Intergranular films in metal-ceramic composites and the promotion of metal particle occlusion

Sintering metal particle (Cu or Ni) reinforced alumina composites, doped with CaO and SiO2 additives, resulted in metal particles found as occlusions within alumina grains, and located at alumina grain boundaries and triple junctions. In composites sintered without additives, only isolated cases of metal particle occlusion were found. In the doped samples, intergranular films were observed at alumina grain boundaries and metal-alumina interfaces, for both types of particles. The occluded particles were found to have a limited size-range of 250 ± 20 nm, while particles at alumina grain boundaries had an average size of ~1.4 ± 0.3 μm. It is suggested that the higher driving force for grain growth during the initial stages of sintering, together with an increase in grain boundary mobility due to the intergranular films, results in increased particle–grain boundary detachment during the initial stages of sintering.