Kinetics of phase separation in Fe-Cr-Mo ternary alloys

Numerical simulations were performed using a model based on the Cahn-Hilliard equation in order to investigate asymptotic behavior of a minor element associated with phase decomposition of the major element in Fe-Cr-Mo ternary alloys. Bifurcation of peaks of Mo along peak tops of Cr concentration occurs in an Fe-40 at%Cr-5 at%Mo alloy at 800 K. Bifurcation of peaks of Cr is also shown in an Fe-40 at%Mo5 at%Cr alloy at 800 K. The amplitude of a peak of Mo in an Fe-40 at%Cr-5 at%Mo alloy at 1025 K increases with time. The asymptotic behavior of Mo or Cr along a trajectory of a peak top of Cr or Mo concentration depends on the sign of the second derivative of the chemical free energy with respect to the concentrations of Cr and Mo. For the case in which both Cr and Mo are within the spinodal region of an Fe-Cr-Mo ternary phase diagram, both Cr and Mo decompose separately and induce separation of the other element. Simulated asymptotic behavior of Mo and Cr in Fe-Cr-Mo ternary alloys is in good agreement with that predicted by the theory proposed by the present authors.