We study the anisotropy of interphase boundaries (IPBs) and antiphase boundaries (APBs) in a binary alloy on an FCC lattice using a recently developed diffuse interface model that uses three (nonconserved) order parameters and a concentration (conserved order parameter). The concentration variation through the interface is added to the previous diffuse interface model. This model has the capability of modeling IPBs and APBs for all orientations with respect to the underlying lattice. The model includes bulk and gradient terms in a free energy functional. The bulk energy model is based on multiparticle interactions for the internal energy and a point approximation to the entropy. The gradient energy terms have two independent parameters that produce cubic and tetragonal anisotropy depending on the phase boundaries. We will illustrate the ordered phases based on the Cu-Au system.

We investigate the interfacial properties of the IPBs by considering order-disorder transitions (A1-L1₂, A1-L1₀), an order-order transition (L1₂-L1₀) and those of APBs (L1₂ and L1₀ phases) in the neighborhood of the congruent and eutectoid points, and away from these points. We perform numerical simulations of interface structures for both IPBs and APBs. Realistic interfacial energy anisotropy of IPBs and APBs are calculated for different orientations and these results are compared with the result obtained from other models (CVM and the previous model). The interfacial energies will be used to determine the equilibrium shapes via the Cahn & Hoffman "ξ-vector". We compute equilibrium shapes for the A1-L1₀ IPBs and L1₂-L1₀ IPBs.