Maraging stainless steel (MSS) is widely employed in aerospace and pressure vessels due to its high strength, high toughness and good corrosion resistance. Microstructure design and combined deoxidation are important strategies for developing high-performance alloy steel. However, the evolution behavior and characteristics of non-metallic inclusions and their effects on the mechanical properties of additively manufactured MSS have not been conclusive for a long time. This work investigated the microstructure, inclusion characteristics, and mechanical properties of laser-directed energy deposited (LDED-ed) MSS from three kinds of raw materials with different deoxidizer contents. The results indicated that the microstructure of As-deposited (AD) MSS specimens primarily consisted of martensite with a minor fraction of retained austenite. After heat treatment (HT), the MSS specimens became fine and equiaxed grains with fine martensite packets/blocks, some reverted austenite, and dispersive Fe2Mo nano-size particles. The HT MSS specimens exhibited an increased strength to 1200 MPa, primarily due to the synergistic effects of Hall–Petch strengthening and precipitation strengthening. The inclusions in the AD MSS specimen were oxides, while those in the HT MSS specimen were composite inclusions, which consisted of oxide, TiN, and MnS. After heat treatment, a slight coarsening of the inclusions was observed; however, their number density remained constant. Compared to the HT counterpart specimen (MSS-I), both the HT MSS-LZr specimen with Zr content of 0.003 wt pct and the HT MSS-HZr specimen with Zr content of 0.026 wt pct by Ti–Al–Zr combined deoxidation had a higher impact toughness, due to the reduced amount of inclusions. The findings elucidate the critical role of combined deoxidation and heat treatment in tailoring microstructure and enhancing the mechanical properties of LDED-ed MSS.

As the primary alloying element in Mg-Al-Zn alloys, aluminum (Al) exerts a crucial influence on their heat treatment behavior and mechanical properties. However, different wire arc additive manufacturing (WAAM) processes lead to significant variations in the as-deposited microstructures of the alloys, making it difficult to clarify the effect of Al content on the microstructure and properties of heat-treated WAAM Mg-Al-Zn alloys from existing studies. In this study, Mg-xAl-Zn (x = 6, 9, 12) alloys were fabricated under unified WAAM process parameters, and the effect of Al content on the heat treatment response, aging precipitation behavior and mechanical properties of the alloys was systematically investigated. The results show that WAAM Mg-6Al-Zn and Mg-9Al-Zn alloys achieve nearly complete dissolution of Mg17Al12 phases after short-time solution heat treatment at 380 °C/2 h and 400 °C/2 h, respectively; whereas residual Mg17Al12 phases remain in the Mg-12Al-Zn alloy even under its optimal solution condition of 420 °C/2 h. The microhardness of the peak-aged alloys increases significantly with increasing Al content and increases with decreasing aging temperature, while the peak aging time is significantly prolonged. Moreover, the peak aging time of WAAM alloys is much shorter than that of as-cast alloys of similar compositions. With increasing Al content, the area fraction of discontinuous precipitation (DP) regions in peak-aged alloys increases significantly from 17.4% to 90.3%, and the average width and spacing of both DP and continuous precipitation (CP) phases are refined. Consequently, the yield strength of the alloys increases markedly while the elongation decreases substantially with increasing Al content, and the ultimate tensile strength presents a trend of first increasing and then decreasing. Hence, the WAAM Mg-9Al-Zn alloy exhibits an optimal balance of ultimate tensile strength (310.2 ± 5.4 MPa) and elongation (5.6 ± 0.8%), showing great potential as a promising candidate material for low-cost and high-performance magnesium alloy components fabricated by WAAM.

