Understanding mechanisms of defect formation in both virgin and recycled powders during laser additive manufacturing and subsequent welding is crucial for producing high-quality components. This study presents a comparative analysis of three AlSi10Mg powders: virgin powder (VP), recycled powder (RP), and environmentally aged powder (EP). Results show that EP contains 4.43 times higher hydrogen and 33.93 times higher oxygen compared to VP, along with a thickened surface oxide layer of 9.65 nm. AlSi10Mg sheets (3 mm in thickness) were fabricated via laser powder bed fusion (LPBF) using different powders and were subsequently welded by gas tungsten arc welding (GTAW). Elevated hydrogen and oxygen contents promoted powder coarsening and agglomeration, reducing effective laser energy density during LPBF and increasing porosity in as-built samples from 0.82 to 18.24

Cryogenic ball valves are essential for the storage and transportation of liquefied gases and fuels in many industrial applications. However, conventional valve ball materials show insufficient tribological performance under cryogenic conditions. To address this issue, an Inconel 718 coating was deposited on an SUS 304 substrate by high-velocity oxygen-fuel (HVOF) spraying, followed by single aging (SA) treatment to improve cryogenic tribological properties. The results show that the SA-treated coating (SA700-4H) exhibits significantly enhanced cryogenic tribological properties. Compared with the as-sprayed coating (N-SA), its friction coefficient and volume wear rate decrease by 13.05% and 52.36%, respectively. Microstructural characterization reveals that SA treatment promotes the precipitation of nanoscale second phases (gamma ', gamma '', and delta). Meanwhile, severely deformed grains undergo recovery and recrystallization, reducing dislocation density and refining the grain structure in the coarse-grain zone. Dislocations facilitate precipitate nucleation, whereas precipitated phases hinder dislocation motion. Furthermore, the cryogenic environment has little influence on grain size or precipitate state, causing only a slight increase in dislocation density. Wear scar analysis indicates that both coatings are dominated by fatigue wear and abrasive wear under cryogenic conditions. Oxides, pores, and particle interfaces act as the main crack-initiation sites and preferential crack-propagation paths. Compared with the N-SA coating, the SA700-4H coating exhibits superior resistance to deformation and plowing due to nanoscale precipitate strengthening and reduced dislocation density, thereby significantly improving its overall cryogenic tribological properties.

The microstructure and mechanical properties of the joint of a novel Al-Mg-Zn-Er-Zr alloy fabricated by multi-pass MIG welding using ER5E61 filler wire were investigated first. The results show that multi-pass MIG welding induces heterogeneous grains in the weld metal: equiaxed grains, columnar grains, and cover-pass feather-like grains. The weld metal exhibits coarse grains (45.81 ± 19.68 μm), a high proportion of high-angle grain boundaries (83.3%), and a low dislocation density compared with the base metal. The joint achieves 316 MPa ultimate tensile strength, 10.5% elongation, and 0.80 joint efficiency with minimum hardness (77.2 HV) in the weld metal. Strengthening mechanism analysis reveals that joint softening mainly stems from the disappearance of deformed structure, reduced dislocation density, and the coarsening and reduction in Al3(Er, Zr) nanophases. Diffuse precipitation of the Al3(Er, Zr) nanophases (19.61 nm, 0.53%) under multi-pass MIG welding compensates for the softening of the welded joint, leading to the retention of high tensile strength despite marked hardness loss, thus demonstrating effective strength preservation.

Fusion welding of L-PBF AlSi10Mg is hindered by severe hydrogen-induced porosity. To address this, a combined strategy of pre-weld hydrogen degassing annealing (PW-HDA, 250–400°C) and Er/Zr microalloying using an AlSi10Mg-Er-Zr filler was employed, followed by low-heat-input laser metal deposition (LMD) butt welding. The results demonstrate that PW-HDA effectively suppressed hydrogen porosity, reducing both pore density and maximum pore size. The AlSi10Mg-Er-Zr filler slightly reduced porosity and refined the α-Al cellular structure and Si-rich eutectic network. Raising the PW-HDA temperature from 250°C to 400°C decreased hydrogen porosity from 3.2

