Mechanism for acceleration of phase separation in Fe-base ternary alloys was investigated with use of a model based on the Cahn-Hilliard equation. Behavior of the minor element in an Fe-base ternary alloy along the trajectory of the peak of the major element is dependent on the sign of the second derivative of the chemical free energy with respect to the concentrations of the major and minor elements. However, the concentration of the major element along the trajectory of its peak top increases with time regardless of the sign of the second derivative of the chemical free energy. The addition of a substitutional element to an Fe-base binary alloy with composition within the spinodal region was found to accelerate phase separation
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