Aluminum (Al) acts as the primary alloying element in Mg-Al-Zn alloys, so its content is of crucial importance for the samples fabricated by wire arc additive manufacturing (WAAM). However, microstructure and property fluctuations of the alloys induced by varying WAAM processes hinder the extracting of consistent Al content-microstructure-property relationships from existing studies. In this study, Mg-xAl-Zn (x = 3, 6, 9, 12) alloys were fabricated via WAAM using consistent process parameters to focus on the influence of Al content alone. The results indicate that all of the four alloys primarily consist of α-Mg grains and Mg17Al12 phase. As Al content increases, the α-Mg grain size decreases from 43.1 μm in Mg-3Al-Zn to 19.7 μm in Mg-12Al-Zn. The content of Mg17Al12 phase increases from near 0% in Mg-3Al-Zn to 7.78% in Mg-12Al-Zn, and a sudden increase observed when Al content reached 12 wt%. The microhardness and yield strength of WAAM Mg-xAl-Zn alloys increase linearly with the increasing of Al content, which is attributed to the synergistic effects of grain refinement strengthening, solid solution strengthening, and second-phase strengthening induced by Al content. However, when the Al content reaches 9 wt%, the elongation and tensile strength decreased because of the excessive Mg17Al12 phase. Among the investigated alloys, Mg-6Al-Zn achieves the optimal strength-ductility balance, with a tensile strength of 266.3 ± 0.4 MPa and an elongation of 13.9 ± 1.4%. Thus, alloys with an Al content of approximately 6 wt% exhibit favorable performance and can be used without heat treatment, while those with Al content exceeding 9 wt% require heat treatment to optimize microstructure and improve ductility.

The long-term success of dental implants is often compromised by bacterial infection and inadequate osseointegration. Conventional surface modifications typically address these issues separately, lacking synergy and long-term stability. Here, we present a full-laser-enabled strategy that combines laser polishing technology and femtosecond laser-induced periodic surface structures (LIPSS), followed by spatially guided silver nanoparticle (AgNP) deposition on 3D-printed titanium. The novelty of current integrated process mainly lies in hierarchical topography regulation and programmable antibacterial ion delivery in a single clean platform. The hierarchical structures guide fibroblast and osteoblast alignment, enhancing cell adhesion and osteogenic differentiation, while also mechanically stretching bacterial membranes to facilitate Ag+ entry. Critically, the hierarchical geometry modulates Ag+ release kinetics, preventing burst release and enabling sustained antibacterial action. In vitro experiments have showed a 74.4% reduction in Porphyromonas gingivalis biofilm formation, a 300% increase in effective Ag+ release duration for ensuring sustained antibacterial efficacy and a 37.6% increase in gingival fibroblast proliferation, while in vivo animal experiments were conducted using Beagle dogs and have confirmed both the reduction of peri-implant inflammation and the enhancement of osseointegration as evidenced by a 38.7% increase in bone-implant contact ratio. This pioneering work unveils a scalable and synergistically optimized methodology for additive manufacturing of next-generation bioactive implants, enabling patient-specific customization of biomechanics and bioactivity.

Laser powder bed fusion offers unprecedented geometric freedom for advanced aerospace transmission systems, but the reliable additive manufacturing of highly alloyed secondary-hardening gear steels is fundamentally challenged by complex non-equilibrium solidification dynamics and the classical strength-ductility trade-off. Accordingly, this study elucidates the non-equilibrium microstructural evolution and the underlying mechanical mechanisms of 16Cr3NiWMoVNbE aviation gear steel fabricated via laser powder bed fusion. Distinct from the conventional coarsened tempered sorbite of wrought counterparts, the as-deposited alloy develops a multi-scale hierarchical architecture featuring ultrafine epitaxial martensitic laths and a highly dense dislocation network. The intrinsic layer-wise thermal cycling functions as a dynamic in-situ self-tempering treatment, which provides the thermodynamic driving force for short-range carbon partitioning. This process not only chemically stabilizes continuous nano-films of retained austenite at lath boundaries but also triggers the dispersive precipitation of nanoscale cementite. Concurrently, in-situ X-ray diffraction confirms that the excellent ductility is sustained by the continuous transformation-induced plasticity effect of the metastable retained austenite films, which effectively relaxes local stress concentrations and provides sustained work-hardening capacity. The as-deposited steel exhibits a quasi-isotropic strength-ductility synergy, successfully overcoming the traditional trade-off dilemma. To rationalize this performance advantage, a Root-Sum-Square superposition model was employed to quantitatively deconstruct the strengthening contributions. The theoretical predictions exhibit exceptional agreement with experimental measurements, revealing that the ultra-high strength is synergistically governed by formidable grain boundary refinement and substantial dislocation hardening, coupled with precipitation and solid solution effects.

