Ordering in fcc lattices by the Cluster Variation Method and Path Probability Method

Abstract

A study synthesizing the kinetic and equilibrium aspects of order-disorder phase transitions is attempted for an fcc system at 50 at% using the Cluster Variation Method and the Path Probability Method. The disorder-L12-L10 phase diagram is calculated using the tetrahedron approximation of the CVM. A perturbation expansion of the free energy functional, followed by a Fourier transformation, provides a concentration wave description of the system, from which the ⟨100⟩ instability locus in the phase diagram and the short range order diffuse intensity are obtained. By employing the Path Probability Method, the time evolution of the pair and the tetrahedron correlation functions as well as fluctuations from the most probable path during an isothermal aging process following a quenching operation are calculated for a system at 1:1 stoichiometry. Finally, the most probable path followed by the system during an isothermal aging process is placed in a thermodynamic configuration space. © 1992, The Japan Institute of Metals. All rights reserved.