| Abstract Scope |
The shape-recovery characteristic of Nitinol is influenced by its chemical composition and thermo-mechanical processing history. Hot-rolled superelastic sheets were isothermally aged at 560 °C for 1, 2, 4, 8, and 15 minutes to study the relationship between lattice recovery and Ni4Ti3 precipitation. TEM, XRD pole figures, DSC, and micro-hardness testing were utilized to establish a correlation between precipitate structure, texture, transformation temperatures, and strength. Coherent Ni4Ti3 precipitates nucleated rapidly, and a complete three-stage B2 → R1 → R2 → B19′ transformation was observed at 2 minutes and re-emerged at 15 minutes. Intermediate durations of 4 and 8 minutes promoted precipitate coarsening and dissolution, which reduced hardness and modified the transformation sequence to two stages. The findings elucidate the way short-term aging alters Nitinol's microstructure and functional response, while providing a viable approach to complement multi-stage superelasticity with mechanical performance. |