Microstructural evolution and formation of extended voids in Ag–Cu metal-matrix composite during prolonged annealing

Prolonged annealing of Ag–Cu metastable metal-matrix composite produced by compaction of Cu@Ag core-shell powder, revealed dramatic transformations in its microstructure. Heat treatment resulted in pronounced changes in particle morphology, extended grain boundary diffusion, and the formation of surface pores at the Cu/Ag interface, as well as extended voids within the bulk material. These phenomena are interpreted as consequences of the reduction of surface, interface and grain boundary energy, and diffusion and wetting processes, including pore migration and coagulation. Based on experimental observations, a model has been developed that explains the growth and migration of the pores leading to the formation of extended voids. This study provides new insight into the mechanisms of microstructural evolution in metal-matrix composites when annealed at relatively high temperatures, and opens pathways for their targeted application in advanced technologies such as electronic contacts. • 700 °C caused the transformation of spherical Cu particulates into polyhedral ones. • Bidirectional Cu–Ag diffusion caused partial or complete grain boundary wetting. • Complete wetting occurred only along general grain boundaries. • Protrusion tongues were formed at special boundaries. • A model was developed explaining voids growth and migration.