THE MICROSTRUCTURE OF PRESSURELESS SINTERED SILVER-TOUGHENED ALUMINA - AN INSITU TEM STUDY

An in situ transmission electron microscopy (TEM) study has been made of the microstructure of a pressureless sintered alumina-silver composite, which consists of both intergranularly and intragranularly positioned silver inclusions in the alumina matrix. The silver grains at the grain boundaries and junctions of the alumina matrix are 1-4 mum in size and angular in morphology. Residual thermal strains result in the formation of either the well-established dislocation rings or deformation twins or both in these intergranularly positioned silver particles. The silver particles entrapped inside alumina grains are 0.1-2 mum in size and rounded in morphology. Deformation twins were not found in these intragranularly positioned silver particles. The weak interfacial bonding between silver inclusions and the alumina matrix is characterized by the occurrence of voids or pores at the interface. Thermal mismatch-induced microcracks were not observed at the interface.