Selective laser melted Al-Mn-Sc alloys have attracted considerable attention as heat-resistant aluminum alloys for additive manufacturing due to their outstanding room-temperature strength and good high-temperature microstructural stability. However, most reported Al-Mn-Sc alloys rely on Mg addition for solid-solution strengthening, which, due to the high diffusivity of Mg, results in relatively low high-temperature strength and thus limits their application at elevated temperatures. Consequently, a Mg-free, Nd-modified AlMn5Sc0.7 alloy was designed and the effects of aging treatment on microhardness, microstructure, and tensile properties were investigated. The results demonstrate that the optimal aging condition for the alloy is 325 °C for 9 h, which represents a peak microhardness of 173 Hv0.05, representing a 44% improvement over the as-built condition. Aging treatment not only increases the volume fraction of primary phases but also induces the precipitation of secondary Al3Sc phases, characterized by a volume fraction of approximately 1.3% and an average size of about 1.5 nm. After heat treatment, the room-temperature ultimate tensile strength and yield strength of the alloy improve from 350 MPa and 310 MPa to 500 MPa and 470 MPa, respectively, primarily due to the modulus strengthening effect of the secondary Al3Sc. Meanwhile, at 250 °C and a strain rate of 8.3×10-5 s-1, the heat-treated alloy retains a high yield strength of 244 MPa. This excellent high-temperature strength arises mainly from the superior thermal stability of the primary and secondary phases, coupled with their effective pinning of grain boundaries and dislocations.

The deformation characteristics and activation mechanisms of kink bands in refractory multi-principal element alloys with local chemical fluctuations (LCFs) were systematically studied. These alloys were fabricated using laser-directed energy deposition technology and characterized by room-temperature compression testing, electron backscatter diffraction (EBSD), transmission electron microscopy (TEM), and high-angle annular dark-field (HAADF) imaging. The results reveal that kinking is a gradual rotational diffusion process, during which the misorientation difference between the kink and the matrix varies. A low Schmid factor is a prerequisite for kink excitation. The slip system closest to the loading axis is passively activated by the applied external force, leading to the accumulation of geometrically necessary dislocations (GNDs) required for lattice rotation. The widespread LCFs within the matrix reduce the migration rate of edge dislocations, promoting GND accumulation and enhancing the propensity for kink band formation. During deformation, the occurrence of kinking enables continuous lattice rotation to accommodate the exceptionally high strain in the vicinity, when the stress concentration in the primary kink cannot be fully released, double kinks are activated to reduce strain energy.

Increasing layer thickness is an effective strategy to improve fabrication efficiency of laser powder bed fusion (LPBF). In this study, effects of layer thickness (40 and 80 μm) on microstructure, crack, and mechanical properties of LPBF-GH3230 are investigated. Increasing layer thickness leads to a deeper molten pool and unique solidification conditions, promoting a columnar-to-equiaxed transition and localized clusters of fine equiaxed grains. Less constrained grain growth condition under high layer thickness introduces a higher fraction of high-angle grain boundaries, thereby increasing microcrack susceptibility. Although a high relative density (∼99.17%) is achieved, microcracks remain unavoidable. Hot isostatic pressing (HIP) was employed to eliminate microcracks. Crack healing behavior involves synergistic effects of diffusion, carbide evolution, and local stress-driven plasticity, including carbide misalignment, matrix extrusion, and carbide embedding mechanisms, resulting in serrated grain boundaries and abnormal carbide segregation. Interdendritic worm-like M23C6 transforms into intragranular block-like M6C. Low lattice misfit between M6C and γ promotes coherent or semi-coherent precipitation along dislocation cells and grain boundaries. Although 80 μm specimens achieve comparable room-temperature tensile properties to 40 μm, high-temperature ductility, particularly for horizontal specimens, is significantly reduced, which is attributed to reduced intergranular deformation compatibility. This work provides insights into high-efficiency LPBF and microstructure-defect-property control in superalloys.

