Interfacial Structure and the Shape Memory Effect

Abstract

The crystallographic reversibility required for shape memory is based on the capacity of crystal interfaces to move freely in the forward and reverse directions in response to changes in temperature and/or stress. Interface mobility is therefore a central issue and it follows that the fine scale structure of the interface is highly significant in determining the micromechanisms by which shape memory occurs. This paper reviews proposed models for the interface of twinned martensite, which is the dominant type of martensite in shape memory alloys. A case is made that the twin termini in the habit plane are facet planes which can be identified as unrotated planes across which forced coherence occurs It is proposed that the alternating twin volumes result in at least partial self-accommodation of the lattice strains over distances corresponding to the spacing of the pair of twin related volumes.