Performance Evaluation of Cf-SiC Composites under High Enthalpy and High Speed Plasma

Carbon based composites particularly C_f-SiC composites are finding wide range of applications at elevated temperature because of their high specific stiffness, excellent ablation resistance, low density, low coefficient of thermal expansion, ability to retain strength at high temperature etc. A number of component of hypersonic vehicles are made from these composites. These composites can be processed through four different routes, namely by polymer impregnation and pyrolysis (PIP), by liquid silicon impregnation (LSI), slurry infiltration and by isothermal chemical vapor impregnation (ICVI). C_f-SiC composites fabricated by liquid silicon impregnation (LSI) and isothermal chemical vapor impregnation (ICVI) are exposed to hypersonic condition. Mass loss of exposed samples was determined by micro balance. Degraded surfaces were examined with the help of scanning electron microscopy. Pyrocarbon/silicon carbide [(PyC/SiC) n ; n = 4] coated C_f-SiC composites fabricated by ICVI process exhibits the best performance. The main material removal mechanism is estimated to be mechanical erosion and evaporation of oxide scale. Materials loss due to sublimation and ablation can be neglected at the test temperature attained.