The GH3230 alloy is a solid-solution strengthened nickel-based superalloy that finds important application in the nuclear power sector, owing to its superior high-temperature strength and corrosion resistance. However, given the limitations in service conditions and cost, a low-cobalt version of the GH3230 superalloy (with Co reduced to 0.034 wt%) was fabricated by laser powder bed fusion (LPBF) to minimize the formation of the long-lived radioactive isotope Co60 under neutron irradiation. Post-processing treatments, including hot isostatic pressing (HIP) and solution treatment (ST), were employed to mitigate the intrinsic defects from the LPBF process and enhance mechanical properties. The results indicate that the post-treatment effectively eliminates the melt pool morphology and predominantly promotes the formation of M6C carbides. The resulting alloy achieves excellent high-temperature performance: creep life at 850 degrees C/78 MPa exceeds 800 h, while at 850 degrees C it retains a tensile strength of similar to 359 MPa and elongation of similar to 86%, which are comparable to those of the conventional high-cobalt counterpart (differences within +/- 5%). This work demonstrates the feasibility of developing high-performance, low-activation nuclear components via the LPBF process.

A novel approach based on in-situ alloying via laser powder bed fusion (LPBF) provides a new idea for design and fabrication of crack-free superalloys with high gamma ' content. This study investigates effect of in-situ alloying and specifically designed heat treatment on microstructure morphology, crack control, and mechanical properties, demonstrating their advantages in crack inhibition and performance enhancement. By mixing mature crack-free superalloy powders (IN718) as matrix and single-crystal superalloy powders (DD6), containing a high content of high-temperature strengthening elements such as Al, Ta, and W, at a mass ratio of 4:1, crack-free AMS14 alloy was successfully prepared. Swirl-like micrometer-scale concentration modulations (microCMs) rich in high-temperature strengthening elements with a thickness of only similar to 5 mu m are introduced in as-built state. Crack inhibition is achieved through matrix element liquid feeding and dispersion of thermal tensile stress by matrix region with high plasticity. Specially designed heat treatment enables release of high-temperature strengthening elements in microCMs and sufficient precipitation of strengthening phases, resulting in a multi-level strengthened microstructure with a relatively high content of gamma ' precipitates, and achieving excellent comprehensive mechanical properties at elevated temperature. Ultimate tensile strength at 650 degrees C reaches 1252.77 +/- 22.31 MPa, while elongation reaches 13.82 +/- 0.89 %. Design concept in this study, which combines in-situ alloying for crack inhibition and heat treatment for release of high-temperature strengthening elements, provides a new approach for designing new high-performance superalloys for additive manufacturing.

The notch, such as hole and chamfer, is unavoidable for aircraft structural components. Stress concentration induced by notch is the leading cause of fatigue failure. It is significant for structural integrity and safety assessment to clarify the intrinsic mechanism causing the difference in fatigue notch sensitivity. The notch fatigue fracture behavior of TC11 samples, fabricated by laser direct energy deposited (LDED) and wrought processes, is studied by high cycle fatigue (HCF) tests, fracture morphology, systematic microstructural characterizations, and theoretical analysis. HCF test results show that the notch fatigue performance of LDED samples reported in this study is superior to that of the wrought ones. The modified critical radius calculated from the equivalent material concept and average strain energy density criterion correlates well with fatigue notch sensitivity q and notch fatigue performance. The thick lamellar alpha phase produces more crack resistance and higher local plasticity around the notch root, causing lower q of LDED samples. Besides, the difference in q caused by build orientations is attributed to the variations in the angle between the c-axis of the fiber texture and load direction, the dominant slip system, the boundaries between soft and hard grains, and the presence of prior beta grain boundaries.

