Phase field simulations of grain growth during sintering of two unequal-sized particles

Sintering is fundamentally a process of bonding between solid particles which typically occurs under high temperatures relative to the material's melting point. The sintering of real powders requires consolidation of unequal-sized particles. The consolidation of unequal particles involves sintering and simultaneous grain growth. In this work, sintering and simultaneous concurrent grain growth of two unequal-sized particles are modeled using a phase field simulation method. The sintering process is revealed to consist of three sub-processes: (1) neck growth, (2) coarsening with concurrent slow grain boundary migration, and (3) rapid grain boundary motion. The observed grain boundary migration with coarsening was not predicted in prior analytical models of sintering. The simulation results are analyzed based on a thermodynamic analysis of the driving forces for different sub-processes. Analytical expressions for grain boundary velocity in the second and the third sub-processes are derived. The slow grain boundary migration is sensitive to the sintering geometry.

Research highlights▶ Sintering of unequal particles occurs in three sub-processes. ▶ The sub-processes are: neck growth, coarsening, grain boundary migration (GBM). ▶ Coarsening is responsible for initial increase of grain size during sintering. ▶ The sub-processes overlap significantly. GB migration starts during coarsening. ▶ Rapid GBM signifies the dominance of grain growth by GBM & completion of coarsening.