Correlating Microstructure and Residual Stress Improvement in HIP Processed LPBF Ti6Al4V Using Nanoindentation Property Mapping

Correlating Microstructure and Residual Stress Improvement in HIP Processed LPBF Ti6Al4V Using Nanoindentation Property Mapping | 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 Correlating Microstructure and Residual Stress Improvement in HIP Processed LPBF Ti6Al4V Using Nanoindentation Property Mapping Lutfun Nipa, Darshpreet Kaur Saini, Bibhudutta Rout, Hector R. Siller This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8726206/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 Integrating microscale mechanical mapping with microstructural and residual-stress analysis provides a robust approach to establishing process–structure–property relationships at a fine scale in additively manufactured (AM) metals. This study examines the microscale mechanical response of Ti-6Al-4V fabricated by laser powder bed fusion (PBF-LB), followed by hot isostatic pressing (HIP) as a post-process, alongside a conventionally processed (CP) sample as a baseline reference for wrought material. Microstructural and nanoindentation mapping, combined with porosity analysis, showed that as-printed (AP) samples exhibited higher hardness (5.74 GPa) due to a fine α′ martensitic network, with 1.927% porosity. HIP reduced porosity to 0.014% and transformed the microstructure to a coarsened α + β phase, yielding slightly lower hardness (5.61 GPa). The CP condition displayed negligible porosity, a fine equiaxed α + β microstructure, and the lowest hardness (4.79 GPa). A coefficient of variation (CV%) analysis further revealed greater hardness variability in HIP than in AP, attributable to their differing β-phase fractions. Residual stress measurements indicated high tensile stress in AP (0.275 GPa), a uniform, near-stress-free state with minimal tensile stress in HIP (~ 0.02 GPa), and moderate tensile stress in CP (0.129 GPa). The experimental results fell within the simulated range, confirming consistency between the two approaches. Validation of experimental and simulated residual-stress results demonstrates the effectiveness of integrating nanoindentation–electron backscatter diffraction (EBSD) mapping to precisely characterize localized mechanical behavior, thereby supporting structural reliability and performance-driven design in AM metals. Ti-6Al-4V Laser Powder Bed Fusion Hot Isostatic Pressing nanoindentation EBSD indent mapping residual stress computed tomography Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 1 Introduction With its superior strength-to-weight ratio, corrosion resistance, and biocompatibility, Ti-6Al-4V (Ti64) is integral to aerospace, biomedical, and high-performance applications [ 1 ]. Traditional manufacturing approaches such as forging and machining have been extensively applied to Ti64; however, the poor machinability of Ti64—due to its low thermal conductivity and high reactivity—leads to high tool wear and material waste, increasing manufacturing costs [ 2 ]. Laser powder bed fusion (PBF-LB), a form of additive manufacturing, enables near-net-shape production with high geometric flexibility and material efficiency. However, its rapid solidification and cyclic thermal exposure often result in residual stress, porosity, and anisotropic microstructures, which can negatively affect mechanical performance. To evaluate these effects, nanoindentation provides a microscale assessment of mechanical properties—such as hardness and modulus—with micromechanical heterogeneity particularly reflected in hardness, as illustrated by EBSD-mapped indent locations in this study. While macro-scale mechanical testing has been extensively reported in the literature, few studies have examined micro-scale mechanical responses—particularly those measured by nanoindentation—of evolving microstructural features and porosity. Porosity and residual stress, governed by varied conditions, critically influence mechanical performance. Post-processing treatments, such as Hot Isostatic Pressing (HIP), are essential for improving the microstructural quality of PBF-LB Ti-64 by reducing porosity and enhancing uniformity. This treatment plays a crucial role in enhancing the mechanical performance of AM components, thereby narrowing the gap relative to conventionally processed Ti-64. This work highlights how tailored post-processing influences microstructure and affects micro-scale mechanical behavior. Table 1 summarizes prior studies and outlines reported microscale mechanical responses across different conditions. Table 1 Key Findings of Ti64 Properties Across Varied Conditions Process and Testing Relevant Literature Findings References PBF-LB Optimized PBF-LB parameters (220 W, 900–1000 mm/s, 0.13 mm HD) achieved peak density (~ 99.4%) and minimal porosity. [ 3 , 4 ] PBF-LB and HIP As-printed samples contain ~ 1.3% β, and another study confirmed a predominantly α′ martensitic microstructure with negligible β content. Sub-transus HIP (~ 950°C) promotes α-spheroidization and lath coarsening (> 5 µm), transforming α′ to an α + β structure and increasing β content. [ 5 – 9 ] At 980°C, HIP treatment led to ~ 6.4% transformed β, while another study with heat treatment (980°C, 2 h) showed α-lath thickening (~ 3.15 ± 0.26 µm) with a β-phase fraction (~ 7.0 ± 0.5%). [ 10 , 11 ] Sub- and super-transus HIP treatments (996°C), reduce porosity, improving microstructural integrity, as Sub-transus treatments generate acicular α-martensite (~ 1.2 µm), grain boundary α, and reveal prior β grains, with higher temperatures reducing α-phase fraction (e.g., 23% at 950°C vs. 73% at 850°C), resulting in coarser α-laths. [ 12 – 15 ] PBF-LB, HIP, and nanoindentation As-printed showed hardness ranging from 3.66 GPa to 8.19 GPa, attributed to dominant α′/α phases; post-HIP treatment reduced hardness to ~ 5.48 GPa due to duplex α + β structure. [ 16 – 18 ] PBF-LB, HIP, and X-ray tomography With optimal parameters, ~ 0.01% pre-HIP porosity was fully eliminated post-HIP, resulting in full density; moreover, at 950°C, reduced porosity began promoting recrystallization. [ 19 , 20 ] Wrought condition and Micro CT Reported α/β microstructures vary widely: one study reported ~ 65% α and 35% β, while another reported ~ 94% α and only 6% β, and µCT confirmed a pore-free structure. [ 21 , 22 ] PBF-LB, XRD, and FEM simulation As-printed samples showed high residual stresses (~ 197–494 MPa by XRD), which were significantly reduced to ~ 44 MPa after an 800°C/2 h post-heat treatment; another study reported ~ 400 MPa (XRD), with FEM-simulated values ranging from 492 to 15 MPa. [ 23 – 25 ] PBF-LB, CT tomography, nanoindentation, and HIP As-built α′ martensitic samples showed the highest hardness, while post-treated α + β had lower; porosity (< 0.2%) influences hardness and strength, as these properties are sensitive to pores. [ 26 , 27 ] This work establishes quantitative process–structure–property relationships for PBF-LB Ti64 by integrating high-resolution nanoindentation mapping with EBSD to resolve intra- and inter-grain hardness variations. Nanoindentation mapping, supported by EBSD data, captures localized mechanical variations, while residual stresses are assessed via XRD and validated through finite element simulation. Porosity was quantified to directly correlate pore fraction with microstructural features and localized mechanical behavior. Unlike prior studies that examined these aspects in isolation, this study provides a unified experimental–computational framework that reveals distinct microscale mechanical behavior and porosity analyses for AP, HIP, and CP conditions. This integrated approach advances understanding of microstructure–property relationships in AM alloys and establishes a benchmark for microscale mechanical characterization, providing valuable insights for aerospace, biomedical, and high-performance engineering applications. Although previous studies have examined PBF-LB processing, HIP treatment, and porosity effects on bulk properties, these factors were often evaluated independently or reported as bulk-averaged responses. The direct link between microscale mechanical heterogeneity, grain morphology, phase distribution, and local defect states remains underexplored. This work addresses this gap by integrating high-resolution nanoindentation mapping with EBSD, X-ray tomography, and residual stress analysis to establish a unified microscale process–structure–property framework for AP- and HIP-treated conditions. The study provides insights into how tailored post-processing modifies intra- and inter-grain properties, thereby enhancing the predictive understanding of microscale mechanical performance in additively manufactured Ti64 components. 2 Materials and Methods 2.1 Powder Analysis The used Ti64 powder exhibited good flowability, with an average flow time of 28 seconds for 50 grams. The measured apparent and tap densities were 2.40 g/cm³ and 2.91 g/cm³, respectively. As shown in Fig. 1 , particle size distribution (PSD) analysis using a Microtrac system indicated an average powder particle size of ~ 39.16 µm, and optical microscopy confirmed a predominantly spherical morphology, which supported uniform powder spreading and consistent melting behavior during PBF-LB. 2.2 Sample Fabrication and Preparation Ti64 cubic samples (5 × 5 × 5 mm³) were fabricated using the PBF-LB system (TruPrint 1000, TRUMPF GmbH). Among the tested laser power–scan speed combinations (hatch spacing 0.065 mm, layer thickness 0.03 mm), the adjusted setting of 160 W and 900 mm/s yielded AP samples with 98.71% relative density (Archimedes’ method) [ 28 ]. Post-fabricated samples were sectioned using electrical discharge machining (EDM) and sequentially mechanically polished with alumina suspensions (5, 1, and 0.03 µm), followed by final polishing with colloidal silica (0.05 and 0.02 µm) to achieve mirror finishes suitable for microstructural and mechanical characterization. Ultrasonic cleaning was performed after polishing to remove residual debris. 2.3 Post-Processing and Testing Details To explore the effects of post-processing, a subset of the AP samples was subjected to HIP using an AIP6-30H system (American Isostatic Presses, Inc., USA). HIP treatment was conducted at 980°C (just below the β-transus at ~ 995°C), at a pressure of 130 MPa, with a 2-hour holding time and a heating and cooling rate of 10°C/min. This near-β-transus HIP condition was selected to promote densification, thereby reducing residual porosity and relieving a substantial portion of the tensile residual stresses, while enabling direct correlation of the resulting microstructural evolution with the mechanical properties measured through nanoindentation and EBSD-based indentation mapping. EBSD was performed on a Thermo Scientific Apreo 2C with EDAX detector (20 kV, 1.3 µm step size), and data acquired using EDAX OIM Analysis™ with identical settings to assess phase distribution, texture, and grain-wise indent locations—revealing PBF-LB and HIP-induced microstructural changes linked to local mechanical behavior, including for conventional one. To obtain micro-scale mechanical properties such as hardness and elastic modulus, nanoindentation was conducted using a KLA Nano Indenter XP (KLA Corporation, Milpitas, California, USA) with a Berkovich diamond tip at 50 mN load, ~ 5000 nm contact depth, and 0.2 s⁻¹ strain rate, with a Poisson’s ratio of 0.33. A (3 × 3) indent grid was applied at the center and corners of each conditioned sample with 50 µm spacing between adjacent indents. Residual stress was measured using a Rigaku SmartLab SE diffractometer to assess surface stress evolution and its relationship to thermal history, which affects mechanical properties. XRD measurements were performed at room temperature using the instrument equipped with Cu Kα radiation (λ = 1.5406 Å) and a secondary monochromator, operated at 40 kV and 50 mA. Scans were collected over a 2θ range of 30°–90°, with a step size of 0.01° and a scan speed of 4°/min, capturing diffraction peaks corresponding to α′/α (hcp) phase, and β (bcc) phases. All samples, with a uniform thickness of 3 mm, were analyzed on the as-printed layer plane in the same orientation to ensure consistency. Additionally, Finite Element simulations (SimScale) were used to estimate residual stress distributions for each sample in a consistent orientation. Porosity analysis of AP, HIP-treated, including baseline CV samples, was performed using a ZEISS Xradia CrystalCT system (Carl Zeiss AG, Oberkochen, Germany), operating at 150 kV and 9.96 W. High-resolution CT scanning of a 2.2 × 4.4 mm region acquired 1,601 projection images, which were reconstructed into slices and analyzed using Dragonfly Pro software. 