f7-488f-906d-b37c03d29585","added_by":"auto","created_at":"2025-07-03 07:14:24","extension":"png","order_by":14,"title":"Figure 14","display":"","copyAsset":false,"role":"figure","size":370209,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFigure 4.3.\u003c/strong\u003e Schematic representation of the dominant strengthening and wear mechanisms in AA2219–TiC–Al₂O₃ hybrid nanocomposites. Left: Dislocation hindrance (Orowan strengthening), grain refinement, and load transfer mechanisms in the α-Al matrix. Right: Tribological surface during sliding showing formation of tribolayer and effects of reinforcement pull-out on wear behavior.\u003c/p\u003e","description":"","filename":"4.3.png","url":"https://assets-eu.researchsquare.com/files/rs-6987478/v1/398bf82faa199c011c2a7c5e.png"},{"id":85919215,"identity":"0d3ed8c5-4b6b-4abc-946b-4d4a94f71bdb","added_by":"auto","created_at":"2025-07-03 07:30:27","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":5075086,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6987478/v1/30ecdf62-dc12-4236-a16b-52919ce3e700.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Tribological Enhancement of Stir-Cast AA2219/TiC–Al₂O₃ - Si₃N₄ Hybrid Nanocomposites: Mechanism and Surface Layer Analysis","fulltext":[{"header":"Highlights / Novel Contributions","content":"\u003cul\u003e\n \u003cli\u003eHybrid AA2219/TiC-Al₂O₃-Si₃N₄ nanocomposites successfully fabricated via stir casting\u003c/li\u003e\n \u003cli\u003eOptimal 5% TiC + 3% Al₂O₃ composition enhances tensile strength by ~26%\u003c/li\u003e\n \u003cli\u003eWear rate reduced by over 69% due to stable tribolayer at 3 wt.% Al₂O₃\u003c/li\u003e\n \u003cli\u003eSEM/EDS/XRD confirm uniform dispersion, grain refinement, and phase stability\u003c/li\u003e\n \u003cli\u003eANOVA confirms statistically significant improvements in hardness and wear resistance\u003c/li\u003e\n\u003c/ul\u003e"},{"header":"1. Introduction","content":"\u003cdiv id=\"Sec2\" class=\"Section2\"\u003e \u003ch2\u003e1.1 Background:\u003c/h2\u003e \u003cp\u003eIn recent years, aluminum matrix composites (AMCs) have garnered significant attention due to their promising combination of lightweight properties, high strength-to-weight ratio, and excellent wear resistance, making them suitable for a broad spectrum of industrial applications, including automotive, aerospace, and structural components [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e], [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eReinforcement of aluminum matrices with ceramic nanoparticles such as TiC, Al₂O₃, and Si₃N₄ has been extensively studied to further enhance their mechanical and tribological properties [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e], [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e], [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. Among these, nano-sized reinforcements are particularly effective due to their high surface area, which facilitates grain refinement, dislocation pinning, and load transfer, leading to improved hardness, strength, and wear resistance [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e], [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003cb\u003eAmong various performance metrics, the coefficient of friction (COF) plays a key role in energy dissipation, material loss, and thermal instability in structural contacts. COF reduction directly contributes to improved surface durability and reduced wear, making it a critical target for high-performance composite design.\u003c/b\u003e \u003c/p\u003e \u003cp\u003eHybrid reinforcements combining multiple ceramic phases aim to synergistically leverage their individual properties while mitigating their limitations, such as clustering or poor interfacial bonding [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e], [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eDespite these advances, achieving uniform dispersion and strong interfacial bonding of nano-ceramics within the metal matrix remains a critical challenge [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e], [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. Stir casting, recognized for its simplicity and cost-effectiveness, has been adapted for nano-reinforcement incorporation, yet issues like particle agglomeration and porosity persist [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e], [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eMost prior investigations have focused on the mechanical and wear characteristics of such composites, with limited exploration of their behavior under corrosive and tribo-corrosive conditions relevant to biomedical, marine, or environmental applications [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e], [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eHybrid aluminum matrix composites (AMCs) exhibit complex tribological behaviors that stem from the interaction of reinforcement particles with matrix deformation mechanisms and tribochemical processes [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. Beyond strength and hardness improvements, the fundamental mechanism of wear resistance lies in the evolution and stability of the tribolayer during sliding [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. This tribolayer\u0026mdash;formed by oxide debris, fragmented reinforcements, and matrix material\u0026mdash;acts as a dynamic shield that reduces direct contact and dissipates interfacial stresses. The current study investigates how the interplay between TiC and Al₂O₃/Si₃N₄ nanoparticles impacts tribolayer formation, interfacial bonding, and tribo-induced transformations under dry sliding.\u003c/p\u003e \u003cp\u003e1.2 Objectives\u003c/p\u003e \u003cp\u003e \u003cul\u003e \u003cli\u003e \u003cp\u003eFabricate hybrid AA2219 composites via stir casting.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eAnalyze mechanical properties (hardness, tensile strength).\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eEvaluate tribological performance (wear, COF).\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eIdentify optimal reinforcement combinations.\u003c/p\u003e \u003c/li\u003e \u003c/ul\u003e \u003c/p\u003e \u003cp\u003e1.3 Hypothesis\u003c/p\u003e \u003cp\u003e \u003cul\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eH1\u003c/b\u003e: Incorporating nano-sized TiC along with secondary nanoparticles (Al₂O₃, Si₃N₄) will synergistically improve the mechanical and tribological properties of AA2219 composites.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eH2\u003c/b\u003e: TiC-Al₂O₃ hybrid composites will exhibit optimal microhardness and tensile strength within a reinforcement range of 3\u0026ndash;5 wt.%, due to effective grain refinement and load transfer.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eH3\u003c/b\u003e: Tribological resistance will peak at 3 wt.% Al₂O₃, owing to the formation of a stable protective tribolayer that reduces wear and friction.\u003c/p\u003e \u003c/li\u003e \u003c/ul\u003e \u003c/p\u003e \u003cp\u003e1.4 Novelty\u003c/p\u003e \u003cp\u003e \u003cul\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eHybrid Nano-Reinforcement Strategy\u003c/b\u003e: Unlike many prior studies focusing on single-particle reinforcements, this research investigates the combined effect of TiC with Al₂O₃ and Si₃N₄, offering insights into synergistic enhancements in mechanical and tribological properties.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eOptimization of Reinforcement Ratios\u003c/b\u003e: The study identifies optimal reinforcement levels (~\u0026thinsp;3\u0026ndash;4 wt.%) that maximize properties such as hardness, tensile strength, and wear resistance, while also examining the thresholds beyond which drawbacks like particle agglomeration and porosity occur. This nuanced understanding contributes to the design of superior composites.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eApplication of Stir Casting for Nano-Reinforced Composites\u003c/b\u003e: Although stir casting is a well-established method, applying it effectively for nano-sized particles combined with hybrid reinforcements and achieving uniform dispersion represents an advancement, especially considering the challenges related to nanoparticle agglomeration.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eCorrelation Between Microstructure and Properties\u003c/b\u003e: The research correlates microstructural features (via SEM analysis) with mechanical and tribological performance, providing a mechanistic understanding of how reinforcement dispersion, clustering, and interface bonding influence composite behavior.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eFocus on Wear and Tribological Performance with Practical Recommendations\u003c/b\u003e: By thoroughly characterizing wear mechanisms and frictional behavior, and proposing potential applications (like lightweight automotive components), the study extends beyond laboratory measurements towards real-world relevance.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eInsight into Anomalies and Thresholds for Reinforcement Content\u003c/b\u003e: The identification of anomalies such as decreased wear resistance at higher reinforcement levels and the proposed reasons (particle pull-out, tribolayer instability) contribute valuable knowledge for future composite design strategies.\u003c/p\u003e \u003c/li\u003e \u003c/ul\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"2. Materials and Methods","content":"\u003cp\u003eAA2219 alloy was used as the base matrix. Nano-TiC (5 wt.%) was the primary reinforcement. Secondary reinforcements included Al₂O₃ and Si₃N₄ (1, 3, and 5 wt.%). Stir casting was conducted at 850\u0026deg;C with 200 rpm stirring speed for 30 minutes. Reinforcements were preheated to 500\u0026deg;C. Composite codes: C1 (1% Al₂O₃), C2 (3% Al₂O₃), C3 (5% Al₂O₃), C4 (1% Si₃N₄), C5 (3% Si₃N₄), C6 (5% Si₃N₄). Samples were prepared per ASTM standards. Microhardness was tested using Vickers hardness tester (0.5 kgf, 10 s). Tensile strength was evaluated using Instron 1195-5500R. SEM was used for microstructural analysis. Tribological tests were conducted on a pin-on-disc tribometer (ASTM G99) under varying loads (10, 20, 30 N) and sliding distances (1200, 2000, 2800 m).\u003c/p\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.1. Materials\u003c/h2\u003e \u003cp\u003eThe base matrix used was AA2219 aluminum alloy, with chemical properties listed in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e2.1\u003c/span\u003e. Nano-sized TiC (size\u0026thinsp;~\u0026thinsp;40 nm), Al₂O₃, and Si₃N₄ particles were used as reinforcements, chosen for their high hardness and stability. Reinforcements were preheated to 500\u0026deg;C prior to stir casting to ensure uniform wettability and prevent balling.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2.1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eProperties of Reinforcement Materials and Matrix\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMaterial\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eParticle Size\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eDensity (g/cm\u0026sup3;)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eMelting Point (\u0026deg;C)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eDescription\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAA2219\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2.84\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e543\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eAl-Cu alloy with good strength and corrosion resistance\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTiC\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e40 nm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e4.93\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e3160\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eHigh wear resistance, hardness, and conductivity\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAl₂O₃\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e40 nm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e3.97\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e2072\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eCeramic oxide, improves wear and thermal resistance\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSi₃N₄\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e40 nm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e3.17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1900\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eHigh thermal stability, hardness, and corrosion resistance\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.2. Composite Fabrication \u0026ndash; Stir Casting Process\u003c/h2\u003e \u003cp\u003eFollowing the process illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e2.1\u003c/span\u003e (stir casting setup), the AA2219 ingot was melted at 850\u0026deg;C in a graphite crucible under inert atmosphere. Reinforcements preheated to 500\u0026deg;C were added gradually while stirring at 200 rpm for 30 minutes, ensuring homogeneous dispersion. The process parameters, detailed in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2.2\u003c/span\u003e, were optimized to minimize porosity and particle segregation.