APPLICATION OF OCTAHEDRON TETRAHEDRON CLUSTER VARIATIONAL METHOD FOR ANALYSIS OF SHORT-RANGE ORDER IN FE-NI-CR FCC ALLOYS

The Octahedron Tetrahedron Cluster Variational Method (OT-CVM) has been extended to the ternary substitutional F.C.C. alloys. A computer program was developed to determine the concentrations of various configurations of the two basic clusters: the regular nearest neighbor tetrahedron and the octahedron defined by six equilateral nearest neighbor triangles. Before the model could be applied to the Fe-Ni-Cr F.C.C. system, pair interchange energies had to be determined. This was done by fitting the experimental data to the model predictions. Application of the model to an alloy with the composition Fe-40Ni-15Cr, wt%, showed a slight deviation of the distribution of atoms from the random distribution at 1273K. Contrary, at 298K, the deviation is much greater.