Strong heating rate-dependent deterioration of shape memory effect in up/step quenched Cu-based alloys: A ductile Cu-Al-Mn alloy as an example

It is generally believed that an up/step-quenching treatment can suppress the deterioration of shape memory effect (SME) due to the martensitic stabilization. However, recent studies have indicated that the SME in an up-quenched ductile Cu-Al-Mn alloy dropped drastically as lowering the recovery heating rate. To understand whether the above strong heating rate-dependent deterioration in the SME can be ascribed to the martensitic stabilization, we carefully investigated the microstructural differences in an up-quenched Cu-17.0Al-10.5Mn (at.%) alloy after deformation and then heating at different rates. The effect of up-quenching time on the SME deterioration induced by lower heating rates was also studied. The results showed that the martensitic stabilization is responsible for strong heating rate dependent deterioration in the SME in the up-quenched Cu-Al-Mn alloy, and whether a certain up quenching treatment can suppress its occurrence is strongly dependent on the recovery heating rate. Available data clearly showed that this dependence also exists in other up/step-quenched Cu-based alloys. The migration, cluster and even collapse of thermodynamically non-equilibrium quenched-in vacancies at the martensite interfaces result in this dependence. The martensite interfaces pinned by the collapsed vacancies cannot be de-pinned through thermal activation. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.