Carbon-Fiber-Reinforced Composites with Graded Carbon-Silicon Carbide Matrix Composition

Carbon-silicon carbide (C-SiC) graded-matrix composites were prepared via chemical vapor infiltration with carbon and SiC codeposition from methyltrichlorosilane (CH₃SiCl₃), acetylene (C₂H₂), argon, and hydrogen. The graded-matrix composites were prepared by gradually varying the source gases, from C₂H₂ to CH₃SiCl₃, in a semicontinuous process. Oxidation resistance, wear, and mechanical tests were conducted, and the microstructure was observed via optical microscopy, electron probe microanalysis, transmission electron microscopy, and scanning electron microscopy. The results show that this material seems to be macroscopically homogeneous, as an integral part of the entire material; however, microscopic examination shows a gradient variation of the matrix sheaths around each fiber. The oxidation resistance of the material is significantly superior to that of a C/C material, which is a promising thermostructural material, because of its low density, good mechanical properties, and good resistance to oxidation.