Study of superelasticity associated with the thermoelastic martensitic transformation in Au—Cd alloys

Abstract Superelastic behaviour in Au-47·5 at.% Cd and Au-49·5 at.% Cd was studied using microscopic surface observation, an analysis of Laue photographs and measurement of the strain distribution. The superelasticity above the transformation temperature, T0, in Au—47·5 at. % Cd alloy was associated with the transformation, β(b.c.c.) β'(orthorhombic) upon loading and β'-β upon unloading. Below T0, superelasticity in a quenched and aged martensite was due to migration of twin boundaries in the martensite crystal. In Au—49-5 at.% Cd alloy, below T0, a significant superelasticity was observed when the specimen axis was near the [100]β pole. This superelasticity was accompanied by the transformation β“(hexagonal) β’ upon loading and β→β” upon unloading. Above T0, the superelasticity observed was identical to that found in Au-47-5 at.% Cd. In the stress-induced transformation, upon loading, a band consisting of alternate layers of the b.c.e. phase and the martensite phase was formed at one end of the specimen ...