Mechanical Behavior and Shape-Memory Effects of Ni_xTi_1-x Alloys with Tunable Mixing of Ni/Ti Powders by Laser-Directed Energy Deposition

As we know, controlling NiTi alloy's microstructure is an urgent problem in additive manufacturing, which directly affects the mechanical properties of the alloy. In laser directed energy deposition (LDED) technology, the simultaneous powder feeding equipment with double powder barrels can effectively control the material ratio and realize the generation of NixTi1-x alloys with different atomic ratios. Firstly, the performance differences of NiTi alloy under different thermal treatments are explored. Based on this, the optimal thermal treatment process is used to adjust the microstructure of NiTi alloy fabricated by laser directed energy deposition by changing the Ni/Ti atomic ratio to improve mechanical properties. The results indicate that Ni4Ti3 precipitates could induce the R phase, change the phase transition, and improve the mechanical properties in Ni-rich NiTi alloys. Besides, the mechanical properties of NixTi1-x alloy can be enhanced by adjusting the Ni/Ti atomic ratio to change the content of Ni4Ti3 precipitates. Ni52Ti48 alloy has a tensile strength of 771 MPa, an elongation of 11.6 %, and a recovery rate of 95.2%.