During the deformation of body-centered cubic (BCC) structured lightweight refractory high-entropy alloys (LRHEAs), strain localization caused by a low strain-hardening rate (SHR) induces premature alloy necking, resulting in poor uniform tensile ductility (UTD) and restricts their processability and applicability. In this study, we improved the SHR of the alloys from negative to 1.5 GPa by tailoring multi-scale heterostructures, including the microscopic bimodal grain distribution, submicron spherical C14 Laves phase, nanoscale local chemical fluctuations (LCFs), and atomic clusters less than 1nm. The strength of the alloy was raised by 13.8%, and the UTD increased by 710% compared with the initial homogenized sample, and overall performance was superior to most LRHEAs. Bimodal grain interfaces can effectively coordinate the strain distribution between the two during deformation, accelerating the generation and storage of geometrically necessary dislocations (GNDs), and the back stress accumulates and increases with strain, stabilizing the hardening ability. Meanwhile, the meticulously dispersed C14 Laves phase plays a role in precipitation strengthening without compromising plasticity. The matrix's LCFs and Al-Zr atomic clusters can further regulate the morphology and distribution of statistically stored dislocations (SSDs). On the one hand, they could effectively pin dislocations and cause them to bend, increasing the migration resistance of SSDs; on the other hand, dislocation tangles resulting from microbands blocking and the interaction of multi-slip systems activate new dislocation sources, which lead to the rapid expansion of secondary microbands in a reticular manner. Those significantly increase the synchronous dislocation multiplication rate and dynamic dislocation density during plastic deformation, maintaining high and sustained SHR of alloys. Therefore, the SHR of LRHEA can be effectively improved by introducing multi-scale heterogeneous structures to optimize the coordination of GND and SSD density and distribution, thus achieving an excellent match between strength and UTD.

Despite their extremely low concentrations in nickel-based superalloys, trace elements have a considerable impact on the microstructure and mechanical properties of these materials. According to the properties of the trace elements, the elements B and Zr are chosen to be introduced into the K4XX superalloy matrix. This paper focuses on the effect of trace alloying elements B and Zr on the transformation of metal carbides morphology, microstructure evolution and mechanical properties during the solidification process. With the addition of 0.004 wt% B and 0.006 wt% Zr in the superalloy matrix, the ultimate tensile strength (UTS) of BK4XX and BZrK4XX is about 1069 MPa and 1078 MPa, which is a 4.2 % and 5.1 % improvement compared to K4XX(1026 MPa). Similarly, the elongation of BK4XX and BZrK4XX is about 10.0 % and 10.6 %, which is also 34.1 % and 41.3 % improvement compared to K4XX(7.5 %). And the morphology of precipitated phase metal carbides also appears to be transformed with the addition of trace elements. The participation of B and Zr elements in the second phase precipitation provides a strengthening effect. This work provides experimental support for the effective control of trace element content in the as-cast nickel-based superalloys, which is helpful to improve the metallurgical quality of the as-cast nickel-based superalloys.

Cryogenic thermal cycling (CTC), a pivotal heat treatment technology for metallic materials, holds promising potential for application in additive manufacturing alloys to improve mechanical properties and reduce residual stress. In this study, the microstructural evolution of selective laser melted AlSi10Mg alloy during CTC treatments, which were conducted at temperatures of -160 degrees C and 160 degrees C sequentially, was investigated. Meanwhile, the mechanical properties and residual stress in both the as-built and CTC-treated specimens were also evaluated using microhardness, tensile, and Raman spectroscopy testing. Results indicate that CTC treatment does not have significantly impact on the morphologies of melt pools and eutectic Si networks. However, it does promote the precipitation of Si phases and the formation of atomic clusters in alloy. Realizing a 3 %-8 % enhancement in the microhardness of alloy along with increases of 4 % and 13 % in ultimate tensile strength and yield strength, respectively. Furthermore, a substantial reduction of 71 % in residual stress is obtained in comparison to the as-built condition. With an increase in the number of CTC cycles, the quantity of precipitates increases notably, and the enhancement of mechanical properties intensifies. However, no marked variation is detected in the residual stress levels.

