Origins of hindrance in densification of Ag/Al2O3 composites

The densification and microstructure development were studied for Ag-matrix composites containing dispersed Al₂O₃ particles to examine the effect of inclusions on the densification of composites. The incorporation of Al₂O₃ particles into Ag matrix hindered densification. Microstructure observation revealed that pores larger than those in the matrix formed around Al₂O₃ particles during sintering. The pore morphology was dependent on the number density of Al₂O₃ particles. When the number density was low, pores remained around an Al₂O₃ particle and coalesced to a large circumferential void at high temperatures. When the number density was intermediate, clusters made of a few Al₂O₃ particles formed and pores within and around clusters remained up to high temperatures. When the number density was high, the distance between clusters became small and the clusters were connected, forming continuous pores (pore channels). The three-dimensional connectivity of Ag was decreased, and the shrinkage between Ag particles resulted in thickening of pore channels. The presence of these large pores was the origin of the hindrance in densification.