Effect of deformation on the stability of stress-induced martensite in nanocrystalline NiTi shape memory alloy

A nanocrystalline Ni-49.8 at%Ti alloy with an average grain size of about 16 nm was acquired by cold-drawing and low-temperature annealing. The stability of stress-induced martensite of the nanocrystalline NiTi alloy was investigated by a differential scanning calorimeter (DSC). The results show that stress-induced B19′ martensite was preserved when the samples were subjected to 14% and 16% prestrain. The DSC measurements reveal that the prestrained samples experience two-stage B19′→B2 transformation upon the first heating process and the transformation temperature increases with an increasing prestrain.