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 continuum formulation that incorporates the underlying symmetries of the FCC crystal in both the bulk and gradient-energy terms of the free energy. The theory is used to compute the orientation dependence of the structure and energy of interphase and antiphase boundaries. The structure of these interfaces compares favourably with previous lattice calculations by Kikuchi & Cahn (1962, 1979). Anisotropy is a natural consequence of the lattice calculation and the multiple-order-parameter continuum formulation presented here. This is in contrast to the ad hoc fashion in which anisotropy is often introduced into a single-order-parameter continuum theory.