Abstract
Abstract To improve fracture toughness of monolithic Al 2 O 3 ceramics, three-dimensional carbon fiber preform was used as reinforcement, and the C/Al 2 O 3 composites without interfacial coating were fabricated through vacuum impregnation-drying-heat treatment route with an Al 2 O 3 sol as starting material. Characteristics of the Al 2 O 3 sol with high solid content were firstly analyzed. Then thermal stability and oxidation resistance of the C/Al 2 O 3 composites were investigated. It is found that the Al 2 O 3 sol is an appropriate raw material for the fabrication of C/Al 2 O 3 composites. The C/Al 2 O 3 composites with a total porosity of 15.5% show a flexural strength of 208.5 MPa and a fracture toughness of 8.1 MPa m 1/2 . Strength loss is observed after the composites were annealed at 1400 °C and 1600 °C under inert atmosphere. Oxidation resistance of the C/Al 2 O 3 composites is unsatisfactory because of the existence of open pores and microcracks. When Al 2 O 3 matrix was modified with SiO 2 , the oxidation resistance is remarkably improved due to the viscous flow effect of SiO 2 .
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