Due to high flexibility, non-mold short working cycle, free-from parts structure, and material constraints, laser additive manufacturing (LAM) has been applied to compose nanoparticle-reinforced metal matrix composites. In this work, cost-effective combined with high-performance 3D network graphene nanosheet (GNS) with TiC particles-reinforced Ti-6Al-4V (TC4) composites were conveniently prepared via the LAM process, leveraging the in situ Ti + C -> TiC chemical reaction. This preparation method facilitated the formation of a highly uniform reinforcement phase network (GNS-TiC/Ti) distributed within the Ti-6Al-4V alpha/beta matrix. The size of the GNS-TC4 grain decreased synchronously as the addition of GNS increased, primarily caused by the in situ TiC nanoparticles pinning effect along grain boundaries, which plays a limiting role in the process of grain growth. Mechanical result indicated that the incorporation of 1 wt% GNS resulted in 1.56 % increase in microhardness and 29.7 % increase in yield strength compared to the direct addition of TiC-reinforced TC4. The analysis of the alloy structure at the subsurface of the fracture revealed the uniform distribution of the situ-generated TiC particles in the alloy matrix, and no defects of the pores were observed around the particle. The reinforced strength of the GNS-TC4 is attributable primarily to shear-lag strengthening and thermal mismatch strengthening mechanism. This work furnishes new thoughts into the preparation of balanced-performance titanium matrix composites when combined with laser additive manufacturing technology.

