Effect of incomplete thermal cycling on the transformation behaviour of NiTi

The effect of partial thermal cycling through incomplete transformation cycles on the transformation behaviour of NiTi was investigated. This investigation was carried out with two purposes: (1) to establish an understanding of the evolution of internal plastic deformation during the process of thermally induced B2 ↔ B19′ martensitic transformation and (2) to provide experimental data for the application of NiTi alloys involving repeated transformation cycles. It was observed that on equal transformation volume basis partial reverse transformation caused the least changes to transformation behaviour, full transformation cycling caused the most severe changes whereas partial forward transformation cycling was in between. These experimental observations indicate that more structural damages are created towards the end of the forward transformation than at the early stages of the transformation and that more structural damages are created during the forward transformation than during the reverse transformation.