Effect of laser remelting and ultrasonic irradiation on crack suppression and properties of Ni-WC laser cladding layer

Effect of laser remelting and ultrasonic irradiation on crack suppression and properties of Ni-WC laser cladding layer | 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 Article Effect of laser remelting and ultrasonic irradiation on crack suppression and properties of Ni-WC laser cladding layer Haifeng Zhang, HuaiChen Guo, Xiaoping Hu, JiYuan Tao, WenHan She, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5886896/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 02 Jun, 2025 Read the published version in Scientific Reports → Version 1 posted 11 You are reading this latest preprint version Abstract This study investigates crack suppression mechanisms in Ni60-WC laser cladding layers on C45E4 steel using ultrasonic irradiation and laser remelting. C45E4 steel, widely used in industrial gears and shafts, suffers from wear and corrosion in heavy-load environments. Laser cladding provides surface reinforcement, but cracks persist due to thermal stress and WC/matrix mismatch. Key findings reveal that ultrasonic cavitation breaks dendrites through micro-jet impacts, while acoustic streaming homogenizes the melt pool, reducing elemental segregation. Laser remelting eliminates cracks by remelting defect-prone regions (e.g., interfacial porosity) and releasing residual stress through thermal equilibrium. ​​The experimental findings demonstrated that ultrasonic waves significantly enhanced the crystal strengthening effect of the fused cladding, resulting in a 17.54% increase in hardness.​​ Furthermore, the combined laser remelting and ultrasonic-assisted process effectively prevented crack formation in the cladding layer and enhanced the hardness of the substrate. Despite partial WC dissolution, ​​hardness improvements remain significant​​ due to grain refinement. This dual-assisted strategy demonstrates practical value for repairing C45E4 components in mining and energy equipment. Physical sciences/Optics and photonics/Applied optics/Laser material processing Physical sciences/Engineering/Mechanical engineering laser cladding ultrasound crack sensitivity remelting Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 Figure 14 Figure 15 Figure 16 Figure 17 1 Introduction Metal-ceramic composite claddings combine metal toughness with ceramic wear resistance, making them ideal for extreme industrial environments [ 1 ] . The fabrication of metal matrix ceramic composite cladding generally entails a variety of methodologies, encompassing cladding, hot press sintering, electrochemical deposition, laser cladding, and other techniques [ 2 – 4 ] . Among the aforementioned technologies, laser cladding technology employs an intense laser beam to simultaneously melt the cladding material and the material of the surface of the substrate. This rapid solidification results in a metallurgically bonded surface cladding layer. The cladding layer produced by this technology exhibits strong adhesive strength to the substrate, a minimal area affected by heat, a reduced dilution rate, excellent wear resistance, high temperature resistance, as well as high corrosion and antioxidant resistance. Consequently, metal-based ceramic composite cladding has gained widespread application [ 5 ] . However, conventional laser cladding tends to produce cracks due to mismatched thermal expansion coefficients, differing thermal properties between materials, and rapid cooling. These factors significantly compromise the integrity and functionality of the cladding layer, thereby restricting its broader adoption and application in laser cladding technologies [ 6 ] . In order to remediate the identified concerns, researchers have investigated a range of methodologies for the elimination of cracks in laser cladding. One such approach entails the manipulation of several process parameters, including laser power, melting rate, and powder feeding speed. The purpose of this manipulation is to prevent or mitigate the formation of cracks [ 7 – 9 ] . Remelting, forging after cladding, and other subsequent treatments [ 10 – 11 ] ;The incorporation of auxiliary processes, including mechanical vibration, ultrasonic vibration, and electromagnetic composite fields, has been demonstrated to further enhance the quality of laser cladding layers [ 12 ][ 16 ] . Modifications to the composition of Si, Bi, and other elements within the cladding powder, as well as the incorporation of rare earth elements in specific amounts, have been demonstrated to enhance the integrity of laser cladding layers [ 17 ] , to minimize or eliminate cracks produced during the laser cladding process. Specifically, laser remelting is an effective method for removing impurities and gases from the material. The mechanism of this process involves the rapid melting and subsequent consolidation of the material's exterior, thereby addressing surface imperfections such as porosity and microcracks. Additionally, laser remelting has been shown to result in a substantial enhancement of fatigue strength and corrosion resistance [ 18 – 20 ] . Ultrasound has been demonstrated to enhance the fluidity of liquid metal within the molten pool, thereby ensuring uniform material mixing. This contributes to the homogenization of the material composition of the molten cladding layer, thereby reducing macro-segregation [ 21 – 23 ] . The effectiveness of laser remelting and ultrasonic action in reducing flaws in the fused cladding layer, as well as enhancing its physical properties, has been a subject of extensive research. Li Y employs laser remelting technology in the context of gray cast iron, with the objective of elucidating the underlying void generation mechanism and subsequent elimination process. The findings indicate that laser remelting is an effective method for eliminating voids in the interface zone. However, it was also observed that the average microhardness of the hardened zone after treatment decreased [ 24 ] . Sourabh Biswas's research examined the impact of laser remelting and the implementation of ultrasonic vibration on the tissue growth and wear properties of Al-SiC composites. The findings indicated that these processes significantly enhanced the organization and thickness of the fused cladding layer, as evidenced by the reduction of the acicular α-Si phase. Following laser remelting, a substantial and significant enhancement in wear endurance was witnessed in Al-SiC composite materials. Furthermore, specimens that underwent ultrasonic vibration-assisted laser melting exhibited variable levels of worn surfaces [ 25 ] . Zhou S. et al. investigated the consequences of employing laser remelting on the organization and properties of composite fused cladding layers. The findings indicate that laser remelting can mitigate cracking and enhance the porosity of the cladding layer. Furthermore, the study proposes that this process can enhance the surface quality of the cladding layer. The microstructure of the remelted cladding layer exhibited finer characteristics compared to the surface of the fused cladding layer. Furthermore, the corrosion resistance of the remelted cladding layer has been found to exceed that of the fused cladding layer. Furthermore, the remelted cladding layer displays a substantially higher microhardness, measuring approximately 1.13 times greater than that of the fused cladding layer [ 26 ] . Zhu L et al. investigated the organization and mechanical characteristics of the ultrasonic vibration-assisted laser melting of Inconel 718 parts. The experimental findings revealed that the ultrasonic vibration conditions resulted in a grain size that was more refined than that achieved through conventional laser melting. Specifically, the study found that the vibration amplitude of 25 µm led to an average grain size that was 0.522 times the size observed in the non-vibration control group. Moreover, the findings demonstrated the efficacy of high-frequency vibrations in decreasing porosity while concurrently enhancing the microhardness and wear resistance of the material under investigation [ 27 ] . In their study of ultrasonic assistance in laser melting of 316L stainless steel cladding layers, Zhuang D, D et al. investigated the organization and properties of the influence and mechanism. Their findings indicate that varying amplitudes of ultrasonic vibration can effectively enhance the micro-forming characteristics of the molten cladding layer. Specifically, an amplitude of 17 was observed to be most effective. The study further elucidates that ultrasonic vibration of 5 µm amplitude yields optimal outcomes. Additionally, ultrasonic vibration has been shown to improve the microscopic forming characteristics of the fused cladding, including processes such as tissue heterogenization, grain refinement, and porosity reduction [ 28 ] . Li J et al. employed a combination of rare earth elements and an ultrasound-assisted laser cladding technology to remediate the phenomenon of dilution that was observed during the laser cladding of titanium alloys. They utilized the titanium alloy's surface as a substrate to prepare a novel multi-major component alloy cladding layer, composed of Ti-Al-Si-Cr-SiC. The outcomes of this study demonstrate that the rare earth composite ultrasound-assisted preparation of the Ti-Al-Si-Cr-SiC cladding layer, which contains the Ti4Cr phase, TiC phase, and the aforementioned eutectic phase (Ti3Al and Ti5Si3), effectively reduces the dilution rate of the cladding layer. This reduction in dilution, in turn, results in the refinement of the cladding layer structure and enhances its abrasion and corrosion resistance [ 29 ] . The experiments previously mentioned have demonstrated that remelting the laser cladding layer effectively eliminates residual stress in the cladding layer. This process also reduces crack formation, enhances defect elimination—such as porosity and cracks—and improves surface quality. Furthermore, the refinement of the microstructure resulting from the remelting process enhances wear and corrosion resistance [ 30 ][ 31 ] . The ultrasonic flow effect, the cavitation effect, and the resultant mechanical effect caused by strong flow, vacuum bubble bursting, grain refinement, and microstructure are more dense. These effects have been shown to reduce porosity and significantly enhance the microhardness of the cladding layer and the tribological properties [ 32 ] . However, there is a paucity of research on the effect of combining these two methods to assist in the preparation of laser cladding layers and enhance mechanical properties, particularly in terms of eliminating cracks. In the aforementioned experiments, the vibration transmission method was predominantly employed to generate an ultrasound effect on the cladding layer. This approach utilizes ultrasound vibration to influence the laser cladding processing. However, the ultrasonic vibration source and the center of the molten pool are generally distant from the ultrasonic propagation of ultrasonic energy in the metal medium, which results in significant attenuations. However, ultrasonic wave propagation in air has been shown to effectively mitigate energy attenuation, thereby enabling greater energy input into the melt pool while maintaining the same power output. In this paper, ultrasonic waves are focused and directed at the molten pool in laser cladding processing at a close distance, and the acoustic energy is fed into the molten pool in the hope of obtaining a high-quality cladding layer. The purpose of this paper is twofold: first, it will examine the impact of remelting and ultrasonic-assisted processes on inhibiting crack formation in the fused cladding layer during laser cladding preparation; and second, it will conduct an investigation into how these two assisted processes affect the microstructure and the mechanical behavior of the fused cladding layer. To this end, four distinct types of fused cladding layers were prepared using the traditional process (unassisted preparation process), ultrasonic irradiation alone, remelting alone, and remelting and ultrasonic irradiation together. A comparative analysis was then conducted of the cracks of the fused cladding layers with those of the microstructures, metallographic compositions, microhardnesses, and abrasion-resistant properties of the layers. This was done to validate the effects of these auxiliary methods on the integrity of the fused cladding layers. The efficacy of these auxiliary methods in enhancing the integrity of the cladding layer was substantiated. 2. Experimental procedure 2.1 Experimental materials The substrate material employed in this experiment is C45E4 steel, with a prepared specimen measuring 100 mm×100 mm×20 mm. To ensure surface flatness meets the experimental requirements, the specimen surface is refined using a surface grinder model M7130G. To further enhance surface flatness, 400-mesh metallographic sandpaper was utilized for material surface polishing. Surface conditions for laser cladding of material surface composite after surface polishing by 400 mesh metallographic sandpaper. Subsequent to grinding, the material surface underwent a cleaning process with acetone to eliminate grease and oil, followed by a final cleaning step with anhydrous ethanol to ensure that the substrate surface was devoid of contaminants such as oil, dust, and other impurities. The composition of the C45E4 steel is outlined in Table 1 . The fused cladding layer was selected to be a Ni-WC composite material, comprising Ni60 allotropic powder with a size distribution ranging between 45 and 150 µm and cast WC powder with a size distribution ranging between 53 and 150 µm. The micromorphology of this composite powder is illustrated in Fig. 1 .The two powders were amalgamated in accordance with a mass ratio of 7:3, yielding a Ni60-WC composite powder comprising 30% WC by mass. A comprehensive review of extant research findings reveals that the content of WC in the nickel-based carbide composite cladding layer exceeds 20%, and the occurrence of substantial cracks is inevitable subsequent to laser cladding [ 33 ] . In this study, a WC content of 30% was selected to enhance the wear resistance of the fused cladding layer. The primary objective of this investigation was to examine the crack inhibition effect of two auxiliary processes. The powders were mixed in a mixer for 24 hours to ensure uniformity. The mixture was subsequently transferred into a DZF-6050 benchtop vacuum drying oven, where it underwent a drying process under vacuum conditions at a temperature of 100°C for a duration of two hours. This step was undertaken with the objective of removing excess moisture and enhancing the fluidity of the powder. The chemical composition of the Ni60 alloy powder and the WC powder is presented in Table 2 . Table 1 Chemical elements of C45E4 steel Elements C Cr Mn Ni P S Si Proportions 0.42 ~ 0.5 ≤ 0.25 0.50 ~ 0.80 ≤ 0.25 ≤ 0.035 ≤ 0.035 0.17 ~ 0.37 Table 2 Important chemical elements of Ni60 and WC powders Elements W C O Fe Cr Si Ni B Ni60 -- 0.82 0.01 1.45 15.98 3.97 Bal. 2.96 WC Bal. 3.94 0.01 0.17 0.0046 0.0020 0.0075 -- 2.2 Experimental equipment and procedures The processing instrumentation utilized in this investigation consists of a powder-feeding laser cladding system that functions in a synchronous manner. This apparatus consists of a fiber laser (model RFT-C3000) developed by Wuhan Ruike Fibre Laser Technology Co. Ltd., with a documented maximum optical output power of 3,000 watts and an operational bandwidth spanning 900 to 1,200 nanometers. To ensure precise laser processing path control, the system is equipped with a six-degree-of-freedom industrial robot, model BRTIRUS0805A, manufactured by Bertrams. As demonstrated in Fig. 2 (b), a schematic representation of the ultrasonic instrument developed in-house and utilized in this study is presented. This instrument boasts a maximum output power of 2200 watts and an operating frequency of 20 kHz. A notable distinction between this instrument and conventional ultrasonic high-frequency vibration assistance lies in the manner in which the ultrasonic waves are applied. In this instrument, the ultrasonic waves are irradiated in a manner that directs acoustic energy into the molten pool. The ultrasonic wave output is shaped into a bulb, which focuses the dispersed ultrasonic energy. The system is further comprised of a chiller, model CW3000, and a double barrel powder feeder, model DF-400, along with auxiliary and associated equipment. Figure 2 (a) presents a schematized representation illustrating the laser cladding system. During the cladding preparation operation, the defocus amount was calibrated to 15 mm, yielding a circular spot with a diameter of 4 mm. Following a series of experiments and assessments, the optimal processing parameters under the prevailing test conditions were ascertained to be laser power of 1200 W, scanning speed of 2.5 mm/s, and powder feeding rate of 2.8 g/min for the cladding process. For the laser remelting operation, the laser power was fixed at 1200 W, but the scanning speed was adjusted to 3 mm/s through a series of experiments due to the reduced remelting rate, which led to excessive melting of the WC. The ultrasonic wave parameters are as follows: amplitude of 8 µm, frequency of 20 kHz, and an angle between the ultrasonic wave and the substrate of 45°.The length and height are 35 mm. Four groups of specimens were set up in this experiment, which are designated S1, S2, S3, and S4. S1 is the fused cladding layer prepared by the conventional method without the application of any auxiliary processes, S2 is the fused cladding layer assisted by ultrasonic irradiation alone, S3 is the fused cladding layer assisted by remelt alone, and S4 is the fused cladding layer assisted by remelt and ultrasonic irradiation in conjunction. The primary parameters of processing for the designated specimens are enumerated in Table 3 . The designation "S4" is attributed to the molten cladding layer, which is influenced by both remelting and ultrasonic irradiation. The flow chart is detailed in Fig. 2 (c). The auxiliary processes and main parameters of processing for the aforementioned specimens are detailed in Table 3 . Table 3 Experimental parameters Ultrasonic amplitude(µm) Remelting power(W) Remelting speed(mm/min) S1 0 0 0 S2 8 0 0 S3 0 1200 3 S4 8 1200 3 2.3 Detection Methods To systematically evaluate the crack suppression effect and mechanical performance of the cladding layers under different processing conditions, comprehensive analyses were conducted focusing on three key aspects: (1) crack density and morphology characterization, (2) microstructure evolution and elemental distribution, and (3) mechanical properties including microhardness and wear resistance. ​​Crack analysis​​ was first performed to quantify the effectiveness of different auxiliary processes. After preparation, the cladding surface was cleaned with ethanol, treated with penetrant, and left for 15 minutes to remove residues. Thereafter, the specimen is coated with a developer, which serves to absorb the penetrant and consequently reveal any underlying cracks. ​​Microstructural characterization​​ aimed to reveal grain refinement mechanisms and WC particle evolution. Following the completion of surface crack detection, the specimen should be cut along the vertical direction of the fused cladding layer and prepared as a test specimen. The specimen is then subjected to a series of sanding steps, utilizing sandpaper with grit sizes of 360, 600, 1000, and 1500, in succession. This is followed by polishing with a machine to meet the requirements for microanalysis and inspection. The removal of residual contaminants from the sample surface was facilitated by ultrasonic cleaning with anhydrous ethanol. To reveal the microstructure details, an aqueous solution of hydrochloric and nitric acids (in a volume ratio of 3:1) was used for etching treatment on the samples for 5 seconds. The resulting materials were then examined using a scanning electron microscope (SEM), model JSM-66510LA, which was equipped with an energy spectrum analysis system (EDS). Accelerating voltage range 20 kV. EDS elemental analysis range (W, Ni, Fe, Cr, C). To assess the hardness, an advanced automatic turret micro Vickers hardness tester, model THV-2MD, was employed for quantitative measurement in accordance with the ASTM E-384 standard. The microhardness measurement load was set at 25 g, with a loading time of 10 s. The testing points were arranged at a spacing of 150 µm to obtain the microhardness value of the fused cladding matrix. When measuring the microhardness in the presence of WC particles, the measuring point was moved to the right by 100 µm. The wear test was conducted using the UNMT-1 friction and wear tester, with the wear mode employing ball and disc reciprocating dry sliding wear, as illustrated in Fig. 3 . The grinding ball utilized in this study is a silicon nitride ball with a diameter of 6.35 mm. The fused cladding wear specimen measures 12 millimeters in length and 5 millimeters in width. The experimental parameters for the wear test are as follows: a load of 20 N, a frequency of 2 Hz, a room temperature of 24°C, a wear time of 20 minutes, and a wear length of 6 mm. The wear morphology is systematically observed and measured using the ZYGO-ZeGagePro 3-D optical profiler to analyze the wear marks after testing, thereby evaluating the wear resistance of the fused cladding. 