Objective Additive manufacturing of Cu/Ni dissimilar metals, integrating high- thermal conductivity, high strength, high reliability, and low cost, is one of the best choices for the generation of liquid rocket engines, capable of achieving material- structure- function engine integration. Currently, the main challenges faced in the preparation of GH4169 using laser- directed energy deposition (LDED) technology on CuCrZr substrates are the high- laser reflectivity and thermal conductivity of copper alloys, as well as the considerable differences in the physical properties of the two alloys, making it difficult to achieve defect- free metallurgical bonding. Stable process manufacturing and control of microstructural properties are also challenges. Herein, we use surface pretreatment processes followed by additive manufacturing to solve the problems of high reflectivity of Cu alloys and interface metallurgical defects and prepare CuCrZr/GH4169 dissimilar metals. Methods This study utilizes five processes, namely thermal spraying, cold spraying, electroplating, physical vapor deposition (PVD), and powder spreading, for surface pretreatment of the CuCrZr alloy. On the pretreated surfaces of the CuCrZr substrates, three processes are employed for single-track cladding experiments; Process 1: laser power set at 4.5 kW, and scanning speed set to 1000 mm/min, without powder feeding; Process 2: laser power set at 4.0 kW, scanning speed set at 1000 mm/min, and a powder feeding rate of 35 g/min, and Process 3: laser power set at 4.5 kW, scanning speed set at 1000 mm/min, and powder feeding rate of 40 g/min. The optimal process is selected for overall additive manufacturing of CuCrZr/GH4169 alloy. Microstructural observations are conducted on the interface of single-track cladding specimens (perpendicular to the laser scanning direction) and the interface of overall dissimilar metals specimens. Ultrasonic nondestructive testing and tensile performance testing are performed on the dissimilar metals specimens. Results and Discussions 1) Single-track cladding deposition GH4169 experiments are conducted on CuCrZr substrates using different surface pretreatments. The results for thermal spraying (Fig. 6) and cold spraying (Fig. 7) samples are excellent . The thermal spraying samples formed a stable melt pool without microcracks, pores, or local unmelted areas at the interface. In the cold spraying samples, local unmelted areas appeared at the edges of the melt pool when the coating thickness increased to 150 mu m. However, the electroplating (Fig. 8) and PVD (Fig. 8) samples did not produce stable melt pools, and there were obvious microcracks and local unmelted areas between the coating and the weld track. The coating prepared by powder spreading process (Fig. 8) showed many unmelted adhesive powders around the weld track, poor continuity of the weld track, unstable melt pool fusion line, and small penetration depth. The thermal spraying experiment yielded the best results. By comparing the main parameters of single-track cladding, the optimal process was selected: thermal spraying was used to deposite the GH4169 alloy coating with 100 mu m thickness on CuCrZr substrate, Process 1 was used to remelt the first layer, followed by Process 2 for deposition. 2) The prepared samples exhibited good bonding characteristics between the two materials. Nondestructive testing results did not reveal major defects (Fig. 10). The interface area of the samples along the deposition direction from the bottom to the top parts can be divided into five regions: CuCrZr substrate, columnar crystal, diffusion, Cu element diffusion, and GH4169 regions (Fig. 11). The tensile strength of the laser- directed deposited CuCrZr/GH4169 dissimilar metals along the deposition direction was 280 MPa +/- 4.24 MPa, with the fracture occurring at the interface, slightly toward the copper alloy side, indicating a ductile fracture. Conclusions This study primarily investigates the impact of surface modification on the laser reflectivity of copper alloys. Various surface modification processes, including thermal spraying, cold spraying, electroplating, PVD, and powder spreading, were used to prepare nickel- based alloy coatings with different compositions and thicknesses on copper alloy surfaces. After determining the optimal preparation process, coating composition, and thickness, the overall material deposition process was explored. The main conclusions are as follows: 1) The results of the single-track cladding experiments showed that the thermal spraying is the preferred pre-treatment process to achieve defect- free bonding between the CuCrZr alloy and the GH4169 nickel- based high- temperature alloy with a stable melt pool. The GH4169 alloy coating prepared by cold spraying was less effective than that prepared by thermal spraying. The interfaces of single-track deposition after surface modification using PVD, electroplating, and powder spreading processes exhibited defects such as local unmelted areas, microcracks, and poor metallurgical quality. 2) The thermal spraying surface modification process on copper substrates can effectively avoid interface defects and forming difficulties under various process conditions, when the surface GH4169 coating thickness reaches 50-150 mu m, resulting in metallurgically bonded interfaces. After comparing the main process parameters using a radar chart, a CuCrZr substrate pretreated with a thermal spray coating (thickness of 100 mu m) was selected. Using Process 1 to remelt the first layer and Process 2 for deposition, samples with dense metallurgical bonding and good appearance were obtained. Nondestructive testing confirmed that internal defects met the GJB 1580A-2004 (Class AA) requirements. 3) The interface region of the prepared CuCrZr/GH4169 dissimilar metals is mainly divided into the CuCrZr alloy substrate, columnar crystal, unmelted powder, Cu element diffusion, and GH4169 alloy zones. The columnar crystal zone is formed by remelting the copper alloy. The unmelted powder zone consists of flaky and spherical particles, mainly from insufficiently melted GH4169 coating and powder. The tensile strength of the CuCrZr/GH4169 dissimilar metals along the deposition direction was 280 MPa +/- 4.24 MPa. The fracture of the tensile samples occurred at the interface, slightly toward the copper alloy side, indicating good bonding at the interface, with the fracture surface confirming ductile fracture.

Selective laser melting (SLM) is an advanced manufacturing technology which can directly produce fully dense near net-shaped components layer by laser from CAD models. In order to improve the building efficiency of the SLM metallic components, a novel building strategy utilizing an ultra-high laser scanning speed (above 4000 mm/s) was developed to fabricate the high-performance Ti6Al4V alloy parts. In this study, the evolution of surface morphology and porosity of Ti6Al4V alloys prepared by SLM under different ultra-high scanning speeds and other process parameters has been systemically investigated. It was found that at high scanning speeds, the defects in the samples primarily consisted of lack of fusion (LoF) defects, with their distribution closely related to the surface structure caused by material build-up. A low porosity level (0.06 %) and well machanical property (sigma UTS = 1134.08 MPa, epsilon = 9.50 %) could still be obtained by adjusting other process parameters, which is mainly due to an increase in the volumetric energy density (VED) reduced the number of LoF defects. Moreover, the amount of LoF defects was not wholly determined by the VED level; the surface morphology also had a significant influence on the porosity of SLM Ti6Al4V samples at a high VED level.

