Martensite destabilization in Au7Cu5Al4 shape-memory alloy

Aging-induced changes in the austenite peak (AP) temperature of Au7Cu5Al4 shape-memory alloy are investigated. Whereas heat treating the parent phase at temperatures >140 °C or aging the martensite for long times at room temperature both stabilized the AP to ∼80 °C, low-temperature excursions into the parent phase caused the subsequent AP to drop to ∼60 °C and the transformation hysteresis to decrease. The evidence indicates that this destabilization of the martensite is caused by time-dependent relaxation of elastic constraint due to parent-phase lath migration during the preceding low-temperature austenitizing treatment. This mechanism of aging is different from that of the better-known symmetry-conforming short-range order phenomenon.