Properties and Microstructure of Molybdenum Disilicide–β′;‐SiAlON Particulate Ceramic Composites

Particulate ceramic composites that were composed of a combustion-synthesized {beta}{prime}-SiAlON matrix and dispersed MoSi{sub 2} particles were hot pressed at 1,600 C in a nitrogen atmosphere. The physical and mechanical properties of the composites that contained 15, 30, and 45 vol% MoSi{sub 2} were evaluated. The average four-point bend strength, fracture toughness, and Vickers hardness of the composites were in the ranges of 500--600 MPa, 3--4 MPa{center_dot}m{sup 1/2}, and 11--13 GPa, respectively. The measured mechanical strength and hardness were very similar to the values that were predicted from the rule of mixtures. The fracture toughness of the combustion-synthesized {beta}{prime}-SiAlON (2.5 MPa{center_dot}m{sup 1/2}) was apparently enhanced by the MoSi{sub 2} particles that were added. The increase in the fracture toughness was predominantly attributed to the residual thermal stress that was induced by the thermal expansion mismatch between the MoSi{sub 2} particles and the {beta}{prime}-SiAlON matrix. The composites showed improved electrical conductivity and oxidation resistance over monolithic {beta}{prime}-SiAlON. High-resolution transmission electron microscopy examination of the composites indicated that the MoSi{sub 2} was chemically well compatible with the {beta}{prime}-SiAlON.