Hot cracking severely limits the reliability of copper/steel dissimilar welds due to strong elemental segregation and thermophysical mismatch. In this study, steel-on-copper lap welding was performed using an adjustable ring mode laser, and the evolution of microstructure, elemental distribution, and crack behavior was systematically investigated using EBSD, TEM, X-ray CT, and nanoindentation. The weld exhibited pronounced spatial heterogeneity, with localized Cu enrichment along grain-boundary-related regions in intergranular crack regions and broader heterogeneous Cu redistribution around transgranular cracks. Crack-adjacent regions showed grain refinement and mechanical heterogeneity, while partitioned EBSD analysis further indicated that higher KAM values and LAGB fractions were mainly retained in the non-recrystallized matrix near transgranular cracks. Nanoindentation results revealed larger scatter in hardness and modulus in cracked regions, indicating a locally unstable mechanical response. The transition between intergranular and transgranular cracking can be interpreted as the result of competition between segregation-induced grain-boundary weakening and stress-assisted intragranular failure associated with thermal mismatch, with Cu redistribution and local microstructural heterogeneity further influencing crack-path selection. These findings identify Cu redistribution and localized intragranular heterogeneity as key factors affecting crack-path selection, providing guidance for suppressing hot cracking and improving the reliability of copper/steel dissimilar laser welds.

The fatigue performance of additively manufactured high-entropy alloys (HEAs) has gradually attracted extensive attention to extend the potential engineering application of HEAs. In the present research, a high-cycle fatigue (HCF) test was employed on the laser powder bed fusion (LPBF)-processed Al-Cr-FeNi-V HEA in order to reveal the comprehensive effect of dislocation cells and multi-precipitates on the fatigue performance. Microstructural evolution (especially the dislocation cells and multi-precipitates) under cyclic loading was investigated systematically to explore the deformation mechanism of LPBFprocessed HEA. During the cyclic loading, dislocations were continuously generated and interacted with the pre-existing dislocations, dislocation cells, and multi-precipitates. The dislocation interaction induced the formation of new dislocation cells in the cell-free regions. B2 precipitates also provide the frame support for the formation of new dislocation cells. Numerous dislocation cells could increase the ability to accommodate dislocations and relieve stress concentrations. Interaction between dislocations and dislocation cells also changed the configuration of cells and promoted the transformation from dislocation cells to subgrains, forming low-angle grain boundaries (LAGBs). LAGBs enhanced the slip continuity of the grain boundary, restrained strain localization, and contributed to the stability of fatigue deformation. Grain rotation and coordinated deformation of adjacent grains could delay crack initiation and enhance the fatigue damage limit. The combined effect of the structure mentioned above facilitated the relatively high fatigue resistance of the LPBF-processed HEA. (c) 2025 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

Increasing powder layer thickness in laser powder bed fusion (LPBF) improves processing efficiency, but its effects on defect evolution, microstructure, and mechanical properties remain insufficiently understood. This study systematically investigates the effects of layer thickness (40, 60, and 80 μm) and build direction (horizontal and vertical) on melt pool characteristics, microstructure evolution, and mechanical properties of LPBF-fabricated AlSi10Mg alloy. The results indicate that high relative densities above 99.6% are achieved for all layer thicknesses, with hydrogen pores mainly distributed along melt pool boundaries. A larger layer thickness results in an increased melt pool size, reduced interlayer remelting, and higher surface roughness. The microstructure comprises an α-Al matrix and a eutectic Si network; finer cellular α-Al, refined Si, and higher dislocation density form at 40 μm due to higher cooling rates, whereas at 80 μm the cells coarsen with increased π-Al8FeMg3Si6 precipitation along cell boundaries. Grain structures comprise <001>-oriented columnar grains and randomly oriented equiaxed grains, and increasing layer thickness promotes equiaxed grain formation while reducing Cube and Goss textures. Mechanical testing reveals that increasing layer thickness decreases the ultimate tensile strength and elongation of horizontal specimens from 432.9 MPa to 8.9% to 419.3 MPa and 5.2%, respectively. Based on strengthening mechanisms, the strength reduction at larger layer thicknesses is mainly due to the decreased load-bearing capacity of the eutectic Si network and weakened solid-solution and Guinier-Preston zone strengthening. Additionally, coarsened eutectic Si, weakened melt pool boundaries, and increased porosity promote crack propagation along melt pool boundaries interfaces, thereby reducing fracture resistance.

