Processing-microstructure-property relationships in reaction hot-pressed MoSi2 and MoSi2/SiCp composites

Monolithic MoSi2 and MoSi2-20vol.%SiC composites have been prepared by reaction hot-pressing Mo and Si or Mo, Si and SiC powder mixtures in the range 1450-1500 degrees C. As Si atoms diffuse into the Mo lattice under external pressure, a complete reaction takes place between Mo and Si leading to the formation of MoSi, phase. The initial Mo particle size affects the grain size of the MoSi, that is formed. Grain boundaries and interfaces of MoSi, with SIC were abrupt on the atomic scale, except for some MoSi2/SiC boundaries, where a 5-8 nm thick amorphous phase, believed to be SiO2, could be seen. MoSi2 was also processed by vacuum hot-pressing MoSi2 powder at 1700 degrees C for comparison. The composites show a moderate increase in flexural strength and hardness over monolithic hot-pressed polycrystalline MoSi,. There is, however, a significant increase in the high-temperature compressive yield strength due to addition of SiC reinforcements. Grain sizes of the MoSi2 matrix strongly influence the fracture toughness and related micromechanisms. (C) 1997 Elsevier Science S.A.