Low-Annealing Temperature Influence in the Microstructure Evolution of Ni₅₃Ti₄₇ Shape Memory Alloy

Near-equiatomic NiTi alloys, commonly known as Nitinol, are recognized for their shape memory effect, superelasticity, high strength, excellent corrosion resistance, and biocompatibility. These properties make Nitinol, particularly in wire form, valuable for use as actuators, leading to significant advancements across various research fields. In this study, NitI alloy samples containing 53 wt% Ni were produced as 1-mm-diameter wires and subjected to annealing at temperatures between 350 and 650 °C for 20 min, followed by water quenching. The study focused on the microstructural, thermal, and mechanical properties before and after heat treatment. Analyses included optical and scanning electron microscopy, EDS microanalysis, and Vickers hardness testing. Results indicated that annealing, especially at 450 °C, altered the microstructure by increasing grain size and metastable particles. Additionally, martensitic transformation temperatures Ms and Af rose with higher annealing temperatures, while hardness decreased and grain size increased.