To enhance the hardness and wear resistance of TA10 titanium alloy, a series of titanium matrix composite (TMC) coatings were fabricated through the intergrowth structure design strategy, employing custom-designed Ti-B4C flux-cored wires via tungsten inert gas (TIG) cladding process. The influence of B4C additions (7, 9, 11 and 13 wt%) on the microstructural evolution and mechanical properties of the TMC coatings was systematically investigated, with particular focus on the formation mechanisms of intergrowth structures and their contribution to coating strengthening. Microstructure characterization revealed that the TMC coatings were primarily composed of micro-to-nanometer-scale eutectic TiB whiskers and TiC particles, micrometer-scale primary TiB prisms and TiC dendrites, as well as TiB/TiC binary intergrowth structures with two distinct morphological features. Notably, locally distributed TiB2/TiB/TiC ternary intergrowth structure was further formed with increasing B4C addition up to 9 wt%. Furthermore, the formation pathways of these intergrowth structures and the underlying mechanisms of microstructure evolution under different B4C contents were systematically elucidated by combining thermodynamic calculations with interface orientation relationship obtained via transmission electron microscopy (TEM). The performance results indicated that the coating hardness exhibited an initial increase followed by a decrease with increasing B4C content, whereas the wear resistance was significantly superior to that of the TA10 substrate. The primary strengthening mechanism of the TMC coatings was derived from in-situ synthesized reinforcements, particularly the TiB2/TiC/TiB and TiB/TiC intergrowth structures. Nanoindentation results confirmed these intergrowth structures exhibited high nanohardness, elastic modulus, and excellent load-bearing capacity, which effectively suppressed matrix plastic deformation and redistributed external loads during the wear process, thereby significantly enhancing of coating hardness and wear resistance.

Steel/copper dissimilar metal lap joints are key structural components for achieving efficient joining in applications such as new energy vehicles (NEVs). However, their welded joints exhibit extremely high hot crack susceptibility. In this study, adjustable ring mode (ARM) laser welding was employed to systematically investigate the joining of low-carbon steels (LCS) with three forms of copper base metal (BM): copper sheets (CS), copper foil stacks (CFS), and gapped copper foil stacks (G-CFS). The results reveal that the thermal conductivity of the base metal (BM) influences molten pool flow and consequently affects hot crack susceptibility. In particular, the low-carbon steels (LCS)/ gapped copper foil stacks (G-CFS) joint, owing to its unique local thermal resistance, optimizes the thermal behavior of the molten pool, thereby achieving completely crack-free welding. Tensile fracture behavior shows that the low-carbon steels (LCS)/ gapped copper foil stacks (G-CFS) joint, exhibiting no crack initiation, achieved the highest tensile strength of 371 MPa. The low-carbon steels (LCS)/ copper foil stacks (CFS) joint exhibiting liquid phase separation demonstrated a tensile strength of 249 MPa, approximately 30.8 % lower than that of the low-carbon steels (LCS)/copper sheets (CS) joint containing hot cracks (360 MPa). This study clarifies the physical mechanism by which the thermophysical properties of the base metal (BM) regulate hot crack initiation in steel/copper lap joints, providing an important theoretical foundation for achieving reliable connections in new energy vehicles (NEVs) systems.

Improving the wear and corrosion resistance of the laser cladded coating on the laminar cooling rolls is essential for ensuring the stability and reliability of steel strip production in industrial processes. Fe-Cr-Ni-Mo-B coatings were fabricated by laser cladding (LC) using water-atomized (WA) and water-gas combined atomization (WGA) powders. The influence of powder state on the microstructure of the LC coating is discussed, thereby elucidating the mechanisms by which the microstructure affects the mechanical properties and corrosion resistance. The results show that both LC coatings are composed of BCC iron, FCC iron, and carbon-boron compounds. The irregular WA powder absorbs more laser energy, forming a hotter melt pool that enhances solute dissolution and reduces hypoeutectic structures. In contrast, the spherical WGA powder yields a stable melt pool and a continuous hypoeutectic skeleton structure. The carbon-boron compounds within the eutectic structure enhance wear resistance by pinning the grain boundaries and impeding dislocation motion. The average coefficient of friction (COF) and wear scar area of the WGA LC coatings at 600 degrees C decrease to 0.3474 mu and 0.0132 mm2, respectively, corresponding to reductions of 11.7 % and 40 % compared to the WA LC coating. However, the formation of carbon-boron compounds also consumes Cr elements in the matrix, resulting in a lower corrosion potential for the WGA LC coating (0.47 V) compared with the WA LC coating (0.7 V). Its passive film is more prone to rupture, thereby diminishing corrosion resistance.

