Phase decomposition in isothermally-aged Fe-Cr alloys

Phase decomposition was studied during aging of an Fe-32 and 40 at.%Cr alloys by means of HRTEM, hardness and the numerical solution of the nonlinear Cahn-Hilliard differential partial equation using the explicit finite difference method. Results of the numerical simulation permitted to describe appropriately the mechanism, morphology and kinetics of phase decomposition during the isothermal aging of this alloy. The growth kinetics of phase decomposition was observed to be very slow during the early stages of aging and it increased considerably as the aging progressed. The morphology of decomposed phases consisted of an interconnected irregular shape with no preferential alignment for short aging times and a further aging caused the change to a plate shape of the decomposed Cr-rich phase aligned in the 〈110〉 directions of the Fe-rich matrix. The increase in hardness seems to be associated with the coherency and nanometer size of the spinodally-decomposed phases in the aged alloy.