The Impact of Pores on Microstructure Evolution: A Phase-Field Study of Pore-Grain Boundary Interaction

Among the most important issues of today’s materials research ceramic materials play a key role as e.g. in Lithium batteries, in fuel cells or in photovoltaics. For all these applications a tailored microstructure is needed, which usually requires sintering: A pressed body of compacted powder redistributes its material and shrinks to a compact body without pores. In a very porous polycrystal, pores constrain the motion of interfaces (pore drag) and no grain growth occurs. During further sintering the number and size of pores decreases and the pore drag effect fades away. Accordingly, in the final stage of sintering grain growth emerges. This grain growth decreases the driving force for sintering and is undesirable, but hard to avoid. Since application of ceramic materials usually requires a dense and fine-grained microstructure, it is of high interest to control the interplay of remaining pores and interface migration during sintering. Unfortunately, the present modeling of sintering does not allow for predicting microstructural evolution in an adequate way. In this study, a previously developed phase-field model of pore-grain boundary interaction during final stage sintering is extended by a pore-interaction module to improve the modeling of final stage sintering. This module handles the growth of pores that come into contact during grain growth. The model with the extensions is used to simulate interface migration in a well-defined model setup. The results show that the present model is appropriate to describe grain growth during the final stage of sintering. However, the need of large scale simulations becomes evident: pore drag depends critically on the local geometry (i.e. position of the pores at grain boundaries, triple lines or quadruple points). The microstructure evolution during final stage sintering in polycrystalline ceramics underlies strong statistical variations in the local geometry. Accordingly, if grain growth in polycrystals in the presence of remaining pores from sintering is considered in detail, large scale simulations are needed to picture the local statistic variation of pore drag in an adequate way.