Kinetics of B2- and D03-type ordering and formation of domain structures in Fe–Al alloys

Abstract

Time-dependent Ginzburg–Landau (TDGL) formulation has been developed for the ordering processes ofB2 and D03 types in binary alloy systems. In the formulation, three order parameters aredefined in order to describe the state of order. Equivalent variants of B2 andD03 structures are distinguished using these order parameters. The mean-field free energyis defined in the form of a Landau-type expansion using the order parametersand a composition parameter. Interface energies due to local variations in thedegrees of order and concentration are given with a gradient square approximation.Kinetic equations are derived from the Ginzburg–Landau-type potential in orderto describe the time-evolutions of the order parameters and the concentration.Numerical simulations of the kinetic equations have been performed for B2- andD03-type ordering as well as concurrent ordering and phase separation to disorderedA2+D03. The simulated results provide a good reproduction of the formation processes of B2 andD03 ordereddomains in an Fe3Al alloy.