Microstructure And Properties Of Matrix Modified C/SiC Composites By Pyrocarbon

Carbon fiber reinforced silicon carbide composites(C/SiC) exhibit outstanding properties, such as low density, high strength, high temperature resistance, good ablation performance and erosion resistance. C/SiC show superior oxidation resistance in comparison to Carbon/Carbon(C/C), and be considered as the most promising thermal structural candidate materials which can be used at high thrust-weight ratio aero-engine, liquid rocket motor(LRM), solid rocket motor(SRD), scamjet motor as well as thermal protection system(TPS) on re-usable shuttles, advanced friction and clutch systems of brake industry. Whereas, ceramic matrix composites(CMC) components, such as leading edges, combustion chambers, thrust nozzles, TPS, brake discs or pads and zero-expansion structures like telescopes or calibration plates which have different working conditions demand C/SiC possessing different mechanical, thermo-physical and environmental properties. In order to vary the properties of C/SiC in a wide range to fulfill the requirements of different applications, the microstructure and phase composition of C/SiC should be tailored. In this research work, carbon fiber reinforced C-SiC binary matrix composites(C/C-SiC) with PyC/SiC alternative multilayered matrix were fabricated by chemical vapor infiltration, the effects of location and quantity of PyC in the matrix on the mechanical properties and oxidation resistance of C/C-SiC were investigated. The main contents and conclusions are as follows:(1) The effects of location and quantity of PyC in the matrix on the mechanical properties of 2D C/C-SiC were investigated. The results show that PyC in the matrix of 2D C/C-SiC can greatly improve the fracture work, fracture toughness and strain to failure compared to those of 2D C/SiC;whereas the flexural strength, tensile strength and modulus of them can be approximately the same. PyC in the outer matrix of fiber bundles is unfavorable for improving the mechanical properties of 2D C/C-SiC.(2) The effects of location and quantity of PyC in the matrix on the mechanical properties and oxidation resistance of 3D C/C-SiC were investigated. The results show that PyC in the outer matrix of fiber bundles was unfavorable for improving the the flexural strength and fracture toughness of 3D C/C-SiC, but can significantly improvethe fracture toughness and strain to failure compared to those of 3D C/SiC.(3) The effects of location and quantity of PyC in the matrix on oxidation resistance of 2D C/C-SiC were investigated. Results show that 2D C/C-SiC and 2D C/SiC had identical oxidation behavior controlled by defects. Both of them had weight loss at 700, 1000, 1300°C, and-the maximum weight loss occurred at 700°C, the minimum weight loss occurred at 1000°C. The relation between residual flexural strength and weight loss of 2D C/C-SiC and 2D C/SiC was identical, residual flexural strength decreased with weight loss increasing. The residual flexural strength of 2D C/C-SiC was controlled by oxidation consumption of carbon phase.