Phase field modeling of the effect of porosity on grain growth kinetics in polycrystalline ceramics

We present a phase field model for investigating grain growth in polycrystalline ceramics containing porosity. Grain growth in such materials is complicated by the interaction between the pores and the grain boundaries, which tends to hinder the kinetics of grain growth. In addition to grain-boundary migration, the model takes into consideration pore-surface diffusion and, whenever effective, other diffusion mechanisms such as volume diffusion and grain-boundary diffusion. The pore-surface diffusion controls the pore mobility. A direct relationship between the model parameters and the material properties is established, which facilitates the quantitative analysis of grain growth. The model is used to investigate the conditions under which porosity is effective in controlling grain growth. Application of the model to ceria shows that grain growth law in this material is sensitive to the level of porosity. In particular, the grain growth in ceria gradually changes from boundary controlled growth to pore controlled growth as porosity increases. The effects of porosity, temperature, grain boundary and surface mobility on grain growth were investigated. The model results agree well with published grain growth experiments.