Lattice study of ω phase formation involving volume change

The incommensurate structure of the omega phase, which has been observed as the pre-transition phenomena of omega phase transformation, was studied by focusing on the elastic strain energy in a domain model using the microscopic theory of elasticity. The convolution theorem was applied to simplify the mathematics of describing an incommensurate ellipsoidal droplet with an internal structure consisting of alternate lamellae of omega and beta phases. It was clear that the decomposition into the two-phase structure yielded much less elastic strain energy than the single omega phase. The interface of the omega and beta lamellae in the incommensurate structure should be (111)(beta) when formed by the simple omega wave k(q(omega)) of Burgers displacement, but the deviation of the interface orientation from the (111)(beta) plane occurs due to the additional volume change by Bain distortion. It was also found that there is no interaction in the elastic strain energy originated by the Burgers displacement and the Bain distortion. (c) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.