Electropulsing treatment (EPT) has been proven to effectively tailor microstructures and improve mechanical properties of titanium alloys within an extremely short time. In this study, the role of EPT in governing martensite decomposition and ductility improvement was systematically investigated in laser powder bed fusion fabricated Ti-0.3Mo-0.8Ni alloy across a pulsed-current density range of 316.7-389.1 A/mm(2). Results demonstrate that the as-built alloy is dominated by acicular metastable alpha' martensite with a high-density dislocation, contributing to high strength but restricting ductility (similar to 14.43%) and resulting in a mixed ductile-brittle fracture. In EPT-processed specimens, alpha ' martensite progressively decomposes into alpha-laths, accompanied by markedly reduced dislocation density with increasing pulsed-current density, thus enhancing ductility and work-hardening capability at the expense of strength. Only limited martensite decomposition was observed in the specimens treated at lower current densities of 316.7 and 331.7 A/mm(2), and a mixed ductile-brittle fracture mode was persisted. The specimens treated at 359 and 367.5 A/mm(2) exhibited near-complete to complete decomposition of alpha ' martensite, accompanied by the formation of basketweave structures consisting of alpha-laths and beta films, as well as the transformation of tangled dislocations into networks, which allow the specimens to achieve a peak elongation of approximately 23% and a fully ductile fracture. However, the formation of Widmanst & auml;tten and grain boundary alpha phases reduced elongation and restored a mixed ductile-brittle fracture in the specimen processed at current density of 389.1 A/mm(2). Finally, heterogeneous alpha-lath fragmentation was observed, primarily driven by polygonization, thermal grooving and transverse fragmentation mechanisms.

The enhancement of the hardness and tribological properties of ball valve surface coatings is imperative for stability and reliability of reusable engines. In this study, Inconel 718 coatings were deposited on SUS 304 substrates using high-velocity oxygen fuel (HVOF) spraying. The effects of direct single aging treatments on the microstructure, mechanical and tribological properties of the HVOF-sprayed Inconel 718 coatings were systematically investigated, revealing the intrinsic relationships between aging temperature, microstructural evolution and performance. The results indicate that the porosity, grain size, oxidation degree and residual compressive stress levels of the coatings subjected to direct single aging treatments (SA600-720) increase with temperature, while the dislocation strengthening effect exhibits a negative correlation with it. Within the range of 600 degrees C to 660 degrees C, the gamma' phase is identified as the primary precipitate, undergoing significant coarsening and redissolution between 640 degrees C and 660 degrees C. From 680 degrees C to 720 degrees C, the gamma" phase becomes the dominant precipitate, with its quantity and size increasing markedly with the aging temperature. The mechanical and tribological properties of the SA700 coating are optimized due to the synergistic effects of dislocation strengthening, precipitation strengthening, and residual compressive stress. Specifically, it achieves a microhardness of 694.9 HV0.1, representing an increase of 25.4 % and 29.2 % over the coatings of as-sprayed (ASC) and solution with double aging treatments (SDA). Moreover, the average friction coefficient, wear mass and wear volume of the SA700 coating are reduced to 0.4125 mu, 0.54 mg, and 0.0066 mm3, respectively, representing decreases of 17.2 %, 45.7 %, and 47.6 % compared to the ASC coating. This study demonstrates that direct single aging treatments effectively enhance the mechanical and tribological properties of HVOF-sprayed Inconel 718 coatings.

