MICROSTRUCTURE AND MECHANICAL-PROPERTIES OF CVI CARBON-FIBER SIC COMPOSITES

Microstructures and mechanical properties of carbon fiber/SiC composites prepared with chemical vapor infiltration (CVI) were examined to optimize the process conditions such as reactant and infiltration temperature. Ethyl-trichloro-silane (ETS) and methyl-trichloro-silane (MTS) were used as a source of SiC. CVI was conducted for 108 ks at maximum under a pressure of 13.3 kPa at 1273-1573 K. The composite with a density higher than 80% was obtained at 1373-1423 K and 1423-1374 K from ETS and MTS, respectively. The main matrix formed was beta SiC for both reactants. However, silicon also deposited in SiC matrix for MTS. Preferential wettability of SiC to the carbon fiber was observed, and graphite was detected in the interface between the matrix and the carbon fiber by TEM. Mechanical properties were evaluated by bend tests at room temperature. High strength of around 800 MPa was obtained for the composites if the thickness of the surface coated layer was less than 50 mum. Apparent fracture toughness of the present carbon fiber/SiC composite was 6-10 MPa m1/2 at room temperature.