The effect of post-quench aging on stabilization of martensite in Cu-Zn-Al and Cu-Zn-Al-Ti-B shape memory alloys

The effect of post-quench aging in polycrystalline beta Cu-Zn-Al and Cu-Zn-Al-Ti-B on the martensite stabilization has been studied. The samples were heat treated at 1073 K and subsequently quenched into water at 373 K. After the quench, the samples were aged in the beta phase, 373 K less than or equal to T less than or equal to 403 K, during 300 s less than or equal to t(beta) less than or equal to 10(5) s. The stabilization tests were performed by applying compressive stresses at temperatures above the reverse transformation temperature, A(f) followed by martensite aging under constant strain. When unloading the sample, it recovers its original shape but the reverse transformation stress is shifted to lower values. The magnitude of the stress shift, a measure of martensite stabilization, is a function of the thermal treatment and aging time. The process continues until a saturation is reached. It was found that the stress shift saturation value depends on the temperature and the aging time in the beta phase. The results show that the stabilization depends on the vacancy concentration and that dislocations can not be the dominating type of vacancy sinks in martensite. (C) 1999 Elsevier Science S.A. All rights reserved.