Movement of Kirkendall markers, second phase particles and the type 0 boundary in two-phase diffusion couple simulations

Most earlier simulation work on diffusion couples containing dispersed phases was limited to one-dimensional models. The models assumed that all diffusion occurs in the matrix phase and that precipitates are point Sources or sinks of solute. Microstructural evolution in the interdiffusion zone and its effect on diffusion kinetics were ignored. In this study, spatial and temporal evolutions of two-phase microstructures are treated explicitly by applying the phase field method. Using a two-phase diffusion couple as an example. it is shown that both precipitates and the so-called Type 0 boundary migrate as a result of the Kirkendall effect. The Type 0 boundary becomes diffuse spreading out over several rows of precipitates in the simulation. Accordingly, "horns" in the diffusion path are less sharp than seen in earlier work but are similar in that they point in the same direction. Also the initial slope of the diffusion path differs significantly from the earlier work. In addition, the phase field method provides a detailed picture of Kirkendall marker movement in a two-phase microstructure. The marker plane bends around precipitates and individual markers move along curved paths. (C) 2003 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.