Reaction-Formed and Melt-Infiltrated SiC Composites

The reaction between liquid silicon and solid carbon can produce a remarkably pure b silicon carbide of high strength, electrical resistivity and thermal conductivity. We are using selective-doping experiments along with thermal and electrical conductivity measurements to study impurity rejection during liquid-solid reaction, which results in high thermal conductivity (270 W/mK) as well as high electrical resistivity (106 W-cm), making this class of materials potentially attractive for electronic packaging and structural and thermal applications. The melt-infiltration processing of Si-SiC starting materials is being studied as an alternative fabrication method for SiC-metal and SiC-metal silicide composites for high thermal conductivity applications. In addition, a collaboration with GE Aircraft Engines is directed towards melt-infiltration processing of refractory silicide matrices for continuous SiC fiber composites, in order to produce high temperature structural composites with increased high temperature performance relative to presently used Si-SiC matrices.

Possible alternative matrix materials for high temperature silicon carbide (SiC) fiber-reinforced composites are being explored. As SiC-based fibers become increasingly refractory, new matrix materials are required to replace the melt-infiltrated Si-SiC matrix currently used in many composites. Melts in the compatibility triangles MoSi2-Mo5Si3C-SiC and VSi2-V5Si3C-SiC, as well as an alloy of these two systems, have been studied in infiltration experiments. Experiments were conducted on porous SiC samples as well as SiC-fiber reinforced composites. Thermodynamically stable multiphase matrices have been identified, with particularly promising results being obtained in a composite with a Mo-V-Si-C alloy matrix. In this system, wetting and infitlration is observed with low reactivity and extensive fiber-pullout being retained after processing.