This study investigates the influence of pre-weld heat treatment (PWHT) temperatures (250 ~ 400 ℃) on laser metal deposition (LMD) welding of laser powder bed fusion (L-PBF) AlSi10Mg alloys using novel AlSi10Mg-Er-Zr filler powders, with particular emphasis on porosity characteristics, mechanical performance, and microstructural evolution of the welded joints. Results show that elevated PWHT temperatures effectively mitigated hydrogen porosity, reducing both pore density and maximum diameter. The synergistic combination of low PWHT temperatures at 250 ~ 280 ℃ using AlSi10Mg-Er-Zr filler powder demonstrated superior mechanical enhancement, achieving 4.3 ~ 7.2% improvement in ultimate tensile strength (UTS) and 3.8 ~ 94.6% increase in elongation at fracture (EF) compared to the conventional AlSi10Mg filler powder. Welded joints produced using AlSi10Mg-Er-Zr filler powder at 280 ℃ PWHT yielded the optimal mechanical performance, achieving a remarkable balance between strength and ductility with an UTS of 259.0 MPa and EF reaching 10.9%. The synergistic combination of AlSi10Mg-Er-Zr filler powder and PWHT not only enhanced microstructure improvement through substantial grain refinement, increased proportions of high-angle grain boundaries (HAGBs), Σ3 grain boundaries, and hard-oriented grains, but also reduced hydrogen porosity in the welds, collectively contributing to the superior mechanical performance of L-PBF AlSi10Mg welded joints.

Vanadium (V) interlayers of 0.4 mm, 0.8 mm, and 1.2 mm thickness were firstly deposited on the TC4 alloy side using a laser metal deposition (LMD) process, which was then combined with a CuCrZr plate as a composite intermediate layer, for dissimilar laser welding of TC4 titanium alloys to 304 stainless steels (SS) successfully. The effects of different thicknesses of V interlayers on the weld shape, microstructure and mechanical properties of TC4/304SS joints were investigated. The results show that a sound TC4/304SS butt joint with full penetration is successfully obtained using the prepared composite interlayer. The TC4/304SS joint exhibits a maximum ultimate tensile strength (UTS) of 418 MPa and an elongation index (EI) of 15 % with a V layer thickness of 1.2 mm. With the V-layer thickness increasing, the size and content of the V-Cu solid solution in the fusion zone (FZ) on the TC4 alloy side are gradually increased without the formation of intermetallic compounds (IMCs) generated.

High susceptibility to hydrogen porosity is frequently observed in weld metal (WM) during fusion welding of laser powder bed fusion (L-PBF) AlSi10Mg alloys. In this work, hydrogen porosity in L-PBF AlSi10Mg alloy welded joints were reduced using vacuum pre-weld heat treatment (HT: 300-500 °C) and Er/Zr-modified filler powder during laser metal deposition (LMD) welding. The results indicate that higher HT temperatures more effectively decrease WM porosity. While the HT minimally affects WM microstructure, it fragments eutectic Si networks in the base material (BM) and reduces Si solid solubility in the Al matrix. Er/Zr addition also reduces porosity, promotes densification of eutectic Si networks, refines α-Al cells, and increases Si solubility. The WM with Er/Zr addition consistently exhibits superior hardness compared to those without Er/Zr addition. Pre-weld HT (300-500 °C) reduces the ultimate tensile strength (UTS) of joints but significantly increases elongation (EI) at fracture. The welded joint with 300 °C HT and Er/Zr-modified filler achieve optimal strength-ductility balance. Er/Zr addition crucially modifiesd the WM microstructure and reduces porosity, thereby enhancing UTS. The combined approach of HT and Er/Zr filler effectively mitigates porosity and improves joint properties.

In this study, vacuum arc melting was employed to investigate the effect of different Cu content on microstructural evolution, mechanical properties, and fracture behavior of Cu–Fe alloys, revealing the underlying correlation between composition-structure-properties-fracture behavior. The results of this study show that as the Cu content increases, the alloy’s microstructure sequentially experiences three stages: solid solution, precipitation of a Cu-rich network through spinodal decomposition, and liquid phase separation forming Fe–rich dendrites. In the low Cu content range, solid solution strengthening causes the tensile strength to reach a peak of 1042 MPa, but the precipitation of the Cu-rich network leads to stress concentration, thereby promoting intergranular brittle fracture, and the strength decreases significantly to 429 MPa. At medium Cu content, the Fe–rich dendrites formed by liquid phase separation slightly increase the strength through Orowan strengthening, but the increase in dendrite size and reduced interface bond strength intensify the tendency for brittle fracture. At high Cu content, as the Cu content increases, the Fe–rich dendrites reduce in size and become more unevenly distributed. During tensile deformation, cracks initiate in the Cu-rich regions. When these cracks reach the Fe–rich dendrites, crack deflection occurs, promoting further crack initiation and propagation within the Cu-rich regions. The fracture mechanism shifts to ductile fracture, resulting in a significant increase in elongation.

