Modelling of phase separation dynamics in iron-based ternary alloys

Mechanism of phase separation in an Fe-X-Y ternary alloy was investigated by using a model based on the Cahn-Hilliard equation for multicomponent system. The asymptotic behavior of the minor element, Y, in the Fe-X-Y ternary alloy along a trajectory of a peak top of the major element, X, is classified into three group according to the sign of the second derivative of the chemical free energy with respect to the concentration of X and the concentration of Y, f_XY. Bifurcation of peaks of the minor element occurs for the case that the sign of f_XY is negative at the initial time and positive at the later stage. The incorporation of elastic term in addition to the chemical portion into the free energy is known to retards phase separation. However the above classification is valid for the case that the elastic strain plays an important role in kinetics of phase separation. Small addtion of a substitutional element to an Fe-based binary alloy with in the spinodal region was found to enhance phase separation.