A GENERALIZED QUASI-CHEMICAL MODEL FOR ORDERED MULTICOMPONENT, MULTI-SUBLATTICE INTERMETALLIC COMPOUNDS WITH ANTI STRUCTURE DEFECTS

A generalized quasi-chemical model was formulated for ordered multi-component, multi-sublattice intermetallic compounds with anti-structure defects. The assumptions made in formulating this model were: (i) the atoms are randomly distributed on each of the sublattices, and (ii) the enthalpy term is due entirely to the interaction of the first-nearest neighbor atoms. Analytical equations were derived for the Gibbs energy and the partial Gibbs energies of the component elements. The equilibrium distributions of the atoms on the various sublattices were obtained by the minimization of the Gibbs energy. From the equilibrium distribution of the atoms, the integral and partial thermodynamic quantities of an intermetallic compound can be readily obtained. The generalized thermodynamic equations reduce to the equations reported in the literature for ordered binary intermetallic compounds exhibiting the B-2, Ll(0) and Ll(2) structures with anti-structure defects. The generalized equations may be used to describe the thermodynamic properties of any ordered intermetallic compound with anti-structure defects. These equations may be used for calculating phase diagrams and defect concentrations in the lattices.