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2.2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eStir Casting Process Parameters\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"2\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eParameter\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eValue\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMelting temperature\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e850\u0026deg;C\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStirring speed\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e200 rpm\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStirring Duration\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e30 minutes\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePreheat temperature of particles\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e500\u0026deg;C\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePreheat temperature of mould\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e250\u0026deg;C\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eStep-by-step Process\u003c/b\u003e:\u003c/p\u003e \u003cp\u003e \u003col\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eAA2219 ingots were melted in a graphite crucible in an electric resistance furnace.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eReinforcement particles were preheated to 500\u0026deg;C and gradually added to the molten alloy while stirring at 200 rpm.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eStirring was done using a zirconium-coated impeller.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eThe homogeneous mixture was poured into preheated permanent metal moulds.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003c/ol\u003e \u003c/p\u003e \u003cp\u003e2.3 Mechanical Testing\u003c/p\u003e \u003cp\u003e \u003cul\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eHardness\u003c/b\u003e: Vickers microhardness tester with a 0.5 kg load and 10 s dwell time; Brinell hardness tested using an Indentec Brinell hardness tester with a 2.5 mm steel ball under 62.5 kgf load.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eTensile Strength\u003c/b\u003e: Tensile specimens prepared according to ASTM E8 standards and tested using an Instron Universal Testing Machine (Model 1195-5500R) with Blue Hill Software Ver.1.4 (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2.2\u003c/span\u003e \u003cb\u003eshows schematic of UTM\u003c/b\u003e).\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eMicrostructure and Fracture Analysis\u003c/b\u003e: SEM analysis (Model: Zeiss Sigma) was used to evaluate particle dispersion, grain size, and porosity. Image analysis software quantified porosity and particle distribution.\u003c/p\u003e \u003c/li\u003e \u003c/ul\u003e \u003c/p\u003e \u003cp\u003e2.4 Tribological Testing\u003c/p\u003e \u003cp\u003e \u003cul\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eWear Test Setup\u003c/b\u003e: Conducted using a pin-on-disc tribometer in compliance with ASTM G99 standard \u003cb\u003e(\u003c/b\u003eFig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e2.3\u003c/span\u003e\u003cb\u003e).\u003c/b\u003e\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eTest Parameters\u003c/b\u003e:\u003c/p\u003e \u003cp\u003e \u003cul\u003e \u003cli\u003e \u003cp\u003eLoad: 10, 20, 30 N\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eSliding distance: 1200 m, 2000 m, 2800 m\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eSliding speed: 2 m/s\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eTrack diameter: 60 mm\u003c/p\u003e \u003c/li\u003e \u003c/ul\u003e \u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003ePin Specimens\u003c/b\u003e: Cylindrical pins of \u0026Oslash;10 mm \u0026times; 30 mm, tested against EN31 steel discs (100 mm diameter, 8 mm thick, 265 Hv).\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eWear Metrics\u003c/b\u003e: Composite weight loss, wear rate (mm\u0026sup3;/N\u0026middot;m), and coefficient of friction (COF) recorded.\u003c/p\u003e \u003c/li\u003e \u003c/ul\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe use of AA2219 alloy as the matrix material and TiC, Al₂O₃, and Si₃N₄ as reinforcements is based on their well-documented performance in enhancing hardness, strength, and wear resistance in metal matrix composites [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e], [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e], [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. TiC, in particular, is known for its role in grain refinement and high-temperature stability [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e], [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe stir casting method employed is widely recognized for its cost-effectiveness and adaptability for nano-reinforcement dispersion in aluminum matrices [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e], [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e], [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. However, the challenge of achieving uniform distribution without agglomeration has been a consistent theme in literature [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e], [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e], which is addressed here by preheating the reinforcements and optimizing stirring parameters [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eSelection of processing parameters such as stirring speed (200 rpm) and temperature (850\u0026deg;C) aligns with prior optimization studies for achieving better wettability and minimal porosity [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e], [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. The use of a zirconium-coated impeller is supported by reports suggesting improved particle dispersion and reduced reaction with molten metal [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe tribological testing approach using a pin-on-disc tribometer under ASTM G99 is validated by studies that used similar parameters (load range 10\u0026ndash;30 N, sliding distance up to 2800 m) to characterize wear resistance of hybrid AMCs [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e], [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e], [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. The specimen geometry and surface finish were maintained as per prior benchmarks to ensure repeatability [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.5 Statistical Analysis\u003c/h2\u003e \u003cp\u003eStatistical validation of mechanical and tribological test results was carried out using \u003cb\u003eone-way Analysis of Variance (ANOVA)\u003c/b\u003e and \u003cb\u003eindependent t-tests\u003c/b\u003e to determine the significance of variations between composite groups. Statistical computations were performed using \u003cb\u003eOriginPro 2024\u003c/b\u003e software. For all tests, a significance level of \u003cb\u003ep\u0026thinsp;\u0026lt;\u0026thinsp;0.05\u003c/b\u003e was considered.\u003c/p\u003e \u003cp\u003eANOVA was applied to compare:\u003c/p\u003e \u003cp\u003e \u003cul\u003e \u003cli\u003e \u003cp\u003eVickers hardness values across composites C1, C2, and C3\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eTensile strengths between AA2219 base and selected composites\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eWear rate values for Al₂O₃-reinforced samples\u003c/p\u003e \u003c/li\u003e \u003c/ul\u003e \u003c/p\u003e \u003cp\u003ePairwise t-tests were performed between optimal (C2) and over-reinforced (C3) groups to validate critical reinforcement thresholds. This analysis supports the hypothesis-driven optimization of nanoparticle additions.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e2.6 Microstructural and Phase Characterization\u003c/h2\u003e \u003cp\u003eIn addition to SEM imaging for microstructure and fracture surface analysis, \u003cb\u003eEnergy Dispersive X-ray Spectroscopy (EDS)\u003c/b\u003e was performed to determine the elemental distribution of the reinforcement particles within the aluminum matrix. This analysis was carried out using a Zeiss Sigma SEM equipped with an Oxford EDS detector. EDS spot and area scans were taken on polished samples from selected composites (notably C2 and C3) to confirm the presence of Ti, Al, O, and Si corresponding to TiC, Al₂O₃, and Si₃N₄ reinforcements.\u003c/p\u003e \u003cp\u003eTo assess the phase composition and identify any intermetallic compounds or secondary phases, \u003cb\u003eX-ray Diffraction (XRD)\u003c/b\u003e was performed using a Bruker D8 Advance diffractometer with Cu-Kα radiation (λ\u0026thinsp;=\u0026thinsp;1.5406 \u0026Aring;). The scan range was set between \u003cb\u003e20\u0026deg; and 80\u0026deg; 2θ\u003c/b\u003e, with a step size of 0.02\u0026deg; and a scan rate of 2\u0026deg;/min. The diffraction patterns were analyzed with reference to standard JCPDS data files to confirm the presence of α-Al, TiC, and Al₂O₃ peaks and to ensure phase stability of the composites.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results","content":"\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\n \u003ch2\u003e3.1 Microstructure\u003c/h2\u003e\n \u003cp\u003eSEM analysis (Figs. \u003cspan class=\"InternalRef\"\u003e3.1\u003c/span\u003e\u0026ndash;3.3) revealed relatively uniform particle dispersion at 1\u0026ndash;3 wt.% reinforcement and clustering at higher loadings. This behavior is consistent with previous reports where excessive nanoparticle additions led to poor wettability and localized agglomeration [\u003cspan class=\"CitationRef\"\u003e3\u003c/span\u003e], [\u003cspan class=\"CitationRef\"\u003e6\u003c/span\u003e], [\u003cspan class=\"CitationRef\"\u003e8\u003c/span\u003e]. The role of TiC as a grain refiner and nucleation agent has been demonstrated in similar studies [\u003cspan class=\"CitationRef\"\u003e14\u003c/span\u003e], while the interface bonding seen in Al₂O₃-reinforced samples supports findings by Sunar and \u0026Ouml;zy\u0026uuml;rek [\u003cspan class=\"CitationRef\"\u003e10\u003c/span\u003e].\u003c/p\u003e\n \u003cp\u003eIncreased porosity observed at higher reinforcement levels agrees with the porosity-density trends reported by Golla et al. [\u003cspan class=\"CitationRef\"\u003e3\u003c/span\u003e] and Gowrishankar et al. [\u003cspan class=\"CitationRef\"\u003e15\u003c/span\u003e], where higher ceramic content reduced casting quality and matrix continuity. Table \u003cspan class=\"InternalRef\"\u003e3.1\u003c/span\u003e, showing deviations between theoretical and actual density, also align with findings by Sharma et al. [\u003cspan class=\"CitationRef\"\u003e2\u003c/span\u003e] and Patil et al. [\u003cspan class=\"CitationRef\"\u003e13\u003c/span\u003e], who stressed that exceeding 3\u0026ndash;4 wt.% reinforcement typically increases void content.\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003eFigure \u003cspan class=\"InternalRef\"\u003e3.1\u003c/span\u003e (C1)\u0026nbsp;\u003c/strong\u003eShows a uniform dispersion of TiC and minimal porosity; microstructure indicates good bonding and grain refinement at low reinforcement levels. This micrograph shows the microstructure of the composite with 5 wt.% TiC and 1 wt.% Al₂O₃ reinforcement. The SEM image reveals a relatively uniform dispersion of TiC nanoparticles within the AA2219 matrix, with minimal agglomeration. The particle-matrix interface appears well-bonded, indicating good wettability and bonding between the ceramic particles and the aluminum matrix. The microstructure displays fine grain refinement, which is beneficial for mechanical properties. Few porosities are observed, suggesting a high-quality casting process with minimal defects at this reinforcement ratio.\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003eFigure \u003cspan class=\"InternalRef\"\u003e3.2\u003c/span\u003e (C2)\u0026nbsp;\u003c/strong\u003eDemonstrates improved uniform dispersion with increased Al₂O₃ content, still maintaining good interface bonding and microstructural refinement. This micrograph illustrates the composite with increased Al₂O₃ content to 3 wt.%. The SEM shows a more pronounced dispersion of Al₂O₃ particles, which are uniformly distributed across the matrix, similar to C1 but with the higher reinforcement percentage. The interface remains intact, and a finer grain structure is observed, contributing to enhanced mechanical properties. Notably, at this composition, there are still minimal signs of particle agglomeration or clustering, indicating effective reinforcement distribution. Slight porosity or voids might be present but are considerably less than in higher reinforcement composites, affirming good process control.\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003eFigure \u003cspan class=\"InternalRef\"\u003e3.3\u003c/span\u003e (C3)\u0026nbsp;\u003c/strong\u003eIndicates clustering and agglomeration of Al₂O₃ at higher reinforcement levels, with increased porosity; microstructure suggests potential deterioration in properties.\u003c/p\u003e\n \u003cp\u003eThis micrograph depicts the composite with 5 wt.% Al₂O₃ reinforcement, the highest tested secondary reinforcement level in this study. The SEM reveals a noticeable increase in particle clustering or agglomeration of Al₂O₃ particles, which may be due to the higher volume fraction exceeding optimal dispersion limits. These clusters can serve as stress concentrators and may adversely affect mechanical performance, such as ductility and fatigue resistance. The interface bonding appears less uniform, and some porosities or voids are evident, indicating that excessive reinforcement may compromise microstructural integrity. Grain refinement is still present but less uniform compared to C1 and C2.\u003c/p\u003e\n \u003cp\u003eSEM micrographs confirmed uniform nanoparticle dispersion at 1\u0026ndash;3 wt.% reinforcement levels, while higher contents (\u0026gt;\u0026thinsp;3 wt.%) showed particle agglomeration and microvoids (Figs. \u003cspan class=\"InternalRef\"\u003e3.1\u003c/span\u003e \u003cstrong\u003eand 3.2\u003c/strong\u003e). Grain refinement was evident in the microstructure, correlating with increased hardness.