3. Results and discussion 3.1. Surface macroscopic morphology and cracking of the cladding layer As illustrated in Fig. 4 , the surface characteristics of laser-fused cladding layers processed by diverse auxiliary procedures are demonstrated. This includes the macroscopic morphology, the appearance of cracks, and the precise contours and roughness of the surface obtained by enlarging typical positions and performing 3D scanning. To guarantee the dependability of the outcomes, four strips of each fused cladding layer prepared by the same process were analyzed. As illustrated in Fig. 4 (a), the surface topography of the fused cladding layer of the S1 specimen is discernible. The figure indicates that the surface displays notable undulations and a considerable number of granular protrusions. The measured surface roughness, Sa, was found to be 12.002 µm, with approximately seven to eight cracks visible. The surface of the fused cladding layer of the S2 specimen is illustrated in Fig. 4 (b). A substantial decrease in surface roughness was observed, with the value of Sa decreasing from 12.002 µm to 11.560 µm compared to the S1 fused cladding layer. Additionally, a significant reduction in the prevalence of cracks was observed, with an average of four to five cracks detected per pass of the aforementioned fused cladding layer. Following the application of ultrasound, the surface of the aforementioned fused cladding layer exhibited significant enhancement in smoothness, a more rounded surface profile, and a substantial reduction in granular protrusions. As illustrated in Fig. 4 (c), the surface of the fused cladding layer of the S3 specimen exhibits a surface roughness Sa of 10.920 µm. The number of microcracks has been reduced to 1–2, and the minor defects resulting from the initial fusion cladding have been rectified. The outcome of these modifications is a surface that is both smoother and more uniform. Figure 4 (d) presents the surface morphology of the fused cladding layer of the S4 specimen. The surface roughness Sa has been significantly reduced to 7.960 µm, and no cracks have been identified on the fused cladding layer. Figures 4 a-b show that both ultrasonic irradiation and remelting reduce surface roughness and crack density in the cladding layer. The S1 fused cladding layer, however, demonstrates increased surface unevenness and more pronounced cracks. The presence of these surface features is attributed to the inhomogeneous melting phenomenon of the fused cladding material during processing, coupled with the unstable flow of the melt during the process. The substantial disparity in the coefficient of thermal expansion between the WC particles and the base metal gives rise to thermal stresses arising from fluctuations in the temperature gradient during rapid cooling processes. This disparity also engenders supplementary phase transition stresses stemming from the occurrence of solid-state phase transitions between the WC and other constituents [ 34 ] . The synergistic effect of these two types of stresses renders the fusion cladding more prone to crack formation. As illustrated in Fig. 4 (a), the S1 specimen exhibited significant transverse cracks (arrowed) along the fusion boundary, attributed to thermal shrinkage stress during solidification. In contrast, S4 (Fig. 4 (d)) showed no visible cracks, likely due to the combined effects of ultrasonic cavitation-induced dendritic fragmentation (reducing microstructural anisotropy) and laser remelting-mediated residual stress relief. The combination of ultrasonic irradiation and remelting has been demonstrated to be more efficacious in reducing roughness and cracks than a single-assisted process. The acoustic flow and cavitation effects generated by the ultrasonic irradiation-assisted process have been demonstrated to enhance the fluidity of the melt pool and produce a fine grain strengthening effect. The acoustic flow effect of ultrasound intensifies the convection within the liquid metal in the melt bath, leading to improved mixing and dispersion of components. Consequently, this enhances the reduction of unmelted particles. Furthermore, the cavitation effect of ultrasound gives rise to the formation and subsequent collapse of minute vacuum bubbles within the melt bath, effectively disrupting the large dendrites that emerge during the processes of solidification and refining of grains. The remelting treatment involves the reheating of the molten cladding, which results in its subsequent melting. The convective effect within the melt pool subsequently leads to the modulation of material inhomogeneity, facilitating defect repair and reducing the Gibbs free energy of the system. In the ultrasound-assisted remelting treatment, the dual advantages of ultrasound and remelting are fully utilized, resulting in enhanced fluidity of the molten pool and improved internal organization homogeneity. This process also results in reduced surface roughness, a notable decline in crack formation, and an improvement in the macroscopic topographical quality of the material. 3.2 Microstructure and phase constituents The objective of this research is to examine how remelting and ultrasonic-assisted techniques affect the metallographic structure of laser-melted cladding layers. A scanning electron microscope (SEM) was employed in this study to inspect and contrast the micro-metallurgical structures of the top, middle, and bottom parts of the cladding layer sections of the S1-S4 samples. Figure 5 presents a microstructural illustration of the top, middle, and bottom regions of the fused cladding sections for specimens S1-S4, with a magnification of 500x.The analysis revealed the presence of unmelted WC particles in the uppermost region of specimen S1. Additionally, the grains at the top of specimen S1 were observed to be coarser compared to those in the top regions of the other specimens. Following the implementation of the ultrasonic-assisted process, a notable refinement in the grain size was observed in the top region of the S2 and S4 specimens. The grains in the middle region of the four specimens exhibited slightly larger dimensions compared to the top region. The presence of conspicuous planar crystals was observed at the interface between the bottom of the cladding zone and the substrate. The presence of columnar dendrites was observed, extending perpendicularly from the planar crystals. A thorough examination of the cross-section drawings of the four specimens revealed no defects such as microcracks, porosity, or inclusions. The average grain size in S4 was smaller than in S1, as shown in Fig. 5 . Finer grains improve plasticity by increasing grain boundary sliding, thereby delaying crack propagation The magnification was adjusted to facilitate further observation and analysis. Figures 6 , 7 , and 8 illustrate the microstructure morphology of the uppermost, central, and lowermost regions of the fused cladding layer sections of S1-S4 specimens at a magnification of 1400x, respectively. Figure 6 (a) illustrates the top microstructure of the S1 cladding section. The composition of the S1 specimen is a nickel-based solid solution combined with carbides and other compounds, as evidenced by the laser cladding process and the material composition used. [ 35 ] . As illustrated in the figure, the presence of unevenly distributed massive carbides of various sizes is observed, along with a considerable amount of honeycomb tissues, which are dispersed in the form of bands. The surrounding area is characterized by the prevalence of cytocrystalline tissues of various dimensions, which function as the origin for the deposition of additional tissues at the boundaries of the cytocrysts. The hypothesis suggests that these cytocrysts emerge from the decomposition of a substantial supercooled nickel-based austenite grain during the cooling process, a premise that is supported by the crystallization theory of metals. Nickel-based austenite undergoes a transition from a state of liquidity to a solid state when exposed to elevated temperatures. This transformation is attributed to the presence of solute elements within the internal structure of the austenite. The solubility of nickel-based austenite decreases with decreasing temperature, As the temperature is reduced, the precipitation of solute elements from the austenite grains occurs. The solute elements gradually coalesce, leading to the formation of closed areas within the grains. This results in the formation of a new nickel-based solid solution grain. The entire austenite grain undergoes gradual decomposition into multiple small grains. The honeycomb organization at austenite grain boundaries consists of a combination of fine grains, carbides, and other compounds. Nickel-based austenite is the initial grain formation from the liquid to the solid state. During the processes of nucleation and growth, the elemental atoms capable of forming nickel-based solid solutions are combined in an orderly manner by diffusion to form the grains. Elemental atoms that do not contribute to the formation of nickel-based solid solutions tend to accumulate at grain boundaries over time. The presence of multiple elemental atoms, in conjunction with the extreme heat and cold associated with the laser cladding process, gives rise to a substantial temperature gradient during the crystallization of the cladding layer. This results in a high nucleation rate and a reduced growth time for the grains. Consequently, there is insufficient time for diffusion of the elements at the austenite grain boundaries, leading to the formation of multiple nuclei within the region. These nuclei do not have sufficient time to grow, resulting in the formation of fine grains and surrounding compounds that exhibit a honeycomb-like organization. As illustrated in Fig. 6 (b), the top microstructure morphology of the fused cladding section of the S2 specimen is evident. A substantial discrepancy in microstructure morphology is evident when comparing this figure to Fig. 6 (a). The original honeycomb organization, which was previously observed as a distribution of bands, now manifests as discontinuous clusters of flocs that are uniformly dispersed within the matrix. The size of the lumpy carbide tissue is significantly reduced, and the number of lumps per unit area is increased and uniformly distributed. The advent of ultrasound-assisted processes has precipitated a profound transformation in the microstructure of the fused cladding layer, provided that all other processing parameters and materials remain constant. The application of ultrasound within the laser bath has been demonstrated to induce cavitation and acoustic flow effects. The phenomenon of cavitation, defined as the generation of a cavitation bubble within the laser-melting pool of liquid under the influence of ultrasonic vibrations, acoustic energy accumulation, and vibration, has been observed to undergo a dramatic collapse and closure when the acoustic energy reaches a threshold. This abrupt collapse can release a substantial amount of energy, thereby generating a powerful impact of the micro-jet and accelerating the diffusion of the material within the melt pool. The microjet has been shown to disrupt the growth of grains, thereby increasing the rate of nucleation and, consequently, the formation of finer grains. The acoustic flow phenomenon signifies that ultrasonic energy, when propagated in a liquid, exerts a force that propels the fluid, with higher frequencies resulting in increased flow rates. In the laser cladding process, the high-powered emission of energy from the laser results in the rapid melting of the cladding powder and a small amount of substrate, forming a molten pool. This process gives rise to a substantial convective effect that occurs within the aforementioned molten pool. The presence of ultrasound serves to augment this convection, thereby intensifying the overall stirring action of the molten pool. This, in turn, leads to a more homogeneous distribution of various substances throughout the molten cladding layer. As illustrated in Fig. 6 (c), the upper microstructural morphology of the S3 fused clad section is revealed. The figure reveals the presence of multiple dendrites and substantial massive phases. A comparison of Fig. 6 (c) with Fig. 6 (a) reveals that the small grains in the original honeycomb organization have grown, while the nickel matrix grains have decreased. Figure 6 (d) presents the upper microstructural morphology of the S4 fused cladding section. It is evident from the figure that the grains have been significantly reduced, and the presence of cellular crystals is pronounced. Additionally, the grains are uniformly dispersed within the matrix, exhibiting a cellular distribution. No obvious massive carbides or dendrites were observed. Compared to S2 and S3, the ultrasonic cavitation and acoustic flow effects are further enhanced. The material elements within the cladding layer are further dispersed and homogenized, and neither matrix grains nor carbides nor other compounds grow, and are tightly clustered in the form of fine cellular crystals.。 Figure 7 (a) shows the microstructure morphology of the middle part of the section of S1 fusion cladding. The figure shows the presence of gray lined massive phase with large size and non-uniform distribution, and the presence of honeycomb fabric, but the distribution pattern of its bands is not obvious. As illustrated in Fig. 7 (b), the central microstructure morphology of the S2 fused cladding section is evident. A comparison with Fig. 7 (a) reveals a substantial reduction in the bulk phase, accompanied by a refinement of the honeycomb structure, with the presence of a modest amount of dendrites. Figure 7 (c) presents the central microstructure morphology of the S3 fusion cladding section. A comparison with the conventional laser cladding method in Fig. 7 (a) reveals that the size of the gray massive phases in the fusion cladding layer formed by this method has increased, and the matrix grains are relatively larger. Figure 7 (d) provides a visual representation of the microstructure of the middle part of the specimen's cross-section of the S4 cladding layer. The grains illustrated in the figure manifest the finest size and the most uniform distribution, bearing resemblance to the microstructure observed in the upper region of the sample. Analyzing the above micromorphology, it can be seen that the grains in the middle part of the melted cladding layer have time to grow relative to the top part due to the low heat dissipation efficiency and relatively small temperature gradient compared to the top part. However, when the remelting and ultrasonic-assisted processes work together, the microstructure formed in the middle region is not much different from that in the top region. Figure 8 (a) shows the lower microstructure morphology of the S1 fused clad section. In it, a clear columnar crystal structure can be observed whose growth direction is perpendicular to the planar crystals at the bottom. In addition, the cytosolic crystals formed by the fragmentation of the columnar crystals can also be seen in the figure. The introduction of the ultrasonic-assisted process resulted in a significant reduction in the columnar crystals of the S2 molten cladding section, as evidenced in Fig. 8 (b). This reduction was not observed in the S1 specimen. The cavitation effect generated by ultrasonic waves in the molten pool has been shown to break down large columnar crystals, thereby refining the grains and reducing the formation of new columnar crystals. The microstructure of the bottom of the melt-coated layer of the S3 sample, as depicted in Fig. 8 (c), exhibits a columnar crystal organization analogous to that observed in the S1 specimen. Figure 8 (d) illustrates the microstructure of the bottom of the S4 melt-coated layer. As illustrated in the figure, the columnar crystals at the bottom have almost disappeared, the grain size has been further reduced, and the grain dispersion has been significantly improved, showing higher structural homogeneity. This enhancement in structural homogeneity can be attributed to the combined effect of ultrasonication and remelting, which has been demonstrated to promote both grain refinement and improved melt pool uniformity. 