Isothermal B2–B19′ martensitic transformation in Ti-rich Ni–Ti shape memory alloy

The athermal/isothermal nature of the B2↔B19′ martensitic transformation was investigated by means of electrical resistance measurements in a Ni49.5Ti50.5 alloy that has elevated transformation temperatures as compared with the near-equiatomic or Ni-rich compositions studied previously. The direct B2–B19′ martensitic transformation shows a clear time dependence, whereas isothermal effects are not revealed for the reverse B19′–B2 transition. The applicability of the C-shaped time–temperature–transformation diagram to interpret the experimental results is discussed.