Microstructure and mechanical properties of carbon fiber needled felt reinforced sol-derived YAG composite

The study concerning the second phase reinforced YAG matrix composites is few although YAG is well known as a desirable thermo structural ceramic. In this paper, low-cost 3D carbon fiber needled felt was used as reinforcement to improve the fracture toughness of YAG, and the carbon fiber needled felt reinforced YAG (C/YAG) composite was fabricated through vacuum impregnation-drying-heat treatment, using the Y₂O₃-Al₂O₃ sol with a high solid content as raw material. The microstructure, mechanical properties, thermal stability and oxidation resistance of C/YAG composite were carefully investigated. Due to the characteristics of reinforcement and the microstructure, the as-fabricated C/YAG composite showed non-catastrophic failure behavior and much higher fracture toughness compared with monolithic YAG ceramic. The flexural strength of C/YAG composite was well retained after annealed at 1700 °C and 1800 °C under inert atmosphere. Although the chemical inertness between carbon fiber and YAG was confirmed up to 1800 °C, the physical bonding of interface was enhanced during annealing, which led to the decrease of fracture work, especially at 1800 °C. The oxidation resistance of C/YAG composite was related to the cracks and pores since YAG is immune to oxidation. The changes of microstructure and flexural strength after oxidation at 1200 °C, 1400 °C and 1600 °C were characterized and analyzed.