Spinodal decomposition in fine grained materials

Abstract

We have used a phase field model to study spinodal decomposition in polycrystalline materials in which the grain size is of the same order to magnitude as the characteristic decomposition wavelength (λSD). In the spirit of phase field models, each grain (i) in our model has an order parameter (ηi) associated with it; ηi has a value of unity inside the ith grain, decreases smoothly through the grain boundary region to zero outside the grain. For a symmetric alloy of composition, c = 0.5, our results show that microstructural evolution depends largely on the difference in the grain boundary energies, γgb, of A-rich (α) and B-rich (β) phases. If γgbα is lower, we find that the decomposition process is initiated with an α layer being formed at the grain boundary. If the grain size is sufficiently small (about the same as λSD), the interior of the grain is filled with the β phase. If the grain size is large (say, about 10λSD or greater), the early stage microstructure exhibits an A-rich grain boundary layer followed by a B-rich layer; the grain interior exhibits a spinodally decomposed microstructure, evolving slowly. Further, grain growth is suppressed completely during the decomposition process.