3 Results and Discussion 3.1 Porosity Analysis X-ray computed tomography revealed a porosity of 1.927% in the AP sample, primarily originating from additive manufacturing process-related defects, such as unmelted powder regions and gas-trapped voids typical of layer-wise fabrication. HIP treatment reduced porosity to 0.014% by maintaining elevated temperature and high isostatic pressure for an extended period, thereby promoting pore closure. The observed reduction in porosity confirms the effectiveness of HIP in mitigating process-induced defects in PBF-LB Ti-64. The conventionally processed sample exhibited negligible porosity. Figures 2 (a) and 2(b) show the 3D reconstructed porosity distribution for AP and HIP samples obtained from CT scan analysis. Porosity analysis was performed not only to quantify defect reduction but also to assess its influence on microscale mechanical variability. The results indicate that, once porosity is minimized, local mechanical response is increasingly governed by grain-scale heterogeneity and phase distribution rather than defect content. The results indicate that both defect population and phase-scale architecture are relevant factors influencing microscale mechanical behavior in additively manufactured Ti64. 3.2 Microscale EBSD Indent Mapping Analysis 3.2.1 EBSD Mapping Analysis for As-Printed Samples The AP sample exhibited a fine, non-equilibrium, acicular α′ martensitic structure, formed at the high cooling rates inherent to the PBF-LB process. EBSD phase mapping confirmed α′ as the dominant phase, with only ~ 2% of the β phase retained, typically located along grain boundaries. This microstructure exhibited pronounced residual stresses and orientation gradients resulting from directional solidification during layer-wise deposition. EBSD orientation maps revealed elongated, columnar prior-β grains aligned with the build direction, containing fine α′ martensite laths, which introduce subtle microstructural heterogeneity, particularly due to the absence of equiaxed α grain boundaries. Though the observed columnar grains were not always aligned with the build direction (BD), as their growth follows local thermal gradients, resulting in tilted or radial orientations. Despite this heterogeneity, the AP condition demonstrated relatively high nanoindentation hardness, attributed to the intrinsically harder and more deformation-resistant α′ phase. The dense α′ lath boundaries act as effective barriers to dislocation motion, thereby strengthening the material. A 3×3 nanoindentation grid spanning intra- and inter-grain regions effectively captured localized mechanical variations associated with microstructural features. Indents positioned within single grains (intra-grain) are primarily influenced by the local phase (either predominantly α′ martensite or retained β grain) and their specific location within the grain structure. In contrast, inter-grain indents, which span across grain boundaries or lie between adjacent grains, are more affected by boundary constraints, residual stress concentrations, and the presence of multiple grain interfaces. Indents located within or adjacent to α′ regions generally exhibited higher hardness than those in retained β-phase regions, underscoring the strength contrast between these phases. Pole figures exhibit strong texture intensity with distinct maxima aligned to the build direction, consistent with columnar prior-β grain growth and orientation gradients induced by directional solidification. Figure 3 (a) shows EBSD orientation maps overlaid with nanoindentation grids annotated with hardness values, along with the phase fraction map in Fig. 3 (b) and the texture pole in Fig. 3 (c). These intra- and inter-grain indents capture localized mechanical behavior and highlight the correlation between local phase distribution, grain morphology, and mechanical response—particularly the strengthening influence of α′ interfaces. 3.2.2 EBSD Mapping Analysis for Hot Isostatic Pressed Samples For HIP-treated samples, a 3×3 nanoindentation grid was employed to examine microstructure–mechanical property relationships following processing at near-β-transus temperature, without inducing full recrystallization. This thermal exposure promoted partial phase transformation and morphological coarsening, decomposing α′ martensite into an equilibrium α + β structure comprising approximately 81.2% α and 18.8% β. Additionally, some grains exhibited slight deviations from the BD due to the combined effects of temperature, pressure, and holding time at near-β-transus HIP conditions. The α laths underwent significant coarsening, increasing spatial separation between microstructural features and enhancing the resolution of indentation responses across distinct regions. As a result, intra-grain indents located within single-phase regions are more clearly resolved in the HIP condition due to the comparatively observable wider α laths—either within α grains or retained β regions—allowing for more direct observation of localized mechanical responses without interference from overlapping features. Inter-grain indentations intersecting grain boundaries or positioned near α–β interfaces revealed subtle mechanical heterogeneity associated with boundary constraints and multiphase interactions. These variations underscore the influence of grain structure and interface character on microscale deformation behavior. Unlike the AP condition, in which hierarchical heterogeneity from variable cooling rates produces variations in α′ lath width, visible in mapping and graded properties, HIP yields a homogeneous microstructure that reduces indentation overlap and clarifies intra- versus inter-grain variability. Overall, the average hardness in the HIP-treated condition is lower than that of the AP sample, consistent with the increased β-phase fraction and the transformation of hard α′ martensite into a softer α + β mixture. The observed hardness distribution reflects the combined effects of phase evolution, grain morphology, and boundary characteristics. Texture pole figures show a reduced but still discernible texture, reflecting partial texture relaxation following near-β-transus HIP processing without full recrystallization and with α′ → α + β decomposition. Figure 4 (a) presents EBSD-based indent mapping overlaid with the nanoindentation grid and corresponding hardness values, illustrating spatial variation in mechanical response across the HIP-treated microstructure, along with the phase fraction map in Fig. 4 (b) and the texture pole in Fig. 4 (c). 3.2.3 EBSD Mapping Analysis for Conventionally Processed Samples The EBSD maps of the CP sample (reference baseline) in the wrought state reveal a refined, equiaxed α-phase microstructure with ~ 94.8% α and 5.2% retained β, where β is primarily located at grain boundaries or interfaces. The 3×3 nanoindentation grid includes indents within α grains and near α–β interfaces. Due to the small, equiaxed grains under these conditions, many indentations—both intra- and inter-grain—lie near multiple boundaries, enabling a localized assessment of microstructure–property variations at the microscale. Hardness in the CP condition was generally lower, reflecting the influence of fine equiaxed α grains, limited β-phase content, and a thermally relaxed microstructure. The absence of rapid solidification effects, as observed in AM, resulted in a more uniform, thermally relaxed microstructure that tends to offer less resistance to localized deformation during nanoindentation. Slight softening near β regions and modest hardening near α grain boundaries were observed, though boundary strengthening effects were less pronounced than in HIP or AP samples. Additionally, the pole figures exhibit weak, diffuse intensity, indicating a near-random crystallographic orientation associated with a refined, equiaxed α-phase microstructure. Figure 5 (a) shows EBSD mapping with nanoindentation of the CP sample, highlighting variations in mechanical response with grain and phase features; Fig. 5 (b) shows the phase fraction map; and Fig. 5 (c) shows the texture pole. 3.3 Microscale Mechanical Properties by Nanoindentation Nanoindentation analysis was performed to evaluate the microscale mechanical response of Ti-64 samples processed via AP, HIP, and CP. The results highlight notable differences in hardness and elastic modulus, reflecting the underlying microstructural features identified via EBSD. The AP sample exhibited the highest average hardness (5.74 ± 0.22 GPa) and modulus (130.51 ± 3.67 GPa), consistent with its high fraction of fine acicular α′ martensite and elongated prior-β grains containing high internal stress. Figures 6 , 7 , and 8 illustrate nanoindentation-based contour maps of hardness, elastic modulus, and corresponding scanning electron surface views for the AP, HIP, and CP Ti64 samples. In contrast, the HIP-treated sample exhibited slightly reduced hardness (5.61 ± 0.49 GPa) while maintaining a similar modulus (130.02 ± 7.57 GPa). These changes correlate with the observed α + β microstructural transformation and α-lath coarsening. The increased β-phase fraction and reduced defect content yield a more homogeneous mechanical response, although the softer β-phase regions and broader α-domains influence the distribution of indentation resistance without a significant loss of microscale strength. The CP sample exhibited the lowest hardness (4.79 ± 0.18 GPa) and modulus (123.12 ± 1.51 GPa), consistent with its stable α + β microstructure, fine equiaxed grains, limited β-phase contrast, and uniform microscale deformation behavior. The absence of α′ and reduced internal stress levels contributed to the decrease in localized hardness. The AP samples exhibited a lower standard deviation due to a relatively uniform α′-martensitic structure, despite higher surface roughness. In contrast, HIP exhibited greater deviation, likely due to increased β-phase content and grain growth, resulting in local variability. The CP condition exhibited the lowest deviation, reflecting its stable α + β microstructure and smoother surface. Overall, these trends validate the strong link between microscale mechanical behavior and microstructural features of phase distribution, grain size, and boundary characteristics, which govern the indentation response under different conditions. The coefficient of variation highlights differences in hardness uniformity; HIP samples (observed ~ 18.8% β-phase) exhibited the highest variability (intra: 11.103%; inter: 6.084%), reflecting the dual-phase nature of the α + β structure, in which the presence of β promotes mechanical scatter. In contrast, AP samples (~ 2% β-phase) showed lower variability (intra: 5.080%; inter: 3.077%), indicating that α′-dominated microstructures with a lower β fraction. The CP sample exhibited the lowest scatter, particularly for inter-grain hardness (1.870%), consistent with its refined equiaxed microstructure and stable processing history. The average hardness values of AP and HIP are similar; however, their markedly different β-phase fractions lead to significant differences in the coefficient of variation (CV%) for intra- and inter-grain indentation responses. Across all conditions, CV for inter-grain indents remained consistently lower than intra-grain indents, suggesting that hardness distribution is more uniform across grains compared to within individual grains. Although the number of indents is limited, CV provides a useful qualitative measure of local hardness scattering, reflecting mechanical property variability along with the grain indentation response across varied conditions. These comparative trends are illustrated in Fig. 9 , highlighting how microstructural phase evolution correlates with local hardness variability across different conditions. 