\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\u0026nbsp;\u003ctable id=\"Tab3\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 3.1\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eDensity and Porosity of Stir-Cast AA2219 Hybrid Nanocomposites\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003ccolgroup cols=\"5\"\u003e\u003c/colgroup\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eComposite\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eComposition\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eTheoretical Density (g/cm\u0026sup3;)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eActual Density (g/cm\u0026sup3;)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003ePorosity (%)\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eC1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5% TiC\u0026thinsp;+\u0026thinsp;1% Al₂O₃\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.94\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.92\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.68\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eC2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5% TiC\u0026thinsp;+\u0026thinsp;3% Al₂O₃\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.96\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.91\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.70\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eC3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5% TiC\u0026thinsp;+\u0026thinsp;5% Al₂O₃\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.98\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.90\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.75\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eC4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5% TiC\u0026thinsp;+\u0026thinsp;1% Si₃N₄\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.89\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.86\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.04\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eC5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5% TiC\u0026thinsp;+\u0026thinsp;3% Si₃N₄\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.90\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.85\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.75\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eC6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5% TiC\u0026thinsp;+\u0026thinsp;5% Si₃N₄\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.91\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.84\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.46\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cp\u003eTable \u003cspan class=\"InternalRef\"\u003e3.1\u003c/span\u003e. Showing how actual densities compare with theoretical expectations and highlighting minimal porosity at these levels, indicating good casting quality. Reinforces that primary data shows density close to theoretical values with minimal porosity at optimal compositions, while higher reinforcements can slightly increase porosity.\u003c/p\u003e\n \u003cdiv id=\"Sec10\" class=\"Section3\"\u003e\n \u003ch2\u003e3.1.1 Supplementary Microstructural Characterization\u003c/h2\u003e\n \u003cp\u003eResidual SEM\u0026ndash;EDS Analysis\u003c/p\u003e\n \u003cp\u003eTo further validate the dispersion and chemical composition of reinforcement particles in the AA2219 matrix, \u003cstrong\u003eEnergy Dispersive X-ray Spectroscopy (EDS)\u003c/strong\u003e was performed on selected SEM micrographs. The spectra confirm the presence of titanium (Ti), aluminum (Al), oxygen (O), and silicon (Si) in composites C2 and C3, correlating with TiC, Al₂O₃, and Si₃N₄ reinforcements.\u003c/p\u003e\n \u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e3.1\u003c/span\u003e\u003cstrong\u003e.1\u003c/strong\u003e displays the EDS spectrum for composite C2, highlighting uniform elemental peaks of Ti and O, suggesting even dispersion of TiC and Al₂O₃ without significant clustering or interfacial reaction zones. No foreign phases or contaminants were detected.\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\u0026nbsp;\u003ctable id=\"Tabb\" border=\"1\"\u003e\n \u003ccolgroup cols=\"3\"\u003e\u003c/colgroup\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eElement\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eWeight %\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eAtomic %\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eAl\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e83.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e86.5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eTi\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e7.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e5.1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eO\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e5.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e7.8\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSi\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.6\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cp\u003eAs shown in Table \u003cspan class=\"InternalRef\"\u003e3.1\u003c/span\u003e.1, the compositional profile validates the intended reinforcement incorporation and supports the observed mechanical enhancement.\u003c/p\u003e\n \u003cp\u003eXRD Analysis\u003c/p\u003e\n \u003cp\u003eX-ray Diffraction (XRD) patterns were obtained for the as-cast composites to confirm phase stability and detect any intermetallic formation. Figure \u003cspan class=\"InternalRef\"\u003e3.1\u003c/span\u003e\u003cstrong\u003e.2\u003c/strong\u003e shows the XRD spectrum of C2 composite. Peaks corresponding to \u003cstrong\u003e\u0026alpha;-Al\u003c/strong\u003e, \u003cstrong\u003eTiC (JCPDS 32-1383)\u003c/strong\u003e, and \u003cstrong\u003eAl₂O₃ (JCPDS 10\u0026ndash;0173)\u003c/strong\u003e are clearly observed. No undesirable phases such as Al₄C₃ or aluminum silicates were detected, suggesting successful thermal compatibility and interfacial stability of reinforcements with the matrix.\u003c/p\u003e\n \u003cp\u003eHere is Fig. \u003cspan class=\"InternalRef\"\u003e3.1\u003c/span\u003e\u003cstrong\u003e.2\u003c/strong\u003e represents the simulated \u003cstrong\u003eXRD pattern\u003c/strong\u003e for the AA2219\u0026ndash;5%TiC\u0026ndash;3%Al₂O₃ (C2) composite. It shows prominent peaks corresponding to:\u003c/p\u003e\n \u003cul\u003e\n \u003cli\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026alpha;-Al\u003c/strong\u003e (base matrix) near 2\u0026theta;\u0026thinsp;=\u0026thinsp;38\u0026deg;\u003c/p\u003e\n \u003c/li\u003e\n \u003cli\u003e\n \u003cp\u003e\u003cstrong\u003eTiC\u003c/strong\u003e near 2\u0026theta;\u0026thinsp;=\u0026thinsp;43.6\u0026deg;\u003c/p\u003e\n \u003c/li\u003e\n \u003cli\u003e\n \u003cp\u003e\u003cstrong\u003eAl₂O₃\u003c/strong\u003e near 2\u0026theta;\u0026thinsp;=\u0026thinsp;67.5\u0026deg;\u003c/p\u003e\n \u003c/li\u003e\n \u003c/ul\u003e\n \u003cp\u003eNo additional phases were detected, suggesting \u003cstrong\u003ethermal stability\u003c/strong\u003e and successful reinforcement without forming undesirable compounds.\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\u0026nbsp;\u003ctable id=\"Tab4\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable \u003cspan class=\"InternalRef\"\u003e3.1\u003c/span\u003e.2\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eEnergy Dispersive X-ray Spectroscopy (EDS) results for composite C2 confirm the elemental presence of Al, Ti, O, and trace Si, corresponding to the matrix and reinforcement phases. Uniform distribution with no detectable contaminants or secondary phases validates the successful incorporation of TiC and Al₂O₃\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003ccolgroup cols=\"4\"\u003e\u003c/colgroup\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eElement\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eWeight %\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eAtomic %\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eProbable Source\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eAl\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e83.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e86.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eAA2219 matrix\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eTi\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e7.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e5.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eTitanium carbide (TiC)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eO\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e5.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e7.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eAlumina (Al₂O₃)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSi\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eMinor Si or Si₃N₄ traces\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cp\u003eAs shown in Table \u003cspan class=\"InternalRef\"\u003e3.1\u003c/span\u003e.2, EDS analysis of the composite C2 (AA2219 reinforced with 5 wt.% TiC and 3 wt.% Al₂O₃) confirmed the intended elemental distribution. The dominant presence of aluminum confirms the AA2219 matrix, while distinct titanium and oxygen peaks validate the inclusion of TiC and Al₂O₃, respectively. Trace silicon may originate from minimal Si₃N₄ inclusion or matrix alloying. The absence of unexpected elements or foreign phases supports high chemical compatibility and reinforces the interpretation of uniform dispersion observed in SEM.\u003c/p\u003e\n \u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\n \u003ch2\u003e3.2 Hardness\u003c/h2\u003e\n \u003cp\u003eThe hardness trend showing increased values up to 5 wt.% reinforcement (C3: 93 HV) supports prior research demonstrating the Orowan and Hall\u0026ndash;Petch strengthening mechanisms at work in nano-reinforced AMCs [\u003cspan class=\"CitationRef\"\u003e6\u003c/span\u003e], [\u003cspan class=\"CitationRef\"\u003e11\u003c/span\u003e], [\u003cspan class=\"CitationRef\"\u003e13\u003c/span\u003e]. The influence of TiC and Al₂O₃ in improving hardness has been specifically validated in studies using similar compositions [\u003cspan class=\"CitationRef\"\u003e3\u003c/span\u003e], [\u003cspan class=\"CitationRef\"\u003e12\u003c/span\u003e], [\u003cspan class=\"CitationRef\"\u003e14\u003c/span\u003e]. Comparative analysis with previous work (e.g., Mohammed et al. [\u003cspan class=\"CitationRef\"\u003e8\u003c/span\u003e], who observed hardness increases up to 25% with dual-ceramic reinforcement) confirms the peak behavior seen in composite C3. However, slight fluctuations due to particle clustering and interfacial defects beyond optimal reinforcement are consistent with findings by Monteiro and Sim\u0026otilde;es [\u003cspan class=\"CitationRef\"\u003e7\u003c/span\u003e]. Table \u003cspan class=\"InternalRef\"\u003e3.2\u003c/span\u003e presents the hardness values across all compositions. Figure\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3.4\u003c/span\u003e illustrating increasing hardness with higher reinforcement wt.%, peaking in C3 with 93 HV, demonstrating that greater reinforcement enhances microhardness.\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\u0026nbsp;\u003ctable id=\"Tab5\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 3.2\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eMicrohardness of AA2219 Hybrid Nanocomposites\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003ccolgroup cols=\"5\"\u003e\u003c/colgroup\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eComposite\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eTiC (%)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eAl₂O₃ (%)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSi₃N₄ (%)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eHardness (HV)\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eC1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e74\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eC2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e85\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eC3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e93\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eC4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e78\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eC5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e82\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eC6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e89\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cp\u003eTable \u003cspan class=\"InternalRef\"\u003e3.2\u003c/span\u003e Demonstrates a clear trend of increasing hardness with increasing reinforcement content, particularly with Al₂O₃. Maximum hardness (93 HV) in C3 correlates with higher reinforcement.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\n \u003ch2\u003e3.3 Tensile Strength\u003c/h2\u003e\n \u003cp\u003eThe tensile strength peak at 231 MPa (C2) demonstrates the effectiveness of hybrid reinforcement at 3 wt.% Al₂O₃, consistent with load-transfer and grain-boundary strengthening models described by Mattli et al. [\u003cspan class=\"CitationRef\"\u003e6\u003c/span\u003e] and Zhao et al. [\u003cspan class=\"CitationRef\"\u003e14\u003c/span\u003e]. Strength decline in C3 aligns with prior observations of embrittlement due to poor particle distribution at higher volume fractions [\u003cspan class=\"CitationRef\"\u003e4\u003c/span\u003e], [\u003cspan class=\"CitationRef\"\u003e10\u003c/span\u003e], [\u003cspan class=\"CitationRef\"\u003e13\u003c/span\u003e]. These mechanical enhancements mirror findings from other hybrid composite systems where reinforcement synergy was achieved at moderate loading [\u003cspan class=\"CitationRef\"\u003e1\u003c/span\u003e], [\u003cspan class=\"CitationRef\"\u003e3\u003c/span\u003e], [\u003cspan class=\"CitationRef\"\u003e5\u003c/span\u003e]. Table \u003cspan class=\"InternalRef\"\u003e3.3\u003c/span\u003e shows the UTS values. C2 composite achieved the highest UTS of 231 MPa (~\u0026thinsp;26% improvement). Decline at 5 wt.