With ER2319 and B₄C powder as feedstocks and additives, respectively, a wire arc additive manufacturing (WAAM) system based on double-pulse melting electrode inert gas shielded welding (DP-MIG) was used to fabricate single-pass multilayer 2319 aluminum alloy. The results showed that, compared with additive manufacturing component without B₄C, the addition of which can effectively reduce the grain size (from 43 μm to 25 μm) of the tissue in the deposited layer area and improve its mechanical properties (from 231 MPa to 286 MPa). Meanwhile, the mechanical properties are better in the transverse than in the longitudinal direction. Moreover, the strengthening mechanism of B₄C on the mechanical properties of aluminum alloy additive manufacturing mainly includes dispersion strengthening from fine and uniform B₄C granular reinforcing phases and fine grain strengthening from the grain refinement of B₄C. These findings shed light on the B₄C induced grain refinement mechanism and improvement of WAAM 2319 Al alloy.

Twin-wire and arc additive manufacturing (T-WAAM) has potential advantages in improving deposition efficiency and manufacturing functionally graded materials (FGMs), thus attracting much attention. However, there are few studies on the droplet transfer mode of T-WAAM. This paper analyzes the droplet transfer mode and arc swing in the “TIG + AC” twin-wire cross-arc additive manufacturing by in-situ observation with high-speed photography, revealing what factors influence the T-WAAM on deposition shaping the quality and what are the key mechanisms for process stability. Experiments show that with the main arc current provided by TIG 100 A and the twin-wire AC arc current 10 A, three different droplet transfer modes, namely the “free transfer + free transfer, bridge transfer + free transfer, bridge transfer + bridge transfer,” can be observed with the twin wires under different feeding speeds. The corresponding deposition and arc swing are quite different in quality. Through comparative analysis, it is found that the frequent extinguishment and ignition of the arc between electrode wires is the main factor for the instability in the additive manufacturing process. The “bridge transfer + free transfer” mode can obtain a large arc swing angle and a stable deposition, in which the cross arc has a significant stirring effect on the molten pool, and the deposition shape is well-made.

NiTi alloy has been widely used due to its excellent shape memory effect, superelasticity, and high damping performance. These excellent properties are mainly derived from its unique phase structure. In order to further explore the effect of different phase ratios on the performance of NiTi alloy, this study successfully prepared NiTi alloys with different atomic ratios by controlling the wire feeding speed to control the atomic ratio in the alloy. The results of TEM showed that the alloy with a lower Ni atomic ratio is enriched with Ti element, while the alloy with a higher Ni atomic ratio has a coexistence of NiTi phase and NiTi₂ phase. At the same time, the compression performance showed that the increase in Ni atomic ratio can improve the compression performance of the alloy. In addition, by constructing a molecular dynamics model of NiTi alloys with different phase ratios, the unloading recovery behavior and phase transformation characteristics of the alloy under external force were analyzed. The results showed that with the increase of the NiTi₂ phase ratio in the alloy, the irrecoverable strain also increases, exceeding the elastic strain limit of the NiTi₂ phase, resulting in the generation of disordered structure and plastic deformation in the late deformation stage. In addition, with the increase of the NiTi₂ phase ratio, the energy dissipation area of the hysteresis curve increases, reflecting a greater energy loss.

In this paper, solution-treated Inconel 625 alloy was selected as the research object. Combined with the low-energy characteristic of annealing twin boundaries and the synergistic strengthening effect of gradient structures, the alloy microstructure was tailored without altering its chemical composition. The evolution mechanism of grain size and twin boundary fraction, as well as their influence on corrosion resistance, were investigated. On this basis, the synergistic strengthening effect of gradient structure and interface regulation on the corrosion and mechanical performance of the alloy was further explored. The results show that a gradient-structured Inconel 625 alloy with abundant annealing twins and high-density grain boundaries can be fabricated by surface nanocrystallization combined with high-temperature short-time annealing. The variation in annealing twin fraction with grain size in interface-modified Inconel 625 complies with the Pande model. In terms of corrosion resistance, the microstructure consisting of fine grains and a high fraction of annealing twins exhibits superior performance compared to coarse grains with identical twin content. Its corrosion potential is tripled, while the corrosion current density is reduced by 11 times, delivering outstanding anti-corrosion capability in NaCl solution. Benefiting from the integrated merits of gradient architecture, annealing twins and fine grains, the interface-tailored Inconel 625 alloy achieves excellent comprehensive performance, with a yield strength of 925 MPa, elongation of 26%, and corrosion current density of 3.02 × 10⁻⁸ A/cm², realizing the integration of high strength, good ductility and superior corrosion resistance for Inconel 625 alloy.