Fabrication of three-dimensional carbon fiber preform reinforced YAG composites from a sol with high solid content

To improve fracture toughness of monolithic YAG ceramics, three-dimensional carbon fiber preform was employed as reinforcement, and the C/YAG composites without interfacial coating were fabricated through vacuum impregnation-drying-heat treatment route with an Y2O3-Al2O3 sol as starting material. Characteristics and high temperature evolution behaviors of the Y2O3-Al2O3 sol with high solid content were analyzed. Then the microstructure and mechanical properties of C/YAG composites were characterized. The results indicate the Y2O3-Al2O3 sol is an appropriate raw material for the fabrication of C/YAG composites. The C/YAG composites show a flexural strength of 294.6 MPa and a fracture toughness of 9.3 MPa m(1/2) although the total porosity reaches 13.8%. The flexural strength is comparable to the full dense monolithic YAG ceramics. The fracture toughness of monolithic YAG ceramic is remarkably enhanced due to the introduction of carbon fiber preform. The mechanical properties can be further improved if the porosity is reduced and the interfacial structure is optimized.