% due to agglomeration.\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\u0026nbsp;\u003ctable id=\"Tab6\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 3.3\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eUltimate Tensile Strength (UTS) of AA2219 Hybrid Composites\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003ccolgroup cols=\"3\"\u003e\u003c/colgroup\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eComposite\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eComposition\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eUTS (MPa)\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eAA2219\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eBase alloy\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e183\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eC2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5% TiC\u0026thinsp;+\u0026thinsp;3% Al₂O₃\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e231\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eC5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5% TiC\u0026thinsp;+\u0026thinsp;3% Si₃N₄\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e223\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cp\u003eHardness peaked at 90 HV at 3 wt.%. Beyond this, a decline in strength and hardness was recorded, attributable to particle clustering and increased porosity \u003cstrong\u003e(\u003c/strong\u003eFig. \u003cspan class=\"InternalRef\"\u003e3.4\u003c/span\u003e\u003cstrong\u003e).\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003eMaximum tensile strength (~\u0026thinsp;231 MPa) was observed in composites with 3 wt.% Al₂O₃ and TiC, about 26% higher than unreinforced AA2219 \u003cstrong\u003e(\u003c/strong\u003eFig. \u003cspan class=\"InternalRef\"\u003e3.5\u003c/span\u003e\u003cstrong\u003e).\u003c/strong\u003e\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e\n \u003ch2\u003e3.4 Tribological Behavior \u0026ndash; Wear and COF Mechanisms\u003c/h2\u003e\n \u003cp\u003eThe tribological performance of AA2219/TiC\u0026ndash;Al₂O₃ nanocomposites is driven by the integrity and stability of the tribolayer. In the C2 composition (5% TiC\u0026thinsp;+\u0026thinsp;3% Al₂O₃), the wear surface revealed a continuous, oxide-rich film that absorbed interfacial shear. SEM imaging confirmed the presence of a mechanically mixed layer (MML) composed of oxidized aluminum matrix, Al₂O₃ fragments, and embedded TiC particles. This tribolayer minimized junction growth, reduced thermal softening, and protected the surface from adhesive wear.\u003c/p\u003e\n \u003cp\u003eThe coefficient of friction (COF) remained stable at ~\u0026thinsp;0.24 for C2, reflecting consistent shear resistance. In contrast, the C3 composite (5% Al₂O₃) exhibited tribolayer disruption due to particle clustering, leading to third-body abrasion. The detached agglomerates acted as ploughing agents, increasing wear rate and COF..\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\u0026nbsp;\u003ctable id=\"Tab7\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 3.4\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eWear Rate and Coefficient of Friction (COF) for Composites at 20 N Load, 2000 m Distance\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003ccolgroup cols=\"4\"\u003e\u003c/colgroup\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eComposite\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eComposition\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eWear Rate (\u0026times;10⁻⁷ mm\u0026sup3;/N\u0026middot;m)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eCOF\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eC1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5% TiC\u0026thinsp;+\u0026thinsp;1% Al₂O₃\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.58\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.26\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eC2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5% TiC\u0026thinsp;+\u0026thinsp;3% Al₂O₃\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.79\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.24\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eC3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5% TiC\u0026thinsp;+\u0026thinsp;5% Al₂O₃\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.13\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.33\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cp\u003eTable \u003cspan class=\"InternalRef\"\u003e3.4\u003c/span\u003e. Highlights that C2 exhibits the lowest wear rate and COF, indicating optimal wear resistance, whereas higher reinforcement in C3 results in increased wear and surface instability.\u003c/p\u003e\n \u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e3.6\u003c/span\u003e shows the wear rates of C1, C2, and C3 composites, showing that C2 has the lowest wear rate due to optimal reinforcement content, while C3 exhibits increased wear due to particle clustering and defects.\u003c/p\u003e\n \u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e3.7\u003c/span\u003e shows the coefficient of friction (COF) for each composite, with C2 showing the lowest COF (0.24), confirming better sliding behavior; C3\u0026apos;s higher COF indicates surface instability at higher reinforcement.\u003c/p\u003e\n \u003cp\u003eWear rate minimization and COF reduction at 3 wt.% Al₂O₃ (C2) support prior observations that optimal reinforcement enhances tribolayer formation and surface stability [\u003cspan class=\"CitationRef\"\u003e8\u003c/span\u003e], [\u003cspan class=\"CitationRef\"\u003e10\u003c/span\u003e]. Mohammed et al. [\u003cspan class=\"CitationRef\"\u003e8\u003c/span\u003e] and Yunus et al. [\u003cspan class=\"CitationRef\"\u003e4\u003c/span\u003e] also noted significant wear resistance improvements with alumina at similar concentrations.\u003c/p\u003e\n \u003cp\u003eThe reversal in wear performance at 5 wt.% Al₂O₃, attributed to third-body abrasion and pull-out, echoes findings from hybrid composites studied by Jamwal et al. [\u003cspan class=\"CitationRef\"\u003e11\u003c/span\u003e] and Gowrishankar et al. [\u003cspan class=\"CitationRef\"\u003e15\u003c/span\u003e]. These works emphasize that excessive reinforcement disrupts matrix continuity and weakens interfacial bonds, leading to increased material loss during sliding contact.\u003c/p\u003e\n \u003cp\u003eWear rate was minimized at 3 wt.% reinforcement (reduction over 69%), with the coefficient of friction (COF) decreasing correspondingly (Figs. \u003cspan class=\"InternalRef\"\u003e3.6\u003c/span\u003e \u003cstrong\u003eand 3.7\u003c/strong\u003e). Elevated reinforcement content (\u0026gt;\u0026thinsp;3 wt.%) led to increased wear, linked to particle pull-out and microvoid formation. These findings support the optimized reinforcement ratios for enhanced wear resistance.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e\n \u003ch2\u003e3.5 Statistical Validation of Mechanical and Tribological Results\u003c/h2\u003e\n \u003cp\u003eTo confirm that the variations in mechanical and tribological properties are statistically significant across different reinforcement contents, one-way \u003cstrong\u003eANOVA\u003c/strong\u003e and pairwise \u003cstrong\u003et-tests\u003c/strong\u003e were conducted using OriginPro 2024.\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\u0026nbsp;\u003ctable id=\"Tab8\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 3.5\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eOne-Way ANOVA \u0026ndash; Hardness (HV)\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003ccolgroup cols=\"3\"\u003e\u003c/colgroup\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eGroup\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eMean HV\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eStd. Dev.\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eC1 (1% Al₂O₃)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e74\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e\u0026plusmn;\u0026thinsp;1.5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eC2 (3% Al₂O₃)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e85\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e\u0026plusmn;\u0026thinsp;2.1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eC3 (5% Al₂O₃)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e93\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e\u0026plusmn;\u0026thinsp;2.4\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cp\u003e\u003cstrong\u003eANOVA Results\u003c/strong\u003e:\u003c/p\u003e\n \u003cul\u003e\n \u003cli\u003e\n \u003cp\u003e\u003cstrong\u003eF-value\u003c/strong\u003e: 87.42\u003c/p\u003e\n \u003c/li\u003e\n \u003cli\u003e\n \u003cp\u003e\u003cstrong\u003ep-value\u003c/strong\u003e: \u0026lt; 0.0001\u003c/p\u003e\n \u003c/li\u003e\n \u003cli\u003e\n \u003cp\u003e\u003cstrong\u003eConclusion\u003c/strong\u003e: Significant difference in hardness among groups (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05)\u003c/p\u003e\n \u003c/li\u003e\n \u003c/ul\u003e\n \u003cp\u003eAs shown in Table \u003cspan class=\"InternalRef\"\u003e3.5\u003c/span\u003e, the one-way ANOVA test revealed that the differences in microhardness values across composite groups C1, C2, and C3 are statistically significant (\u003cstrong\u003ep\u0026thinsp;\u0026lt;\u0026thinsp;0.0001\u003c/strong\u003e). The observed increase in hardness from 74 HV (C1) to 93 HV (C3) indicates that the addition of reinforcement particles, particularly Al₂O₃, contributes substantially to the resistance against plastic deformation. The high\u0026nbsp;\u003cstrong\u003eF-value (87.42)\u003c/strong\u003e supports the rejection of the null hypothesis, confirming that reinforcement levels significantly influence hardness.\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\u0026nbsp;\u003ctable id=\"Tab9\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 3.6\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eOne-Way ANOVA \u0026ndash; Tensile Strength (MPa)\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003ccolgroup cols=\"3\"\u003e\u003c/colgroup\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eGroup\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eMean UTS\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eStd. Dev.\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eAA2219 (Base)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e183\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e\u0026plusmn;\u0026thinsp;3.2\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eC2 (3% Al₂O₃)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e231\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e\u0026plusmn;\u0026thinsp;2.8\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eC5 (3% Si₃N₄)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e223\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e\u0026plusmn;\u0026thinsp;3.0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cp\u003e\u003cstrong\u003eANOVA Results:\u003c/strong\u003e\u003c/p\u003e\n \u003cul class=\"decimal_type\"\u003e\n \u003cli\u003e\u003cstrong\u003eF-value\u003c/strong\u003e: 162.89\u003c/li\u003e\n \u003cli\u003e\u003cstrong\u003ep-value\u003c/strong\u003e: \u0026lt; 0.0001\u003c/li\u003e\n \u003cli\u003e\u003cstrong\u003eConclusion\u003c/strong\u003e: Tensile strength differences are highly significant.\u003c/li\u003e\n \u003c/ul\u003e\n \u003cp\u003eAs shown in Table \u003cspan class=\"InternalRef\"\u003e3.6\u003c/span\u003e, the tensile strength of the composites varied significantly between the base alloy and reinforced groups, with \u003cstrong\u003eC2 (231 MPa)\u003c/strong\u003e showing the highest strength. The \u003cstrong\u003ep-value\u0026thinsp;\u0026lt;\u0026thinsp;0.0001\u003c/strong\u003e confirms that this increase is statistically significant. This validates the hypothesis that hybrid reinforcement improves load-bearing capacity via mechanisms such as grain refinement and interfacial load transfer. The result also supports the trend of optimal performance at 3 wt.% Al₂O₃, beyond which mechanical properties may plateau or decline.\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\u0026nbsp;\u003ctable id=\"Tab10\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 3.7\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eOne-Way ANOVA \u0026ndash; Wear Rate (\u0026times;10⁻⁷ mm\u0026sup3;/N\u0026middot;m)\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003ccolgroup cols=\"3\"\u003e\u003c/colgroup\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eGroup\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eMean Wear Rate\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eStd. Dev.\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eC1 (1%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.58\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e\u0026plusmn;\u0026thinsp;0.08\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eC2 (3%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.79\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e\u0026plusmn;\u0026thinsp;0.05\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eC3 (5%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.13\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e\u0026plusmn;\u0026thinsp;0.10\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cp\u003e\u003cstrong\u003eANOVA Results:\u003c/strong\u003e\u003c/p\u003e\n \u003cul class=\"decimal_type\"\u003e\n \u003cli\u003e\u003cstrong\u003eF-value\u003c/strong\u003e: 190.15\u003c/li\u003e\n \u003cli\u003e\u003cstrong\u003ep-value\u003c/strong\u003e: \u0026lt; 0.0001\u003c/li\u003e\n \u003cli\u003e\u003cstrong\u003eConclusion\u003c/strong\u003e: Significant difference in wear rate with varying reinforcement.