3.4 Residual Stress Evaluation through X-ray Diffraction and Simulation Residual stress analysis was conducted on three conditioned samples of Ti64—AP, HIP, and CP—using both experimental XRD and simulation. The Halder–Wagner method was applied using SmartLab Studio II (Rigaku) to extract lattice strain values from XRD peak broadening, with analysis spanning measurement to data interpretation. Peaks with excessive Full Width at Half Maximum (FWHM) or overlap with the internal standard (Rigaku-RSRP-43275G) were excluded to ensure accuracy. Through this analysis, lattice strain values of 0.28% for AP, 0.03% for HIP, and 0.14% for CP were obtained. Using a simplified elastic model derived from Hooke’s Law, residual stresses were calculated by Eq. 1: \(\:\sigma\:=\frac{E.ϵ}{(1+\vartheta\:)}\) (Eq. 1) where ε is the measured lattice strain, E is the elastic modulus (measured via nanoindentation for each condition), and ν is Poisson’s ratio, constant 0.33 across all samples. Using this formulation and the respective moduli (AP: 130.51 GPa, HIP: 130.02 GPa, CP: 123.12 GPa, the calculated residual stresses were for AP is 0.275 GPa (high tensile); for HIP is 0.020 GPa (near-stress-free state with minimal tensile stress); and for CP is 0.129 GPa (moderate tensile). Figure 10 presents the XRD patterns of the AP, HIP, and CP samples. All patterns exhibit reflections corresponding to the hexagonal close-packed (hcp) structured α′/α phase (100), (002), (101), (102), (110), (103)/(211), (112), and (201) along with a faint body-centered cubic (bcc) β(110) reflection near 2θ ≈ 39.5°, consistent with the dual-phase structure typical of Ti64 [ 12 , 29 ]. In the AP condition (Fig. 10 a), the α′/α peaks display significant broadening, particularly for (100) ≈ 35.1°, (002) ≈ 38.4°, and (101) ≈ 40.5°. The broadened profiles and absence of distinct β reflections indicate a fine acicular α′ martensitic microstructure formed under the rapid cooling rates of the PBF-LB process. The measured lattice strain of 0.28% and calculated high tensile residual stress of ≈ 0.275 GPa confirm substantial internal stress accumulation due to steep thermal gradients during solidification [ 30 ]. Following HIP treatment (Fig. 10 b), the α-phase peaks sharpen significantly, indicating recovery of the hcp lattice and microstructural coarsening as the metastable α′ martensite decomposes [ 29 , 31 ]. A very weak but distinct β(200) reflection appears at ~ 57°, confirming the presence of a small amount of retained or reprecipitated β phase following near-β-transus HIP. Because the β(211) reflection normally occurs at ~ 69–72° and overlaps the α(103) peak, it commonly appears only as a weak shoulder rather than a stand-alone peak in HIP-treated Ti64, which is consistent with the subtle feature observed in Fig. 10 (b). No resolvable β(110) peak is detected near ~ 39°, as this region is dominated by the strong α(002) and α(101) reflections. Any β(110) contribution, if present, remains below detection sensitivity or is fully masked by these α peaks. The appearance of the β(200) peak, combined with substantial narrowing of α reflections, provides clear evidence of the α′ → α + β transformation and associated microstructural recovery. Lattice strain decreases to 0.03%, and the calculated residual stress drops to ~ 0.02 GPa, confirming nearly complete stress relaxation and homogenization of the microstructure. The improved definition of the α(103) reflection and the subtle presence of β(211) near ~ 71–72° further indicate enhanced crystallographic order and the re-establishment of the equilibrium α + β phase distribution following HIP. The CP sample (Fig. 10 c) exhibits sharp α reflections and a well-defined β(110) peak characteristic of a thermally equilibrated α + β microstructure. With moderate lattice strain (0.14%) and tensile stress (0.129 GPa), it reflects the balanced state typical of conventional thermo-mechanical processing [ 32 ]. Overall, the XRD results confirm the progressive α′ → α + β transformation sequence from AP → HIP → CP, consistent with decreasing internal strain and increasing phase stability. The experimental stress hierarchy (AP > CP > HIP) is consistent with finite-element simulations, validating the correlation between microstructural evolution and residual stress. The weak β(200) reflection near 57° provides clear evidence of partial β stabilization rather than measurement noise, reinforcing that HIP below the β-transus (~ 995°C) effectively converts metastable α′ to equilibrium α + β while minimizing residual stresses and enhancing lattice uniformity. Simulated stress contour maps for AP, HIP, and CP are presented using a common color scale, with boundary conditions defined by density, a constant Poisson’s ratio, and nanoindentation-derived modulus. The simulations confirm experimental trends while providing additional spatial context. For AP, surface stress ranged from ~ 0.27 to 0.35 GPa, indicating high tensile residual stress and consistency with localized thermal gradients from the PBF-LB process. Notably, steep thermal gradients and rapid cooling at the discontinuities led to pronounced stress concentrations at the corners of the AP sample during layer-wise solidification. HIP showed a nearly uniform near-stress-free state of ~ (-0.05 to 0.03) GPa, reflecting effective stress relief and homogenization post-HIP. Additionally, the stress distribution for the CP sample ranged from ~(0.11 to 0.19 GPa, with only minor corner stress concentration, consistent with moderate tensile residual stresses arising from its conventional thermal history. Table 2 summarizes the experimental and simulated residual stresses and the corresponding boundary conditions for AP, HIP, and CP. Figure 11 shows simulated surface-residual-stress contour maps for each condition, corresponding to the same plane analyzed experimentally. The agreement between experimental values and simulated ranges validates the combined experimental–computational approach for characterizing surface-level residual stresses in Ti64. Table 2 Residual stress results (experimental & simulated) with boundary conditions Sample Condition Lattice Strain, ε (%) Experimental Residual Stress (GPa) Simulated Residual Stress (GPa) Boundary Conditions for Simulation Elastic Modulus, E (GPa) Poisson’s ratio, ν Relative Density (%) AP 0.28±.06 0.275 ~ 0.27 to 0.35 130.51 0.33 ~ 98.17 HIP 0.03±.05 0.020 ~ -0.05 to 0.03 130.02 0.33 ~ 99.99 CP 0.14±.03 0.129 ~ 0.11 to 0.19 123.12 0.33 ~ 100 4 Conclusion High-resolution nanoindentation mapping integrated with EBSD effectively characterized localized hardness variations in PBF-LB Ti64 processed under AP, HIP, and reference CP conditions. Intra- and inter-grain mapping using nanoindentation revealed hardness trends linked to grain morphology, phase fractions, and boundary characteristics. Porosity analysis confirmed a reduction from 1.927% in the as-printed condition to 0.014% after HIP treatment, whereas the as-printed state, despite its higher porosity, exhibited slightly higher hardness (5.74 GPa) due to the presence of a fine α′ martensitic microstructure. HIP exhibited slightly lower hardness (5.61 GPa) with improved uniformity from phase coarsening and defect mitigation, while CP showed the lowest hardness (4.79 GPa) with a uniform response from an equilibrium α + β structure. Although AP and HIP exhibited similar average hardness, HIP (~ 18.8% β) showed higher variability (intra: 11.103%; inter: 6.084%), indicating β-phase–driven local heterogeneity, while AP (~ 2% β) was more uniform (intra: 5.080%; inter: 3.077%). CP showed the lowest scatter (inter: 1.87%), reflecting its stable equiaxed microstructure and establishing a baseline for microscale mechanical behavior. Additionally, residual stresses, measured by XRD and supported by finite element simulations, showed high tensile stress in AP (0.275 GPa experimentally; 0.27–0.35 GPa simulated), a uniform, near-stress-free state with minimal tensile stress in HIP (~ 0.02 GPa experimentally; ~–0.05 − 0.03 GPa simulated), and moderate tensile stress in CP (0.129 GPa experimentally; 0.11–0.19 GPa simulated), with simulations closely matching experimental observations. This pronounced reduction and homogenization of residual stress following HIP represents a key contribution of the present work, demonstrating the effectiveness of post-processing in mitigating AM-induced thermal stresses. The near-stress-free condition achieved after HIP is critical for stabilizing the microstructure and reducing stress-driven variability in localized mechanical response, thereby enhancing the reliability of micro-scale mechanical performance. Overall, these results establish clear process–structure–property relationships across as-printed, post-processed, and conventional Ti64, demonstrating a transferable framework for optimizing AM Ti64 for performance-critical aerospace, biomedical, and engineering applications. Declarations Author Contribution L.N. conceptualized the experiments, investigated and developed the fabrication and overall characterization of samples, analyzed the experimental results, and wrote the main manuscript text. D.K.S. investigated and developed the X-Ray Diffraction (XRD) of samples, analyzed the characterization results, and reviewed the manuscript text. B.R. analyzed and validated the experimental and characterization results, provided experimental resources, and reviewed the main manuscript text. H.R.S. conceptualized the experiments, supervised experimental work, administered the project, contributed to funding acquisition, and reviewed and edited the main manuscript text. Acknowledgement Research was sponsored by the Office of Naval Research and was accomplished under Grant Number W911NF-23-1-0148. The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the official policies, either expressed or implied, of the Army Research Office or the U.S. Government. The U.S. Government is authorized to reproduce and distribute reprints for Government purposes, notwithstanding any copyright notation herein. Additional support was provided by the Center for Agile & Adaptive Additive Manufacturing, funded through the State of Texas Appropriation (#190405–105–805008–220). Also, the authors gratefully acknowledge the X-Ray Diffraction Laboratory, Department of Chemistry, for access to XRD facilities and assistance during measurements. Data Availability The data are available upon request. References Marin E, Lanzutti A (2024) Biomedical Applications of Titanium Alloys: A Comprehensive Review. 