Transformation behaviour with thermal cycling in Ti50Ni43Cu7 shape memory alloy

The transformation behaviour of Ti50Ni43Cu7 Shape memory alloy was investigated by differential scanning calorimeter (DSC) in order to reveal the effects of thermal cycles with the repetition of the transformation. The thermal cycles tend to lower the transformation characteristic temperatures between the high and low temperature phases. The M-s, M-f and A(f) all decrease gradually while only the A(s) increases progressively during the initial thermal cycling process, with increasing number of thermal cycles above the 10th, the M-s, M-f, A(s) and A(r) almost remain as constant regardless of the thermal cycles. But thermal cycles could not introduce "R" phase. With increasing of the thermal cycling times, the martensitic transformation latent heats (Delta H'(B2 -> B19)) and the reverse transformation heats (Delta H'(B19 -> B2)) of the Ti50Ni43Cu7 alloy all linearly decrease, but the decrease amplitude is not high. It is thought that introduced defects due to the thermal cycling play an intrinsic role in the complicated behaviour of Ti50Ni43Cu7 alloys. (c) 2006 Elsevier B.V. All rights reserved.