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; however, the microstructural mechanisms that occur during the early stages of these treatments remain largely unrecorded. In this study, a hot-rolled superelastic sheet was annealed for 60 s at temperatures of 520 °C, 540 °C, 560 °C, 580 °C, and 600 °C. After annealing, the samples were analyzed using transmission electron microscopy, electron backscatter diffraction, x-ray diffraction, and differential scanning calorimetry. After a 1-min heat treatment at 520–600 °C, the dislocation density drops by three orders of magnitude. The texture shifts from a rolling a-fiber (<110>|| RD) to a c-rich state ({111} || ND) with increasing {001}. At 520 °C, the change is mostly recovery; by 560 °C, orientation near {111}<112> dominates; at 580–600 °C, growth/coarsening broadens the c fiber and partially de-textures the sheet. Simultaneously, defect-assisted precipitation of coherent Ni4Ti3 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 1-min treatment at moderate temperatures can achieve fine grains and minimal defect content. The study offers a commercially viable method for rapid, customizable post-processing of NiTi components.