Influences of aging and thermomechanical treatments on the martensitic transformation and superelasticity of highly Ni-rich Ti-51.5 at.% Ni shape memory alloy

• Applying aging and thermomechanical treatments change the features of DSC curves.
• Optimum aging temperatures for reaching very good superelasticity was determined.
• Applying cold work before aging treatment improved the superelastic behavior of the alloy.
• Highly Ni-rich Ti-51.5 at.% Ni NiTi alloy can exhibit excellent superelasticity.

This paper evaluates influences of aging and thermomechanical treatments on the martensitic transformation and superelasticity of a highly Ni-rich Ti-51.5 at.% Ni. For this purpose, the alloy was subjected to aging and thermomechanical treatments. One group of sample was aged for 1 h at 300–700 °C with 100 °C intervals. The other group firstly was cold rolled to a reduction of 20% and then aged for 1 h at the previous temperature range. Results showed that solution annealed and aged samples at 700 °C showed no superelasticity because of high nickel content in the matrix of the alloy. For the aged samples, complete superelasticity was observed by aging at 400 and 500 °C. Applying 20% cold rolling before aging led to increase aging temperature for observing good superelastic behavior. Compared to the aged samples at 300 and 600 °C, for cold worked and aged samples at 300 and 600 °C, recovered strain after unloading at 5% strain, was increased 0.8 and 0.7%, respectively.