3.3 Evolution of WC particles WC exhibits favorable wettability with nickel-based alloys, frequently serving as a reinforcing agent to enhance their wear resistance. However, significant disparities in the thermophysical properties of WC and nickel-based alloys result in an escalation of defects within the fused cladding layer as the WC content increases. This paper proposes the application of laser remelting technology and ultrasonic assisted processes as a means to mitigate cracking defects in high-WC content nickel-based fused cladding layers. In order to investigate the presence of WC particles within the fused cladding layer, these particles were observed, and elemental analysis at various locations was conducted using EDS technology to understand the distribution of WC and its surrounding metallurgical environment. As illustrated in Fig. 9 , the morphology of WC particles in the fused cladding layer is evident. Figures 9 (a) and 9(b) illustrate the state of carbides in the fused cladding layer in the absence of any assisting processes. Figure 9 (c) depicts the state of WC after applying the remelting aiding process, while Fig. 9 (d) shows the state of WC after both the remelting and ultrasonic-assisted processes have been applied. Observation of Fig. 10 (a) reveals two intact WC particles with good wettability with the substrate, and no defects such as porosity or cracks are found around the particles. Large dendrites are observed surrounding the WC. Figure 9 (b) offers a magnified perspective of the WC particles situated within the upper left quadrant of Fig. 10 (a). In the figure, there are obvious edges with different degrees of cladding around the WC particles, indicating that the WC particles have melted around them, and more small particles with the same degree of cladding as the WC exist beyond the edges. To further determine the material composition of the different regions in the figure, the EDS technique was used to determine the elemental composition at different locations. Figure 10 shows the elemental composition at various locations. The elemental composition of the region at point 1 in Fig. 9 (b) is primarily composed of W and C, thereby identifying it as WC particles. A comparative analysis of points 1 and 2 reveals that the atomic percentage of Cr, Fe, and Ni elements is significantly higher at point 2. This observation suggests that this region consists of a new compound formed by W and C element atoms in the free state with nearby matrix elements (Cr, Fe, Ni) following the melting of the WC particle edges. The region identified as point 3 is characterized by the presence of matrix elements, with a minor presence of free W elements that have diffused into it due to its proximity to WC. As illustrated in Fig. 9 (C), the melting of WC particles at their edges is discernible, accompanied by the formation of prominent dendrites with distinct linings. Analyzing the elemental composition of the 4-point and 5-point regions, it can be seen that the 4-point region is a high-carbon type nickel-iron alloy FeNi30 (Ni35%), and the 5-point region is very similar to the elemental composition of the 2-point region, and it is believed that due to the remelting-assisted process, the molten pool receives more energy, which makes the new compounds formed by W and C elements and the matrix elements have a driving force to grow up and thus form the dendritic crystals. Looking at Fig. 9 (d), the grains are more refined due to a combination of remelting and ultrasound-assisted processes. A deeply lined massive organization with a core of daisy-like tissue appears. The elemental composition of the bulk tissue, the daisy-like tissue and its core were examined separately (points 6, 7 and 8). The elemental composition of the 6-point region is very similar to that of the 2-point and 5-point regions, forming the same compounds. The elemental content of the 7-point region is similar to that of the 3-point region, but the W elemental content of the 7-point region is higher than that of the 3-point region, indicating that there are more free W elements in this region. The high W elemental content of the 8-point region and the significant increase in matrix elements compared to the 1-point region indicate that the core of the daisy-like organization is not a WC granule. However, observation shows that no intact WC particles are found in the vicinity. Therefore, it can be assumed that the 8-point region is the core of the small WC particles that eventually melted. Since the original WC particles in this region are completely melted, the content of W and C elements is high, and due to the short solidification time, there is not enough time for diffusion. A compound with a high W element content was formed, with the matrix elements diffusing in during solidification. Based on the observation of Fig. 9 and the analysis of Fig. 10 , the following conclusions can be drawn: If the larger WC particles do not completely melt during the laser melting process, their cores still retain the morphology of the larger WC particles, with a small amount of melting at their edges. The partially melted WC forms free W and C elements, which form bonds with nearby matrix elements during solidification. The smaller WC particles are completely melted, and their core region has a high content of W and C elements that are too late to diffuse sufficiently during solidification, forming compounds with high W and C element content. 3.4XRD analysis Based on the analysis of the XRD inspection results in Fig. 11 , it can be observed that there is a remarkable similarity in the phase composition of the four processing methods, containing the main metallographic phases: γ-Ni(Fe), FeNi3, W2C, WC, Fe2W2C (M6C), with typical compounds being M6C and M23C6. The appearance of the W2C phase is consistent with the previous analysis: the edges of the WC particles or small WC particles melted, and the free W and C elements produced by the melting did not diffuse in time and were able to form the W2C phase during the solidification process. The diffused elements formed compounds with other matrix elements. The presence of γ-Ni (Fe) solid solution, FeNi3 metal compounds, Fe2W2C carbides was found in the fused cladding layer, the appearance of these phases contain Fe elements, indicating that the Fe element content is higher than the increase in the content of fused powder, i.e., part of the matrix melted, and the diffusion through the molten pool diluted the Ni60 fused cladding layer. Comparison of the XRD curves of S1-S4 samples shows that the diffraction peak to the left of the main peak of S3 sample disappears. This diffraction peak is mainly the result of compound diffraction, indicating that laser remelting can attenuate the formation of compounds. The combined remelting and ultrasonic irradiation also mitigated residual stress, a critical factor in crack suppression. As shown in Fig. 6 (a–d), the full-width at half-maximum (FWHM) of the Ni (111) diffraction peak decreased from 0.42° (S1) to 0.35° (S4), suggesting reduced lattice distortion and compressive stress accumulation. The XRD peak shift toward lower angles in S4 (Fig. 6 ) further indicates compressive stress relaxation compared to S1. These mechanisms collectively suppressed crack initiation sites and propagation pathways, as corroborated by the crack-free surface morphology in S4 (Fig. 4 d). 3.5 Microhardness As demonstrated in Fig. 12 , the presentation of the microhardness curves from the top to the bottom of the fused cladding layer for the four specimens is accompanied by the average microhardness values in the fused cladding region. It is noteworthy that WC particles were deliberately excluded from the microhardness tests, thereby ensuring that the observed curves exclusively represent the microhardness of the fused cladding portion of the cladding layer, excluding the WC particles. A comparison of the average hardness in the fused cladding region reveals that the fused cladding obtained using S1 exhibits high hardness, averaging 707 HV. The extreme heat and cold effects of fusion cladding result in a short liquid-to-solid conversion time, thereby preventing sufficient diffusion of elements. Consequently, the matrix forms a liquid-saturated solid solution, thereby creating a solid solution that strengthens the material. The ultrasonic process, when introduced, led to a considerable augmentation in the microhardness of the fused cladding layer, reaching an average of approximately 753 HV, representing a 6.51% increase. This increase in hardness is attributable to the propagation effect of ultrasound in the liquid metal bath. The effects of ultrasound, such as cavitation and acoustic flow, have been demonstrated to facilitate the formation of cytosolic crystals and grain refinement, thereby resulting in a denser and more homogeneous structure. The application of remelting technology to the conventional molten cladding layer resulted in a decline in S3 microhardness, with the mean hardness diminishing to 648 HV, representing an 8.35% reduction. This decline is attributed chiefly to the weakening of solid solution strengthening during the remelting process. The joint application of remelting and ultrasonic-assisted technology enhances the microhardness of the fused cladding layer, with the average microhardness of S4 reaching 831HV0.025, representing an increase of 17.54%. The concurrent application of remelting and ultrasonic assistance processes ensures that the cladding layer absorbs substantial light and acoustic energy, predominantly converted into heat. This likely elevates the melt pool's temperature above that of the initial cladding. The subsequent rapid cooling period serves to enhance the magnitude of the temperature difference during the processes of both solidification and crystallization when compared to the initial cladding. This enhancement facilitates solid solution strengthening. Furthermore, the cavitation and acoustic effects of ultrasonic waves have been demonstrated to homogenize the material composition of the cladding layer, thereby enhancing nucleation and preventing the formation of dendrites. This process leads to a strengthening of the crystals due to the fine grain size that results. 3.6 Wear resistance The incorporation of WC hard phase has been demonstrated to enhance the wear resistance of Ni60 fused cladding. Empirical evidence has demonstrated a direct correlation between an increase in the hard phase content and an enhancement in wear resistance. However, it is imperative to acknowledge that an augmented hard phase content may precipitate crack formations in the cladding layer. To address this challenge and enhance the wear resistance of the fused cladding layer, this paper proposes an innovative process that incorporates ultrasonic and remelting techniques. This process aims to prevent crack formation during the preparation stage, thereby enhancing the overall durability and functionality of the cladding layer. The ball and disk reciprocating dry wear test method is employed in the present study to assess the wear resistance of specimens S1-S4 under uniform wear conditions, with a concomitant observation and analysis of these specimens' wear morphology. The experimental findings indicate that the wear volume attributable to the cladding layer's high wear resistance is minimal. Consequently, substantial errors occur when employing weight measurement to discern varying degrees of wear resistance. This paper proposes a novel calibration approach for wear evaluation, commencing with scanning and precise measurement of wear scars to accurately map their three-dimensional topography. Subsequent to this, a precise two-dimensional profile of a representative wear scar's cross-section is generated, with the software meticulously calculating the enclosed area and determining the profile's maximum width and depth. The minimization of error is achieved by collecting data at four discrete points on each wear scar, thereby acquiring four datasets per specimen, from which an average is derived. The study adopts the mean cross-sectional area of wear scars as the calibration standard for wear volume, considering consistent wear scar lengths and uniform material density loss. In the experimental design, measures were taken to circumvent random effects and enhance the precision of the data. To this end, the cross-sectional profile curves were measured at four representative wear marks, situated at the midpoint of the wear marks, subsequent to the removal of the initial and terminal wear marks. As demonstrated in Fig. 13 and Fig. 14 , Figs. 13 (a)-(d) and Fig. 14 illustrate the contour curves of the cross-sections of the wear marks for specimens S1-S4. The maximum width and depth of the abrasion mark sections are indicated in the figure, and the values of the areas enclosed by the contour curves and the average values are specified by the labels on the left side of the figure. A thorough examination of the data presented in the figure reveals that the average wear amount of S1 fusion cladding is 1976.95 µm 2 . A comparative analysis of the wear amount of other specimens indicates that the wear resistance of S1 specimen is comparable to that of S4 specimen, and it is higher than that of S3 specimen but lower than that of S4 specimen. A further analysis of the cross-sectional profile reveals that the bottom area of the S1 wear mark section is flat, suggesting that during the wear process, the ball crown of silicon nitride on the wear vice is gradually smoothed out. The average Vickers hardness of silicon nitride is approximately 2200, which is sufficient to flatten such a hard wear vice, indicating that the fusion cladding layer possesses high abrasion resistance. The mean abrasion of the S2 fusion cladding layer is 1520.63 µm 2 , which is the lowest among the four types of samples and indicates the highest level of abrasion resistance. The depth of the abrasion marks is similar to that of the S1 sample, yet the width of the marks is the narrowest. From the above tests and analysis, it can be seen that the S2 sample was added to the ultrasonic assisted process during the cladding process, which can refine the grains, enhance the convection effect of the molten bath, and make the cladding layer material homogeneous [ 36 ][ 37 ] . The mean wear amount of the S3 fused cladding layer was 3127.65 µm², which was the greatest wear amount and the least effective wear resistance among the four specimens. The width and thickness of the wear marks were the greatest. The implementation of the laser remelting technique resulted in a reduction in the presence of cracks and an enhancement in the roughness of the fused cladding layer. The findings of this study, as indicated by the detection and analysis, suggest that the hard-phase WC particles underwent a process of partial decomposition, melting, and synthesis with other elements, resulting in the formation of new compounds. The average wear amount of the S4 fused cladding layer is 2058.19 µm², which is comparable to that of the S1 specimen. A comparison of the abrasion cross-section profiles of S1 and S4 reveals that the latter's profile is a spherical crown cross section, while that of S1 is a biased flat cross section. The substrate's average microhardness, measured as HV 0.025 , was found to be 707 for S1 and 831 for S4. In conjunction with the above discussion, it can be seen that the S4 specimens underwent additional remelting during the preparation process, while an ultrasonically assisted process was incorporated. Both processes were added with the primary purpose of eliminating cracking defects, but they also reduced the content of hard phase WC, resulting in lower wear resistance. The concurrent implementation of ultrasound resulted in the refinement of grains within the cladding, an enhancement of the overall mechanical properties, and a more uniform material distribution. This suggests that the wear resistance of the cladding can be improved. The comparable wear resistance observed between S1 and S4 indicates that the reduction in hard phase content, which is typically associated with a decrease in wear resistance, is counterbalanced by the extent to which the ultrasonically assisted process refines grains and homogenizes the material, thereby enhancing the wear resistance of the cladding. The reduction of hard phases in S4 weakened the wear resistance despite its higher hardness due to partial WC dissolution caused by remelting. The number of cracks in S2 was lower than that of S1, and there were no pores or inclusions in the microstructure. Cracks are the initiation point of wear, and the reduction of defects directly slows down the wear process. Therefore, compared to S1 and S4, the S2 sample has the best wear resistance. As illustrated in Fig. 15 , the wear morphology and three-dimensional profiles of specimens S1-S4 are presented. The wear morphology of specimen S1 reveals a relatively flat bottom with a small number of small and large craters, which are traces left by WC particles after exfoliation during the wear process. The large craters are localized areas where minor adhesive wear has occurred, causing the surface to flake off. The bottom of the wear pattern shows a distinctive gouge, which is believed to be the participation of exfoliated WC particles in the wear. The WC particles on the fused cladding flaked off and adhered or embedded to the spherical pair of grinding vice, and as the spherical pair of grinding vice moved as a hard point, it left a furrow on the fused cladding like a plow. Sample S2 shows a superposition of multiple grooves at the bottom of the wear pattern, while the wear pattern is smoother at the sides. The wear pattern of specimen S3 also showed exfoliation pits of WC particles and large traces of adherent wear. The wear pattern of specimen S4 also showed exfoliation pits of WC particles but did not show large traces of adherent wear. As demonstrated in Fig. 16 , the friction coefficients of the S1-S4 materials are presented as a function of applied force. The variation in the friction of the different specimens is evident. The S1 specimen demonstrates the highest friction coefficient and exhibits the most substantial fluctuations in its curve. This observation indicates that the material inhomogeneity and the presence of hard phases in the S1 specimen enhance the wear resistance of the cladding layer. In comparison, the S2 specimen exhibited a lower friction coefficient, yet its magnitude was notably higher than those of the S3 and S4 specimens. A comparison of the friction coefficient curves of S1 and S2 reveals that the latter is relatively smooth, suggesting that ultrasonic waves have strengthened the cladding layer by precipitating the formation of fine crystals and homogenizing the distribution of material within the cladding layer. In contrast, the friction coefficient curves for S3 and S4 in the smooth wear stage exhibit a close and flat profile with a narrow fluctuation range. The presence of WC in the remelting process during part of the melting results in the reduction of the hard phase in the fusion cladding layer, leading to a decrease in wear resistance and a reduction in the overall coefficient of friction. The incorporation of an ultrasonic-assisted process in the S4 sample has been shown to yield a fine crystal strengthening effect, resulting in a more uniform material distribution, thereby leading to a reduction in the overall coefficient of static friction. 