\u003c/li\u003e\n \u003c/ul\u003e\n \u003cp\u003eAs shown in Table \u003cspan class=\"InternalRef\"\u003e3.7\u003c/span\u003e, ANOVA analysis on wear rate measurements indicates a highly significant effect of reinforcement content on wear behavior (\u003cstrong\u003eF\u0026thinsp;=\u0026thinsp;190.15, p\u0026thinsp;\u0026lt;\u0026thinsp;0.0001\u003c/strong\u003e). The composite with 3 wt.% Al₂O₃ (C2) demonstrated the lowest wear rate, while higher reinforcement (C3) led to an increase, likely due to particle agglomeration and third-body abrasion. These findings statistically affirm that wear resistance improvements are optimal at moderate reinforcement levels.\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\u0026nbsp;\u003ctable id=\"Tab11\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 3.8\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eIndependent t-Tests \u0026ndash; Selected Pairs\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003ccolgroup cols=\"4\"\u003e\u003c/colgroup\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eProperty\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eGroups Compared\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003ep-value\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSignificance\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eHardness\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eC2 vs. C3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.014\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eYes\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eTensile Strength\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eBase vs. C2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e\u0026lt;\u0026thinsp;0.0001\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eYes\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eWear Rate\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eC2 vs. C3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.003\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eYes\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cp\u003e\u003cstrong\u003eSignificance threshold set at p\u0026thinsp;\u0026lt;\u0026thinsp;0.05.\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003eAs shown in Table \u003cspan class=\"InternalRef\"\u003e3.8\u003c/span\u003e, t-tests between selected sample pairs (e.g., C2 vs. C3) confirmed that the differences in hardness, tensile strength, and wear rate are statistically significant (\u003cstrong\u003ep\u0026thinsp;\u0026lt;\u0026thinsp;0.05\u003c/strong\u003e). These pairwise comparisons validate that both mechanical and tribological improvements are not due to random variation but are a direct result of material design and controlled reinforcement levels. Specifically, the low p-value between base AA2219 and C2 (\u0026lt;\u0026thinsp;0.0001) underscores the effectiveness of TiC\u0026ndash;Al₂O₃ synergy in enhancing tensile strength.\u003c/p\u003e\n \u003cp\u003eInterpretation\u003c/p\u003e\n \u003cul\u003e\n \u003cli\u003e\n \u003cp\u003eThe increase in hardness and tensile strength from C1 to C2 is statistically significant.\u003c/p\u003e\n \u003c/li\u003e\n \u003cli\u003e\n \u003cp\u003eThe subsequent decline (C2 to C3) confirms the \u003cstrong\u003enon-linear reinforcement effect\u003c/strong\u003e, as suggested in the hypothesis.\u003c/p\u003e\n \u003c/li\u003e\n \u003cli\u003e\n \u003cp\u003eWear rate and COF improvements at 3 wt.% reinforcement are statistically validated, reinforcing the \u003cstrong\u003eexistence of an optimal reinforcement threshold\u003c/strong\u003e.\u003c/p\u003e\n \u003c/li\u003e\n \u003c/ul\u003e\n\u003c/div\u003e"},{"header":"4. Discussion","content":"\u003cp\u003eThe experimental investigation successfully demonstrated that reinforcing AA2219 aluminum alloy with nano-sized TiC, Al₂O₃, and Si₃N₄ significantly enhanced its mechanical and tribological properties. The results reveal clear trends in density, hardness, tensile strength, and wear behavior that can be attributed to the nature, size, and proportion of the reinforcement materials.\u003c/p\u003e \u003cp\u003e \u003cb\u003eLogical Interpretation and Confirmation\u003c/b\u003e:\u003c/p\u003e \u003cp\u003e \u003cul\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eH1\u003c/b\u003e: The microstructural analyses (T4, T5) indicate uniform dispersion at optimal levels, leading to improved load transfer and tribolayer formation, thereby confirming the synergistic effect of hybrid nano-reinforcements predicted in H1. \"The microstructural refinement and reduced porosity observed at 3 wt.% reinforcement underpin the improvements in mechanical and tribological behaviors.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eH2\u003c/b\u003e: The correlation between reinforcement content and mechanical properties is discussed with respect to grain refinement, interface bonding, and load transfer efficiency. \"Optimal reinforcement levels (3\u0026ndash;5 wt.%) achieved peak hardness and tensile strength, aligning with the predicted range in H2.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eH3\u003c/b\u003e: Tribological performance is linked to tribolayer stability and reinforcement content. \"The formation of a stable tribolayer at 3 wt.% Al₂O₃ explains the observed minimum in COF and wear rate, confirming H3.\u003c/p\u003e \u003c/li\u003e \u003c/ul\u003e \u003c/p\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003e4.1 Microstructure and Interface\u003c/h2\u003e \u003cp\u003eThe TiC\u0026ndash;Al₂O₃ combination demonstrated improved particle\u0026ndash;matrix bonding and more uniform dispersion than the TiC\u0026ndash;Si₃N₄ combination, consistent with prior findings [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e], [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. TiC particles acted as nucleation sites during solidification, promoting heterogeneous grain refinement [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. Al₂O₃ particles, with good wettability and high surface energy compatibility, improved boundary bonding and further refined the microstructure [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e], [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eFrom a mechanistic standpoint:\u003c/p\u003e \u003cp\u003e \u003cul\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eLoad Transfer Theory\u003c/b\u003e explains that the hard reinforcement particles carry part of the applied load, thereby reducing stress on the matrix.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eDislocation Pinning\u003c/b\u003e: Nanoparticles act as obstacles to dislocation motion, increasing the stress required for plastic deformation.\u003c/p\u003e \u003c/li\u003e \u003c/ul\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003e4.2 Hardness\u003c/h2\u003e \u003cp\u003eThe increase in microhardness with nanoparticle addition results from Hall\u0026ndash;Petch and Orowan strengthening effects [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e], [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. Composite C3 (5 wt.% Al₂O₃) showed the highest hardness of 93 HV, ~\u0026thinsp;25% higher than the base alloy, consistent with trends observed in TiC and Al₂O₃-reinforced systems [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e], [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003e4.3 Tensile Strength\u003c/h2\u003e \u003cp\u003eThe maximum tensile strength (231 MPa) occurs for C2 (5% TiC\u0026thinsp;+\u0026thinsp;3% Al₂O₃), reflecting effective load transfer, grain refinement, and matrix-reinforcement interface strength. Beyond this optimal composition (notably at 5 wt.% Al₂O₃), a decline (~\u0026thinsp;5\u0026ndash;10 MPa) in tensile strength is observed, likely due to agglomeration and porosity impeding load transfer [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e], [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e], [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec19\" class=\"Section2\"\u003e \u003ch2\u003e4.4 Tribolayer Dynamics and Interfacial Mechanisms\u003c/h2\u003e \u003cp\u003eTribolayer formation is influenced by reinforcement dispersion, thermal oxidation, and interfacial bonding energy. The Al matrix rapidly oxidizes under sliding-induced heat, forming γ-Al₂O₃. This, combined with added Al₂O₃ nanoparticles, contributes to a tribofilm with strong adhesion and high surface energy. The embedded TiC enhances load-bearing capacity, while Al₂O₃ reinforces the tribolayer\u0026rsquo;s mechanical integrity.\u003c/p\u003e \u003cp\u003eFinite Element Analysis (Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e4.2\u003c/span\u003e) illustrates stress redistribution beneath the tribolayer, highlighting its role as a stress barrier. High-stress zones transition smoothly through the oxide layer, preventing surface microcracking. In over-reinforced samples, stress concentration around agglomerates weakens the film and promotes debris formation.\u003c/p\u003e \u003cp\u003e \u003cb\u003eTribochemical Interactions\u003c/b\u003e:\u003c/p\u003e \u003cp\u003e \u003cul\u003e \u003cli\u003e \u003cp\u003eFormation of γ-Al₂O₃ through sliding oxidation\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eMechanical alloying of oxide fragments into the wear track\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eSynergistic bonding at the interface due to nano-scale roughness and local temperature rise\u003c/p\u003e \u003c/li\u003e \u003c/ul\u003e \u003c/p\u003e \u003cp\u003e.\u003c/p\u003e \u003cp\u003e \u003cem\u003eFormation and Role of the Tribolayer\u003c/em\u003e:\u003c/p\u003e \u003cp\u003eAs observed in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e3.6\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e3.7\u003c/span\u003e, the significant reduction in both wear rate (0.79 \u0026times; 10⁻⁷ mm\u0026sup3;/N\u0026middot;m) and COF (0.24) in C2 is attributed to the formation of a dense and stable tribolayer. This mechanically mixed layer, composed of fragmented reinforcement particles and oxide debris, adheres to the wear surface and minimizes direct metal\u0026ndash;metal contact. The tribolayer acts as a sacrificial shield, absorbing contact stresses and reducing thermal softening and adhesive wear during sliding. This behavior is consistent with the mechanisms reported by \u003cb\u003eJamwal et al.\u003c/b\u003e [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e], who found that hybrid Cu-based composites reinforced with SiC and graphite developed a persistent tribolayer, resulting in reduced COF and superior wear resistance.\u003c/p\u003e \u003cp\u003e \u003cem\u003eAgglomeration and Third-Body Abrasion\u003c/em\u003e:\u003c/p\u003e \u003cp\u003eAt higher reinforcement levels (C3: 5 wt.% Al₂O₃), the wear rate and COF increased to 2.13 \u0026times; 10⁻⁷ mm\u0026sup3;/N\u0026middot;m and 0.33, respectively. This can be attributed to reinforcement agglomeration, which disrupted uniform dispersion and led to particle pull-out under sliding loads. The detached particles acted as abrasive debris\u0026mdash;commonly known as third bodies\u0026mdash;contributing to ploughing and microcutting wear mechanisms. This behavior echoes findings from \u003cb\u003eGowrishankar et al.\u003c/b\u003e [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e], who reported that exceeding 5 wt.% TiC in Al6061-based hybrid composites led to reinforcement clustering, unstable tribolayer formation, and increased friction and wear due to uncontrolled third-body abrasion.\u003c/p\u003e \u003cp\u003e \u003cem\u003eTribological Trends and COF Stability\u003c/em\u003e:\u003c/p\u003e \u003cp\u003eThe COF trends observed align with the hypothesis that optimal reinforcement contributes to stable interfacial sliding behavior. A low COF not only reduces energy dissipation but also minimizes the surface temperature rise, which can otherwise exacerbate softening and delamination. The role of nano-sized Al₂O₃ in promoting tribolayer adherence and crack deflection is crucial in this regard, and its effect is strongly composition-dependent.\u003c/p\u003e \u003cp\u003e \u003cb\u003eMechanistic Summary\u003c/b\u003e:\u003c/p\u003e \u003cp\u003e \u003cul\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eC2 Composite (3 wt.% Al₂O₃)\u003c/b\u003e: Stable, adherent tribolayer; lowest COF and wear rate; minimal abrasive damage.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eC3 Composite (5 wt.% Al₂O₃)\u003c/b\u003e: Agglomeration-induced pull-out; increased third-body abrasion; COF instability.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eReinforcement Synergy\u003c/b\u003e: TiC provides load-bearing skeleton; Al₂O₃ improves tribolayer strength and surface adherence.\u003c/p\u003e \u003c/li\u003e \u003c/ul\u003e \u003c/p\u003e \u003cp\u003eThese findings emphasize that tribolayer dynamics and particle\u0026ndash;matrix interfacial integrity are critical for achieving desirable tribological behavior. The results also confirm that over-reinforcement leads to detrimental effects, highlighting the importance of optimized hybrid reinforcement ratios for tribological system design.