Superficial stress and strain at coherent interfaces

The thermodynamics of a coherent interface separating two non-hydrostatical ly stressed crystals is examined using the Gibbsian paradigm of a dividing surface and associated superficial quantities. Cahn-Hilliard diffuse interf ace theory is used to derive equations governing the equilibrium compositio n, stress, and strain profiles through a planar surface of discontinuity. E xpressions are then obtained for the superficial stress and strain (excess volume) assuming the isotropic elastic constants are independent of composi tion and the lattice parameter is a quadratic function of the composition. Materials parameters are identified for which the superficial stress become s independent of the position of the dividing surface, and the dependence o f the superficial stress on the application of a stress normal to the inter face, as well as the strain components in the plane of the interface, is ca lculated for various compositional strains. The superficial stress is estim ated to be of the order 1-10(3) dynes/cm and can be tither positive or nega tive in sign. (C) 2000 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.