3.7 Mechanism of action of remelting and ultrasonic assisted processes The processes of solidification of the melt during the preparation of the molten cladding layer are principally governed by thermal conduction, absent any ancillary mechanisms. The rapid cooling rate gives rise to a pronounced temperature gradient, which in turn precipitates the crystallization of a columnar structure at the bottom of the melt pool. This phenomenon can result in the manifestation of various anisotropies. The absence of supplementary energy input or agitation effects during the rapid solidification process leads to substantial residual tensile stress. The underlying causes of this residual stress can be attributed to thermal stress, phase change stress, and WC particles. The tensile stress resulting from this process exceeds the tensile strength of the substrate, thereby inducing cracks [ 38 ] . In the context of laser cladding, the employment of ultrasonic vibration during the process facilitates the transmission of energy into the molten pool via acoustic waves. This approach entails the utilization of ultrasonic energy within the molten pool, thereby disrupting the conventional crystallization process. The impact of ultrasound on these processes has been demonstrated to include the refinement of grain size, the heterogeneity of material within the aforementioned pool, the reduction of uneven heat distribution, the minimization of porosity and defects, and the promotion of the microstructure of the cladding layer. The process of laser melting involves the utilization of ultrasonic waves, which result in the molten liquid undergoing internal vibrations. These vibrations are caused by acoustic waves, leading to the application of tensile stress to a specific local area. This, in turn, causes the gas dissolved in the liquid to reach supersaturation and subsequently escape, resulting in the formation of small bubbles. Alternatively, a significant tensile stress can exert force on a cavity, causing it to traverse a localized region of the liquid. The growth of cavitation bubbles (i.e., small bubbles and cavities) persists, and when the sound pressure attains a particular threshold, the cavitation bubbles undergo a dramatic collapse, releasing a substantial amount of energy. This process leads to the generation of high temperatures and pressures in a confined area in close proximity. The subsequent rapid cooling of the melt pool leads to an increase in the degree of subcooling, thereby initiating the nucleation process of the crystals within the melt pool. The local high temperatures and pressures engendered by the cavitation effect promote the nucleation process, and concurrently, the substantial energy release exerts a destructive effect on the already formed dendrites (e.g., broken columnar crystals and dendrites). Consequently, the melt pool is characterized by the predominance of fine equiaxed crystals. The application of laser energy, characterized by its potency, prompts the metal to undergo a phase transition, resulting in the formation of a molten pool. However, the temperature distribution exhibits inhomogeneity and may be well approximated by a Gaussian distribution. The presence of temperature gradients gives rise to thermal convection effects within the aforementioned molten pool. Furthermore, the propagation of ultrasound through a molten metal gives rise to an acoustic flow effect, characterized by a steady liquid flow. This acoustic flow effect is further amplified by the ultrasound-induced convection effect within the molten pool, leading to a complex and dynamic thermal environment. The convection effect has the capacity to enhance the transmission of substances in disparate regions, promote the homogenization of substances of different compositions in the molten pool, help eliminate compositional segregation, and promote the diffusion of elemental atoms. The convective effect also leads to a more uniform temperature distribution within the melt pool, thereby reducing the internal temperature gradient. This, in turn, fosters the formation of equilibrium crystals. Figure 17 provides a schematic representation of the principle of ultrasonic waves acting on the molten pool. Conventional laser cladding typically produces columnar crystals at the base of the melt pool and dendrites at its center, as shown in Fig. 17 (a). However, the incorporation of ultrasound, through its cavitation and convection effects, has the potential to enhance convection within the melt pool, thereby disrupting the integrity of both columnar and dendritic crystals. This disruption is demonstrated in Fig. 17 (b) [ 39 ] . Laser remelting facilitates the rapid melting and crystallization processes of the cladding layer, thereby enabling the subsequent diffusion of elemental atoms. In accordance with the principle of systemic energy minimization, laser remelting leads to a reduction in the total systemic energy of the material in the melt pool during solidification, including a reduction in residual tensile stresses. Furthermore, the process of laser remelting results in additional melting of WC particles, thereby reducing residual stresses that are caused by variations in thermophysical properties [ 40 ] . In the domain of materials science and mechanical engineering, the concurrent implementation of remelting and ultrasonic vibrations has emerged as a methodology for enhancing the microstructure and properties of fused claddings. The energy input from ultrasound refines the grain structure, while remelting releases residual stresses. The combined effect of these processes leads to enhanced overall mechanical properties of the cladding. Specifically, the melting of selected WC particles is counterbalanced by a complementary mechanism, thereby achieving a harmonious balance in the microstructure and mechanical properties of the cladding. It is this synergistic interplay that ultimately elevates the overall performance of the cladding. The effectiveness of crack suppression in S4 is attributable to multiple synergistic effects. Ultrasonic cavitation has been shown to destroy dendrites (Fig. 6 b), promote grain refinement, and reduce elemental segregation (Fig. 10 ). The process of remelting has been observed to eliminate pre-existing porosity (Fig. 4 ) and induce thermal equilibrium to release residual stress. The combined action of these effects enhances epitaxial nucleation, refines grains, and improves toughness. These mechanisms complement each other to achieve a crack-free structure with optimized mechanical properties. 4. Conclusions In this study, ultrasonic-assisted laser remelting and irradiation-mode laser remelting were utilized to produce Ni60/WC fused clad layers. The process yields a fusion cladding that is characterized by the absence of cracks and a hardness and wear resistance that is comparable to that of conventional fusion cladding. A comprehensive analysis was conducted, encompassing examination of the gross morphology, crack initiation, microstructure, microhardness, and tribological properties of the cladding layers produced by different methods. Furthermore, the investigation focused on the effects and mechanisms of remelting and ultrasonic vibration on the structure and characteristics of these coatings. The ensuing conclusions were derived from this comprehensive investigation: (1) Cracks were inhibited by either ultrasonic-assisted treatment (4–5 cracks) or remelting alone (1–3 cracks) compared to conventional cladding methods (5–8 cracks). However, when remelting and ultrasonic treatment (0 cracks) were performed simultaneously, a more significant effect was observed than with a single treatment. This suggests a synergistic rather than additive effect of the two methods. (2)The cavitation and acoustic flow effects of ultrasound have been demonstrated to refine grains, reduce elemental segregation, and homogenize the distribution of different substances. Furthermore, remelting-assisted processes have been shown to promote grain growth. The application of remelting and ultrasonic assistance in a concurrent manner serves to accentuate the impact of grain refinement. (3)Large particles of WC melt at the edges, and the free W and C elements form compounds with the matrix elements. In contrast, smaller particles of WC undergo complete melting, resulting in the formation of compounds with a high concentration of W and C elements. (4)The metallographic composition of the fused cladding layers prepared by different processes is essentially equivalent. The predominant metallographic phases are as follows: γ-Ni(Fe), FeNi3, WC, W2C, M6C, and M23C6 compounds. (5)The ultrasound-assisted process increases the hardness of the Ni60 substrate, while the remelting-assisted process decreases the hardness of the substrate. The combination of the two processes increased the hardness by 17.54% compared to the conventional cladding. The wear resistance of the cladding layer combining the two assisted processes increased by 34.19% compared to that of the remelted cladding layer, which is comparable to that of the conventional cladding layer. In the end, by applying remelting with the aid of ultrasonic waves, a cladding layer is obtained that is reduction in crack formation and whose hardness and wear resistance are not too different from those of conventional cladding. 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Cite Share Download PDF Status: Published Journal Publication published 02 Jun, 2025 Read the published version in Scientific Reports → Version 1 posted Editor assigned by journal 22 May, 2025 Editorial decision: Revision requested 22 May, 2025 Reviews received at journal 06 May, 2025 Reviewers agreed at journal 26 Apr, 2025 Reviews received at journal 24 Apr, 2025 Reviewers agreed at journal 24 Apr, 2025 Reviews received at journal 24 Apr, 2025 Reviewers agreed at journal 24 Apr, 2025 Reviewers invited by journal 24 Apr, 2025 Submission checks completed at journal 21 Apr, 2025 First submitted to journal 21 Apr, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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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-5886896","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":447717831,"identity":"69dcbcf4-306b-4b0e-a844-8dc4e4dd6d83","order_by":0,"name":"Haifeng Zhang","email":"","orcid":"","institution":"Changchun University","correspondingAuthor":false,"prefix":"","firstName":"Haifeng","middleName":"","lastName":"Zhang","suffix":""},{"id":447717832,"identity":"dafa123a-719b-4abc-9dd2-6f962a3445d1","order_by":1,"name":"HuaiChen Guo","email":"","orcid":"","institution":"Changchun University","correspondingAuthor":false,"prefix":"","firstName":"HuaiChen","middleName":"","lastName":"Guo","suffix":""},{"id":447717833,"identity":"e5e4b4c0-45ba-4cd7-8bba-b1cba3847627","order_by":2,"name":"Xiaoping Hu","email":"","orcid":"","institution":"Changchun University","correspondingAuthor":false,"prefix":"","firstName":"Xiaoping","middleName":"","lastName":"Hu","suffix":""},{"id":447717834,"identity":"949cd1ed-8832-423a-ad37-fda1875340c6","order_by":3,"name":"JiYuan Tao","email":"","orcid":"","institution":"Changchun University","correspondingAuthor":false,"prefix":"","firstName":"JiYuan","middleName":"","lastName":"Tao","suffix":""},{"id":447717835,"identity":"97ef956a-493f-4166-ae6b-b0af62644798","order_by":4,"name":"WenHan She","email":"","orcid":"","institution":"Changchun University","correspondingAuthor":false,"prefix":"","firstName":"WenHan","middleName":"","lastName":"She","suffix":""},{"id":447717836,"identity":"d08058e0-b977-432c-a49f-8b27d61eb48d","order_by":5,"name":"Changlong Zhao *","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAwklEQVRIie3RMQrCMBTG8ZRAXJ7tmqLoFTKJQ6AHcUmWTDq5dOgQUPQ83RwLAV0Crh1TegFHR9tNp8RNMP/9B+/jIRSL/WCFyXonSgpkokPNDQhzls9TaELJHVDeHRVfUBEoksO0YVIbIHlft6jiGy/BOBVOXgYyU/s1uqqd9hGCEWPSjmS7ook2fgIDofI0HmYDCcUwEgWEQiBhmCgmLAcCwxYRsoVlxnTPkhbLs6nbR8X95IMHv+aNfCtisVjsP3oBEu45SAilSrsAAAAASUVORK5CYII=","orcid":"","institution":"Changchun University","correspondingAuthor":true,"prefix":"","firstName":"Changlong","middleName":"Zhao","lastName":"*","suffix":""}],"badges":[],"createdAt":"2025-01-23 09:23:15","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5886896/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5886896/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s41598-025-05046-5","type":"published","date":"2025-06-02T15:57:24+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":81410347,"identity":"083dc2e2-74be-4c6e-bd56-6b6e119066e5","added_by":"auto","created_at":"2025-04-25 20:15:46","extension":"jpeg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":4606226,"visible":true,"origin":"","legend":"\u003cp\u003e(a). Ni60 powder micro-morphology; (b). WC powder micro-morphology .\u003c/p\u003e","description":"","filename":"floatimage1.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-5886896/v1/84da136d160329bbe73816ba.jpeg"},{"id":81410348,"identity":"9e260153-6afa-4fb8-8677-c7bb0333692c","added_by":"auto","created_at":"2025-04-25 20:15:46","extension":"jpeg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":4601277,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Schematic diagram of laser cladding; (b) working diagram of ultrasonic waves；（c）flow chart；\u003c/p\u003e","description":"","filename":"floatimage2.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-5886896/v1/acce0fce7399e67536c50f58.jpeg"},{"id":81410344,"identity":"6f0611d1-b55c-4fd4-b338-26dfdf3b0bbb","added_by":"auto","created_at":"2025-04-25 20:15:45","extension":"jpeg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":3149034,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic diagram of friction wear experiment\u003c/p\u003e","description":"","filename":"floatimage3.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-5886896/v1/c58d54b9b05e9b24c2e2f37d.jpeg"},{"id":81410749,"identity":"80f3651a-23f8-4739-82a5-f59b154e832a","added_by":"auto","created_at":"2025-04-25 20:23:46","extension":"jpeg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":10475503,"visible":true,"origin":"","legend":"\u003cp\u003eMacroscopic morphology of conventional and remelt- and ultrasound-assisted cladding layers (a) cladding layer without any assistance applied; (b) ultrasound-assisted cladding layer; (c) remelt-assisted cladding layer; and (d) remelt- and ultrasound-assisted cladding layer.\u003c/p\u003e","description":"","filename":"floatimage4.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-5886896/v1/448a81e1d54f3b1bb967329a.jpeg"},{"id":81410358,"identity":"e3f5e36d-ec18-426e-b325-59ad3092f026","added_by":"auto","created_at":"2025-04-25 20:15:46","extension":"jpeg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":9791792,"visible":true,"origin":"","legend":"\u003cp\u003eMicrostructure morphology of the top, middle and bottom of the fusion-coated layers of specimens S1-S4\u003c/p\u003e","description":"","filename":"floatimage5.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-5886896/v1/9103af530c98ee51d34900e0.jpeg"},{"id":81410352,"identity":"0f1ed9e4-72ce-4860-938f-60fc256506c1","added_by":"auto","created_at":"2025-04-25 20:15:46","extension":"jpeg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":11175981,"visible":true,"origin":"","legend":"\u003cp\u003eMicrostructure of the top regions of the fused cladding layers (a) S1, (b) S2, (c) S3 and (d) S4.\u003c/p\u003e","description":"","filename":"floatimage6.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-5886896/v1/d3bd824ef70e487ee6434071.jpeg"},{"id":81410363,"identity":"83900fc2-6b0c-4acb-a4f9-04adb4b915dd","added_by":"auto","created_at":"2025-04-25 20:15:46","extension":"jpeg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":12635359,"visible":true,"origin":"","legend":"\u003cp\u003eMicrostructure of the central regions of the fused cladding layers (a) S1, (b) S2, (c) S3 and (d) S4.\u003c/p\u003e","description":"","filename":"floatimage7.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-5886896/v1/fec477dc256ae71bae2a603f.jpeg"},{"id":81410752,"identity":"e274ef50-1443-46f5-baa7-7c124e646069","added_by":"auto","created_at":"2025-04-25 20:23:46","extension":"jpeg","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":12372006,"visible":true,"origin":"","legend":"\u003cp\u003eMicrostructure of the bottom regions of the fused cladding layers (a) S1, (b) S2, (c) S3 and (d) S4.\u003c/p\u003e","description":"","filename":"floatimage8.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-5886896/v1/b44ef13a68ff58ddc508ac8a.jpeg"},{"id":81410751,"identity":"05f2a229-319f-4cc3-b433-ab647f912b30","added_by":"auto","created_at":"2025-04-25 20:23:46","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":689361,"visible":true,"origin":"","legend":"\u003cp\u003eFragmentation of WC particles in the cladding layer (a) large particle WC melting, (b) enlarged view of large particle WC melting, (c) feathery crystals around WC and (d) small particle WC melting\u003c/p\u003e","description":"","filename":"floatimage9.png","url":"https://assets-eu.researchsquare.com/files/rs-5886896/v1/467eaaab422c4e9bd165b75f.png"},{"id":81410750,"identity":"eaff0642-e03c-4c24-8bf6-8bb7124a9368","added_by":"auto","created_at":"2025-04-25 20:23:46","extension":"jpeg","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":2476989,"visible":true,"origin":"","legend":"\u003cp\u003eeds analyses in different regions ;(a)Point 1; (b)Point 2; (c)Point 3; (d)Point 4; (e)Point 5; (f)Point 6; (g)Point 7; (h)Point 8;\u003c/p\u003e","description":"","filename":"floatimage10.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-5886896/v1/d541f8c1f118c84c76c86d33.jpeg"},{"id":81410365,"identity":"1835d169-1146-4e43-9748-ddeecfc42c19","added_by":"auto","created_at":"2025-04-25 20:15:46","extension":"jpeg","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":696733,"visible":true,"origin":"","legend":"\u003cp\u003eX-ray diffraction patterns of the fused cladding layer with different assisted methods.\u003c/p\u003e","description":"","filename":"floatimage11.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-5886896/v1/916606bcffd993010561d45c.jpeg"},{"id":81410368,"identity":"ee160f7f-938a-40f0-ab68-e514fc8c95b6","added_by":"auto","created_at":"2025-04-25 20:15:46","extension":"jpeg","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":1806250,"visible":true,"origin":"","legend":"\u003cp\u003eMicrohardness and average hardness of fused cladding layers with different assisted methods.\u003c/p\u003e","description":"","filename":"floatimage12.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-5886896/v1/69d8a76fe20a62121f8f8f6c.jpeg"},{"id":81410349,"identity":"ecd0151a-a2e3-4648-9ad3-5da70371b30f","added_by":"auto","created_at":"2025-04-25 20:15:46","extension":"jpeg","order_by":13,"title":"Figure 13","display":"","copyAsset":false,"role":"figure","size":5778572,"visible":true,"origin":"","legend":"\u003cp\u003eExperimental wear of frictional wear of fused cladding layers with different assisted modes. (a) S1, (b) S2, (c) S3 and (d) S4\u003c/p\u003e","description":"","filename":"floatimage13.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-5886896/v1/6adf4eef10b54da05cb47443.jpeg"},{"id":81410755,"identity":"5c75c278-d3d5-440a-9091-716000d489e0","added_by":"auto","created_at":"2025-04-25 20:23:46","extension":"jpeg","order_by":14,"title":"Figure 14","display":"","copyAsset":false,"role":"figure","size":993208,"visible":true,"origin":"","legend":"\u003cp\u003eAverage wear loss, width, and depth of frictional wear of fused cladding in different assisted modes.\u003c/p\u003e","description":"","filename":"floatimage14.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-5886896/v1/a5473c1fb202df19053568ce.jpeg"},{"id":81410753,"identity":"d148ce04-e8c9-440d-af5b-92e0b46bb354","added_by":"auto","created_at":"2025-04-25 20:23:46","extension":"jpeg","order_by":15,"title":"Figure 15","display":"","copyAsset":false,"role":"figure","size":6871996,"visible":true,"origin":"","legend":"\u003cp\u003e3D morphological contours of dry sliding wear traces of the fused cladding with different assisted methods and microscopic magnification of dry sliding wear traces of the fused cladding with different assisted methods. (a) S1, (b) S2, (c) S3 and (d) S4\u003c/p\u003e","description":"","filename":"floatimage15.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-5886896/v1/a8755d46e8ca67b5e258d9d6.jpeg"},{"id":81410375,"identity":"9dd86866-ebd0-4969-b35d-e60e9a8b6caa","added_by":"auto","created_at":"2025-04-25 20:15:47","extension":"jpeg","order_by":16,"title":"Figure 16","display":"","copyAsset":false,"role":"figure","size":1229657,"visible":true,"origin":"","legend":"\u003cp\u003eFriction coefficient of the fused cladding layer with different assistance methods.\u003c/p\u003e","description":"","filename":"floatimage16.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-5886896/v1/c1caba8cd31b0617caa079ee.jpeg"},{"id":81410756,"identity":"03f802cd-27a1-4828-ad4a-5b46055d6b07","added_by":"auto","created_at":"2025-04-25 20:23:47","extension":"jpeg","order_by":17,"title":"Figure 17","display":"","copyAsset":false,"role":"figure","size":1887504,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic diagram of the principle of ultrasonic waves acting on the fused cladding layer.\u003c/p\u003e","description":"","filename":"floatimage17.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-5886896/v1/b53e66dffcf5f2b7da70831b.jpeg"},{"id":84243183,"identity":"c36f1f5d-70c9-4006-a982-74d9a0defc66","added_by":"auto","created_at":"2025-06-09 16:12:51","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":92244371,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5886896/v1/22d424a6-65b3-4479-b2df-1b992db33dce.