Effect of Phase Structure on the Properties of Additively Manufactured NiTi Alloy Based on Molecular Dynamics Simulation

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.