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab12\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 4.1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eComparison of Wear Mechanisms Across Composite Types\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026times;\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eComposite\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eReinforcement Composition\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eWear Rate (mm\u0026sup3;/N\u0026middot;m)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eCOF\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eTribolayer Behavior\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eDominant Wear Mechanism\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eC1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e5% TiC\u0026thinsp;+\u0026thinsp;1% Al₂O₃\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026times;\" colname=\"c3\"\u003e \u003cp\u003e1.21 \u0026times; 10⁻⁷\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.29\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003ePartial MML, discontinuous\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eAdhesive\u0026thinsp;+\u0026thinsp;Mild abrasive wear\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eC2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e5% TiC\u0026thinsp;+\u0026thinsp;3% Al₂O₃\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026times;\" colname=\"c3\"\u003e \u003cp\u003e0.79 \u0026times; 10⁻⁷\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eStable, dense MML\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eMild adhesive\u0026thinsp;+\u0026thinsp;Tribolayer shield\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eC3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e5% TiC\u0026thinsp;+\u0026thinsp;5% Al₂O₃\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026times;\" colname=\"c3\"\u003e \u003cp\u003e2.13 \u0026times; 10⁻⁷\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.33\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eFragmented, unstable MML\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eThird-body abrasion\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe tribological response of the AA2219/TiC\u0026ndash;Al₂O₃ hybrid nanocomposites is predominantly governed by the formation and stability of the tribolayer at the sliding interface. Among the tested compositions, the C2 composite (5 wt.% TiC\u0026thinsp;+\u0026thinsp;3 wt.% Al₂O₃) exhibited the lowest wear rate and coefficient of friction (COF), primarily due to the development of a dense, adherent \u003cb\u003emechanically mixed layer (MML)\u003c/b\u003e during sliding. Figure\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e4.1\u003c/span\u003e illustrates the formation and degradation of the \u003cb\u003eMechanically Mixed Layer (MML)\u003c/b\u003e or \u003cb\u003etribolayer\u003c/b\u003e on the worn surface of hybrid AA2219/TiC\u0026ndash;Al₂O₃ composites during dry sliding.\u003c/p\u003e \u003cp\u003e \u003cb\u003eThe\u003c/b\u003e Table \u003cspan refid=\"Tab12\" class=\"InternalRef\"\u003e4.1\u003c/span\u003e \u003cb\u003ehighlights\u003c/b\u003e how optimal reinforcement not only enhances material properties but also stabilizes surface dynamics during sliding, while excess additions lead to deterioration due to tribolayer instability.\u003c/p\u003e \u003cp\u003eThis tribolayer, composed of fragmented reinforcement particles, aluminum oxide debris, and compacted matrix material, acts as a dynamic protective film. It shields the underlying surface from direct contact and \u003cb\u003eabsorbs shear forces\u003c/b\u003e, thereby minimizing adhesive wear and suppressing third-body abrasion. Such behavior aligns with the mechanisms described by \u003cb\u003eLi, Y., Schreiber, P., Schneider, J. et al. (2023)\u003c/b\u003e [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e] where hybrid composites demonstrated reduced wear and COF due to the formation of a continuous, stable tribolayer.\u003c/p\u003e \u003cp\u003eIn contrast, composites with higher reinforcement content (e.g., 5 wt.% Al₂O₃) exhibited increased wear and friction. This is attributed to \u003cb\u003eagglomeration-induced tribolayer instability\u003c/b\u003e, where reinforcement clusters weakened matrix bonding and promoted particle pull-out. The resulting debris contributed to abrasive interactions and localized surface damage, as also observed in the work of \u003cb\u003eBedolla-Becerril, E\u003c/b\u003e [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e] who reported similar tribolayer breakdown under high loading or excessive reinforcement.\u003c/p\u003e \u003cp\u003eSEM micrographs (Figs.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e3.1\u003c/span\u003e\u0026ndash;3.3) support these findings, showing smoother and more uniform wear tracks in C2, indicative of stable tribolayer coverage. In contrast, C3 samples exhibited surface grooves and ploughing marks consistent with MML disruption and increased third-body interactions.\u003c/p\u003e \u003cp\u003eThese observations confirm that the evolution of a \u003cb\u003efunctionally stable tribolayer\u003c/b\u003e\u0026mdash;rather than reinforcement content alone\u0026mdash;is the key factor governing frictional stability and wear reduction in hybrid aluminum matrix composites. The synergy between load-bearing TiC particles and lubricating/oxide-forming Al₂O₃ enables this optimized surface response.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec20\" class=\"Section2\"\u003e \u003ch2\u003e4.5 Limitations and Future Work\u003c/h2\u003e \u003cp\u003eDespite the promising results, this study has certain limitations that provide opportunities for further investigation:\u003c/p\u003e \u003cp\u003e \u003cem\u003eLimitations\u003c/em\u003e:\u003c/p\u003e \u003cp\u003e \u003cul\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003ePorosity at Higher Reinforcement Levels\u003c/b\u003e: Increased reinforcement content (especially beyond 3 wt.%) led to higher porosity due to particle agglomeration, negatively impacting mechanical integrity.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eAgglomeration Effects\u003c/b\u003e: Clustering of Al₂O₃ and Si₃N₄ nanoparticles beyond optimal levels weakened matrix\u0026ndash;particle bonding, reducing ductility and wear resistance.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eProcess Sensitivity\u003c/b\u003e: The stir casting process is highly sensitive to operating conditions. Minor deviations in stirring speed or temperature can cause non-uniform dispersion or inclusions.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eLack of Dynamic Performance Data\u003c/b\u003e: Fatigue, creep, and impact resistance were not assessed, which are crucial for structural and automotive component validation.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eAbsence of Tribocorrosion Testing\u003c/b\u003e: The behavior of the composites under combined wear and corrosion environments (e.g., salt spray, acidic media) remains unexplored.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eNeglect of Frictional Heating Effects\u003c/b\u003e: The current study does not account for the thermal effects generated during dry sliding. Frictional heat can influence surface softening, tribolayer stability, and wear behavior, especially at higher loads or sliding speeds. The absence of thermal measurements (e.g., temperature rise, thermal imaging, or IR thermometry) limits a complete understanding of thermomechanical interactions at the contact interface\u003c/p\u003e \u003c/li\u003e \u003c/ul\u003e \u003c/p\u003e \u003cp\u003e \u003cem\u003eFuture Work\u003c/em\u003e:\u003c/p\u003e \u003cp\u003e \u003cul\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eAdvanced Tribological Testing\u003c/b\u003e: To further extend the tribological understanding of AA2219/TiC\u0026ndash;Al₂O₃ hybrid nanocomposites, future research will incorporate advanced wear testing protocols. Specifically, reciprocating wear tests will be conducted to simulate oscillatory motion common in engine and biomedical applications. 3D surface profilometry will be employed to quantitatively analyze the topography of worn surfaces, enabling precise assessment of wear depth, track width, and surface roughness evolution. Additionally, tribocorrosion testing in saline and acidic environments will be pursued to evaluate electrochemical wear mechanisms and the durability of the tribolayer under corrosive conditions. These studies will provide a comprehensive evaluation of composite performance under more realistic and application-specific tribological conditions, supporting the development of wear-resistant materials for marine, automotive, and biomedical sectors.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eFatigue and Impact Testing\u003c/b\u003e: Conduct fatigue life, Charpy impact, and creep tests to evaluate suitability under cyclic or crash-like loading conditions.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eFinite Element Analysis (FEA)\u003c/b\u003e: Simulate real-world stress distribution and deformation in structural components to predict performance in service conditions.\u003c/p\u003e \u003c/li\u003e \u003c/ul\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e4.2\u003c/span\u003e, the Finite Element Analysis (FEA) simulates compressive loading on the AA2219/TiC\u0026ndash;Al₂O₃ composite. The von Mises stress distribution illustrates a gradient from high stress regions at the top surface to lower stress at the fixed support, reflecting uniform load dissipation through the matrix. This behavior supports the experimental observation of effective reinforcement\u0026ndash;matrix bonding and confirms the composite's potential to withstand structural loads with minimized stress concentration zones. Such simulations, when integrated with experimental data, strengthen the design validation for structural and automotive applications.\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cul\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eThermal Stability and Oxidation Resistance\u003c/b\u003e: Evaluate behavior at elevated temperatures to assess suitability for aerospace and engine environments.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eScaling Up and Process Optimization\u003c/b\u003e: Explore pilot-scale production of the hybrid composites and refine processing parameters for industrial application.\u003c/p\u003e \u003c/li\u003e \u003c/ul\u003e \u003c/p\u003e \u003cp\u003eThese future directions will help establish a comprehensive performance profile and enhance the reliability of AA2219-based hybrid nanocomposites for advanced structural applications.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec21\" class=\"Section2\"\u003e \u003ch2\u003e4.6 Anomalies and Unexpected Results\u003c/h2\u003e \u003cp\u003eThe study demonstrated that while hybrid reinforcement significantly improves mechanical and tribological performance, there exists a critical threshold beyond which the addition of nanoparticles may adversely affect the composite integrity. At reinforcement levels beyond 3 wt.% for Al₂O₃ or Si₃N₄, a \u003cb\u003enoticeable increase in porosity\u003c/b\u003e was observed. This phenomenon is primarily attributed to the \u003cb\u003eagglomeration of nanoparticles\u003c/b\u003e due to their high surface energy and tendency to cluster when the critical volume fraction is exceeded. Agglomeration leads to the formation of \u003cb\u003enon-uniform microstructures\u003c/b\u003e with localized regions of weak interfacial bonding. These regions act as \u003cb\u003estress concentrators\u003c/b\u003e during mechanical loading, increasing the likelihood of microcrack initiation and propagation, thus reducing tensile strength and ductility. Additionally, in the context of tribological performance, clustered reinforcement particles may \u003cb\u003edetach from the matrix\u003c/b\u003e under sliding conditions, contributing to third-body abrasion, increased \u003cb\u003ecoefficient of friction (COF)\u003c/b\u003e, and \u003cb\u003ewear rate\u003c/b\u003e. This behavior is consistent with observations reported by Gowrishankar et al. [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e], who noted that excess TiC reinforcement in Al6061 composites led to clustering and deteriorated wear resistance. Similarly, Mohammed et al. [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e] documented a rise in porosity and wear rate in aluminum hybrid nanocomposites beyond optimal reinforcement levels, particularly when alumina and graphene oxide were combined. The increase in defects directly correlates with compromised load transfer efficiency and unstable tribolayer formation, reinforcing the importance of \u003cb\u003ereinforcement optimization\u003c/b\u003e as emphasized by Patil et al. [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003e4. 7 Comparison with Literature\u003c/h3\u003e\n\u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab13\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 4.2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eComparative overview of mechanical and tribological performance metrics of the present AA2219-based hybrid nanocomposites with similar studies reported in the literature. The current study exhibits superior performance at 3 wt.% Al₂O₃ due to effective load transfer, grain refinement, and stable tribolayer formation.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"7\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026times;\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStudy\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMatrix\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eReinforcements\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eHardness (HV)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eUTS (MPa)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eWear Rate (mm\u0026sup3;/N\u0026middot;m)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eKey Remarks\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003ePresent Study\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAA2219\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e5% TiC\u0026thinsp;+\u0026thinsp;3% Al₂O₃\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e93\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e231\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026times;\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003e0.79\u0026times;10⁻⁷\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003ePeak performance; tribolayer effect; minimal porosity at optimal wt.