Phase stability of CuAlMn shape memory alloys

Abstract

Abstract Thermoelastic martensitic transformations in single crystals of two CuAlMn shape memory alloys were investigated using tension/compression stress–strain tests, thermal cycling tests, stress recovery tests and calorimetric measurements. Pseudoelastic behaviour was observed in the as-quenched samples stressed above the A f temperature. Near the M s temperature the stress–strain response changed and became pseudoplastic. A pronounced dependence of the thermoplastic behaviour on the transformation history was found. The samples once subjected to tension/compression cycling at a temperature near or below M s remained pseudoplastic during subsequent stress–strain experiments at higher temperatures, and a large increase of the A f temperature was observed. This stabilisation of martensite is similar to that observed on CuAlNi, and can be ascribed to the detwinning of the martensitic phase and formation of a single variant of the γ 1 ′ martensite.