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Mater Lett 301. https://doi.org/10.1016/j.matlet.2021.130273 Nipa L, Siller HR, Mirshams RA (2025) Nanoindentation-driven analysis of mechanical properties in LPBF TI6AL4V. Proceedings of the ASME 20th International Manufacturing Science and Engineering Conference. https://doi.org/10.1115/MSEC2025-155436 du Plessis A, Macdonald E (2020) Hot isostatic pressing in metal additive manufacturing: X-ray tomography reveals details of pore closure. Additive Manuf 34. https://doi.org/10.1016/j.addma.2020.101191 Tosi R, Leung CLA, Tan X et al (2022) Revealing the microstructural evolution of electron beam powder bed fusion and hot isostatic pressing Ti-6Al-4V in-situ shelling samples using X-ray computed tomography. Additive Manuf 57. https://doi.org/10.1016/j.addma.2022.102962 Beyl K, Mutombo K, Kloppers CP (2019) Tensile properties and microstructural characterization of additive manufactured, investment cast and wrought Ti6Al4V alloy. In: IOP Conference Series: Materials Science and Engineering. 10.1088/1757-899X/655/1/012023 Tevet O, Svetlizky D, Harel D et al (2022) Measurement of the Anisotropic Dynamic Elastic Constants of Additive Manufactured and Wrought Ti6Al4V Alloys. Materials 15: https://doi.org/10.3390/ma15020638 Aversa A, Carrozza A, Mercurio V et al (2025) A Comparison Between the Residual Stresses of Ti6Al4V and Ti-6Al-2Sn-4Zr-6Mo Processed by Laser Powder Bed Fusion. Materials 18. https://doi.org/10.3390/ma18030689 Bian P, Jammal A, Xu K et al (2025) A Review of the Evolution of Residual Stresses in Additive Manufacturing During Selective Laser Melting Technology. Materials 18. https://doi.org/10.3390/ma18081707 Song J, Wu W, Zhang L et al (2018) Role of scanning strategy on residual stress distribution in Ti-6Al-4V alloy prepared by selective laser melting. Optik 170:342–352. https://doi.org/10.1016/j.ijleo.2018.05.128 Kan WH, Chiu LNS, Lim CVS et al (2022) A critical review on the effects of process-induced porosity on the mechanical properties of alloys fabricated by laser powder bed fusion. J Mater Sci 57:9818–9865. https://doi.org/10.1007/s10853-022-06990-7 García-Hernández C, García-Cabezón C, González-Diez F et al (2025) Effect of processing on microstructure, mechanical properties, corrosion and biocompatibility of additive manufacturing Ti-6Al-4V orthopaedic implants. https://doi.org/10.1038/s41598-025-98349-6 . Scientific Reports15: ASTM International ASTM B962 -15 Standard Test Methods for Density of Compacted or Sintered Powder Metallurgy (PM) Products Using Archimedes’ Principle. ASTM International Jaber H, Kónya J, Kulcsár K, Kovács T (2022) Effects of Annealing and Solution Treatments on the Microstructure and Mechanical Properties of Ti6Al4V Manufactured by Selective Laser Melting. Materials 15. https://doi.org/10.3390/ma15051978 Thijs L, Verhaeghe F, Craeghs T et al (2010) A study of the microstructural evolution during selective laser melting of Ti-6Al-4V. Acta Mater 58:3303–3312. https://doi.org/10.1016/j.actamat.2010.02.004 Xu W, Brandt M, Sun S et al (2015) Additive manufacturing of strong and ductile Ti-6Al-4V by selective laser melting via in situ martensite decomposition. Acta Mater 85:74–84. https://doi.org/10.1016/j.actamat.2014.11.028 Boyer R, WG,CEW (ed) (1994) Materials properties handbook: Titanium alloys. ASM International 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. 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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-8726206","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":582491231,"identity":"64f48653-3c31-4cf3-b713-d48f13ac5844","order_by":0,"name":"Lutfun Nipa","email":"","orcid":"","institution":"University of North Texas","correspondingAuthor":false,"prefix":"","firstName":"Lutfun","middleName":"","lastName":"Nipa","suffix":""},{"id":582491232,"identity":"e8d8bb04-f746-4a2f-beaa-9fc69a1eb58f","order_by":1,"name":"Darshpreet Kaur Saini","email":"","orcid":"","institution":"University of North Texas","correspondingAuthor":false,"prefix":"","firstName":"Darshpreet","middleName":"Kaur","lastName":"Saini","suffix":""},{"id":582491233,"identity":"d67e051f-bcb0-4f2a-a593-ef83f42ca793","order_by":2,"name":"Bibhudutta Rout","email":"","orcid":"","institution":"University of North Texas","correspondingAuthor":false,"prefix":"","firstName":"Bibhudutta","middleName":"","lastName":"Rout","suffix":""},{"id":582491234,"identity":"e31cb874-2341-404a-8196-675e6a00fda2","order_by":3,"name":"Hector R. 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02:38:04","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8726206/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8726206/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":101753558,"identity":"c9f2e991-bbc6-4055-943d-dd96e5de88a6","added_by":"auto","created_at":"2026-02-03 10:40:14","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":679214,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Optical image of Ti64 powder and (b) corresponding particle size distribution (PSD)\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-8726206/v1/cc75f8ee4130a742eb483b1b.png"},{"id":101672288,"identity":"19d7f010-7844-4ff9-be78-9d32e1bd7d7a","added_by":"auto","created_at":"2026-02-02 12:59:13","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":130208,"visible":true,"origin":"","legend":"\u003cp\u003e3D reconstructed porosity distribution for (a) as-printed (AP) and (b) hot isostatic pressed (HIP) samples\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-8726206/v1/e15dda4722739c5942457d9b.png"},{"id":101753288,"identity":"419deb6f-45ee-471b-a7e9-a7428acec3ae","added_by":"auto","created_at":"2026-02-03 10:39:37","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":832583,"visible":true,"origin":"","legend":"\u003cp\u003e(a) EBSD IPF map of the as-printed (AP) sample with nanoindentation grids showing hardness variation across intra- and inter-grain regions, (b) phase fraction map, and (c) texture pole figure\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-8726206/v1/055d086de6e4308916edf9f2.png"},{"id":101753458,"identity":"938ab687-257d-4fbd-a752-e2c5f9645f31","added_by":"auto","created_at":"2026-02-03 10:40:06","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":615181,"visible":true,"origin":"","legend":"\u003cp\u003e(a) EBSD IPF map of the hot isostatic pressed (HIP) sample with nanoindentation grids showing hardness variation across intra- and inter-grain regions, (b) phase fraction map, and (c) texture pole figure\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-8726206/v1/47b3a509189c4971c6127b36.png"},{"id":101672289,"identity":"d4b0ce5a-ef26-428d-8a21-924661e9d615","added_by":"auto","created_at":"2026-02-02 12:59:14","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":596127,"visible":true,"origin":"","legend":"\u003cp\u003e(a) EBSD IPF map of the conventionally processed (CP) sample with nanoindentation grids showing hardness variation across intra- and inter-grain regions, (b) phase fraction map, and (c) texture pole figure\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-8726206/v1/ade4a0836c10aa2d7e69a30f.png"},{"id":101672297,"identity":"7ccfb08a-0475-40a6-9199-06e7a48f0099","added_by":"auto","created_at":"2026-02-02 12:59:14","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":342581,"visible":true,"origin":"","legend":"\u003cp\u003eAs-printed (AP) condition – (a) hardness map, (b) elastic modulus map with color bar, and (c) scanning electron micrograph highlighting indent locations with an inset showing the actual indent impression\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-8726206/v1/fff80e22efabbe4c3070d6f2.png"},{"id":101672292,"identity":"33e1c572-84d3-4c07-817e-e53266516c36","added_by":"auto","created_at":"2026-02-02 12:59:14","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":270378,"visible":true,"origin":"","legend":"\u003cp\u003eHot isostatic pressed (HIP) condition – (a) hardness map, (b) elastic modulus map with color bar, and (c) scanning electron micrograph highlighting indent locations with an inset showing the actual indent impression\u003c/p\u003e","description":"","filename":"floatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-8726206/v1/43982c26d19d38da639a90be.png"},{"id":101672294,"identity":"5e83d0b6-80f2-49c8-8765-5b35bd020209","added_by":"auto","created_at":"2026-02-02 12:59:14","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":271387,"visible":true,"origin":"","legend":"\u003cp\u003eConventionally processed (CP) condition – (a) hardness map, (b) elastic modulus map with color bar, and (c) scanning electron micrograph highlighting indent locations with an inset showing the actual indent impression\u003c/p\u003e","description":"","filename":"floatimage8.png","url":"https://assets-eu.researchsquare.com/files/rs-8726206/v1/9a96665dbe6e6ec4dff0a7d5.png"},{"id":101672293,"identity":"59e94122-bd46-47d0-aa31-bb44f086392d","added_by":"auto","created_at":"2026-02-02 12:59:14","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":151306,"visible":true,"origin":"","legend":"\u003cp\u003eComparative coefficient of variation (CV%) of intra- and inter-grain hardness across different conditions\u003c/p\u003e","description":"","filename":"floatimage9.png","url":"https://assets-eu.researchsquare.com/files/rs-8726206/v1/5ef347de28503a642412240c.png"},{"id":101754255,"identity":"96533304-92a5-446e-b963-f2ce6ebd0a7e","added_by":"auto","created_at":"2026-02-03 10:42:09","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":306547,"visible":true,"origin":"","legend":"\u003cp\u003eXRD patterns of (a) as-printed (AP), (b) hot isostatic pressed (HIP), and (c) conventionally processed (CP) showing α′/α and β across varied conditions\u003c/p\u003e","description":"","filename":"floatimage10.png","url":"https://assets-eu.researchsquare.com/files/rs-8726206/v1/b45403899bf36808a97f46d8.png"},{"id":101672296,"identity":"af633217-9ab7-4acb-8ed8-d3d708ffde4c","added_by":"auto","created_at":"2026-02-02 12:59:14","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":302182,"visible":true,"origin":"","legend":"\u003cp\u003eSimulated residual stress maps with color bar for (a) as-printed (AP) with high tensile stress (0.27–0.35 GPa), (b) hot isostatic pressed (HIP) showing a uniform, near-stress-free state with minimal tensile stress (~-0.05 to 0.03 GPa), and (c) conventionally processed (CP) with moderate tensile stress (0.11 to 0.19 GPa)\u003c/p\u003e","description":"","filename":"floatimage11.png","url":"https://assets-eu.researchsquare.com/files/rs-8726206/v1/1de3a2be73d1659502f18337.png"},{"id":101755771,"identity":"a362e0f1-68fb-4ba0-bfa0-6bfb02192851","added_by":"auto","created_at":"2026-02-03 10:54:39","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":5333861,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8726206/v1/20f6efe0-1987-4ee8-bb9f-9ee2a30c321d.