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Effect of laser remelting and ultrasonic irradiation on crack suppression and properties of Ni-WC laser cladding layer","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003eMetal-ceramic composite claddings combine metal toughness with ceramic wear resistance, making them ideal for extreme industrial environments \u003csup\u003e[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eThe fabrication of metal matrix ceramic composite cladding generally entails a variety of methodologies, encompassing cladding, hot press sintering, electrochemical deposition, laser cladding, and other techniques \u003csup\u003e[\u003cspan additionalcitationids=\"CR3\" citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]\u003c/sup\u003e. Among the aforementioned technologies, laser cladding technology employs an intense laser beam to simultaneously melt the cladding material and the material of the surface of the substrate. This rapid solidification results in a metallurgically bonded surface cladding layer. The cladding layer produced by this technology exhibits strong adhesive strength to the substrate, a minimal area affected by heat, a reduced dilution rate, excellent wear resistance, high temperature resistance, as well as high corrosion and antioxidant resistance. Consequently, metal-based ceramic composite cladding has gained widespread application \u003csup\u003e[\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]\u003c/sup\u003e .\u003c/p\u003e \u003cp\u003eHowever, conventional laser cladding tends to produce cracks due to mismatched thermal expansion coefficients, differing thermal properties between materials, and rapid cooling. These factors significantly compromise the integrity and functionality of the cladding layer, thereby restricting its broader adoption and application in laser cladding technologies\u003csup\u003e[\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]\u003c/sup\u003e. In order to remediate the identified concerns, researchers have investigated a range of methodologies for the elimination of cracks in laser cladding. One such approach entails the manipulation of several process parameters, including laser power, melting rate, and powder feeding speed. The purpose of this manipulation is to prevent or mitigate the formation of cracks \u003csup\u003e[\u003cspan additionalcitationids=\"CR8\" citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]\u003c/sup\u003e. Remelting, forging after cladding, and other subsequent treatments \u003csup\u003e[\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]\u003c/sup\u003e;The incorporation of auxiliary processes, including mechanical vibration, ultrasonic vibration, and electromagnetic composite fields, has been demonstrated to further enhance the quality of laser cladding layers \u003csup\u003e[\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e][\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]\u003c/sup\u003e. Modifications to the composition of Si, Bi, and other elements within the cladding powder, as well as the incorporation of rare earth elements in specific amounts, have been demonstrated to enhance the integrity of laser cladding layers \u003csup\u003e[\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]\u003c/sup\u003e, to minimize or eliminate cracks produced during the laser cladding process. Specifically, laser remelting is an effective method for removing impurities and gases from the material. The mechanism of this process involves the rapid melting and subsequent consolidation of the material's exterior, thereby addressing surface imperfections such as porosity and microcracks. Additionally, laser remelting has been shown to result in a substantial enhancement of fatigue strength and corrosion resistance \u003csup\u003e[\u003cspan additionalcitationids=\"CR19\" citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]\u003c/sup\u003e. Ultrasound has been demonstrated to enhance the fluidity of liquid metal within the molten pool, thereby ensuring uniform material mixing. This contributes to the homogenization of the material composition of the molten cladding layer, thereby reducing macro-segregation \u003csup\u003e[\u003cspan additionalcitationids=\"CR22\" citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]\u003c/sup\u003e. The effectiveness of laser remelting and ultrasonic action in reducing flaws in the fused cladding layer, as well as enhancing its physical properties, has been a subject of extensive research.\u003c/p\u003e \u003cp\u003eLi Y employs laser remelting technology in the context of gray cast iron, with the objective of elucidating the underlying void generation mechanism and subsequent elimination process. The findings indicate that laser remelting is an effective method for eliminating voids in the interface zone. However, it was also observed that the average microhardness of the hardened zone after treatment decreased\u003csup\u003e[\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]\u003c/sup\u003e. Sourabh Biswas's research examined the impact of laser remelting and the implementation of ultrasonic vibration on the tissue growth and wear properties of Al-SiC composites. The findings indicated that these processes significantly enhanced the organization and thickness of the fused cladding layer, as evidenced by the reduction of the acicular α-Si phase. Following laser remelting, a substantial and significant enhancement in wear endurance was witnessed in Al-SiC composite materials. Furthermore, specimens that underwent ultrasonic vibration-assisted laser melting exhibited variable levels of worn surfaces \u003csup\u003e[\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]\u003c/sup\u003e. Zhou S. et al. investigated the consequences of employing laser remelting on the organization and properties of composite fused cladding layers. The findings indicate that laser remelting can mitigate cracking and enhance the porosity of the cladding layer. Furthermore, the study proposes that this process can enhance the surface quality of the cladding layer. The microstructure of the remelted cladding layer exhibited finer characteristics compared to the surface of the fused cladding layer. Furthermore, the corrosion resistance of the remelted cladding layer has been found to exceed that of the fused cladding layer. Furthermore, the remelted cladding layer displays a substantially higher microhardness, measuring approximately 1.13 times greater than that of the fused cladding layer\u003csup\u003e[\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]\u003c/sup\u003e. Zhu L et al. investigated the organization and mechanical characteristics of the ultrasonic vibration-assisted laser melting of Inconel 718 parts. The experimental findings revealed that the ultrasonic vibration conditions resulted in a grain size that was more refined than that achieved through conventional laser melting. Specifically, the study found that the vibration amplitude of 25 \u0026micro;m led to an average grain size that was 0.522 times the size observed in the non-vibration control group. Moreover, the findings demonstrated the efficacy of high-frequency vibrations in decreasing porosity while concurrently enhancing the microhardness and wear resistance of the material under investigation\u003csup\u003e[\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]\u003c/sup\u003e. In their study of ultrasonic assistance in laser melting of 316L stainless steel cladding layers, Zhuang D, D et al. investigated the organization and properties of the influence and mechanism. Their findings indicate that varying amplitudes of ultrasonic vibration can effectively enhance the micro-forming characteristics of the molten cladding layer. Specifically, an amplitude of 17 was observed to be most effective. The study further elucidates that ultrasonic vibration of 5 \u0026micro;m amplitude yields optimal outcomes. Additionally, ultrasonic vibration has been shown to improve the microscopic forming characteristics of the fused cladding, including processes such as tissue heterogenization, grain refinement, and porosity reduction \u003csup\u003e[\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]\u003c/sup\u003e. Li J et al. employed a combination of rare earth elements and an ultrasound-assisted laser cladding technology to remediate the phenomenon of dilution that was observed during the laser cladding of titanium alloys. They utilized the titanium alloy's surface as a substrate to prepare a novel multi-major component alloy cladding layer, composed of Ti-Al-Si-Cr-SiC. The outcomes of this study demonstrate that the rare earth composite ultrasound-assisted preparation of the Ti-Al-Si-Cr-SiC cladding layer, which contains the Ti4Cr phase, TiC phase, and the aforementioned eutectic phase (Ti3Al and Ti5Si3), effectively reduces the dilution rate of the cladding layer. This reduction in dilution, in turn, results in the refinement of the cladding layer structure and enhances its abrasion and corrosion resistance \u003csup\u003e[\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]\u003c/sup\u003e .\u003c/p\u003e \u003cp\u003eThe experiments previously mentioned have demonstrated that remelting the laser cladding layer effectively eliminates residual stress in the cladding layer. This process also reduces crack formation, enhances defect elimination\u0026mdash;such as porosity and cracks\u0026mdash;and improves surface quality. Furthermore, the refinement of the microstructure resulting from the remelting process enhances wear and corrosion resistance \u003csup\u003e[\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e][\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]\u003c/sup\u003e. The ultrasonic flow effect, the cavitation effect, and the resultant mechanical effect caused by strong flow, vacuum bubble bursting, grain refinement, and microstructure are more dense. These effects have been shown to reduce porosity and significantly enhance the microhardness of the cladding layer and the tribological properties \u003csup\u003e[\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]\u003c/sup\u003e. However, there is a paucity of research on the effect of combining these two methods to assist in the preparation of laser cladding layers and enhance mechanical properties, particularly in terms of eliminating cracks. In the aforementioned experiments, the vibration transmission method was predominantly employed to generate an ultrasound effect on the cladding layer. This approach utilizes ultrasound vibration to influence the laser cladding processing. However, the ultrasonic vibration source and the center of the molten pool are generally distant from the ultrasonic propagation of ultrasonic energy in the metal medium, which results in significant attenuations. However, ultrasonic wave propagation in air has been shown to effectively mitigate energy attenuation, thereby enabling greater energy input into the melt pool while maintaining the same power output. In this paper, ultrasonic waves are focused and directed at the molten pool in laser cladding processing at a close distance, and the acoustic energy is fed into the molten pool in the hope of obtaining a high-quality cladding layer.\u003c/p\u003e \u003cp\u003eThe purpose of this paper is twofold: first, it will examine the impact of remelting and ultrasonic-assisted processes on inhibiting crack formation in the fused cladding layer during laser cladding preparation; and second, it will conduct an investigation into how these two assisted processes affect the microstructure and the mechanical behavior of the fused cladding layer.\u003c/p\u003e \u003cp\u003eTo this end, four distinct types of fused cladding layers were prepared using the traditional process (unassisted preparation process), ultrasonic irradiation alone, remelting alone, and remelting and ultrasonic irradiation together. A comparative analysis was then conducted of the cracks of the fused cladding layers with those of the microstructures, metallographic compositions, microhardnesses, and abrasion-resistant properties of the layers. This was done to validate the effects of these auxiliary methods on the integrity of the fused cladding layers. The efficacy of these auxiliary methods in enhancing the integrity of the cladding layer was substantiated.\u003c/p\u003e"},{"header":"2. Experimental procedure","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Experimental materials\u003c/h2\u003e \u003cp\u003eThe substrate material employed in this experiment is C45E4 steel, with a prepared specimen measuring 100 mm\u0026times;100 mm\u0026times;20 mm. To ensure surface flatness meets the experimental requirements, the specimen surface is refined using a surface grinder model M7130G. To further enhance surface flatness, 400-mesh metallographic sandpaper was utilized for material surface polishing. Surface conditions for laser cladding of material surface composite after surface polishing by 400 mesh metallographic sandpaper. Subsequent to grinding, the material surface underwent a cleaning process with acetone to eliminate grease and oil, followed by a final cleaning step with anhydrous ethanol to ensure that the substrate surface was devoid of contaminants such as oil, dust, and other impurities. The composition of the C45E4 steel is outlined in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. The fused cladding layer was selected to be a Ni-WC composite material, comprising Ni60 allotropic powder with a size distribution ranging between 45 and 150 \u0026micro;m and cast WC powder with a size distribution ranging between 53 and 150 \u0026micro;m. The micromorphology of this composite powder is illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.The two powders were amalgamated in accordance with a mass ratio of 7:3, yielding a Ni60-WC composite powder comprising 30% WC by mass. A comprehensive review of extant research findings reveals that the content of WC in the nickel-based carbide composite cladding layer exceeds 20%, and the occurrence of substantial cracks is inevitable subsequent to laser cladding \u003csup\u003e[\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]\u003c/sup\u003e. In this study, a WC content of 30% was selected to enhance the wear resistance of the fused cladding layer. The primary objective of this investigation was to examine the crack inhibition effect of two auxiliary processes.\u003c/p\u003e \u003cp\u003eThe powders were mixed in a mixer for 24 hours to ensure uniformity. The mixture was subsequently transferred into a DZF-6050 benchtop vacuum drying oven, where it underwent a drying process under vacuum conditions at a temperature of 100\u0026deg;C for a duration of two hours. This step was undertaken with the objective of removing excess moisture and enhancing the fluidity of the powder. The chemical composition of the Ni60 alloy powder and the WC powder is presented in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e.\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\u003eChemical elements of C45E4 steel\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"8\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eElements\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eC\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCr\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eMn\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eNi\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eP\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eS\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eSi\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eProportions\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.42\u0026thinsp;~\u0026thinsp;0.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026le;\u0026thinsp;0.25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.50\u0026thinsp;~\u0026thinsp;0.80\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u0026le;\u0026thinsp;0.25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u0026le;\u0026thinsp;0.035\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e\u0026le;\u0026thinsp;0.035\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e0.17\u0026thinsp;~\u0026thinsp;0.37\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 \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\u003eImportant chemical elements of Ni60 and WC powders\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"9\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"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=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eElements\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eW\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eC\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eO\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eFe\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eCr\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eSi\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eNi\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c9\"\u003e \u003cp\u003eB\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNi60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e--\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.82\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e1.45\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e15.98\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e3.97\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eBal.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e2.96\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eWC\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eBal.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e3.94\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.0046\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.0020\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e0.0075\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\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\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Experimental equipment and procedures\u003c/h2\u003e \u003cp\u003eThe processing instrumentation utilized in this investigation consists of a powder-feeding laser cladding system that functions in a synchronous manner. This apparatus consists of a fiber laser (model RFT-C3000) developed by Wuhan Ruike Fibre Laser Technology Co. Ltd., with a documented maximum optical output power of 3,000 watts and an operational bandwidth spanning 900 to 1,200 nanometers. To ensure precise laser processing path control, the system is equipped with a six-degree-of-freedom industrial robot, model BRTIRUS0805A, manufactured by Bertrams. As demonstrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(b), a schematic representation of the ultrasonic instrument developed in-house and utilized in this study is presented. This instrument boasts a maximum output power of 2200 watts and an operating frequency of 20 kHz. A notable distinction between this instrument and conventional ultrasonic high-frequency vibration assistance lies in the manner in which the ultrasonic waves are applied. In this instrument, the ultrasonic waves are irradiated in a manner that directs acoustic energy into the molten pool. The ultrasonic wave output is shaped into a bulb, which focuses the dispersed ultrasonic energy. The system is further comprised of a chiller, model CW3000, and a double barrel powder feeder, model DF-400, along with auxiliary and associated equipment. Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(a) presents a schematized representation illustrating the laser cladding system.