ANISOTROPY OF INTERFACES IN AN ORDERED ALLOY - A MULTIPLE-ORDER-PARAMETER MODEL

A multiple-order-parameter theory of ordering on a binary face-centred -cubic (FCC) crystal lattice is developed, and adapted to provide a co ntinuum formulation that incorporates the underlying symmetries of the FCC crystal in both the bulk and gradient-energy terms of the free en ergy. The theory is used to compute the orientation dependence of the structure and energy of interphase and antiphase boundaries. The struc ture of these interfaces compares favourably with previous lattice cal culations by Kikuchi & Cahn (1962, 1979). Anisotropy is a natural cons equence of the lattice calculation and the multiple-order-parameter co ntinuum formulation presented here. This is in contrast to the ad hoc fashion in which anisotropy is often introduced into a single-order-pa rameter continuum theory.