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Correlating Microstructure and Residual Stress Improvement in HIP Processed LPBF Ti6Al4V Using Nanoindentation Property Mapping","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003eWith its superior strength-to-weight ratio, corrosion resistance, and biocompatibility, Ti-6Al-4V (Ti64) is integral to aerospace, biomedical, and high-performance applications [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. Traditional manufacturing approaches such as forging and machining have been extensively applied to Ti64; however, the poor machinability of Ti64\u0026mdash;due to its low thermal conductivity and high reactivity\u0026mdash;leads to high tool wear and material waste, increasing manufacturing costs [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Laser powder bed fusion (PBF-LB), a form of additive manufacturing, enables near-net-shape production with high geometric flexibility and material efficiency. However, its rapid solidification and cyclic thermal exposure often result in residual stress, porosity, and anisotropic microstructures, which can negatively affect mechanical performance. To evaluate these effects, nanoindentation provides a microscale assessment of mechanical properties\u0026mdash;such as hardness and modulus\u0026mdash;with micromechanical heterogeneity particularly reflected in hardness, as illustrated by EBSD-mapped indent locations in this study. While macro-scale mechanical testing has been extensively reported in the literature, few studies have examined micro-scale mechanical responses\u0026mdash;particularly those measured by nanoindentation\u0026mdash;of evolving microstructural features and porosity. Porosity and residual stress, governed by varied conditions, critically influence mechanical performance.\u003c/p\u003e \u003cp\u003ePost-processing treatments, such as Hot Isostatic Pressing (HIP), are essential for improving the microstructural quality of PBF-LB Ti-64 by reducing porosity and enhancing uniformity. This treatment plays a crucial role in enhancing the mechanical performance of AM components, thereby narrowing the gap relative to conventionally processed Ti-64. This work highlights how tailored post-processing influences microstructure and affects micro-scale mechanical behavior. Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e summarizes prior studies and outlines reported microscale mechanical responses across different conditions.\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 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eKey Findings of Ti64 Properties Across Varied Conditions\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\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 \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eProcess and Testing\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eRelevant Literature Findings\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eReferences\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePBF-LB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOptimized PBF-LB parameters (220 W, 900\u0026ndash;1000 mm/s, 0.13 mm HD) achieved peak density (~\u0026thinsp;99.4%) and minimal porosity.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e[\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003ePBF-LB and HIP\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAs-printed samples contain\u0026thinsp;~\u0026thinsp;1.3% β, and another study confirmed a predominantly α\u0026prime; martensitic microstructure with negligible β content. Sub-transus HIP (~\u0026thinsp;950\u0026deg;C) promotes α-spheroidization and lath coarsening (\u0026gt;\u0026thinsp;5 \u0026micro;m), transforming α\u0026prime; to an α\u0026thinsp;+\u0026thinsp;β structure and increasing β content.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e[\u003cspan additionalcitationids=\"CR6 CR7 CR8\" citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAt 980\u0026deg;C, HIP treatment led to ~\u0026thinsp;6.4% transformed β, while another study with heat treatment (980\u0026deg;C, 2 h) showed α-lath thickening (~\u0026thinsp;3.15\u0026thinsp;\u0026plusmn;\u0026thinsp;0.26 \u0026micro;m) with a β-phase fraction (~\u0026thinsp;7.0\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5%).\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e[\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSub- and super-transus HIP treatments (\u0026lt;\u0026thinsp;996\u0026deg;C / \u0026gt;996\u0026deg;C), reduce porosity, improving microstructural integrity, as Sub-transus treatments generate acicular α-martensite (~\u0026thinsp;1.2 \u0026micro;m), grain boundary α, and reveal prior β grains, with higher temperatures reducing α-phase fraction (e.g., 23% at 950\u0026deg;C vs. 73% at 850\u0026deg;C), resulting in coarser α-laths.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e[\u003cspan additionalcitationids=\"CR13 CR14\" citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePBF-LB, HIP, and nanoindentation\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAs-printed showed hardness ranging from 3.66 GPa to 8.19 GPa, attributed to dominant α\u0026prime;/α phases; post-HIP treatment reduced hardness to ~\u0026thinsp;5.48 GPa due to duplex α\u0026thinsp;+\u0026thinsp;β structure.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e[\u003cspan additionalcitationids=\"CR17\" citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePBF-LB, HIP, and X-ray tomography\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eWith optimal parameters, ~\u0026thinsp;0.01% pre-HIP porosity was fully eliminated post-HIP, resulting in full density; moreover, at 950\u0026deg;C, reduced porosity began promoting recrystallization.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e[\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eWrought condition and Micro CT\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eReported α/β microstructures vary widely: one study reported\u0026thinsp;~\u0026thinsp;65% α and 35% β, while another reported\u0026thinsp;~\u0026thinsp;94% α and only 6% β, and \u0026micro;CT confirmed a pore-free structure.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e[\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePBF-LB, XRD, and FEM simulation\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAs-printed samples showed high residual stresses (~\u0026thinsp;197\u0026ndash;494 MPa by XRD), which were significantly reduced to ~\u0026thinsp;44 MPa after an 800\u0026deg;C/2 h post-heat treatment; another study reported\u0026thinsp;~\u0026thinsp;400 MPa (XRD), with FEM-simulated values ranging from 492 to 15 MPa.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e[\u003cspan additionalcitationids=\"CR24\" citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePBF-LB, CT tomography, nanoindentation, and HIP\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAs-built α\u0026prime; martensitic samples showed the highest hardness, while post-treated α\u0026thinsp;+\u0026thinsp;β had lower; porosity (\u0026lt;\u0026thinsp;0.2%) influences hardness and strength, as these properties are sensitive to pores.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e[\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]\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\u003eThis work establishes quantitative process\u0026ndash;structure\u0026ndash;property relationships for PBF-LB Ti64 by integrating high-resolution nanoindentation mapping with EBSD to resolve intra- and inter-grain hardness variations. Nanoindentation mapping, supported by EBSD data, captures localized mechanical variations, while residual stresses are assessed via XRD and validated through finite element simulation. Porosity was quantified to directly correlate pore fraction with microstructural features and localized mechanical behavior. Unlike prior studies that examined these aspects in isolation, this study provides a unified experimental\u0026ndash;computational framework that reveals distinct microscale mechanical behavior and porosity analyses for AP, HIP, and CP conditions. This integrated approach advances understanding of microstructure\u0026ndash;property relationships in AM alloys and establishes a benchmark for microscale mechanical characterization, providing valuable insights for aerospace, biomedical, and high-performance engineering applications.\u003c/p\u003e \u003cp\u003eAlthough previous studies have examined PBF-LB processing, HIP treatment, and porosity effects on bulk properties, these factors were often evaluated independently or reported as bulk-averaged responses. The direct link between microscale mechanical heterogeneity, grain morphology, phase distribution, and local defect states remains underexplored. This work addresses this gap by integrating high-resolution nanoindentation mapping with EBSD, X-ray tomography, and residual stress analysis to establish a unified microscale process\u0026ndash;structure\u0026ndash;property framework for AP- and HIP-treated conditions. The study provides insights into how tailored post-processing modifies intra- and inter-grain properties, thereby enhancing the predictive understanding of microscale mechanical performance in additively manufactured Ti64 components.\u003c/p\u003e"},{"header":"2 Materials and Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Powder Analysis\u003c/h2\u003e \u003cp\u003eThe used Ti64 powder exhibited good flowability, with an average flow time of 28 seconds for 50 grams. The measured apparent and tap densities were 2.40 g/cm\u0026sup3; and 2.91 g/cm\u0026sup3;, respectively. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, particle size distribution (PSD) analysis using a Microtrac system indicated an average powder particle size of ~\u0026thinsp;39.16 \u0026micro;m, and optical microscopy confirmed a predominantly spherical morphology, which supported uniform powder spreading and consistent melting behavior during PBF-LB.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Sample Fabrication and Preparation\u003c/h2\u003e \u003cp\u003eTi64 cubic samples (5 \u0026times; 5 \u0026times; 5 mm\u0026sup3;) were fabricated using the PBF-LB system (TruPrint 1000, TRUMPF GmbH). Among the tested laser power\u0026ndash;scan speed combinations (hatch spacing 0.065 mm, layer thickness 0.03 mm), the adjusted setting of 160 W and 900 mm/s yielded AP samples with 98.71% relative density (Archimedes\u0026rsquo; method) [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. Post-fabricated samples were sectioned using electrical discharge machining (EDM) and sequentially mechanically polished with alumina suspensions (5, 1, and 0.03 \u0026micro;m), followed by final polishing with colloidal silica (0.05 and 0.02 \u0026micro;m) to achieve mirror finishes suitable for microstructural and mechanical characterization. Ultrasonic cleaning was performed after polishing to remove residual debris.