FERROELASTICITY OR RUBBER-LIKE BEHAVIOR IN STABILIZED CU-ZN-AL SINGLE-CRYSTALS

The ferroelasticity, or more commonly the rubber effect, has been stud ied in Cu-14.4 at.% Zn-16.8 at.% Al single crystals. The 18R single cr ystals were stress induced in tension at various temperatures, and the n aged in the martensitic stale for given temperatures and times. Afte rwards compressive stresses were applied, leading to the diffusionless transformation to another 18R martensitic variant, which on unloading retransformed back to the original variant. This process is associate d with a corresponding shape change. It has been observed that initial ly the transformation stress increases with annealing time, until a pl ateau is reached, followed by another increase at larger times. From t he influence of the ageing temperature on the velocity of the change i n the transformation stress an activation energy of 67 kJ/mol is deriv ed. This value is lower than that controlling the stabilization of the martensite with respect to the beta phase matrix of 97 kJ/mol, and im plies that the mechanism which is responsible for the rubber like beha viour is different from that for stabilization. The reason for this is discussed and a possible interpretation is given. (C) 1998 Acta Metal lurgica Inc.