A model for the rubber-llke behaviour in CU-Zn-Al martensitea.

Abstract

In a previous paper the rubber like behavior of Cu-Zn-Al martensites was described and the crystallography of the corresponding transformation was analyzed. It was shown that the deformation of the martensite leads to the appearance of a new martensite variant of a structure identical to the original one. The new variant must have a higher free energy, in order that a force exists which moves the interface back on releasing, the stress. Possible mechanisms which produce an increase in energy during the movement of the interface between the variants are: a) creation of defects or of a new structure at the moving interface, b) Transformation of existing dislocations or long range order domain boundaries into higher energy defects during the transformation and c) a change of short range disorder. The first two possibilities were rejected in (1), the third will be discussed in this paper. It will be shown that the contribution of short range disorder can account for the observed rubber like behavior in Cu-Zn-Al alloys, and that the driving force which is calculated agrees well with the experimentally determined stress which is necessary to induce the martensite.