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This article focuses on investigating the effect of printing direction on the mechanical properties of Cu–10Sn alloys prepared by laser powder bed fusion (LPBF) technology. Specimens with different forming angles (0°, 15°, 30°, 45°, 60°, 75°, and 90°) were fabricated using LPBF technology, and their mechanical properties were systematically tested. During the testing process, we used an Instron 5985 electronic universal material testing machine to accurately evaluate the mechanical properties of the material at a constant strain rate of 10−3/s. The experimental results showed that the mechanical properties of the specimens were the best when the test direction was perpendicular to the growth direction (i.e., the 0° direction). As the angle between the test direction and the growth direction increased, the mechanical properties of the material exhibited a trend of first decreasing, then increasing, and then decreasing again, which was consistent with the direction of the microtexture of the specimens. The root cause of this trend lies in the significant change in the stress direction borne by the columnar crystals under different load directions. Specifically, as the load direction gradually transitions from being parallel to the columnar crystals to perpendicular to them, the stress direction of the columnar crystals also shifts from the radial direction to the axial direction. Due to the differences in the number and strength of grain boundaries in different stress directions, this directly leads to changes in mechanical properties. In particular, when the specimen is loaded in the radial direction of the columnar crystals, the grain boundary density is higher, and these grain boundaries provide greater resistance during dislocation migration, thus significantly hindering tensile deformation and enabling the material to exhibit superior tensile properties. Among all the tested angles, the laser powder bed fusion specimen with a forming angle of 0° exhibited the best mechanical properties, with a tensile strength of 723 MPa, a yield strength of 386 MPa, and an elongation of 33%. In contrast, the specimen with a forming angle of 90° performed the worst in terms of tensile properties. These findings provide important insights for us to deeply understand the mechanical properties of Cu–10Sn alloys prepared by LPBF. [ABSTRACT FROM AUTHOR]

Friction stir welding (FSW) was introduced to join laser powder bed fusion (LPBF) AlSi10Mg alloys in this study. Microstructure and texture evolution, microhardness distribution and tensile properties of the FSW joints were investigated. The evolution of grain size, grain boundary and misorientation angles distribution, dynamic recrystallization and crystallographic texture in various regions of the FSW joint concerning base metal (BM), thermo-mechanically affected zone (TMAZ), upper part of nugget zone (UPNZ) and low part of nugget zone (LPNZ) was characterized by using electron back-scattered diffraction (EBSD). The analysis reveals a strong texture evolution of shear components on the TMAZ, UPNZ and LPNZ as well as a fully recrystallized grain structure on the UPNZ and LPNZ. Additionally, a gradual evolution in Si-rich eutectic from continuous cellular networks in the BM to totally globularized particles in the UPNZ and LPNZ occurs in the FSW joint. The microhardness rapidly decreases to the TMAZ from the BM through heat affected zone (HAZ) reaching the lowest value of ∼65.0 HV at the TMAZ/NZ boundary. The FSW joint in LPBF AlSi10Mg alloys exhibits an ultimate tensile strength (UTS) of 247 MPa and an elongation-to-failure (EI) of 8.8%. The UTS of FSW joints is reduced compared to the BM, but the EI has been increased by 160%, implying an improvement in tensile ductility. [Display omitted] • Friction stir welding was introduced to weld laser powder bed fusion AlSi10Mg. • New shear textures of F, R-Goss and R-Cube components are developed in the FSW joint. • LAGBs are increased in the TMAZ, and a high fraction of HAGBs is developed in the NZ. • FSW of LPBF AlSi10Mg results in a gradual evolution of Si-rich phase morphology in the joint. • FSW of LPBF AlSi10Mg produces the highest UTS of 247.0 MPa and the maximum EI of 8.8%. [ABSTRACT FROM AUTHOR]

Titanium-tantalum (Ti-Ta) alloy has excellent biomechanical properties with high strength and low Young's modulus, showing great application potential in the biomedical industry. In this study, Ti-Ta alloy samples were prepared by laser powder bed fusion (LPBF) technology with mixed pure 75 wt.% Ti and 25 wt.% Ta powders as the feedstock. The maximum relative density of Ti-Ta samples prepared by LPBF reached 99.9%. It is well-accepted that four nonequilibrium phases, namely, α′, α″ and metastable β phase exist in Ti-Ta alloys. The structure of α′, α″ and β are hexagonal close-packed (HCP), base-centered orthorhombic (BCO) and body-centered cubic (BCC), respectively. X-ray Diffraction (XRD) analysis showed that the α′ phase transformed to the α″ phase with the increase of energy density. The lamellar α′/α″ phases and the α″ twins were generated in the prior β phase. The microstructure and mechanical properties of the Ti-Ta alloy were optimized with different LPBF processing parameters. The samples prepared by LPBF energy density of 381 J/mm3 had a favorable ultimate strength (UTS) of 1076 ± 2 MPa and yield strength of 795 ± 16 MPa. The samples prepared by LPBF energy density of 76 had excellent ductility, with an elongation of 31% at fracture. [ABSTRACT FROM AUTHOR]

