Effect of γ precipitates on the martensitic transformation of β CuZnAl studied by calorimetry

Abstract

1. i) The temperatures for forward transformation are always lower than standard ones in the domain of t{black star} studied. This cannot be explained by a change in the composition of the β phase and therefore implies a relative stabilisation of β phase versus martensite. 2. ii) The temperatures for reverse transformation are lower than the standard ones for growing times t{black star} ≤ 20 s and higher for t{black star} > / 40 s. A change of behaviour in this time interval is also present in acoustic emission results. It could be atributed to a change in the coherence of the precipitates. 3. iii) The cycle of hysteresis is always wider than the standard one. This is associated with an increase of friction. All the aforementioned effects are permanent. Therefore, it is possible to modify the martensitic transformation of shape memory alloys in a reproducible and controllable manner. © 1989.