Theoretical Analysis of Phase Decomposition in Real Alloy Systems based on the Non-Linear Diffusion Equation

Abstract

A Khachaluryan type diffusion equation including solute atom occupation probability in atom site which should be so called discrete type non-linear diffusion equation, is proposed. The composition dependence of atomic interchange energy is taken into account so as to be applicable for the real alloy system, and the non-linear composition fluctuation is also introduced. The two dimensional computer simulations are performed for the phase decomposition of the Al-Zn, Cu-Co and Fe-Mo binary alloy systems by utilizing the thermodynamic data on the equilibrium phase diagrams. The microstructures theoretically obtained are coincident with experimental results of the real alloys. A long and loose solute concentration is developed with progress of annealing at the single phase region of phase diagram, that is caused by a non-linear effect of the composition fluctuation. Such the solute concentration effectively assists the nucleation of precipitate particularly in the lower solute content alloys.