Thermal stability and oxidation resistance of C/Al2O3 composites fabricated from a sol with high solid content

To improve fracture toughness of monolithic Al2O3 ceramics, three-dimensional carbon fiber preform was used as reinforcement, and the C/Al2O3 composites without interfacial coating were fabricated through vacuum impregnation-drying-heat treatment route with an Al2O3 sol as starting material. Characteristics of the Al2O3 sol with high solid content were firstly analyzed. Then thermal stability and oxidation resistance of the C/Al2O3 composites were investigated. It is found that the Al2O3 sol is an appropriate raw material for the fabrication of C/Al2O3 composites. The C/Al2O3 composites with a total porosity of 15.5% show a flexural strength of 208.5 MPa and a fracture toughness of 8.1 MPa m1/2. Strength loss is observed after the composites were annealed at 1400 °C and 1600 °C under inert atmosphere. Oxidation resistance of the C/Al2O3 composites is unsatisfactory because of the existence of open pores and microcracks. When Al2O3 matrix was modified with SiO2, the oxidation resistance is remarkably improved due to the viscous flow effect of SiO2.