Effect of aging on shape memory behavior in Ti-50.9at%Ni alloy

Effect of aging on shape memory behavior, i.e. transformation temperatures, deformation behavior, multi-stage martensitic and R-phase transformations and morphology of precipitates, was systematically investigated for a Ti-50.9at%Ni alloy. The specimens were solation-treated at 1073K for 3.6ks followed by aging between 373K and 673K for 0.3ks up to 10800ks. Martensitic and R-phase transformation temperatures significantly varied depending on aging time and temperature except for specimens aged at 373K. R-phase transformation was recognized after aging at 473K for more than 36ks. Two-stage R-phase transformation appeared after aging at 473K over 36ks. Multi-stage martensitic transformation (MSMT) appeared at 673K from 1.2ks to 36ks. The critical stress for slip estimated from the strain vs. temperature curves exceeded 370MPa when aged at 573K for 180ks. It was confirmed that the dense and fine precipitates formed through aging resulted in superior shape memory characteristics.