Ti6Al4V alloys fabricated via Laser Powder Bed Fusion (LPBF) exhibit excellent mechanical properties, rendering them highly desirable for advanced engineering applications. However, the relatively limited build size of LPBF components constrains their use in large-scale parts. To address this limitation, the joining of LPBF-fabricated Ti6Al4V alloys using welding technique has emerged as a viable strategy for manufacturing large-scale components. However, the ductility of the welded LPBF Ti6Al4V is significantly reduced after welding as reported in the literature. In this study, a Laser Metal Deposition (LMD) process was employed to weld of LPBF Ti6Al4V alloys, with particular focus on improving the ductility in the welded joints. The microstructure of the WM in the as-welded joint contained continuous grain boundaries alpha (alpha GB) and coarse Widmanstatten grain boundary alpha (alpha WGB) with inhomogeneously sized alpha martensite, which resulted in a deficiency of ductility. To further enhance ductility, a post-weld annealing heat treatment was conducted at a temperature slightly below the beta-transus temperature. This treatment facilitated a transformation of the WM microstructure into a mixture of lamellar and globular alpha phases with an intergranularly dispersed beta phase. During heat treatment, the nucleation mechanism of alpha WGB shifted from induced nucleation to interface instability nucleation. Consequently, the fracture location transitioned from weak interfaces between alpha GB and alpha WGB in the as-welded condition to the alpha + beta basket-weave structures within the beta-Ti columnar grains of the WM. Compared to the as-welded joints, the heat-treated joints exhibited a 10 % reduction in Ultimate Tensile Strength (UTS) but demonstrated a remarkable 110 % increase in Elongation Index (EI), achieving a better strength-ductility balance.

Two different thicknesses of CuCrZr plates combined with laser deposited V layer were designed as a composite intermediate layer to laser welding of TC4 alloy to 304 stainless steel (SS). The effect of different thicknesses of CuCrZr plates on microstructure and mechanical properties of Ti/steel welded joint was investigated. The results show that a sound Ti/steel joint with full penetration has been successfully achieved using the prepared composite interlayer. When the thickness of CuCrZr plates was increased to 1 mm from 0.5 mm, an unmelted CuCrZr zone was observed, which hindered the diffusion of Fe and V elements. A small amount of clustered FeV intermetallic compounds (IMCs) were found in fusion zone (FZ) with 0.5-mm-thick CuCrZr plates; however, no sign of IMCs formation was observed in FZs using 1-mm-thick CuCrZr plates. Compared to 0.5-mm-thick CuCrZr plates, the application of 1-mm-thick CuCrZr plates resulted in a more uniform hardness distribution of the FZs, as well as stronger ultimate tensile strength (415 MPa) and elongation (5.2

In the present study, cold metal transfer welding is conducted to join laser powder bed fusion (L‐PBF) AlSi10Mg alloys with conventional Al–Mg alloys and Er and Zr modified Al–Mg (Al–Mg–Er–Zr) alloys, respectively. The porosity, microstructural evolution, and mechanical properties of dissimilar AlSi10Mg/Al–Mg and AlSi10Mg/Al–Mg–Er–Zr joints are investigated. The results show that the AlSi10Mg/Al–Mg–Er–Zr joint exhibits reduced porosity in the weld metal (WM), decreasing from 2.4% to 2.1%, compared to the AlSi10Mg/Al–Mg joint. The AlSi10Mg/Al–Mg–Er–Zr joint exhibits significant microstructural improvements in the WM, including grain refinement, a lower Schmid factor, and a higher geometrically necessary dislocation density. The ultimate tensile strength (UTS) values of the AlSi10Mg/Al–Mg and AlSi10Mg/Al–Mg–Er–Zr joints are 187.6 and 203.3 MPa, respectively. This demonstrates that the AlSi10Mg/Al–Mg–Er–Zr joint achieves a significantly higher UTS, which can be primarily attributed to the reduced porosity, grain refinement, and enhanced solid solution strengthening in the WM.