Processing-microstructure-properties relationships of MoSi2-SiC composites

Silicon carbide green bodies with and without carbon-fibre reinforcement were infiltrated with MoSi2-Si-X to produce high-temperature resistant materials. X is Cr, Ti, Al or B respectively. By adding silicon and one of these components to MoSi2 the melting point is lowered dramatically. The composites could be processed by melt infiltration at max. 1600 C. During infiltration the additives react within the infiltrated body with carbon or silicon to form high-temperature resistant carbides or silicides. Thermodynamic calculations were performed to analyse the reactions during infiltration. The infiltration parameters were studied with respect to the resulting microstructure and properties. By fitting the amount of additives to the quantity of carbon in the SiC-body (or vice versa) no decrease in strength could be observed up to 1500 C. The fracture toughness can be increased by the use of high-modulus carbon fibres. The most promising X-element for a high-temperature resistant material is titanium. 18 refs.