\u003c/p\u003e \u003cp\u003eDuring the cladding preparation operation, the defocus amount was calibrated to 15 mm, yielding a circular spot with a diameter of 4 mm. Following a series of experiments and assessments, the optimal processing parameters under the prevailing test conditions were ascertained to be laser power of 1200 W, scanning speed of 2.5 mm/s, and powder feeding rate of 2.8 g/min for the cladding process. For the laser remelting operation, the laser power was fixed at 1200 W, but the scanning speed was adjusted to 3 mm/s through a series of experiments due to the reduced remelting rate, which led to excessive melting of the WC. The ultrasonic wave parameters are as follows: amplitude of 8 \u0026micro;m, frequency of 20 kHz, and an angle between the ultrasonic wave and the substrate of 45\u0026deg;.The length and height are 35 mm. Four groups of specimens were set up in this experiment, which are designated S1, S2, S3, and S4. S1 is the fused cladding layer prepared by the conventional method without the application of any auxiliary processes, S2 is the fused cladding layer assisted by ultrasonic irradiation alone, S3 is the fused cladding layer assisted by remelt alone, and S4 is the fused cladding layer assisted by remelt and ultrasonic irradiation in conjunction. The primary parameters of processing for the designated specimens are enumerated in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. The designation \"S4\" is attributed to the molten cladding layer, which is influenced by both remelting and ultrasonic irradiation. The flow chart is detailed in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(c). The auxiliary processes and main parameters of processing for the aforementioned specimens are detailed in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eExperimental parameters\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eUltrasonic amplitude(\u0026micro;m)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eRemelting power(W)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eRemelting speed(mm/min)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eS1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eS2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eS3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1200\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eS4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1200\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Detection Methods\u003c/h2\u003e \u003cp\u003eTo systematically evaluate the crack suppression effect and mechanical performance of the cladding layers under different processing conditions, comprehensive analyses were conducted focusing on three key aspects: (1) crack density and morphology characterization, (2) microstructure evolution and elemental distribution, and (3) mechanical properties including microhardness and wear resistance.\u003c/p\u003e \u003cp\u003e​​Crack analysis​​ was first performed to quantify the effectiveness of different auxiliary processes. After preparation, the cladding surface was cleaned with ethanol, treated with penetrant, and left for 15 minutes to remove residues. Thereafter, the specimen is coated with a developer, which serves to absorb the penetrant and consequently reveal any underlying cracks. ​​Microstructural characterization​​ aimed to reveal grain refinement mechanisms and WC particle evolution. Following the completion of surface crack detection, the specimen should be cut along the vertical direction of the fused cladding layer and prepared as a test specimen. The specimen is then subjected to a series of sanding steps, utilizing sandpaper with grit sizes of 360, 600, 1000, and 1500, in succession. This is followed by polishing with a machine to meet the requirements for microanalysis and inspection. The removal of residual contaminants from the sample surface was facilitated by ultrasonic cleaning with anhydrous ethanol. To reveal the microstructure details, an aqueous solution of hydrochloric and nitric acids (in a volume ratio of 3:1) was used for etching treatment on the samples for 5 seconds. The resulting materials were then examined using a scanning electron microscope (SEM), model JSM-66510LA, which was equipped with an energy spectrum analysis system (EDS). Accelerating voltage range 20 kV. EDS elemental analysis range (W, Ni, Fe, Cr, C). To assess the hardness, an advanced automatic turret micro Vickers hardness tester, model THV-2MD, was employed for quantitative measurement in accordance with the ASTM E-384 standard. The microhardness measurement load was set at 25 g, with a loading time of 10 s. The testing points were arranged at a spacing of 150 \u0026micro;m to obtain the microhardness value of the fused cladding matrix. When measuring the microhardness in the presence of WC particles, the measuring point was moved to the right by 100 \u0026micro;m. The wear test was conducted using the UNMT-1 friction and wear tester, with the wear mode employing ball and disc reciprocating dry sliding wear, as illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. The grinding ball utilized in this study is a silicon nitride ball with a diameter of 6.35 mm. The fused cladding wear specimen measures 12 millimeters in length and 5 millimeters in width. The experimental parameters for the wear test are as follows: a load of 20 N, a frequency of 2 Hz, a room temperature of 24\u0026deg;C, a wear time of 20 minutes, and a wear length of 6 mm. The wear morphology is systematically observed and measured using the ZYGO-ZeGagePro 3-D optical profiler to analyze the wear marks after testing, thereby evaluating the wear resistance of the fused cladding.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results and discussion","content":"\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e\u003cb\u003e3.1. Surface macroscopic morphology and cracking of the cladding layer\u003c/b\u003e\u003c/h2\u003e \u003cp\u003eAs illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, the surface characteristics of laser-fused cladding layers processed by diverse auxiliary procedures are demonstrated. This includes the macroscopic morphology, the appearance of cracks, and the precise contours and roughness of the surface obtained by enlarging typical positions and performing 3D scanning. To guarantee the dependability of the outcomes, four strips of each fused cladding layer prepared by the same process were analyzed.\u003c/p\u003e \u003cp\u003eAs illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(a), the surface topography of the fused cladding layer of the S1 specimen is discernible. The figure indicates that the surface displays notable undulations and a considerable number of granular protrusions. The measured surface roughness, Sa, was found to be 12.002 \u0026micro;m, with approximately seven to eight cracks visible. The surface of the fused cladding layer of the S2 specimen is illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(b). A substantial decrease in surface roughness was observed, with the value of Sa decreasing from 12.002 \u0026micro;m to 11.560 \u0026micro;m compared to the S1 fused cladding layer. Additionally, a significant reduction in the prevalence of cracks was observed, with an average of four to five cracks detected per pass of the aforementioned fused cladding layer. Following the application of ultrasound, the surface of the aforementioned fused cladding layer exhibited significant enhancement in smoothness, a more rounded surface profile, and a substantial reduction in granular protrusions. As illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(c), the surface of the fused cladding layer of the S3 specimen exhibits a surface roughness Sa of 10.920 \u0026micro;m. The number of microcracks has been reduced to 1\u0026ndash;2, and the minor defects resulting from the initial fusion cladding have been rectified. The outcome of these modifications is a surface that is both smoother and more uniform. Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(d) presents the surface morphology of the fused cladding layer of the S4 specimen. The surface roughness Sa has been significantly reduced to 7.960 \u0026micro;m, and no cracks have been identified on the fused cladding layer.\u003c/p\u003e \u003cp\u003eFigures \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea-b show that both ultrasonic irradiation and remelting reduce surface roughness and crack density in the cladding layer. The S1 fused cladding layer, however, demonstrates increased surface unevenness and more pronounced cracks. The presence of these surface features is attributed to the inhomogeneous melting phenomenon of the fused cladding material during processing, coupled with the unstable flow of the melt during the process. The substantial disparity in the coefficient of thermal expansion between the WC particles and the base metal gives rise to thermal stresses arising from fluctuations in the temperature gradient during rapid cooling processes. This disparity also engenders supplementary phase transition stresses stemming from the occurrence of solid-state phase transitions between the WC and other constituents\u003csup\u003e[\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]\u003c/sup\u003e. The synergistic effect of these two types of stresses renders the fusion cladding more prone to crack formation. As illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(a), the S1 specimen exhibited significant transverse cracks (arrowed) along the fusion boundary, attributed to thermal shrinkage stress during solidification. In contrast, S4 (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(d)) showed no visible cracks, likely due to the combined effects of ultrasonic cavitation-induced dendritic fragmentation (reducing microstructural anisotropy) and laser remelting-mediated residual stress relief.\u003c/p\u003e \u003cp\u003eThe combination of ultrasonic irradiation and remelting has been demonstrated to be more efficacious in reducing roughness and cracks than a single-assisted process. The acoustic flow and cavitation effects generated by the ultrasonic irradiation-assisted process have been demonstrated to enhance the fluidity of the melt pool and produce a fine grain strengthening effect. The acoustic flow effect of ultrasound intensifies the convection within the liquid metal in the melt bath, leading to improved mixing and dispersion of components. Consequently, this enhances the reduction of unmelted particles. Furthermore, the cavitation effect of ultrasound gives rise to the formation and subsequent collapse of minute vacuum bubbles within the melt bath, effectively disrupting the large dendrites that emerge during the processes of solidification and refining of grains. The remelting treatment involves the reheating of the molten cladding, which results in its subsequent melting. The convective effect within the melt pool subsequently leads to the modulation of material inhomogeneity, facilitating defect repair and reducing the Gibbs free energy of the system. In the ultrasound-assisted remelting treatment, the dual advantages of ultrasound and remelting are fully utilized, resulting in enhanced fluidity of the molten pool and improved internal organization homogeneity. This process also results in reduced surface roughness, a notable decline in crack formation, and an improvement in the macroscopic topographical quality of the material.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Microstructure and phase constituents\u003c/h2\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe objective of this research is to examine how remelting and ultrasonic-assisted techniques affect the metallographic structure of laser-melted cladding layers. A scanning electron microscope (SEM) was employed in this study to inspect and contrast the micro-metallurgical structures of the top, middle, and bottom parts of the cladding layer sections of the S1-S4 samples.\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e presents a microstructural illustration of the top, middle, and bottom regions of the fused cladding sections for specimens S1-S4, with a magnification of 500x.The analysis revealed the presence of unmelted WC particles in the uppermost region of specimen S1. Additionally, the grains at the top of specimen S1 were observed to be coarser compared to those in the top regions of the other specimens. Following the implementation of the ultrasonic-assisted process, a notable refinement in the grain size was observed in the top region of the S2 and S4 specimens. The grains in the middle region of the four specimens exhibited slightly larger dimensions compared to the top region. The presence of conspicuous planar crystals was observed at the interface between the bottom of the cladding zone and the substrate. The presence of columnar dendrites was observed, extending perpendicularly from the planar crystals. A thorough examination of the cross-section drawings of the four specimens revealed no defects such as microcracks, porosity, or inclusions. The average grain size in S4 was smaller than in S1, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e. Finer grains improve plasticity by increasing grain boundary sliding, thereby delaying crack propagation\u003c/p\u003e \u003cp\u003eThe magnification was adjusted to facilitate further observation and analysis. 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 the microstructure morphology of the uppermost, central, and lowermost regions of the fused cladding layer sections of S1-S4 specimens at a magnification of 1400x, respectively. Figure\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e(a) illustrates the top microstructure of the S1 cladding section. The composition of the S1 specimen is a nickel-based solid solution combined with carbides and other compounds, as evidenced by the laser cladding process and the material composition used. \u003csup\u003e[\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]\u003c/sup\u003e. As illustrated in the figure, the presence of unevenly distributed massive carbides of various sizes is observed, along with a considerable amount of honeycomb tissues, which are dispersed in the form of bands. The surrounding area is characterized by the prevalence of cytocrystalline tissues of various dimensions, which function as the origin for the deposition of additional tissues at the boundaries of the cytocrysts. The hypothesis suggests that these cytocrysts emerge from the decomposition of a substantial supercooled nickel-based austenite grain during the cooling process, a premise that is supported by the crystallization theory of metals. Nickel-based austenite undergoes a transition from a state of liquidity to a solid state when exposed to elevated temperatures. This transformation is attributed to the presence of solute elements within the internal structure of the austenite. The solubility of nickel-based austenite decreases with decreasing temperature, As the temperature is reduced, the precipitation of solute elements from the austenite grains occurs. The solute elements gradually coalesce, leading to the formation of closed areas within the grains. This results in the formation of a new nickel-based solid solution grain. The entire austenite grain undergoes gradual decomposition into multiple small grains. The honeycomb organization at austenite grain boundaries consists of a combination of fine grains, carbides, and other compounds. Nickel-based austenite is the initial grain formation from the liquid to the solid state. During the processes of nucleation and growth, the elemental atoms capable of forming nickel-based solid solutions are combined in an orderly manner by diffusion to form the grains. Elemental atoms that do not contribute to the formation of nickel-based solid solutions tend to accumulate at grain boundaries over time. The presence of multiple elemental atoms, in conjunction with the extreme heat and cold associated with the laser cladding process, gives rise to a substantial temperature gradient during the crystallization of the cladding layer. This results in a high nucleation rate and a reduced growth time for the grains. Consequently, there is insufficient time for diffusion of the elements at the austenite grain boundaries, leading to the formation of multiple nuclei within the region. These nuclei do not have sufficient time to grow, resulting in the formation of fine grains and surrounding compounds that exhibit a honeycomb-like organization.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAs illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e(b), the top microstructure morphology of the fused cladding section of the S2 specimen is evident. A substantial discrepancy in microstructure morphology is evident when comparing this figure to Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e(a). The original honeycomb organization, which was previously observed as a distribution of bands, now manifests as discontinuous clusters of flocs that are uniformly dispersed within the matrix. The size of the lumpy carbide tissue is significantly reduced, and the number of lumps per unit area is increased and uniformly distributed. The advent of ultrasound-assisted processes has precipitated a profound transformation in the microstructure of the fused cladding layer, provided that all other processing parameters and materials remain constant. The application of ultrasound within the laser bath has been demonstrated to induce cavitation and acoustic flow effects. The phenomenon of cavitation, defined as the generation of a cavitation bubble within the laser-melting pool of liquid under the influence of ultrasonic vibrations, acoustic energy accumulation, and vibration, has been observed to undergo a dramatic collapse and closure when the acoustic energy reaches a threshold. This abrupt collapse can release a substantial amount of energy, thereby generating a powerful impact of the micro-jet and accelerating the diffusion of the material within the melt pool. The microjet has been shown to disrupt the growth of grains, thereby increasing the rate of nucleation and, consequently, the formation of finer grains. The acoustic flow phenomenon signifies that ultrasonic energy, when propagated in a liquid, exerts a force that propels the fluid, with higher frequencies resulting in increased flow rates. In the laser cladding process, the high-powered emission of energy from the laser results in the rapid melting of the cladding powder and a small amount of substrate, forming a molten pool. This process gives rise to a substantial convective effect that occurs within the aforementioned molten pool. The presence of ultrasound serves to augment this convection, thereby intensifying the overall stirring action of the molten pool. This, in turn, leads to a more homogeneous distribution of various substances throughout the molten cladding layer.\u003c/p\u003e \u003cp\u003eAs illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e(c), the upper microstructural morphology of the S3 fused clad section is revealed. The figure reveals the presence of multiple dendrites and substantial massive phases. A comparison of Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e(c) with Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e(a) reveals that the small grains in the original honeycomb organization have grown, while the nickel matrix grains have decreased. Figure\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e(d) presents the upper microstructural morphology of the S4 fused cladding section. It is evident from the figure that the grains have been significantly reduced, and the presence of cellular crystals is pronounced. Additionally, the grains are uniformly dispersed within the matrix, exhibiting a cellular distribution. No obvious massive carbides or dendrites were observed. Compared to S2 and S3, the ultrasonic cavitation and acoustic flow effects are further enhanced. The material elements within the cladding layer are further dispersed and homogenized, and neither matrix grains nor carbides nor other compounds grow, and are tightly clustered in the form of fine cellular crystals.。