Chuan Yang

Sn–58Bi specimens produced through severe plastic deformation (SPD) typically exhibit excellent superplastic properties. However, the dimensions of SPD-prepared specimens are limited, and the process involves complex multistep procedures, which limit their practical engineering applications. Therefore, developing alternative fabrication techniques with greater flexibility and scalability is particularly important. In this study, a Sn–58Bi alloy was fabricated using laser powder bed fusion (LPBF). After the processing parameters were optimized, Sn–58Bi with remarkable superplasticity was successfully fabricated via additive manufacturing for the first time. Tensile tests revealed elongations to failure of 740% at room temperature (298 K) and 1 395.5% at 353 K. In situ scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) analyses indicated that grain boundary sliding (GBS) and phase boundary sliding (PBS), which are predominantly influenced by diffusion processes, were the primary mechanisms of superplastic deformation in the LPBF-fabricated Sn–58Bi alloy. This study provides a new strategy for enhancing alloy ductility through LPBF and offers theoretical insights into the additive manufacturing of superplastic polycrystalline alloys.

According to the binary phase diagram, Fe-Pb are immiscible under equilibrium conditions and are hard to metallurgically bond. To solve this problem, in this work, the instantaneous high-temperature and high-pressure environments generated during electromagnetic pulse welding (MPW) were utilized to achieve the miscibility of Fe and Pb, enabling the effective bonding of Fe-Pb bi-metallic tubes. The effects of MPW parameters, including discharge voltage and radial gap, on interfacial bond strength and microstructure were analyzed. Optimal bonding occurred at 10.5 kV discharge voltage and a 1.6 mm radial gap, forming a continuous transition layer. Lower energy input reduced bond strength, while excessive energy caused shear deformations. Microstructure analysis revealed that the diffusion zone significantly enhanced the bond strength. Measured bond strength values were 7.6 MPa at optimal conditions. These results demonstrate that MPW is a feasible method for fabricating Fe-Pb bi-metal tubes, offering a promising way for immiscible metals metallurgical welding.

This research investigated the relationship between volume energy density and the microstructure, density, and mechanical properties of the Ti-5Al-5Mo-3V-1Cr-1Fe alloy fabricated via the SLM process. The results indicate that an increase in volume energy density can promote a transition from a columnar to an equiaxed grain structure and suppress the anisotropy of mechanical properties. Specifically, at a volume energy density of 83.33 J/mm³, the average aspect ratio of β grains reached 0.77, accompanied by the formation of numerous nano-precipitated phases. Furthermore, the relative density of the alloy initially increased and then decreased as the volume energy density increased. At a volume energy density of 83.33 J/mm³, the relative density reached 99.6%. It is noteworthy that an increase in volume energy density increases the β grain size. Consequently, with a volume energy density of 83.33 J/mm³, the alloy exhibited an average grain size of 63.92 μm, demonstrating optimal performance with a yield strength of 1003.06 MPa and an elongation of 18.16%. This is mainly attributable to the fact that an increase in volume energy density enhances thermal convection within the molten pool, leading to alterations in molten pool morphology and a reduction in temperature gradients within the alloy. The reduction in temperature gradients promotes equiaxed grain transformation and grain refinement by increasing constitutive supercooling at the leading edge of the solid–liquid interface. The evolution of molten pool morphology mainly inhibits columnar grain growth and refines grain by changing the grain growth direction. This study provided a straightforward method for inhibiting anisotropy and enhancing mechanical properties.

Ni₄₇Ti₄₄Nb₉ alloys were successfully fabricated by laser powder bed fusion (LPBF) technique with different laser powers. The phase transformation behavior, tensile properties and shape memory response before and after heat treating were also investigated. The Ni₄₇Ti₄₄Nb₉ LPBF alloys have good shaping properties, though a few defects were discovered. Phase transformation peaks did not appear in the as-built samples, but were observed in the heat-treated samples. The phase transformation temperatures of the heat-treated samples increase with the increase in laser power. The tension test at room temperature indicates that the LPBF samples exhibit poor tensile ductility, which may be related to the existence of pores and Ti₂Ni or Ti₄Ni₂O_x phase during the LPBF process. However, the LPBF samples after heat treating still possess good shape memory effect (with recovery strain about 7.82–8%) and relatively high reverse transformation temperature (about 36–52.6 °C) when deformed to 8%.