Investigation on alumina/molybdenum particulate composites

Dense alumina/molybdenum composites were fabricated by vacuum hot pressing mixtures of Al2O3 powder containing 10 to 20 vol% of Mo particulate. Microstructures were studied and discussed in terms of starting composition and characteristics of the powders. Due to the presence of oxygen impurities in the starting molybdenum powder, the dense composites contain, besides Mo particles, Mo-oxide particles present as a separate phase attached to Mo particles or within alumina matrix and also the phase Al2(MoO4)3. Alumina matrix exhibits a bimodal microstructure: regions of equiaxed grains are close to areas with coarse platelike grains. The driving mechanisms of microstructural evolution are suggested and the influence of microstructure on properties are discussed as well. Due to large Mo particle aggregates, the composites show a lower strength than that of monolithic alumina. Improvement of toughness is due to reinforcing mechanisms, which are originated both by the second phase particles and by the presence of elongated alumina grains. Moreover, the effects of aging the materials under air at room temperature and of oxidation at high temperature on the surface structure were investigated.