Impact of Short-Term Annealing on Microstructure and Transformation Temperatures of Hot-Rolled Superelastic Nitinol

Brief heat treatments offer an energy-efficient method for adjusting the microstructure and properties of Nitinol; yet, the microstructural mechanisms occurring during early stages of these treatments remain largely unrecorded. In this study, a hot-rolled superelastic sheet was annealed for 60 seconds at temperatures of 520, 540, 560, 580, and 600 ºC. After annealing, the samples were analyzed using transmission electron microscopy, electron backscatter diffraction, X-ray diffraction, and differential scanning calorimetry. After a 1-minute heat treatment at 520–600 ºC, the dislocation density drops by three orders of magnitude. The texture shifts from a rolling α-fiber (<110> || RD) to a recrystallized, γ-rich state ({111} || ND) with increasing {001}. At 520 ºC, the change is mostly recovery; by 560 ºC, oriented recrystallization near {111} <112> dominates; at 580–600 ºC, growth/coarsening broadens the γ fiber and partially de-textures the sheet. Simultaneously, defect-assisted precipitation of coherent Ni ₄ Ti ₃ plates preserved the recovered texture and stabilized a multi-step transformation. Quantitative correlations among recovery, texture retention, and nanoscale precipitation were established, demonstrating that a one-minute treatment at moderate temperatures can achieve fine grains and minimal defect content. The study offers a commercially viable method for the rapid and customizable post-processing of NiTi components.