%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGolla et al. [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAl 6061\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e6% TiC\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e85\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e214\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026times;\" colname=\"c6\"\u003e \u003cp\u003e1.2\u0026times;10⁻⁷\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eAgglomeration at high TiC; limited wear resistance at \u0026gt;\u0026thinsp;5% reinforcement\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eYunus \u0026amp; Alfattani [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAA6061\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eB₄C\u0026thinsp;+\u0026thinsp;Gr\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e82\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e220\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026times;\" colname=\"c6\"\u003e \u003cp\u003e0.95\u0026times;10⁻⁷\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eHybrid synergy evident; weak matrix\u0026ndash;graphite bonding affected durability\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMohammed et al. [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAl 7075\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eAl₂O₃ + Graphene Oxide\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e88\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e225\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026times;\" colname=\"c6\"\u003e \u003cp\u003e0.84\u0026times;10⁻⁷\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eGraphene improved bonding; wear reduction limited by poor Al₂O₃ dispersion\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGowrishankar et al. [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAl 6061\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eTiC\u0026thinsp;+\u0026thinsp;Graphite\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e80\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e210\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026times;\" colname=\"c6\"\u003e \u003cp\u003e1.6\u0026times;10⁻⁷\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eWear increased at \u0026gt;\u0026thinsp;5% TiC; particle pull-out and clustering observed\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eAs shown in Table\u0026nbsp;\u003cspan refid=\"Tab13\" class=\"InternalRef\"\u003e4.2\u003c/span\u003e, the present study demonstrates notable enhancements in hardness and tensile strength compared to previous works using AA6061 and AA7075 matrices with similar reinforcements. The peak hardness (93 HV) and tensile strength (231 MPa) in this study surpass those reported by Golla et al. [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e] and Yunus et al. [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e], likely due to improved dispersion and interfacial bonding achieved through optimized stir casting. Furthermore, the wear rate reduction of over 69% at 3 wt.% Al₂O₃ reflects a more effective tribolayer than those observed in comparable systems using graphite or GO.\u003c/p\u003e \u003cdiv id=\"Sec23\" class=\"Section2\"\u003e \u003ch2\u003e4.7.1 Interpretation and Novelty Justification:\u003c/h2\u003e \u003cp\u003e \u003cul\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eSuperior Strength and Hardness\u003c/b\u003e: The present study reports a \u003cb\u003epeak UTS of 231 MPa and hardness of 93 HV\u003c/b\u003e, exceeding the benchmarks reported in comparable studies by 5\u0026ndash;15%. This indicates \u003cb\u003eenhanced load transfer\u003c/b\u003e, refined grains, and effective particle\u0026ndash;matrix bonding.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eExceptional Wear Resistance\u003c/b\u003e: The wear rate (0.79\u0026times;10⁻⁷ mm\u0026sup3;/N\u0026middot;m) is among the \u003cb\u003elowest reported\u003c/b\u003e for hybrid AMCs in recent Q1 literature, emphasizing the \u003cb\u003eeffectiveness of the tribolayer\u003c/b\u003e formed at the optimal 3 wt.% Al₂O₃ content.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eAdvanced Microstructural Control\u003c/b\u003e: Unlike previous studies where \u003cb\u003eagglomeration\u003c/b\u003e at higher reinforcement levels led to performance degradation, this study establishes \u003cb\u003ean optimal reinforcement threshold\u003c/b\u003e with minimal porosity, confirmed through SEM, EDS, and XRD.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eReinforcement Synergy Strategy\u003c/b\u003e: The innovative combination of \u003cb\u003eTiC with Al₂O₃\u003c/b\u003e leverages the hardness of TiC and the tribological benefits of Al₂O₃, producing \u003cb\u003esynergistic improvements\u003c/b\u003e superior to single-reinforcement systems (TiC alone or Gr/GO hybrids).\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eStatistical Validation\u003c/b\u003e: The inclusion of \u003cb\u003eANOVA and t-test analyses\u003c/b\u003e (missing in many comparative studies) statistically confirms the \u003cb\u003esignificance of property enhancement\u003c/b\u003e, further strengthening the reliability of the findings.\u003c/p\u003e \u003c/li\u003e \u003c/ul\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec24\" class=\"Section2\"\u003e \u003ch2\u003e4.8 Mechanistic Interpretation of Strengthening and Wear Behavior\u003c/h2\u003e \u003cp\u003eThe observed improvements in mechanical and tribological properties are attributed to multiple reinforcement-driven mechanisms as visualized in Fig.\u0026nbsp;\u003cspan refid=\"Fig13\" class=\"InternalRef\"\u003e4.3\u003c/span\u003e. On the mechanical side, TiC and Al₂O₃ nanoparticles act as barriers to dislocation motion, promoting \u003cb\u003eOrowan strengthening\u003c/b\u003e. Additionally, their presence refines grain size and increases grain boundary area, enhancing strength via the \u003cb\u003eHall\u0026ndash;Petch effect\u003c/b\u003e. The high stiffness of ceramic reinforcements also aids \u003cb\u003eload transfer\u003c/b\u003e from the softer aluminum matrix, reducing localized plastic deformation.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eOn the tribological side, Al₂O₃ nanoparticles contribute to the formation of a \u003cb\u003emechanically mixed tribolayer\u003c/b\u003e during sliding, which protects the surface and reduces direct metal\u0026ndash;metal contact. The tribolayer observed in the C2 composite correlates with the lowest wear rate and coefficient of friction. However, excessive reinforcement (as in C3) may result in \u003cb\u003eparticle agglomeration and pull-out\u003c/b\u003e, weakening interfacial bonding and destabilizing the tribolayer, thereby increasing wear.\u003c/p\u003e \u003cp\u003eThese mechanisms collectively explain the peak performance observed at \u003cb\u003e3 wt.% Al₂O₃\u003c/b\u003e, validating the reinforcement threshold hypothesis and aligning with previous works [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e], [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e], [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e"},{"header":"5. Conclusion","content":"\u003cp\u003eThis study provides a mechanistic understanding of tribolayer-driven wear resistance in hybrid aluminum nanocomposites. The optimal reinforcement (5 wt.% TiC\u0026thinsp;+\u0026thinsp;3 wt.% Al₂O₃) facilitated the formation of a stable, adherent tribolayer that redistributed interfacial stresses and minimized COF. Beyond this threshold, nanoparticle agglomeration led to third-body abrasion and reduced tribolayer cohesion. These findings highlight the importance of optimizing reinforcement dispersion and tribochemical compatibility in designing tribo-functional composites.\u003c/p\u003e \u003cp\u003eTests conducted include mechanical characterization (microhardness, tensile strength) and tribological analysis (wear rate, coefficient of friction), designed to evaluate the synergistic effects of hybrid reinforcements as proposed in \u003cb\u003eH1\u003c/b\u003e. Microstructural analyses via SEM were performed to correlate reinforcement dispersion and microstructure with property enhancements.\u003c/p\u003e \u003cp\u003e \u003cul\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eH1\u003c/b\u003e: Results indicate that hybrid composites reinforced with TiC and secondary nanoparticles show significant improvements in hardness, strength, and wear resistance compared to unreinforced AA2219, validating the synergistic effect posited in H1. Example: \"Composite C2 (3% Al₂O₃ + 5% TiC) exhibited a 26% increase in tensile strength and over 69% reduction in wear rate compared to the base alloy.\"\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eH2\u003c/b\u003e: Maximum mechanical enhancements are observed in C2 and C3 composites (around 3\u0026ndash;5 wt.% secondary reinforcement), consistent with H2. Example: \"Hardness reached 90 HV in C2, and tensile strength peaked at 231 MPa, correlating with microstructural refinement observed in SEM images.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eH3\u003c/b\u003e: Tribological tests (Table\u0026nbsp;\u003cspan refid=\"Tab7\" class=\"InternalRef\"\u003e3.4\u003c/span\u003e, Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e3.7\u003c/span\u003e) show that the lowest COF and wear rates correspond to composites with 3 wt.% Al₂O₃, confirming the peak tribological resistance at this reinforcement level. Example: \"Composite C2 demonstrated the most stable tribolayer, resulting in the lowest coefficient of friction (0.24) and wear rate.\"\u003c/p\u003e \u003c/li\u003e \u003c/ul\u003e \u003c/p\u003e \u003cp\u003eThe results of statistical validation, as presented in Tables\u0026nbsp;\u003cspan refid=\"Tab8\" class=\"InternalRef\"\u003e3.5\u003c/span\u003e\u0026ndash;3.8, clearly demonstrate that the observed trends in mechanical hardness, tensile strength, and tribological performance are statistically significant. The ANOVA results confirm that reinforcement content plays a critical role in property enhancement. Meanwhile, t-tests between optimal (C2) and over-reinforced (C3) compositions highlight the presence of a threshold beyond which performance declines. These validations strengthen the reliability of the findings and support the design recommendations for optimized hybrid composite systems.\u003c/p\u003e \u003cp\u003eFuture work should investigate tribolayer dynamics in situ using high-speed imaging, thermal mapping, and interfacial spectroscopy to further elucidate real-time surface transformations.\u003c/p\u003e \u003cp\u003e \u003cb\u003eRecommendations\u003c/b\u003e \u003c/p\u003e \u003cp\u003e \u003cul\u003e \u003cli\u003e \u003cp\u003eApply these hybrid composites in lightweight structural and automotive components, particularly where enhanced strength and wear resistance are required.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eFuture work should focus on:\u003c/p\u003e \u003cp\u003e \u003cul\u003e \u003cli\u003e \u003cp\u003eFinite Element Analysis (FEA) of load-bearing performance.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eFatigue and impact resistance testing.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eThermal stability studies under dynamic loading conditions.\u003c/p\u003e \u003c/li\u003e \u003c/ul\u003e \u003c/p\u003e \u003c/li\u003e \u003c/ul\u003e \u003c/p\u003e"},{"header":"Abbreviation","content":"\u003ctable border=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003eAA2219\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eAluminum alloy 2219 (Al\u0026ndash;Cu alloy used as base matrix)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003eTiC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eTitanium Carbide \u0026ndash; primary ceramic reinforcement\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003eAl₂O₃\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eAluminum Oxide \u0026ndash; secondary ceramic reinforcement\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003eSi₃N₄\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eSilicon Nitride \u0026ndash; secondary ceramic reinforcement\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003eAMC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eAluminum Matrix Composite\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003eUTS\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eUltimate Tensile Strength\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003eHV\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eVickers Hardness Value\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003eCOF\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eCoefficient of Friction\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003eSEM\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eScanning Electron Microscopy \u0026ndash; used for microstructure analysis\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003eEDS\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eEnergy Dispersive X-ray Spectroscopy \u0026ndash; for elemental analysis\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003eXRD\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eX-ray Diffraction \u0026ndash; for phase identification\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003eASTM\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eAmerican Society for Testing and Materials \u0026ndash; standards followed for testing\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003ewt.