The development of high-temperature titanium alloys for aerospace propulsion systems requires good thermostability and fatigue resistance under high temperature loading conditions. This study comparatively investigated the microstructural characteristics and fatigue performance of Ti-6Al-4Zr-4Mo-2Sn-1W-0.2Si duplex titanium alloys fabricated respectively via laser-directed energy deposition additive manufacturing (AM) and conventional forging technologies. The results revealed that the forged titanium alloy contained fine grains with a heterogeneously duplex structure consisting of large-size near-spherical primary alpha and hard beta(t) phases. By contrast, the AMed titanium alloy contained columnar grains with an interior homogenous basketweave structure containing a few unstable high angle boundaries (HABs) and a high ratio of low angle boundaries (LABs). Although the room-temperature tensile strengths of two types of alloys were similar (similar to 1100 MPa), the AMed titanium alloy suggested superior high temperature mechanical properties with 8 % higher strength retention at 550 degrees C than the forged alloy (882 vs. 811 MPa). With an increase of total strain amplitude (Delta epsilon(t)), the fatigue life of the specimen was prone to decreasing, associated with the declined texture intensity and activity of basal slip system of (0 0 0 1) [1 1 (2) over bar 0]. Under the same Delta epsilon(t) value of 0.6 %, the high temperature fatigue lives of the AMed alloys were 6-7 times longer than the forged counterparts. Fractographic analysis of the fatigue specimens revealed that surface slip cracking accompanied by oxide formation served as the predominant fatigue crack initiation mechanism, followed by striation patterns observed in crack propagation paths. Compared to the forged alloy, the higher fatigue properties of the AMed titanium alloy were mainly attributed to a higher thermostability and optimum microstructure design (fewer HABs and high ratio of LABs) resisting fatigue cracking. These findings offer a guide for the fabrication of next-generation titanium alloys requiring simultaneous hightemperature strength and fatigue resistance in aerospace applications.

Among the refractory high-entropy alloys (RHEAs), the Al-containing RHEAs with the coherent A2/B2 microstructure exhibit terrible room-temperature ductility due to the continuous B2 matrix and the Al-Zr precipitates along grain boundaries (GBs). The present study utilizes mixed powders that have fabricated A2/B2 RHEA with no defects, uniform microstructure, dispersed nanoscale ellipsoidal B2 domains, and smooth GBs by optimizing process parameters and leveraging the intrinsic thermal-cycling of additive manufacturing without expensive Ru element or post-treatments. The alloy's large tensile plasticity is attributed to the diffusion of secondary microbands that effectively address the strain localization caused by the "softening of the slip plane" of primary microbands, and high yield strength is primarily related to solid solution strengthening and B2 strengthening. This work represents a valuable attempt to prepare defect-free, low-cost, and homogeneous A2/B2 RHEAs using laser in-situ alloying technology and provides valuable insights into the deformation behavior of coherent A2/B2 alloys.

Mg-Gd-Y-Zr alloys, with high Gd and Y solubility, demonstrate significant application potential due to effective precipitation strengthening but face challenges from lengthy aging times. Hereby we fabricate a Mg-6Gd-3Y-0.5Zr alloy via laser-directed energy deposition (LDED) technique. Taking the advantages of fine microstructures and supersaturation resulting from rapid solidification, direct aging (T5) can be conducted. T5 achieves peak hardness and tensile strength comparable to conventional solution and aging treatment (T6) yet in half the aging time, attributed to pipe diffusion via dislocations induced by tension-compression cycles during LDED. This study advances efficient heat treatments for LDED-fabricated precipitation-strengthening alloys. [GRAPHICS]