Interaction between martensitic structure and defects in β⇆β′+γ′ cycling in CuAlNi single crystals.: Model for the inhibition of γ′ martensite

The authors have previously reported an estimate of the energy associated with the inhibition effect of gamma' martensite after beta <-> beta' + gamma' cycling in CuAlNi single crystals. In this paper, a microscopic model is proposed to explain the gamma' inhibition, related to the localized interaction between a dislocation array and the twinned gamma' structure. Dislocations with Burgers vector [100](beta) and line direction [111](beta) in an isotropic beta matrix are considered. The model takes into account the interaction between the martensitic stress-free transformation strains and the stress field created by the dislocation arrays. It is shown that the interaction is different for each twin-related variant in the gamma' martensite. The energy necessary to maintain the right volume relationship of the twinned gamma' variants to produce an undistorted beta/gamma' habit plane is defined as the inhibition energy. A value of around 12 J mol(-1) was obtained, which is in reasonable agreement with experimental results. (C) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.