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Post-Processing and Testing Details\u003c/h2\u003e \u003cp\u003eTo explore the effects of post-processing, a subset of the AP samples was subjected to HIP using an AIP6-30H system (American Isostatic Presses, Inc., USA). HIP treatment was conducted at 980\u0026deg;C (just below the β-transus at ~\u0026thinsp;995\u0026deg;C), at a pressure of 130 MPa, with a 2-hour holding time and a heating and cooling rate of 10\u0026deg;C/min. This near-β-transus HIP condition was selected to promote densification, thereby reducing residual porosity and relieving a substantial portion of the tensile residual stresses, while enabling direct correlation of the resulting microstructural evolution with the mechanical properties measured through nanoindentation and EBSD-based indentation mapping. EBSD was performed on a Thermo Scientific Apreo 2C with EDAX detector (20 kV, 1.3 \u0026micro;m step size), and data acquired using EDAX OIM Analysis\u0026trade; with identical settings to assess phase distribution, texture, and grain-wise indent locations\u0026mdash;revealing PBF-LB and HIP-induced microstructural changes linked to local mechanical behavior, including for conventional one. To obtain micro-scale mechanical properties such as hardness and elastic modulus, nanoindentation was conducted using a KLA Nano Indenter XP (KLA Corporation, Milpitas, California, USA) with a Berkovich diamond tip at 50 mN load, ~\u0026thinsp;5000 nm contact depth, and 0.2 s⁻\u0026sup1; strain rate, with a Poisson\u0026rsquo;s ratio of 0.33. A (3 \u0026times; 3) indent grid was applied at the center and corners of each conditioned sample with 50 \u0026micro;m spacing between adjacent indents. Residual stress was measured using a Rigaku SmartLab SE diffractometer to assess surface stress evolution and its relationship to thermal history, which affects mechanical properties. XRD measurements were performed at room temperature using the instrument equipped with Cu Kα radiation (λ\u0026thinsp;=\u0026thinsp;1.5406 \u0026Aring;) and a secondary monochromator, operated at 40 kV and 50 mA. Scans were collected over a 2θ range of 30\u0026deg;\u0026ndash;90\u0026deg;, with a step size of 0.01\u0026deg; and a scan speed of 4\u0026deg;/min, capturing diffraction peaks corresponding to α\u0026prime;/α (hcp) phase, and β (bcc) phases. All samples, with a uniform thickness of 3 mm, were analyzed on the as-printed layer plane in the same orientation to ensure consistency. Additionally, Finite Element simulations (SimScale) were used to estimate residual stress distributions for each sample in a consistent orientation. Porosity analysis of AP, HIP-treated, including baseline CV samples, was performed using a ZEISS Xradia CrystalCT system (Carl Zeiss AG, Oberkochen, Germany), operating at 150 kV and 9.96 W. High-resolution CT scanning of a 2.2 \u0026times; 4.4 mm region acquired 1,601 projection images, which were reconstructed into slices and analyzed using Dragonfly Pro software.\u003c/p\u003e \u003c/div\u003e"},{"header":"3 Results and Discussion","content":"\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Porosity Analysis\u003c/h2\u003e \u003cp\u003eX-ray computed tomography revealed a porosity of 1.927% in the AP sample, primarily originating from additive manufacturing process-related defects, such as unmelted powder regions and gas-trapped voids typical of layer-wise fabrication. HIP treatment reduced porosity to 0.014% by maintaining elevated temperature and high isostatic pressure for an extended period, thereby promoting pore closure. The observed reduction in porosity confirms the effectiveness of HIP in mitigating process-induced defects in PBF-LB Ti-64. The conventionally processed sample exhibited negligible porosity. Figures\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(a) and 2(b) show the 3D reconstructed porosity distribution for AP and HIP samples obtained from CT scan analysis.\u003c/p\u003e\u003cp\u003ePorosity analysis was performed not only to quantify defect reduction but also to assess its influence on microscale mechanical variability. The results indicate that, once porosity is minimized, local mechanical response is increasingly governed by grain-scale heterogeneity and phase distribution rather than defect content. The results indicate that both defect population and phase-scale architecture are relevant factors influencing microscale mechanical behavior in additively manufactured Ti64.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Microscale EBSD Indent Mapping Analysis\u003c/h2\u003e \u003cdiv id=\"Sec9\" class=\"Section3\"\u003e \u003ch2\u003e3.2.1 EBSD Mapping Analysis for As-Printed Samples\u003c/h2\u003e \u003cp\u003eThe AP sample exhibited a fine, non-equilibrium, acicular α\u0026prime; martensitic structure, formed at the high cooling rates inherent to the PBF-LB process. EBSD phase mapping confirmed α\u0026prime; as the dominant phase, with only\u0026thinsp;~\u0026thinsp;2% of the β phase retained, typically located along grain boundaries. This microstructure exhibited pronounced residual stresses and orientation gradients resulting from directional solidification during layer-wise deposition. EBSD orientation maps revealed elongated, columnar prior-β grains aligned with the build direction, containing fine α\u0026prime; martensite laths, which introduce subtle microstructural heterogeneity, particularly due to the absence of equiaxed α grain boundaries. Though the observed columnar grains were not always aligned with the build direction (BD), as their growth follows local thermal gradients, resulting in tilted or radial orientations. Despite this heterogeneity, the AP condition demonstrated relatively high nanoindentation hardness, attributed to the intrinsically harder and more deformation-resistant α\u0026prime; phase. The dense α\u0026prime; lath boundaries act as effective barriers to dislocation motion, thereby strengthening the material.\u003c/p\u003e \u003cp\u003eA 3\u0026times;3 nanoindentation grid spanning intra- and inter-grain regions effectively captured localized mechanical variations associated with microstructural features. Indents positioned within single grains (intra-grain) are primarily influenced by the local phase (either predominantly α\u0026prime; martensite or retained β grain) and their specific location within the grain structure. In contrast, inter-grain indents, which span across grain boundaries or lie between adjacent grains, are more affected by boundary constraints, residual stress concentrations, and the presence of multiple grain interfaces. Indents located within or adjacent to α\u0026prime; regions generally exhibited higher hardness than those in retained β-phase regions, underscoring the strength contrast between these phases. Pole figures exhibit strong texture intensity with distinct maxima aligned to the build direction, consistent with columnar prior-β grain growth and orientation gradients induced by directional solidification. Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(a) shows EBSD orientation maps overlaid with nanoindentation grids annotated with hardness values, along with the phase fraction map in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(b) and the texture pole in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(c). These intra- and inter-grain indents capture localized mechanical behavior and highlight the correlation between local phase distribution, grain morphology, and mechanical response\u0026mdash;particularly the strengthening influence of α\u0026prime; interfaces.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section3\"\u003e \u003ch2\u003e3.2.2 EBSD Mapping Analysis for Hot Isostatic Pressed Samples\u003c/h2\u003e \u003cp\u003eFor HIP-treated samples, a 3\u0026times;3 nanoindentation grid was employed to examine microstructure\u0026ndash;mechanical property relationships following processing at near-β-transus temperature, without inducing full recrystallization. This thermal exposure promoted partial phase transformation and morphological coarsening, decomposing α\u0026prime; martensite into an equilibrium α\u0026thinsp;+\u0026thinsp;β structure comprising approximately 81.2% α and 18.8% β. Additionally, some grains exhibited slight deviations from the BD due to the combined effects of temperature, pressure, and holding time at near-β-transus HIP conditions. The α laths underwent significant coarsening, increasing spatial separation between microstructural features and enhancing the resolution of indentation responses across distinct regions.\u003c/p\u003e \u003cp\u003eAs a result, intra-grain indents located within single-phase regions are more clearly resolved in the HIP condition due to the comparatively observable wider α laths\u0026mdash;either within α grains or retained β regions\u0026mdash;allowing for more direct observation of localized mechanical responses without interference from overlapping features. Inter-grain indentations intersecting grain boundaries or positioned near α\u0026ndash;β interfaces revealed subtle mechanical heterogeneity associated with boundary constraints and multiphase interactions. These variations underscore the influence of grain structure and interface character on microscale deformation behavior.\u003c/p\u003e \u003cp\u003eUnlike the AP condition, in which hierarchical heterogeneity from variable cooling rates produces variations in α\u0026prime; lath width, visible in mapping and graded properties, HIP yields a homogeneous microstructure that reduces indentation overlap and clarifies intra- versus inter-grain variability. Overall, the average hardness in the HIP-treated condition is lower than that of the AP sample, consistent with the increased β-phase fraction and the transformation of hard α\u0026prime; martensite into a softer α\u0026thinsp;+\u0026thinsp;β mixture. The observed hardness distribution reflects the combined effects of phase evolution, grain morphology, and boundary characteristics. Texture pole figures show a reduced but still discernible texture, reflecting partial texture relaxation following near-β-transus HIP processing without full recrystallization and with α\u0026prime; \u0026rarr; α\u0026thinsp;+\u0026thinsp;β decomposition. Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(a) presents EBSD-based indent mapping overlaid with the nanoindentation grid and corresponding hardness values, illustrating spatial variation in mechanical response across the HIP-treated microstructure, along with the phase fraction map in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(b) and the texture pole in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(c).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section3\"\u003e \u003ch2\u003e3.2.3 EBSD Mapping Analysis for Conventionally Processed Samples\u003c/h2\u003e \u003cp\u003eThe EBSD maps of the CP sample (reference baseline) in the wrought state reveal a refined, equiaxed α-phase microstructure with ~\u0026thinsp;94.8% α and 5.2% retained β, where β is primarily located at grain boundaries or interfaces. The 3\u0026times;3 nanoindentation grid includes indents within α grains and near α\u0026ndash;β interfaces. Due to the small, equiaxed grains under these conditions, many indentations\u0026mdash;both intra- and inter-grain\u0026mdash;lie near multiple boundaries, enabling a localized assessment of microstructure\u0026ndash;property variations at the microscale.\u003c/p\u003e \u003cp\u003eHardness in the CP condition was generally lower, reflecting the influence of fine equiaxed α grains, limited β-phase content, and a thermally relaxed microstructure. The absence of rapid solidification effects, as observed in AM, resulted in a more uniform, thermally relaxed microstructure that tends to offer less resistance to localized deformation during nanoindentation. Slight softening near β regions and modest hardening near α grain boundaries were observed, though boundary strengthening effects were less pronounced than in HIP or AP samples. Additionally, the pole figures exhibit weak, diffuse intensity, indicating a near-random crystallographic orientation associated with a refined, equiaxed α-phase microstructure. Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e(a) shows EBSD mapping with nanoindentation of the CP sample, highlighting variations in mechanical response with grain and phase features; Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e (b) shows the phase fraction map; and Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e(c) shows the texture pole.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Microscale Mechanical Properties by Nanoindentation\u003c/h2\u003e \u003cp\u003eNanoindentation analysis was performed to evaluate the microscale mechanical response of Ti-64 samples processed via AP, HIP, and CP. The results highlight notable differences in hardness and elastic modulus, reflecting the underlying microstructural features identified via EBSD.\u003c/p\u003e \u003cp\u003eThe AP sample exhibited the highest average hardness (5.74\u0026thinsp;\u0026plusmn;\u0026thinsp;0.22 GPa) and modulus (130.51\u0026thinsp;\u0026plusmn;\u0026thinsp;3.67 GPa), consistent with its high fraction of fine acicular α\u0026prime; martensite and elongated prior-β grains containing high internal stress. Figures\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e,\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e, and \u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e illustrate nanoindentation-based contour maps of hardness, elastic modulus, and corresponding scanning electron surface views for the AP, HIP, and CP Ti64 samples.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn contrast, the HIP-treated sample exhibited slightly reduced hardness (5.61\u0026thinsp;\u0026plusmn;\u0026thinsp;0.49 GPa) while maintaining a similar modulus (130.02\u0026thinsp;\u0026plusmn;\u0026thinsp;7.57 GPa). These changes correlate with the observed α\u0026thinsp;+\u0026thinsp;β microstructural transformation and α-lath coarsening. The increased β-phase fraction and reduced defect content yield a more homogeneous mechanical response, although the softer β-phase regions and broader α-domains influence the distribution of indentation resistance without a significant loss of microscale strength.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe CP sample exhibited the lowest hardness (4.79\u0026thinsp;\u0026plusmn;\u0026thinsp;0.18 GPa) and modulus (123.12\u0026thinsp;\u0026plusmn;\u0026thinsp;1.51 GPa), consistent with its stable α\u0026thinsp;+\u0026thinsp;β microstructure, fine equiaxed grains, limited β-phase contrast, and uniform microscale deformation behavior. The absence of α\u0026prime; and reduced internal stress levels contributed to the decrease in localized hardness. The AP samples exhibited a lower standard deviation due to a relatively uniform α\u0026prime;-martensitic structure, despite higher surface roughness. In contrast, HIP exhibited greater deviation, likely due to increased β-phase content and grain growth, resulting in local variability. The CP condition exhibited the lowest deviation, reflecting its stable α\u0026thinsp;+\u0026thinsp;β microstructure and smoother surface.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eOverall, these trends validate the strong link between microscale mechanical behavior and microstructural features of phase distribution, grain size, and boundary characteristics, which govern the indentation response under different conditions. The coefficient of variation highlights differences in hardness uniformity; HIP samples (observed\u0026thinsp;~\u0026thinsp;18.8% β-phase) exhibited the highest variability (intra: 11.103%; inter: 6.084%), reflecting the dual-phase nature of the α\u0026thinsp;+\u0026thinsp;β structure, in which the presence of β promotes mechanical scatter. In contrast, AP samples (~\u0026thinsp;2% β-phase) showed lower variability (intra: 5.080%; inter: 3.077%), indicating that α\u0026prime;-dominated microstructures with a lower β fraction. The CP sample exhibited the lowest scatter, particularly for inter-grain hardness (1.870%), consistent with its refined equiaxed microstructure and stable processing history. The average hardness values of AP and HIP are similar; however, their markedly different β-phase fractions lead to significant differences in the coefficient of variation (CV%) for intra- and inter-grain indentation responses. Across all conditions, CV for inter-grain indents remained consistently lower than intra-grain indents, suggesting that hardness distribution is more uniform across grains compared to within individual grains. Although the number of indents is limited, CV provides a useful qualitative measure of local hardness scattering, reflecting mechanical property variability along with the grain indentation response across varied conditions. These comparative trends are illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e, highlighting how microstructural phase evolution correlates with local hardness variability across different conditions.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003e3.4 Residual Stress Evaluation through X-ray Diffraction and Simulation\u003c/h2\u003e \u003cp\u003eResidual stress analysis was conducted on three conditioned samples of Ti64\u0026mdash;AP, HIP, and CP\u0026mdash;using both experimental XRD and simulation. The Halder\u0026ndash;Wagner method was applied using SmartLab Studio II (Rigaku) to extract lattice strain values from XRD peak broadening, with analysis spanning measurement to data interpretation. Peaks with excessive Full Width at Half Maximum (FWHM) or overlap with the internal standard (Rigaku-RSRP-43275G) were excluded to ensure accuracy. Through this analysis, lattice strain values of 0.28% for AP, 0.03% for HIP, and 0.14% for CP were obtained. Using a simplified elastic model derived from Hooke\u0026rsquo;s Law, residual stresses were calculated by Eq.\u0026nbsp;1:\u003c/p\u003e \u003cp\u003e \u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e\\(\\:\\sigma\\:=\\frac{E.ϵ}{(1+\\vartheta\\:)}\\)\u003c/span\u003e \u003c/span\u003e (Eq.\u0026nbsp;1)\u003c/p\u003e \u003cp\u003ewhere ε is the measured lattice strain, E is the elastic modulus (measured via nanoindentation for each condition), and ν is Poisson\u0026rsquo;s ratio, constant 0.33 across all samples. Using this formulation and the respective moduli (AP: 130.51 GPa, HIP: 130.02 GPa, CP: 123.12 GPa, the calculated residual stresses were for AP is 0.275 GPa (high tensile); for HIP is 0.020 GPa (near-stress-free state with minimal tensile stress); and for CP is 0.129 GPa (moderate tensile). Figure\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e presents the XRD patterns of the AP, HIP, and CP samples. All patterns exhibit reflections corresponding to the hexagonal close-packed (hcp) structured α\u0026prime;/α phase (100), (002), (101), (102), (110), (103)/(211), (112), and (201) along with a faint body-centered cubic (bcc) β(110) reflection near 2θ\u0026thinsp;\u0026asymp;\u0026thinsp;39.5\u0026deg;, consistent with the dual-phase structure typical of Ti64 [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIn the AP condition (Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003ea), the α\u0026prime;/α peaks display significant broadening, particularly for (100)\u0026thinsp;\u0026asymp;\u0026thinsp;35.1\u0026deg;, (002)\u0026thinsp;\u0026asymp;\u0026thinsp;38.4\u0026deg;, and (101)\u0026thinsp;\u0026asymp;\u0026thinsp;40.5\u0026deg;. The broadened profiles and absence of distinct β reflections indicate a fine acicular α\u0026prime; martensitic microstructure formed under the rapid cooling rates of the PBF-LB process. The measured lattice strain of 0.28% and calculated high tensile residual stress of \u0026asymp;\u0026thinsp;0.275 GPa confirm substantial internal stress accumulation due to steep thermal gradients during solidification [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eFollowing HIP treatment (Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003eb), the α-phase peaks sharpen significantly, indicating recovery of the hcp lattice and microstructural coarsening as the metastable α\u0026prime; martensite decomposes [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]. A very weak but distinct β(200) reflection appears at ~\u0026thinsp;57\u0026deg;, confirming the presence of a small amount of retained or reprecipitated β phase following near-β-transus HIP. Because the β(211) reflection normally occurs at ~\u0026thinsp;69\u0026ndash;72\u0026deg; and overlaps the α(103) peak, it commonly appears only as a weak shoulder rather than a stand-alone peak in HIP-treated Ti64, which is consistent with the subtle feature observed in Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e(b). No resolvable β(110) peak is detected near ~\u0026thinsp;39\u0026deg;, as this region is dominated by the strong α(002) and α(101) reflections. Any β(110) contribution, if present, remains below detection sensitivity or is fully masked by these α peaks. The appearance of the β(200) peak, combined with substantial narrowing of α reflections, provides clear evidence of the α\u0026prime; \u0026rarr; α\u0026thinsp;+\u0026thinsp;β transformation and associated microstructural recovery. Lattice strain decreases to 0.03%, and the calculated residual stress drops to ~\u0026thinsp;0.02 GPa, confirming nearly complete stress relaxation and homogenization of the microstructure. The improved definition of the α(103) reflection and the subtle presence of β(211) near ~\u0026thinsp;71\u0026ndash;72\u0026deg; further indicate enhanced crystallographic order and the re-establishment of the equilibrium α\u0026thinsp;+\u0026thinsp;β phase distribution following HIP.\u003c/p\u003e \u003cp\u003eThe CP sample (Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003ec) exhibits sharp α reflections and a well-defined β(110) peak characteristic of a thermally equilibrated α\u0026thinsp;+\u0026thinsp;β microstructure. With moderate lattice strain (0.14%) and tensile stress (0.129 GPa), it reflects the balanced state typical of conventional thermo-mechanical processing [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. Overall, the XRD results confirm the progressive α\u0026prime; \u0026rarr; α\u0026thinsp;+\u0026thinsp;β transformation sequence from AP \u0026rarr; HIP \u0026rarr; CP, consistent with decreasing internal strain and increasing phase stability. The experimental stress hierarchy (AP\u0026thinsp;\u0026gt;\u0026thinsp;CP\u0026thinsp;\u0026gt;\u0026thinsp;HIP) is consistent with finite-element simulations, validating the correlation between microstructural evolution and residual stress. The weak β(200) reflection near 57\u0026deg; provides clear evidence of partial β stabilization rather than measurement noise, reinforcing that HIP below the β-transus (~\u0026thinsp;995\u0026deg;C) effectively converts metastable α\u0026prime; to equilibrium α\u0026thinsp;+\u0026thinsp;β while minimizing residual stresses and enhancing lattice uniformity.