Effect of Heat Treatment on the Microstructure and Properties of Ni51.3Ti Shape Memory Alloy by Wire Arc Additive Manufacturing

Wire arc additive manufacturing (WAAM) technology is widely used in the fabrication of large-size NiTi shape memory alloy components because of its simplicity and high deposition efficiency. However, WAAM induces anisotropy along the height direction of the components, which greatly affects the material’s stability. To address this issue, post-heat treatment processes can be employed to enhance microstructural uniformity and mechanical properties. This paper investigates the effects of different solution treatments and solution treatment combined with short-time aging treatment on the microstructure, phase transformation, and mechanical properties of 15-layer arc additively manufactured Ni_51.3Ti alloy. The results indicate that after solution treatment and short-time aging treatment, there is no significant change in the grain size of the NiTi samples on the X-Y plane, and the samples still exhibit a preferred [001] crystallographic orientation. During aging at 45°C, the precipitation of the Ni₄Ti₃ phase causes the B2 → B19′ transformation to change to B2 → R → B19′ transformation. Heat treatment makes the microstructure of the NiTi alloy more uniform, effectively improving the cyclic tensile properties of samples in the 0° direction and increasing the strain recovery rate of the material to over 95%. This study provides an effective heat treatment method for arc additively manufactured Ni_51.3Ti alloy.