Effect of annealing on deformation-induced martensite stabilisation of NiTi

It is known that deformation via martensitic transformation stabilises the martensite in NiTi shape-memory alloys, as manifested in the increase of the temperature for the reverse transformation of the deformed martensite. This stabilisation has direct implication to the design of shape-memory devices. This study investigates the effect of annealing temperature after cold working on the martensite stabilisation effect of a Ti–50.2 at% Ni alloy. It is found that the stabilisation effect, measured as the increase of the reverse transformation temperature, decreases with decreasing annealing temperature. This implies that, for near-equiatomic NiTi alloys, the pseudoelastic behaviour, which is achieved at low annealing temperatures, is less affected by the stabilisation effect than the shape-memory effect, which is optimised by annealing at high annealing temperatures.