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eSimulated stress contour maps for AP, HIP, and CP are presented using a common color scale, with boundary conditions defined by density, a constant Poisson\u0026rsquo;s ratio, and nanoindentation-derived modulus. The simulations confirm experimental trends while providing additional spatial context. For AP, surface stress ranged from ~\u0026thinsp;0.27 to 0.35 GPa, indicating high tensile residual stress and consistency with localized thermal gradients from the PBF-LB process. Notably, steep thermal gradients and rapid cooling at the discontinuities led to pronounced stress concentrations at the corners of the AP sample during layer-wise solidification. HIP showed a nearly uniform near-stress-free state of ~ (-0.05 to 0.03) GPa, reflecting effective stress relief and homogenization post-HIP. Additionally, the stress distribution for the CP sample ranged from ~(0.11 to 0.19 GPa, with only minor corner stress concentration, consistent with moderate tensile residual stresses arising from its conventional thermal history. Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e summarizes the experimental and simulated residual stresses and the corresponding boundary conditions for AP, HIP, and CP. Figure\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e shows simulated surface-residual-stress contour maps for each condition, corresponding to the same plane analyzed experimentally. The agreement between experimental values and simulated ranges validates the combined experimental\u0026ndash;computational approach for characterizing surface-level residual stresses in Ti64.\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\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eResidual stress results (experimental \u0026amp; simulated) with boundary conditions\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=\"char\" char=\"\u0026plusmn;\" 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=\"left\" 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=\".\" 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\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eSample Condition\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eLattice Strain, ε (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eExperimental Residual Stress (GPa)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eSimulated Residual Stress (GPa)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c7\" namest=\"c5\"\u003e \u003cp\u003eBoundary Conditions for Simulation\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eElastic Modulus, E (GPa)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003ePoisson\u0026rsquo;s ratio, ν\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eRelative Density (%)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAP\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e0.28\u0026plusmn;.06\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.275\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e~\u0026thinsp;0.27 to 0.35\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e130.51\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.33\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e~\u0026thinsp;98.17\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHIP\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e0.03\u0026plusmn;.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.020\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e~ -0.05 to 0.03\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e130.02\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.33\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e~\u0026thinsp;99.99\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCP\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e0.14\u0026plusmn;.03\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.129\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e~\u0026thinsp;0.11 to 0.19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e123.12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.33\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e~\u0026thinsp;100\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 \u003c/div\u003e"},{"header":"4 Conclusion","content":"\u003cp\u003eHigh-resolution nanoindentation mapping integrated with EBSD effectively characterized localized hardness variations in PBF-LB Ti64 processed under AP, HIP, and reference CP conditions. Intra- and inter-grain mapping using nanoindentation revealed hardness trends linked to grain morphology, phase fractions, and boundary characteristics. Porosity analysis confirmed a reduction from 1.927% in the as-printed condition to 0.014% after HIP treatment, whereas the as-printed state, despite its higher porosity, exhibited slightly higher hardness (5.74 GPa) due to the presence of a fine α\u0026prime; martensitic microstructure. HIP exhibited slightly lower hardness (5.61 GPa) with improved uniformity from phase coarsening and defect mitigation, while CP showed the lowest hardness (4.79 GPa) with a uniform response from an equilibrium α\u0026thinsp;+\u0026thinsp;β structure. Although AP and HIP exhibited similar average hardness, HIP (~\u0026thinsp;18.8% β) showed higher variability (intra: 11.103%; inter: 6.084%), indicating β-phase\u0026ndash;driven local heterogeneity, while AP (~\u0026thinsp;2% β) was more uniform (intra: 5.080%; inter: 3.077%). CP showed the lowest scatter (inter: 1.87%), reflecting its stable equiaxed microstructure and establishing a baseline for microscale mechanical behavior.\u003c/p\u003e \u003cp\u003eAdditionally, residual stresses, measured by XRD and supported by finite element simulations, showed high tensile stress in AP (0.275 GPa experimentally; 0.27\u0026ndash;0.35 GPa simulated), a uniform, near-stress-free state with minimal tensile stress in HIP (~\u0026thinsp;0.02 GPa experimentally; ~\u0026ndash;0.05\u0026thinsp;\u0026minus;\u0026thinsp;0.03 GPa simulated), and moderate tensile stress in CP (0.129 GPa experimentally; 0.11\u0026ndash;0.19 GPa simulated), with simulations closely matching experimental observations. This pronounced reduction and homogenization of residual stress following HIP represents a key contribution of the present work, demonstrating the effectiveness of post-processing in mitigating AM-induced thermal stresses. The near-stress-free condition achieved after HIP is critical for stabilizing the microstructure and reducing stress-driven variability in localized mechanical response, thereby enhancing the reliability of micro-scale mechanical performance. Overall, these results establish clear process\u0026ndash;structure\u0026ndash;property relationships across as-printed, post-processed, and conventional Ti64, demonstrating a transferable framework for optimizing AM Ti64 for performance-critical aerospace, biomedical, and engineering applications.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eL.N. conceptualized the experiments, investigated and developed the fabrication and overall characterization of samples, analyzed the experimental results, and wrote the main manuscript text. D.K.S. investigated and developed the X-Ray Diffraction (XRD) of samples, analyzed the characterization results, and reviewed the manuscript text. B.R. analyzed and validated the experimental and characterization results, provided experimental resources, and reviewed the main manuscript text. H.R.S. conceptualized the experiments, supervised experimental work, administered the project, contributed to funding acquisition, and reviewed and edited the main manuscript text.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eResearch was sponsored by the Office of Naval Research and was accomplished under Grant Number W911NF-23-1-0148. The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the official policies, either expressed or implied, of the Army Research Office or the U.S. Government. The U.S. Government is authorized to reproduce and distribute reprints for Government purposes, notwithstanding any copyright notation herein. Additional support was provided by the Center for Agile \u0026amp; Adaptive Additive Manufacturing, funded through the State of Texas Appropriation (#190405\u0026ndash;105\u0026ndash;805008\u0026ndash;220). Also, the authors gratefully acknowledge the X-Ray Diffraction Laboratory, Department of Chemistry, for access to XRD facilities and assistance during measurements.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eThe data are available upon request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eMarin E, Lanzutti A (2024) Biomedical Applications of Titanium Alloys: A Comprehensive Review. 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ASM International\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"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":"Ti-6Al-4V, Laser Powder Bed Fusion, Hot Isostatic Pressing, nanoindentation, EBSD indent mapping, residual stress, computed tomography","lastPublishedDoi":"10.21203/rs.3.rs-8726206/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8726206/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eIntegrating microscale mechanical mapping with microstructural and residual-stress analysis provides a robust approach to establishing process\u0026ndash;structure\u0026ndash;property relationships at a fine scale in additively manufactured (AM) metals. This study examines the microscale mechanical response of Ti-6Al-4V fabricated by laser powder bed fusion (PBF-LB), followed by hot isostatic pressing (HIP) as a post-process, alongside a conventionally processed (CP) sample as a baseline reference for wrought material. Microstructural and nanoindentation mapping, combined with porosity analysis, showed that as-printed (AP) samples exhibited higher hardness (5.74 GPa) due to a fine α\u0026prime; martensitic network, with 1.927% porosity. HIP reduced porosity to 0.014% and transformed the microstructure to a coarsened α\u0026thinsp;+\u0026thinsp;β phase, yielding slightly lower hardness (5.61 GPa). The CP condition displayed negligible porosity, a fine equiaxed α\u0026thinsp;+\u0026thinsp;β microstructure, and the lowest hardness (4.79 GPa). A coefficient of variation (CV%) analysis further revealed greater hardness variability in HIP than in AP, attributable to their differing β-phase fractions. Residual stress measurements indicated high tensile stress in AP (0.275 GPa), a uniform, near-stress-free state with minimal tensile stress in HIP (~\u0026thinsp;0.02 GPa), and moderate tensile stress in CP (0.129 GPa). The experimental results fell within the simulated range, confirming consistency between the two approaches. Validation of experimental and simulated residual-stress results demonstrates the effectiveness of integrating nanoindentation\u0026ndash;electron backscatter diffraction (EBSD) mapping to precisely characterize localized mechanical behavior, thereby supporting structural reliability and performance-driven design in AM metals.\u003c/p\u003e","manuscriptTitle":"Correlating Microstructure and Residual Stress Improvement in HIP Processed LPBF Ti6Al4V Using Nanoindentation Property Mapping","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-02-02 12:58:57","doi":"10.21203/rs.3.rs-8726206/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":"9ab2d560-827d-49a9-a6e2-f0f5ffc0e7ff","owner":[],"postedDate":"February 2nd, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-04-29T07:24:20+00:00","versionOfRecord":[],"versionCreatedAt":"2026-02-02 12:58:57","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8726206","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8726206","identity":"rs-8726206","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}