Zinc (Zn) alloys have recently revolutionized and shown promising usage for degradable biomedical implants (BMI). However, due to the low strength of pure Zn, its application in the biomedical industry was limited. In the current research, an innovative biodegradable Zn-0.4Li-0.4Cu alloy produced by laser powder bed fusion (LPBF) with good mechanical properties was investigated. The Zn-0.4Li-0.4Cu alloy showed superior mechanical properties (tensile strength at 296 MPa, yield strength at 260 MPa, and after heat treatment elongation at 8.3 %), a record for biodegradable Zn alloys, as a consequence of grain refinement, second-phase precipitation of intermetallic compounds, and solid solution strengthening. The impacts of Cu and Li on the microstructures, mechanical behaviors, corrosive behavior and deterioration rate of the Zn-0.4Li-0.4Cu alloy were studied. The addition of Cu and inherent fast-cooling rate of the LPBF process are favorable for promoting the nucleation events, leading to the refinement of grains. In addition, the formation of the second-phase precipitates (CuZn 4 and ZnLi 4) in the matrix was founded to further improve the mechanical properties. Moreover, the alloy showed a consistent degradation manner and a suitable degradation rate of 0.023 mm/year. Based on the findings shown above, the biodegradable Zn-0.4Li-0.4Cu alloy can be a potential candidate for vascular stents and medical applications due to its excellent mechanical properties and adequate degrading behavior. • The Zn-0.4Li-0.4Cu alloy produced by laser powder bed fusion (LPBF) demonstrated exceptional mechanical properties, with a tensile strength greater than 296 MPa, and elongation of 8.3 %. • The superior mechanical properties of the as-LPBF-built Zn-0.4Li-0.4Cu alloy can be attributed to the morphology and distribution of the intermetallic compounds and dislocations. • The novel biodegradable Zn-0.4Li-0.4Cu alloy is a promising candidate for fabricating degradable biomedical implants due to its strength, reasonable ductility, and satisfactory degradation rate. [ABSTRACT FROM AUTHOR]

• The microstructure of LPBF-NiTi alloy was regulated by switching the heat transfer mode. • The grain morphology of LPBF-NiTi alloy exhibited fine grain at the conduction mode. • The grain morphology of LPBF-NiTi alloy exhibited coarse grain at the keyhole mode. The function-graded NiTi part is one of the greatest potential smart materials due to its superelasticity, shape memory, biocompatibility and the ability of coupling complex functionality. Laser powder bed fusion (LPBF) is a promising method for the preparation of microstructure-gradient NiTi parts. The microstructure of the NiTi alloy prepared by LPBF was tailored by switching the heat transfer modes through the variation of the process parameters. The LPBF-fabricated NiTi alloy with fine grains is obtained in the conduction mode because the laser energy is enough to melt the powder while, the growth of the grains is restricted without enough power. In comparison, the coarse grains penetrating through two or more layers is obtained in the keyhole mode, due to the appearance of the keyholes reheating the previous layers. This work proved the feasibility for the preparation of microstructure-gradient NiTi alloys by LPBF. [ABSTRACT FROM AUTHOR]

W-based composites with the different immiscible second phases (Cu and Cu10Sn) were prepared by laser powder bed fusion (LPBF). The immiscible W phase and Cu/α-Cu phases were prone to separate during LPBF. The melted W phase could easily fuse together and form W matrix, and Cu or α-Cu phase distributed within the gaps among W phase. Cu or α-Cu phase can provide a gradient cooling way for the solidification of W phase through the transformation of 'solid-liquid-gas' during LPBF. The evaporation of Cu or Sn accelerated the heat dissipation, which caused the grain refinement of W. Higher thermal conductivity of Cu than α-Cu leads to the relative finer grain size of W phase in W-Cu composite. The heat conduction direction between W phase and Cu/α-Cu also affected the grain morphology. Heat continued transferred from W to Cu/α-Cu induced the columnar grain growth of W, the interlacing distribution of W and Cu/α-Cu made the growth of W columnar grains radiate out from the center Cu/α-Cu phase. Remarkable, cracks were severely restrained in W phase simultaneously although W phase melted completely. This is not only related to improvement of strength and ductility of W caused by grain refinement, but also because of the interlacing distribution of W and Cu/α-Cu phases, which could effectively reduce the stress degree in W phase during LBPF. [Display omitted] • W-Cu and W-Cu10Sn composites with free crack were successfully prepared by LPBF. • W phase formed skeleton structure in both W-Cu and W-Cu10Sn composites. • The addition of Cu/ Cu10Sn induced the grain refinement of W phase. [ABSTRACT FROM AUTHOR]