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-co mponent, 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) th e enthalpy term is due entirely to the interaction of the first-neares t neighbor atoms. Analytical equations were derived for the Gibbs ener gy and the partial Gibbs energies of the component elements. The equil ibrium distributions of the atoms on the various sublattices were obta ined by the minimization of the Gibbs energy. From the equilibrium dis tribution of the atoms, the integral and partial thermodynamic quantit ies of an intermetallic compound can be readily obtained. The generali zed thermodynamic equations reduce to the equations reported in the li terature for ordered binary intermetallic compounds exhibiting the B-2 , Ll(0) and Ll(2) structures with anti-structure defects. The generali zed 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 concen trations in the lattices.