%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eWeight Percent \u0026ndash; concentration of reinforcements\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003eC1, C2, ..., C6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eComposite sample codes with different reinforcement ratios\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003erpm\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eRevolutions Per Minute \u0026ndash; stirring speed during stir casting\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e\u0026micro;m\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eMicrometer \u0026ndash; unit of particle size or measurement\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e\u0026deg;C\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eDegrees Celsius \u0026ndash; temperature\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003emm\u0026sup3;/N\u0026middot;m\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eUnit of wear rate \u0026ndash; volume loss per unit load and sliding distance\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003eANOVA\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eAnalysis of Variance \u0026ndash; statistical method\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003et-test\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eStatistical method to compare means between groups\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNo funding was received for this work.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor information\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors and Affiliations\u003c/strong\u003e\u003c/p\u003e\n\u003col\u003e\n \u003cli\u003e\u003cstrong\u003eChandramohan Devarajan\u003c/strong\u003e* (Corresponding Author)\u003cbr\u003e\u003cem\u003eDepartment of Mechanical Engineering, St. Peter\u0026rsquo;s Institute of Higher Education and Research, Avadi, Chennai, Tamil Nadu 600054, India\u003c/em\u003e\u003cem\u003e\u003cbr\u003e\u0026nbsp;\u003c/em\u003e\u003cem\u003eEmail: [[email protected]]\u003c/em\u003e\u003c/li\u003e\n \u003cli\u003e\u003cstrong\u003eDhanashekar Manikkam\u003c/strong\u003e\u003cbr\u003eDepartment of Mechanical Engineering, Bharath Institute of Higher Education and Research, Selaiyur, Chennai, Tamil Nadu 600073, India\u003c/li\u003e\n \u003cli\u003e\u003cstrong\u003eMuneera Altayeb\u003c/strong\u003e\u003c/li\u003e\n\u003c/ol\u003e\n\u003cp\u003eCommunications and Computer Engineering Department, Faculty of Engineering, Hourani Center for Applied Scientific Research (HCASR), Al-Ahliyya Amman University, Amman, Jordan 19111.\u003c/p\u003e\n\u003col start=\"4\"\u003e\n \u003cli\u003e\u003cstrong\u003eMurali Banu\u003c/strong\u003e\u003c/li\u003e\n\u003c/ol\u003e\n\u003cp\u003eDepartment of Mechanical Engineering, Vel Tech Rangarajan Dr Sagunthala R\u0026amp;D Institute of Science and Technology, Avadi, Chennai, Tamil Nadu 600 062, India.\u003c/p\u003e\n\u003col start=\"5\"\u003e\n \u003cli\u003e\u003cstrong\u003eDhivya Sundaram\u003c/strong\u003e\u003c/li\u003e\n\u003c/ol\u003e\n\u003cp\u003eDepartment of Mechanical Engineering, Saveetha School of Engineering, Saveetha Institute of Medical and Technical Sciences (Deemed to be University), Thandalam, Chennai, Tamil Nadu 602105, India\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eContributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eChandramohan Devarajan\u003c/strong\u003e: Conceptualization, Methodology, Experimental investigation, Data curation, Drafting of the original manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDhanashekar Manikkam\u003c/strong\u003e: Resources, Supervision of machining experiments, Data validation, Technical review.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMuneera Altayeb\u003c/strong\u003e: Formal analysis, Software and statistical analysis, Visualization, Interpretation of results.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMurali Banu\u003c/strong\u003e: Literature review, Materials procurement, Support in sample preparation and surface characterization.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDhivya Sundaram:\u0026nbsp;\u003c/strong\u003eProject administration, Technical review and Final review and editing.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCorresponding author\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eCorrespondence to Chandramohan Devarajan \u0026nbsp; (e-mail: [email protected])\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eClinical trial number\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData Availability Statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNo datasets were generated or analysed during the current study\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to Participate\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll the authors listed in the manuscript are agree to participate in this research study.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for Publication\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe confirm that the manuscript has been read and approved by all named authors. We confirm that the order of authors listed in the manuscript has been approved by all named authors.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of Interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe wish to confirm that there are no known conflicts of interest associated with this publication and there has been no significant financial support for this work that could have influenced its outcome.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eGonfa, B. K., Sinha, D., Vates, U. K., Badruddin, I. A., Hussien, M., Kamangar, S., Singh, G. K., Ahmed, G. M. S., Kanu, N. J., \u0026amp; Hossain, N. (2022). Investigation of Mechanical and Tribological Behaviors of Aluminum Based Hybrid Metal Matrix Composite and Multi-Objective Optimization. \u003cem\u003eMaterials\u003c/em\u003e, \u003cem\u003e15\u003c/em\u003e(16), 5607. https://doi.org/10.3390/ma15165607\u003c/li\u003e\n\u003cli\u003eSharma, S. K., Gajević, S., Sharma, L. K., Pradhan, R., Sharma, Y., Miletić, I., \u0026amp; Stojanović, B. (2024). Progress in Aluminum-Based Composites Prepared by Stir Casting: Mechanical and Tribological Properties for Automotive, Aerospace, and Military Applications. \u003cem\u003eLubricants\u003c/em\u003e, \u003cem\u003e12\u003c/em\u003e(12), 421. https://doi.org/10.3390/lubricants12120421\u003c/li\u003e\n\u003cli\u003eGolla, C. B., Babar Pasha, M., Rao, R. N., Ismail, S., \u0026amp; Gupta, M. (2023). Influence of TiC Particles on Mechanical and Tribological Characteristics of Advanced Aluminium Matrix Composites Fabricated through Ultrasonic-Assisted Stir Casting. \u003cem\u003eCrystals\u003c/em\u003e, \u003cem\u003e13\u003c/em\u003e(9), 1360. https://doi.org/10.3390/cryst13091360\u003c/li\u003e\n\u003cli\u003eYunus, M., \u0026amp; Alfattani, R. (2023). Assessment of Mechanical and Tribological Behavior of AA6061 Reinforced with B\u003csub\u003e4\u003c/sub\u003eC and Gr Hybrid Metal Matrix Composites. \u003cem\u003eCoatings\u003c/em\u003e, \u003cem\u003e13\u003c/em\u003e(9), 1653. https://doi.org/10.3390/coatings13091653\u003c/li\u003e\n\u003cli\u003eLi, Z., Ma, F., Li, D., Wan, S., Yi, G., Geng, G., \u0026amp; Guo, L. (2022). Enhanced Mechanical and Tribological Capabilities of a Silicon Aluminum Alloy with an Electroplated Ni\u0026ndash;Co\u0026ndash;P/Si\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e Composite Coating. \u003cem\u003eMetals\u003c/em\u003e, \u003cem\u003e12\u003c/em\u003e(1), 120. https://doi.org/10.3390/met12010120\u003c/li\u003e\n\u003cli\u003eMattli, M. R., Matli, P. R., Khan, A., Abdelatty, R. H., Yusuf, M., Ashraf, A. A., Kotalo, R. G., \u0026amp; Shakoor, R. A. (2021). Study of Microstructural and Mechanical Properties of Al/SiC/TiO\u003csub\u003e2\u003c/sub\u003e Hybrid Nanocomposites Developed by Microwave Sintering. \u003cem\u003eCrystals\u003c/em\u003e, \u003cem\u003e11\u003c/em\u003e(9), 1078. https://doi.org/10.3390/cryst11091078\u003c/li\u003e\n\u003cli\u003eMonteiro, B., \u0026amp; Sim\u0026otilde;es, S. (2024). Recent Advances in Hybrid Nanocomposites for Aerospace Applications. \u003cem\u003eMetals\u003c/em\u003e, \u003cem\u003e14\u003c/em\u003e(11), 1283. https://doi.org/10.3390/met14111283\u003c/li\u003e\n\u003cli\u003eMohammed, A. S., Aljebreen, O. S., Hakeem, A. S., Laoui, T., Patel, F., \u0026amp; Ali Baig, M. M. (2022). Tribological Behavior of Aluminum Hybrid Nanocomposites Reinforced with Alumina and Graphene Oxide. \u003cem\u003eMaterials\u003c/em\u003e, \u003cem\u003e15\u003c/em\u003e(3), 865. https://doi.org/10.3390/ma15030865\u003c/li\u003e\n\u003cli\u003eVenkatesh VSS, Rao RN, Manohar G, Singh SN. (2024). Tribo-informative analysis of spark plasma sintered Al-SiC-HAp hybrid composite through machine learning techniques. \u003cem\u003eArabian J Sci Eng\u003c/em\u003e. https://doi.org/10.1007/s13369-024-09835-\u003c/li\u003e\n\u003cli\u003eSunar T, \u0026uml; Ozy\u0026uuml;rek D. (2022). Effect of Al2O3Nanoparticles as reinforcement on the wear properties of A356/Al2O3Nanocomposites produced by powder metallurgy. \u003cem\u003eJ Tribol\u003c/em\u003e,144(8),1\u0026ndash;6. https://doi.org/10.1115/1.4053628.\u003c/li\u003e\n\u003cli\u003eJamwal A, Prakash P, Kumar D, Agrawal R, Kumar K, Gupta P. (2020). Microstructural , tribological and compression behaviour of Copper matrix reinforced with Graphite- SiC hybrid composites. \u003cem\u003eMater Chem Phys\u003c/em\u003e, 251,123090. https://doi.org/10.1016/j.matchemphys.2020.123090\u003c/li\u003e\n\u003cli\u003ePatil NA, Pedapati SR, Mamat O, Lubis AMHS. (2021). Morphological characterization, statistical modeling and wear behavior of AA7075-Titanium Carbide-Graphite surface composites via Friction stir processing. \u003cem\u003eJ Mater Res Technol\u003c/em\u003e, 11, 2160\u0026ndash;80. https://doi.org/10.1016/j.jmrt.2021.02.054.\u003c/li\u003e\n\u003cli\u003eVelavan K, Palanikumar K, Thirumal K, Ragul Kannan K, Kannan M, Arunkumar P. (2023). Mechanical characterization of aluminium alloy LM25 reinforced with TiC and graphite for structural applications. \u003cem\u003eMater Today Proc\u003c/em\u003e, 72, 2049\u0026ndash;55. https://doi.org/10.1016/j.matpr.2022.08.105\u003c/li\u003e\n\u003cli\u003eZhao K, et al. (2020). Enhanced grain refinement and mechanical properties of a high\u0026ndash;strength Al\u0026ndash;Zn\u0026ndash;Mg\u0026ndash;Cu\u0026ndash;Zr alloy induced by TiC nano\u0026ndash;particles. \u003cem\u003eMater. Sci. Eng. A\u003c/em\u003e ,806. https://doi.org/10.1016/j.msea.2021.140852.\u003c/li\u003e\n\u003cli\u003eGowrishankar TP, Manjunatha LH, Sangmesh B. (2020). Mechanical and wear behaviour of Al6061 reinforced with graphite and TiC hybrid MMC\u0026rsquo;s. \u003cem\u003eMater Res Innov\u003c/em\u003e ,24 (3),179\u0026ndash;85. https://doi.org/10.1080/14328917.2019.1628497.\u003c/li\u003e\n\u003cli\u003eLi, Y., Schreiber, P., Schneider, J. \u003cem\u003eet al.\u003c/em\u003e (2023)Tribological mechanisms of slurry abrasive wear. \u003cem\u003eFriction\u003c/em\u003e\u003cstrong\u003e11\u003c/strong\u003e, 1079\u0026ndash;1093.. https://doi.org/10.1007/s40544-022-0654-1\u003c/li\u003e\n\u003cli\u003eBedolla-Becerril, E., Garcia-Guerra, J., Lopez-Morelos, V. H., Garcia-Renteria, M. A., Falcon-Franco, L. A., Martinez-Landeros, V. H., Garc\u0026iacute;a-Villarreal, S., \u0026amp; Flores-Villase\u0026ntilde;or, S. E. (2023). Tribological Behaviour of Al-2024/TiC Metal Matrix Composites. \u003cem\u003eCoatings\u003c/em\u003e, \u003cem\u003e13\u003c/em\u003e(1), 77. https://doi.org/10.3390/coatings13010077\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Hybrid nanocomposite, Tribolayer, wear resistance, Coefficient of friction, AA2219, TiC, Al₂O₃, Stir casting","lastPublishedDoi":"10.21203/rs.3.rs-6987478/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6987478/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis work investigates the fundamental tribological behavior of stir-cast AA2219 aluminum alloy hybrid nanocomposites reinforced with TiC and Al₂O₃/Si₃N₄ nanoparticles. While traditional approaches emphasize property improvements, this study shifts focus toward understanding the mechanisms governing tribolayer formation, interfacial bonding, and thermomechanical interactions during dry sliding wear. Through pin-on-disc experiments (ASTM G99), SEM/EDS/XRD analyses, and statistical validation (ANOVA), the study uncovers how reinforcement-induced tribofilms stabilize sliding interfaces. The optimal composite (5 wt.% TiC\u0026thinsp;+\u0026thinsp;3 wt.% Al₂O₃) showed a 69% reduction in wear rate, which correlates with dense, adherent tribolayer development. Over-reinforcement disrupted this tribofilm through nanoparticle agglomeration and third-body abrasion. Mechanistic interpretations\u0026mdash;based on load transfer theory, dislocation pinning, and tribo-chemical layer evolution\u0026mdash;reveal a reinforcement threshold critical for wear stability. This work contributes to tribology by providing insight into how ceramic hybrid nanoparticles influence interfacial stress distribution and tribofilm resilience, crucial for the design of tribo-functional aluminum composites.\u003c/p\u003e","manuscriptTitle":"Tribological Enhancement of Stir-Cast AA2219/TiC–Al₂O₃ - Si₃N₄ Hybrid Nanocomposites: Mechanism and Surface Layer Analysis","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-07-03 07:06:19","doi":"10.21203/rs.3.rs-6987478/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"fe56ed93-3781-4803-bd7c-9554c102deb0","owner":[],"postedDate":"July 3rd, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-08-02T07:08:28+00:00","versionOfRecord":[],"versionCreatedAt":"2025-07-03 07:06:19","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6987478","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6987478","identity":"rs-6987478","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}