A two-stage study of the sintering mechanism and pore morphology evolution by phase field modeling

Sintering is a critical solid-state bonding process, which largely governs the performance of key components in power electronics and biomedicine through its pore evolution dynamics. This study employs Ballistic Deposition Algorithm (BDA) to construct polydisperse powder systems and single-pore models, integrated with phase-field simulations to elucidate pore evolution mechanisms. For polydisperse systems, in addition to the positive correlation between the initial packing density and the densification rate, the curvature difference between particles of different sizes also provides an additional capillary driving force, significantly enhancing the densification rate. Focusing on the residual pores in the system, the theory of critical coordination number (Np) of pores is proposed under the model conditions used in this study (two-dimensional and isotropic interfacial energy), which holds that when N_p≥4, the interfacial tension balance causes a sudden drop in the pore closure rate, consistent with the classical concept of a critical pore coordination number. By changing the diffusion coefficient, it has been found that grain boundary diffusion significantly affects the sintering rate. The body diffusion optimizes the densification process in the later stage, while surface diffusion is related to the formation of the sinter neck and the initiation of pore coarsening. A two-stage model for pore closure is proposed, i.e., the stage of grain boundary reorientation and the stage driven by curvature gradient for neck contraction. The established initial packing-diffusion path-pore morphology correlation model is studied, which systematically summarizes the evolution laws of pores, thereby being expected to provide theoretical guidance for engineering applications.