Research On The Fabrication Of C/sic Composite Using C/c Foam Preform Via Gaseous Silicon Infiltration Process

Carbon fiber reinforced silicon carbide composite (C/SiC) has been considered to be one of the most promising materials used for optical mirrors due to their unique characteristics such as low density, high Young's modulus, low coefficient of thermal expansion and high thermal conductivity. In order to solve the problems existed in the gaseous silicon infiltration (GSI) process which was caused by the nonuniformity of the porosity distribution of C/C preform, a novel carbon fiber reinforced carbon foam composite preform was firstly made by bubbling technology and the C/SiC composite exhibits excellent mechanical properties after adopted this preform.The effects of porosity and pore size distribution (PSD) of C/C preform on the performance of C/SiC composites were studied. The C/SiC composite derived from the C/C preform with a porosity of 48.41% and the mode pore diameter of 18μm shows excellent mechanical properties, while its bend strength is 146MPa and Young's modulus is 221GPa.When the pore size of C/C preform is less than 10μm, the gaseous silicon will agglomerate in the small holes. The reaction will be terminated by the volume expansion during the formation of SiC. Otherwise, after the formation of SiC, if the pore size is larger than 10μm, closed pores will appear in the composite.A novel type of C/C foam preform was made by introducing the bubbling technology into the fabrication process of conventional C/C preform. The C/SiC composite shows best performance when the PSD of the rayon-based C/C preform is about 20μm. Its bend strength and Young's modulus are 137MPa and 150GPa respectively. The poorer performance of rayon-based carbon felt and siliconization of carbon fibers are responsible for the low mechanical properties of C/SiC composite.The CVD SiC coating contributed more to the improvement of performance of C/SiC composite than the CVD C coating did. After the T700 carbon felt being treated after CVD SiC 15 hours, the C/SiC shows excellent mechanical properties, with the bend strength of 156MPa and Young's modulus of 289GPa.The high thermal treatment (HTT) can ignite the transformation of closed pores to open pores, which is beneficial to the optimization of PSD. The C/C foam preform with the HTTed showed better performance than the one didn't. The bend strength and Young's modulus are 165MPa and 322GPa respectively, while its ratio of thermal conductivity is 106.2W·m-1·K-1.