Pressure-Pulsed Chemical Vapor Infiltration of SiC to Three-Dimensional Carbon Fiber/SiC Preform Prepared by Polymer Impregnation and Pyrolysis.

Abstract

Preforms were prepared by PIP (Polymer Impregnation and Pyrolysis) processing using polycarbosilane to 3-dimensional orthogonal weave fabrics of pitch-based carbon fiber. Porous matrices of the preforms were still more filled with β-SiC by PCVI (Pressure Pulsed Chemical Vapor Infiltration) processing using source gas mixture of SiCl4-CH4-H2 system to obtain dense 3-dimensional carbon fiber reinforced SiC matrix composites (3D-C/SiC). In the PCVI process, influence of the processing conditions on densification of the matrices was investigated in detail. The PCVI filling up to 120000 pulses were carried out under various conditions with varying temperature, residence time and gas flow rate. Then the filling-ratio was evaluated from changes in density and porosity, and crystal-phases of deposits were identified by XRD. The filling-ratio and the phase of deposits varied with the PCVI processing conditions. The PCVI processing under the conditions of 1373K in temperature, 1.5s in residence time, 4mol% each of SiCl4 and CH4 in molar-concentration and 80kPa in total pressure gave the highest filling-ratio. In this case, the number of pulses and operating time necessary for saturation of the filling-ratio were 60000 pulses and 192ks, respectively. The porosity of the densest composite was about 6% from macrosurface to 0.5mm in depth and less than 9% even to 1.5mm in depth. Also, it was found that higher total pressure was effective for increasing filling-speed without increasing the porosity, but disadvantageous in the consumption of the source gases.