High-Superelasticity NiTi Shape Memory Alloy by Directed Energy Deposition-Arc and Solution Heat Treatment

Directed energy deposition-arc (DED-Arc) technology has the advantages of simple equipment, low manufacturing cost and high deposition rate, while the use of DED-Arc has problems of microstructure inhomogeneity, position dependence of macroscopic mechanical properties and anisotropy. Therefore, it is necessary to carry out a subsequent heat treatment to improve its microstructure uniformity, mechanical properties and superelasticity. In this investigation, the DED-Arc 15-layer NiTi alloy thin-walled parts with the solution treatment at different process parameters were studied to analyze the effects of solution heat treatment on microstructure, phase composition, phase transformation, microhardness, tensile and superelasticity. The temperature range of solution treatment is 800–1050 °C, and the treatment time range is 1–5.5 h. The results show that after solution treatment at 800 °C/1 h, the content of precipitated phase decreases, the grain is refined, the microhardness increases, and the mechanical properties in the 0° direction are improved. The strain recovery rate after 10 tensile cycles has increased from 37.13% (as-built) to 49.25% (solid solution treatment). This research provides an effective post treatment method for high-performance DED-Arc NiTi shape memory alloys.