CVM calculations of phase equilibria in the Fe-Cu-Co system including both chemical and magnetic interactions

Abstract

Phase equilibria in the Fe-Cu-Co system are investigated in the temperature range 723K-1273K using the cluster variation method (CVM) in the irregular tetrahedron approximation in the bcc lattice and in the regular tetrahedron approximation in the fcc lattice. Previous calculations of the binary limiting systems have shown the interest of introducing both chemical and magnetic interactions to treat the equilibrium between phases of different structures in the case of ferromagnetic alloys. This treatment is extended here in the case of the ternary system. Magnetic interactions are considered explicitly between nearest neighbours in a spin-1/2 treatment. The considered system in the CVM is thus a quinary system Fe+ Fe- Cu Co+ Co-. The input parameters of the model are obtained from available thermodynamic data: mixing enthalpies, Curie temperatures and binary diagrams. As a result several isothermal sections of the Fe-Cu-Co system are calculated between 723K and 1273K which compare favourably with literature data concerning the binary systems, and experimental results recently established in our laboratory.