Influence of heat treatlment on shape memory properties of a Cu-Al-Be alloy containing chromium

Abstract

In this paper, by comparing the shape memory behaviour, phase structure, substructure of martensite, and the recovery behaviour of quenched in vacancies from 20 to 200°C of direct quenched and step quenched Cu-11.58AI-0.41Be-0.2Cr (wt-%) alloy, the effect of heat treatment on shape memory properties was analysed. It was found that the Cu-Ar-Be-Cr alloy tested exhibited low starting temperatures and very high final temperatures of shape recovery. The shape memory properties of the step quenched Cu-AI-Be-Cr alloy were better than those of the direct quenched Cu-AI-Be-Cr alloy. It was also found that the crystal structure, substructure of martensite, and vacancy concentration all affected the shape memory properties, and that a mixed mechanism was responsible for the stabilisation of martensite. Some abnormal defects such as non-basal plane planar defects and dislocations were observed in the martensite obtained by direct quenching, which is one of the reasons for the stabilisation of the martensite. The recovery behaviour of quenched in vacancies revealed that the vacancy concentration mainly affects the starting temperature of shape recovery.