\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e(a) shows the microstructure morphology of the middle part of the section of S1 fusion cladding. The figure shows the presence of gray lined massive phase with large size and non-uniform distribution, and the presence of honeycomb fabric, but the distribution pattern of its bands is not obvious. As illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e(b), the central microstructure morphology of the S2 fused cladding section is evident. A comparison with Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e(a) reveals a substantial reduction in the bulk phase, accompanied by a refinement of the honeycomb structure, with the presence of a modest amount of dendrites. Figure\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e(c) presents the central microstructure morphology of the S3 fusion cladding section. A comparison with the conventional laser cladding method in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e(a) reveals that the size of the gray massive phases in the fusion cladding layer formed by this method has increased, and the matrix grains are relatively larger. Figure\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e(d) provides a visual representation of the microstructure of the middle part of the specimen's cross-section of the S4 cladding layer. The grains illustrated in the figure manifest the finest size and the most uniform distribution, bearing resemblance to the microstructure observed in the upper region of the sample.\u003c/p\u003e \u003cp\u003eAnalyzing the above micromorphology, it can be seen that the grains in the middle part of the melted cladding layer have time to grow relative to the top part due to the low heat dissipation efficiency and relatively small temperature gradient compared to the top part. However, when the remelting and ultrasonic-assisted processes work together, the microstructure formed in the middle region is not much different from that in the top region.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e(a) shows the lower microstructure morphology of the S1 fused clad section. In it, a clear columnar crystal structure can be observed whose growth direction is perpendicular to the planar crystals at the bottom. In addition, the cytosolic crystals formed by the fragmentation of the columnar crystals can also be seen in the figure. The introduction of the ultrasonic-assisted process resulted in a significant reduction in the columnar crystals of the S2 molten cladding section, as evidenced in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e(b). This reduction was not observed in the S1 specimen. The cavitation effect generated by ultrasonic waves in the molten pool has been shown to break down large columnar crystals, thereby refining the grains and reducing the formation of new columnar crystals. The microstructure of the bottom of the melt-coated layer of the S3 sample, as depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e(c), exhibits a columnar crystal organization analogous to that observed in the S1 specimen. Figure\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e(d) illustrates the microstructure of the bottom of the S4 melt-coated layer. As illustrated in the figure, the columnar crystals at the bottom have almost disappeared, the grain size has been further reduced, and the grain dispersion has been significantly improved, showing higher structural homogeneity. This enhancement in structural homogeneity can be attributed to the combined effect of ultrasonication and remelting, which has been demonstrated to promote both grain refinement and improved melt pool uniformity.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Evolution of WC particles\u003c/h2\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eWC exhibits favorable wettability with nickel-based alloys, frequently serving as a reinforcing agent to enhance their wear resistance. However, significant disparities in the thermophysical properties of WC and nickel-based alloys result in an escalation of defects within the fused cladding layer as the WC content increases. This paper proposes the application of laser remelting technology and ultrasonic assisted processes as a means to mitigate cracking defects in high-WC content nickel-based fused cladding layers. In order to investigate the presence of WC particles within the fused cladding layer, these particles were observed, and elemental analysis at various locations was conducted using EDS technology to understand the distribution of WC and its surrounding metallurgical environment.\u003c/p\u003e \u003cp\u003eAs illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e, the morphology of WC particles in the fused cladding layer is evident. Figures\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e(a) and 9(b) illustrate the state of carbides in the fused cladding layer in the absence of any assisting processes. Figure\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e(c) depicts the state of WC after applying the remelting aiding process, while Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e(d) shows the state of WC after both the remelting and ultrasonic-assisted processes have been applied. Observation of Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e(a) reveals two intact WC particles with good wettability with the substrate, and no defects such as porosity or cracks are found around the particles. Large dendrites are observed surrounding the WC. Figure\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e(b) offers a magnified perspective of the WC particles situated within the upper left quadrant of Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e(a). In the figure, there are obvious edges with different degrees of cladding around the WC particles, indicating that the WC particles have melted around them, and more small particles with the same degree of cladding as the WC exist beyond the edges. To further determine the material composition of the different regions in the figure, the EDS technique was used to determine the elemental composition at different locations. Figure\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e shows the elemental composition at various locations. The elemental composition of the region at point 1 in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e(b) is primarily composed of W and C, thereby identifying it as WC particles. A comparative analysis of points 1 and 2 reveals that the atomic percentage of Cr, Fe, and Ni elements is significantly higher at point 2. This observation suggests that this region consists of a new compound formed by W and C element atoms in the free state with nearby matrix elements (Cr, Fe, Ni) following the melting of the WC particle edges. The region identified as point 3 is characterized by the presence of matrix elements, with a minor presence of free W elements that have diffused into it due to its proximity to WC. As illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e(C), the melting of WC particles at their edges is discernible, accompanied by the formation of prominent dendrites with distinct linings. Analyzing the elemental composition of the 4-point and 5-point regions, it can be seen that the 4-point region is a high-carbon type nickel-iron alloy FeNi30 (Ni35%), and the 5-point region is very similar to the elemental composition of the 2-point region, and it is believed that due to the remelting-assisted process, the molten pool receives more energy, which makes the new compounds formed by W and C elements and the matrix elements have a driving force to grow up and thus form the dendritic crystals. Looking at Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e(d), the grains are more refined due to a combination of remelting and ultrasound-assisted processes. A deeply lined massive organization with a core of daisy-like tissue appears. The elemental composition of the bulk tissue, the daisy-like tissue and its core were examined separately (points 6, 7 and 8). The elemental composition of the 6-point region is very similar to that of the 2-point and 5-point regions, forming the same compounds. The elemental content of the 7-point region is similar to that of the 3-point region, but the W elemental content of the 7-point region is higher than that of the 3-point region, indicating that there are more free W elements in this region. The high W elemental content of the 8-point region and the significant increase in matrix elements compared to the 1-point region indicate that the core of the daisy-like organization is not a WC granule. However, observation shows that no intact WC particles are found in the vicinity. Therefore, it can be assumed that the 8-point region is the core of the small WC particles that eventually melted. Since the original WC particles in this region are completely melted, the content of W and C elements is high, and due to the short solidification time, there is not enough time for diffusion. A compound with a high W element content was formed, with the matrix elements diffusing in during solidification.\u003c/p\u003e \u003cp\u003eBased on the observation of Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e and the analysis of Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e, the following conclusions can be drawn: If the larger WC particles do not completely melt during the laser melting process, their cores still retain the morphology of the larger WC particles, with a small amount of melting at their edges. The partially melted WC forms free W and C elements, which form bonds with nearby matrix elements during solidification. The smaller WC particles are completely melted, and their core region has a high content of W and C elements that are too late to diffuse sufficiently during solidification, forming compounds with high W and C element content.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.4XRD analysis\u003c/h2\u003e \u003cp\u003eBased on the analysis of the XRD inspection results in Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e, it can be observed that there is a remarkable similarity in the phase composition of the four processing methods, containing the main metallographic phases: γ-Ni(Fe), FeNi3, W2C, WC, Fe2W2C (M6C), with typical compounds being M6C and M23C6.\u003c/p\u003e \u003cp\u003eThe appearance of the W2C phase is consistent with the previous analysis: the edges of the WC particles or small WC particles melted, and the free W and C elements produced by the melting did not diffuse in time and were able to form the W2C phase during the solidification process. The diffused elements formed compounds with other matrix elements. The presence of γ-Ni (Fe) solid solution, FeNi3 metal compounds, Fe2W2C carbides was found in the fused cladding layer, the appearance of these phases contain Fe elements, indicating that the Fe element content is higher than the increase in the content of fused powder, i.e., part of the matrix melted, and the diffusion through the molten pool diluted the Ni60 fused cladding layer. Comparison of the XRD curves of S1-S4 samples shows that the diffraction peak to the left of the main peak of S3 sample disappears. This diffraction peak is mainly the result of compound diffraction, indicating that laser remelting can attenuate the formation of compounds. The combined remelting and ultrasonic irradiation also mitigated residual stress, a critical factor in crack suppression. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e(a\u0026ndash;d), the full-width at half-maximum (FWHM) of the Ni (111) diffraction peak decreased from 0.42\u0026deg; (S1) to 0.35\u0026deg; (S4), suggesting reduced lattice distortion and compressive stress accumulation. The XRD peak shift toward lower angles in S4 (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e) further indicates compressive stress relaxation compared to S1. These mechanisms collectively suppressed crack initiation sites and propagation pathways, as corroborated by the crack-free surface morphology in S4 (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ed).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e3.5 Microhardness\u003c/h2\u003e \u003cp\u003eAs demonstrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e, the presentation of the microhardness curves from the top to the bottom of the fused cladding layer for the four specimens is accompanied by the average microhardness values in the fused cladding region. It is noteworthy that WC particles were deliberately excluded from the microhardness tests, thereby ensuring that the observed curves exclusively represent the microhardness of the fused cladding portion of the cladding layer, excluding the WC particles. A comparison of the average hardness in the fused cladding region reveals that the fused cladding obtained using S1 exhibits high hardness, averaging 707 HV. The extreme heat and cold effects of fusion cladding result in a short liquid-to-solid conversion time, thereby preventing sufficient diffusion of elements. Consequently, the matrix forms a liquid-saturated solid solution, thereby creating a solid solution that strengthens the material. The ultrasonic process, when introduced, led to a considerable augmentation in the microhardness of the fused cladding layer, reaching an average of approximately 753 HV, representing a 6.51% increase. This increase in hardness is attributable to the propagation effect of ultrasound in the liquid metal bath. The effects of ultrasound, such as cavitation and acoustic flow, have been demonstrated to facilitate the formation of cytosolic crystals and grain refinement, thereby resulting in a denser and more homogeneous structure. The application of remelting technology to the conventional molten cladding layer resulted in a decline in S3 microhardness, with the mean hardness diminishing to 648 HV, representing an 8.35% reduction. This decline is attributed chiefly to the weakening of solid solution strengthening during the remelting process. The joint application of remelting and ultrasonic-assisted technology enhances the microhardness of the fused cladding layer, with the average microhardness of S4 reaching 831HV0.025, representing an increase of 17.54%. The concurrent application of remelting and ultrasonic assistance processes ensures that the cladding layer absorbs substantial light and acoustic energy, predominantly converted into heat. This likely elevates the melt pool's temperature above that of the initial cladding. The subsequent rapid cooling period serves to enhance the magnitude of the temperature difference during the processes of both solidification and crystallization when compared to the initial cladding. This enhancement facilitates solid solution strengthening. Furthermore, the cavitation and acoustic effects of ultrasonic waves have been demonstrated to homogenize the material composition of the cladding layer, thereby enhancing nucleation and preventing the formation of dendrites. This process leads to a strengthening of the crystals due to the fine grain size that results.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e3.6 Wear resistance\u003c/h2\u003e \u003cp\u003eThe incorporation of WC hard phase has been demonstrated to enhance the wear resistance of Ni60 fused cladding. Empirical evidence has demonstrated a direct correlation between an increase in the hard phase content and an enhancement in wear resistance. However, it is imperative to acknowledge that an augmented hard phase content may precipitate crack formations in the cladding layer. To address this challenge and enhance the wear resistance of the fused cladding layer, this paper proposes an innovative process that incorporates ultrasonic and remelting techniques. This process aims to prevent crack formation during the preparation stage, thereby enhancing the overall durability and functionality of the cladding layer. The ball and disk reciprocating dry wear test method is employed in the present study to assess the wear resistance of specimens S1-S4 under uniform wear conditions, with a concomitant observation and analysis of these specimens' wear morphology.\u003c/p\u003e \u003cp\u003eThe experimental findings indicate that the wear volume attributable to the cladding layer's high wear resistance is minimal. Consequently, substantial errors occur when employing weight measurement to discern varying degrees of wear resistance. This paper proposes a novel calibration approach for wear evaluation, commencing with scanning and precise measurement of wear scars to accurately map their three-dimensional topography. Subsequent to this, a precise two-dimensional profile of a representative wear scar's cross-section is generated, with the software meticulously calculating the enclosed area and determining the profile's maximum width and depth. The minimization of error is achieved by collecting data at four discrete points on each wear scar, thereby acquiring four datasets per specimen, from which an average is derived. The study adopts the mean cross-sectional area of wear scars as the calibration standard for wear volume, considering consistent wear scar lengths and uniform material density loss.\u003c/p\u003e \u003cp\u003eIn the experimental design, measures were taken to circumvent random effects and enhance the precision of the data. To this end, the cross-sectional profile curves were measured at four representative wear marks, situated at the midpoint of the wear marks, subsequent to the removal of the initial and terminal wear marks. As demonstrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig13\" class=\"InternalRef\"\u003e13\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan refid=\"Fig14\" class=\"InternalRef\"\u003e14\u003c/span\u003e, Figs.\u0026nbsp;\u003cspan refid=\"Fig13\" class=\"InternalRef\"\u003e13\u003c/span\u003e(a)-(d) and Fig.\u0026nbsp;\u003cspan refid=\"Fig14\" class=\"InternalRef\"\u003e14\u003c/span\u003e illustrate the contour curves of the cross-sections of the wear marks for specimens S1-S4. The maximum width and depth of the abrasion mark sections are indicated in the figure, and the values of the areas enclosed by the contour curves and the average values are specified by the labels on the left side of the figure. A thorough examination of the data presented in the figure reveals that the average wear amount of S1 fusion cladding is 1976.95 \u0026micro;m\u003csup\u003e2\u003c/sup\u003e. A comparative analysis of the wear amount of other specimens indicates that the wear resistance of S1 specimen is comparable to that of S4 specimen, and it is higher than that of S3 specimen but lower than that of S4 specimen. A further analysis of the cross-sectional profile reveals that the bottom area of the S1 wear mark section is flat, suggesting that during the wear process, the ball crown of silicon nitride on the wear vice is gradually smoothed out. The average Vickers hardness of silicon nitride is approximately 2200, which is sufficient to flatten such a hard wear vice, indicating that the fusion cladding layer possesses high abrasion resistance. The mean abrasion of the S2 fusion cladding layer is 1520.63 \u0026micro;m\u003csup\u003e2\u003c/sup\u003e, which is the lowest among the four types of samples and indicates the highest level of abrasion resistance. The depth of the abrasion marks is similar to that of the S1 sample, yet the width of the marks is the narrowest. From the above tests and analysis, it can be seen that the S2 sample was added to the ultrasonic assisted process during the cladding process, which can refine the grains, enhance the convection effect of the molten bath, and make the cladding layer material homogeneous\u003csup\u003e[\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e][\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]\u003c/sup\u003e. The mean wear amount of the S3 fused cladding layer was 3127.65 \u0026micro;m\u0026sup2;, which was the greatest wear amount and the least effective wear resistance among the four specimens. The width and thickness of the wear marks were the greatest. The implementation of the laser remelting technique resulted in a reduction in the presence of cracks and an enhancement in the roughness of the fused cladding layer. The findings of this study, as indicated by the detection and analysis, suggest that the hard-phase WC particles underwent a process of partial decomposition, melting, and synthesis with other elements, resulting in the formation of new compounds. The average wear amount of the S4 fused cladding layer is 2058.19 \u0026micro;m\u0026sup2;, which is comparable to that of the S1 specimen. A comparison of the abrasion cross-section profiles of S1 and S4 reveals that the latter's profile is a spherical crown cross section, while that of S1 is a biased flat cross section. The substrate's average microhardness, measured as HV\u003csub\u003e0.025\u003c/sub\u003e, was found to be 707 for S1 and 831 for S4. In conjunction with the above discussion, it can be seen that the S4 specimens underwent additional remelting during the preparation process, while an ultrasonically assisted process was incorporated. Both processes were added with the primary purpose of eliminating cracking defects, but they also reduced the content of hard phase WC, resulting in lower wear resistance. The concurrent implementation of ultrasound resulted in the refinement of grains within the cladding, an enhancement of the overall mechanical properties, and a more uniform material distribution. This suggests that the wear resistance of the cladding can be improved. The comparable wear resistance observed between S1 and S4 indicates that the reduction in hard phase content, which is typically associated with a decrease in wear resistance, is counterbalanced by the extent to which the ultrasonically assisted process refines grains and homogenizes the material, thereby enhancing the wear resistance of the cladding. The reduction of hard phases in S4 weakened the wear resistance despite its higher hardness due to partial WC dissolution caused by remelting. The number of cracks in S2 was lower than that of S1, and there were no pores or inclusions in the microstructure. Cracks are the initiation point of wear, and the reduction of defects directly slows down the wear process. Therefore, compared to S1 and S4, the S2 sample has the best wear resistance.