Study of martensitic stabilisation under stress in Cu–Al–Be shape memory alloy single crystal

Martensitic stabilisation phenomenon in the copper-based shape memory alloys has been invariably related to thermomechanical treatments and post-quench history. This phenomenon degrades shape memory properties and reduces their potential for industrial applications. In the present work, superelastic tests in a single crystal of Cu–Al–Be alloy were realised to study the martensitic stabilisation processes. Direct quenched samples have been studied in a special apparatus which allows to measure simultaneously stress–strain and electrical resistance. Two experimental procedures were used: superelastic cycles (8% strain) and ageing in mixed state. In the second test, the sample is submitted to a 4% strain by superelasticity which leads to a mixture of β-phase and single variants of martensite separated by parallel interfaces. After 24 h, the sample is strained up to 8% and finally the stress is removed leading to a total strain recovery. The stress–strain as well as the resistivity curves show a very different behaviour between the volume fraction which have been aged in the martensitic state and the one aged in the β-phase state. The results are discussed in terms of thermal treatment influence and stabilisation processes.