1992 Volume 32 Issue 8 Pages 926-931
Microstructure and mechanical properties of carbon fiber/SiC composites prepared by chemical vapor infiltration (CVI) using ethyl-trichloro-silane (ETS) and methyl-trichloro-silane (MTS) as sources of SiC have been examined. The CVI was conducted under non-isothermal condition keeping a pressure of 13.3 kPa and temperature of 1273-1573 K at the downstream side. The highest degree of infiltration with a density higher than 80% was obtained. Main matrix formed was β 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 phase 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 ETS. However the fracture strength strongly depended on the thickness of SiC layer covering the composite as well as porosity. The strength increased with decreasing both surface coated layer and porosity. Apparent fracture toughness of the present carbon fiber/SiC composite was 6-10 MPam1/2 at room temperature.