Effects of martensitic stabilisation in Cu-Al-Be shape memory alloys

Abstract

Single crystals of a Cu-Al-Be alloy with transformation temperatures above room temperature were submitted to three different thermal treatments: I - direct quenching in water at room temperature followed by an annealing, 2 - step quenching and 3 - direct quenching. Measurements realised by differential thermal analysis shows that some results of stabilisation are similar to other copper based alloys. Nevertheless, direct quench in water leads to a double reverse martensitic transformation. Amplitude and temperature of the first transformation depends on annealing time at 100°C. However, the second transformation is always at the same temperature of 265°C. A shape memory effect is also observed for each of these two steps of the reverse martensitic transformation. These results of martensitic stabilisation for the Cu-Al-Be alloy are discussed in terms of thermal treatment influencing on mechanical lock of interfaces by vacancies (pinning), elimination vacancy mechanisms and order-disorder transitions.