\u003c/p\u003e \u003cp\u003eAs illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig15\" class=\"InternalRef\"\u003e15\u003c/span\u003e, the wear morphology and three-dimensional profiles of specimens S1-S4 are presented. The wear morphology of specimen S1 reveals a relatively flat bottom with a small number of small and large craters, which are traces left by WC particles after exfoliation during the wear process. The large craters are localized areas where minor adhesive wear has occurred, causing the surface to flake off. The bottom of the wear pattern shows a distinctive gouge, which is believed to be the participation of exfoliated WC particles in the wear. The WC particles on the fused cladding flaked off and adhered or embedded to the spherical pair of grinding vice, and as the spherical pair of grinding vice moved as a hard point, it left a furrow on the fused cladding like a plow. Sample S2 shows a superposition of multiple grooves at the bottom of the wear pattern, while the wear pattern is smoother at the sides. The wear pattern of specimen S3 also showed exfoliation pits of WC particles and large traces of adherent wear. The wear pattern of specimen S4 also showed exfoliation pits of WC particles but did not show large traces of adherent wear.\u003c/p\u003e \u003cp\u003eAs demonstrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig16\" class=\"InternalRef\"\u003e16\u003c/span\u003e, the friction coefficients of the S1-S4 materials are presented as a function of applied force. The variation in the friction of the different specimens is evident. The S1 specimen demonstrates the highest friction coefficient and exhibits the most substantial fluctuations in its curve. This observation indicates that the material inhomogeneity and the presence of hard phases in the S1 specimen enhance the wear resistance of the cladding layer. In comparison, the S2 specimen exhibited a lower friction coefficient, yet its magnitude was notably higher than those of the S3 and S4 specimens. A comparison of the friction coefficient curves of S1 and S2 reveals that the latter is relatively smooth, suggesting that ultrasonic waves have strengthened the cladding layer by precipitating the formation of fine crystals and homogenizing the distribution of material within the cladding layer. In contrast, the friction coefficient curves for S3 and S4 in the smooth wear stage exhibit a close and flat profile with a narrow fluctuation range. The presence of WC in the remelting process during part of the melting results in the reduction of the hard phase in the fusion cladding layer, leading to a decrease in wear resistance and a reduction in the overall coefficient of friction. The incorporation of an ultrasonic-assisted process in the S4 sample has been shown to yield a fine crystal strengthening effect, resulting in a more uniform material distribution, thereby leading to a reduction in the overall coefficient of static friction.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003e3.7 Mechanism of action of remelting and ultrasonic assisted processes\u003c/h2\u003e \u003cp\u003eThe processes of solidification of the melt during the preparation of the molten cladding layer are principally governed by thermal conduction, absent any ancillary mechanisms. The rapid cooling rate gives rise to a pronounced temperature gradient, which in turn precipitates the crystallization of a columnar structure at the bottom of the melt pool. This phenomenon can result in the manifestation of various anisotropies. The absence of supplementary energy input or agitation effects during the rapid solidification process leads to substantial residual tensile stress. The underlying causes of this residual stress can be attributed to thermal stress, phase change stress, and WC particles. The tensile stress resulting from this process exceeds the tensile strength of the substrate, thereby inducing cracks\u003csup\u003e[\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e]\u003c/sup\u003e .\u003c/p\u003e \u003cp\u003eIn the context of laser cladding, the employment of ultrasonic vibration during the process facilitates the transmission of energy into the molten pool via acoustic waves. This approach entails the utilization of ultrasonic energy within the molten pool, thereby disrupting the conventional crystallization process. The impact of ultrasound on these processes has been demonstrated to include the refinement of grain size, the heterogeneity of material within the aforementioned pool, the reduction of uneven heat distribution, the minimization of porosity and defects, and the promotion of the microstructure of the cladding layer.\u003c/p\u003e \u003cp\u003eThe process of laser melting involves the utilization of ultrasonic waves, which result in the molten liquid undergoing internal vibrations. These vibrations are caused by acoustic waves, leading to the application of tensile stress to a specific local area. This, in turn, causes the gas dissolved in the liquid to reach supersaturation and subsequently escape, resulting in the formation of small bubbles. Alternatively, a significant tensile stress can exert force on a cavity, causing it to traverse a localized region of the liquid. The growth of cavitation bubbles (i.e., small bubbles and cavities) persists, and when the sound pressure attains a particular threshold, the cavitation bubbles undergo a dramatic collapse, releasing a substantial amount of energy. This process leads to the generation of high temperatures and pressures in a confined area in close proximity. The subsequent rapid cooling of the melt pool leads to an increase in the degree of subcooling, thereby initiating the nucleation process of the crystals within the melt pool. The local high temperatures and pressures engendered by the cavitation effect promote the nucleation process, and concurrently, the substantial energy release exerts a destructive effect on the already formed dendrites (e.g., broken columnar crystals and dendrites). Consequently, the melt pool is characterized by the predominance of fine equiaxed crystals.\u003c/p\u003e \u003cp\u003eThe application of laser energy, characterized by its potency, prompts the metal to undergo a phase transition, resulting in the formation of a molten pool. However, the temperature distribution exhibits inhomogeneity and may be well approximated by a Gaussian distribution. The presence of temperature gradients gives rise to thermal convection effects within the aforementioned molten pool. Furthermore, the propagation of ultrasound through a molten metal gives rise to an acoustic flow effect, characterized by a steady liquid flow. This acoustic flow effect is further amplified by the ultrasound-induced convection effect within the molten pool, leading to a complex and dynamic thermal environment. The convection effect has the capacity to enhance the transmission of substances in disparate regions, promote the homogenization of substances of different compositions in the molten pool, help eliminate compositional segregation, and promote the diffusion of elemental atoms. The convective effect also leads to a more uniform temperature distribution within the melt pool, thereby reducing the internal temperature gradient. This, in turn, fosters the formation of equilibrium crystals.\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig17\" class=\"InternalRef\"\u003e17\u003c/span\u003e provides a schematic representation of the principle of ultrasonic waves acting on the molten pool. Conventional laser cladding typically produces columnar crystals at the base of the melt pool and dendrites at its center, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig17\" class=\"InternalRef\"\u003e17\u003c/span\u003e(a). However, the incorporation of ultrasound, through its cavitation and convection effects, has the potential to enhance convection within the melt pool, thereby disrupting the integrity of both columnar and dendritic crystals. This disruption is demonstrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig17\" class=\"InternalRef\"\u003e17\u003c/span\u003e(b)\u003csup\u003e[\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e]\u003c/sup\u003e .\u003c/p\u003e \u003cp\u003eLaser remelting facilitates the rapid melting and crystallization processes of the cladding layer, thereby enabling the subsequent diffusion of elemental atoms. In accordance with the principle of systemic energy minimization, laser remelting leads to a reduction in the total systemic energy of the material in the melt pool during solidification, including a reduction in residual tensile stresses. Furthermore, the process of laser remelting results in additional melting of WC particles, thereby reducing residual stresses that are caused by variations in thermophysical properties \u003csup\u003e[\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e]\u003c/sup\u003e .\u003c/p\u003e \u003cp\u003eIn the domain of materials science and mechanical engineering, the concurrent implementation of remelting and ultrasonic vibrations has emerged as a methodology for enhancing the microstructure and properties of fused claddings. The energy input from ultrasound refines the grain structure, while remelting releases residual stresses. The combined effect of these processes leads to enhanced overall mechanical properties of the cladding. Specifically, the melting of selected WC particles is counterbalanced by a complementary mechanism, thereby achieving a harmonious balance in the microstructure and mechanical properties of the cladding. It is this synergistic interplay that ultimately elevates the overall performance of the cladding. The effectiveness of crack suppression in S4 is attributable to multiple synergistic effects. Ultrasonic cavitation has been shown to destroy dendrites (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eb), promote grain refinement, and reduce elemental segregation (Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e). The process of remelting has been observed to eliminate pre-existing porosity (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e) and induce thermal equilibrium to release residual stress. The combined action of these effects enhances epitaxial nucleation, refines grains, and improves toughness. These mechanisms complement each other to achieve a crack-free structure with optimized mechanical properties.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"4. Conclusions","content":"\u003cp\u003eIn this study, ultrasonic-assisted laser remelting and irradiation-mode laser remelting were utilized to produce Ni60/WC fused clad layers. The process yields a fusion cladding that is characterized by the absence of cracks and a hardness and wear resistance that is comparable to that of conventional fusion cladding. A comprehensive analysis was conducted, encompassing examination of the gross morphology, crack initiation, microstructure, microhardness, and tribological properties of the cladding layers produced by different methods. Furthermore, the investigation focused on the effects and mechanisms of remelting and ultrasonic vibration on the structure and characteristics of these coatings. The ensuing conclusions were derived from this comprehensive investigation:\u003c/p\u003e \u003cp\u003e(1) Cracks were inhibited by either ultrasonic-assisted treatment (4\u0026ndash;5 cracks) or remelting alone (1\u0026ndash;3 cracks) compared to conventional cladding methods (5\u0026ndash;8 cracks). However, when remelting and ultrasonic treatment (0 cracks) were performed simultaneously, a more significant effect was observed than with a single treatment. This suggests a synergistic rather than additive effect of the two methods.\u003c/p\u003e \u003cp\u003e(2)The cavitation and acoustic flow effects of ultrasound have been demonstrated to refine grains, reduce elemental segregation, and homogenize the distribution of different substances. Furthermore, remelting-assisted processes have been shown to promote grain growth. The application of remelting and ultrasonic assistance in a concurrent manner serves to accentuate the impact of grain refinement.\u003c/p\u003e \u003cp\u003e(3)Large particles of WC melt at the edges, and the free W and C elements form compounds with the matrix elements. In contrast, smaller particles of WC undergo complete melting, resulting in the formation of compounds with a high concentration of W and C elements.\u003c/p\u003e \u003cp\u003e(4)The metallographic composition of the fused cladding layers prepared by different processes is essentially equivalent. The predominant metallographic phases are as follows: γ-Ni(Fe), FeNi3, WC, W2C, M6C, and M23C6 compounds.\u003c/p\u003e \u003cp\u003e(5)The ultrasound-assisted process increases the hardness of the Ni60 substrate, while the remelting-assisted process decreases the hardness of the substrate. The combination of the two processes increased the hardness by 17.54% compared to the conventional cladding. The wear resistance of the cladding layer combining the two assisted processes increased by 34.19% compared to that of the remelted cladding layer, which is comparable to that of the conventional cladding layer.\u003c/p\u003e \u003cp\u003eIn the end, by applying remelting with the aid of ultrasonic waves, a cladding layer is obtained that is reduction in crack formation and whose hardness and wear resistance are not too different from those of conventional cladding.\u003c/p\u003e"},{"header":"Declarations","content":" \u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eThe methodology was proposed and the experiments were performed by Z.H.F. and G.H.C.; H.X.P. analyzed the data; T.J.Y. and S.W.H. wrote the article; and Z.C.L. reviewed the comments.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eData availabilityAll data generated or analyzed during this study are included in this published article.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eBandyopadhyay, A., Zhang, Y. \u0026amp; Bose, S. 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Technol.\u003c/em\u003e \u003cb\u003e408\u003c/b\u003e, 126789 (2021).\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"laser cladding, ultrasound, crack sensitivity, remelting","lastPublishedDoi":"10.21203/rs.3.rs-5886896/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5886896/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis study investigates crack suppression mechanisms in Ni60-WC laser cladding layers on C45E4 steel using ultrasonic irradiation and laser remelting. C45E4 steel, widely used in industrial gears and shafts, suffers from wear and corrosion in heavy-load environments. Laser cladding provides surface reinforcement, but cracks persist due to thermal stress and WC/matrix mismatch. Key findings reveal that ultrasonic cavitation breaks dendrites through micro-jet impacts, while acoustic streaming homogenizes the melt pool, reducing elemental segregation. Laser remelting eliminates cracks by remelting defect-prone regions (e.g., interfacial porosity) and releasing residual stress through thermal equilibrium. ​​The experimental findings demonstrated that ultrasonic waves significantly enhanced the crystal strengthening effect of the fused cladding, resulting in a 17.54% increase in hardness.​​ Furthermore, the combined laser remelting and ultrasonic-assisted process effectively prevented crack formation in the cladding layer and enhanced the hardness of the substrate. Despite partial WC dissolution, ​​hardness improvements remain significant​​ due to grain refinement. This dual-assisted strategy demonstrates practical value for repairing C45E4 components in mining and energy equipment.\u003c/p\u003e","manuscriptTitle":"Effect of laser remelting and ultrasonic irradiation on crack suppression and properties of Ni-WC laser cladding layer","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-04-25 20:15:41","doi":"10.21203/rs.3.rs-5886896/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"editorAssigned","content":"","date":"2025-05-22T05:54:01+00:00","index":"","fulltext":""},{"type":"decision","content":"Revision requested","date":"2025-05-22T05:46:22+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-05-07T02:26:50+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"165110231393860077662030085228377624631","date":"2025-04-27T00:26:42+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-04-25T01:05:41+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"223917954469668337535791919454147387312","date":"2025-04-25T00:58:49+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-04-24T14:13:13+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"167087606432575286063338921398832964274","date":"2025-04-24T13:38:56+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-04-24T04:08:30+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-04-21T15:47:16+00:00","index":"","fulltext":""},{"type":"submitted","content":"Scientific Reports","date":"2025-04-21T15:14:25+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"4b9d9b3c-6846-497a-bc5f-4bcf7e7feb09","owner":[],"postedDate":"April 25th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":47656018,"name":"Physical sciences/Optics and photonics/Applied optics/Laser material processing"},{"id":47656019,"name":"Physical sciences/Engineering/Mechanical engineering"}],"tags":[],"updatedAt":"2025-06-09T16:09:12+00:00","versionOfRecord":{"articleIdentity":"rs-5886896","link":"https://doi.org/10.1038/s41598-025-05046-5","journal":{"identity":"scientific-reports","isVorOnly":false,"title":"Scientific Reports"},"publishedOn":"2025-06-02 15:57:24","publishedOnDateReadable":"June 2nd, 2025"},"versionCreatedAt":"2025-04-25 20:15:41","video":"","vorDoi":"10.1038/s41598-025-05046-5","vorDoiUrl":"https://doi.org/10.1038/s41598-025-05046-5","workflowStages":[]},"version":"v1","identity":"rs-5886896","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5886896","identity":"rs-5886896","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}