Preparation and characterization of SiC/SiC composites fabricated via Liquid Silicon Infiltration

SiC/SiC composites consist of silicon carbide fibers embedded in a silicon carbide matrix. As an alternative to classic CVI and PIP routes, Liquid Silicon Infiltration (LSI) was chosen as a technique with short process times to obtain composites with low porosity. Silicon Carbide composites show good thermal shock resistance, a low coefficient of thermal expansion and excellent physical and chemical stability at elevated temperatures and are therefore regarded as interesting candidates for various applications in combustion chamber environments. An interphase to control the fibre-matrix bonding and to prevent reaction during processing needs to be used. During processing the fibres were coated via CVD and then infiltrated via liquid polymer infiltration. As protective CVD coating Y2O3 was chosen and applied on single rovings. After pyrolysis a porous carbon network is created. During LSI liquid silicon will react with carbon forming a dense SiC matrix. To obtain a stoichiometric SiC matrix it is important to control porosity and improve the carbon yield by synthesizing new polymers. As carbon source different novolac-type phenolic resins were used, as well graphite fillers. The effectiveness of Liquid Silicon Infiltration depending on carbon source and pore morphology and stability of the SiC fibres during LSI is studied. The resulting microstructural and mechanical properties are discussed and first results of the Y2O3 protective coating are shown