Thermal shock resistance of carbon fiber preform reinforced sol-derived YAG composites

Abstract

Thermal shock behaviors of the carbon fiber needled felt reinforced sol-derived YAG (C/YAG) composites were investigated under static air at first. It is found that the preexistent cracks were enlarged and some new cracks were generated during thermal shock because of the obvious thermal expansion mismatch between carbon fiber and YAG. After thermal shock from 1200 °C or 1400 °C to room temperature for 10 times, mass losses of 3.64% and 2.75% are detected, respectively, due to the oxidation of carbon fibers. At the same time, the C/YAG composites retain only 34.7% and 30.8% of their original flexural strengths. After the infiltration of SiO2 sol and its in-situ mullitization at 1300 °C, the cracks in surface layer of the C/YAG composites were well repaired, and the resistance to crack growth and propagation was strengthened. Accordingly, after the same thermal shock conditions, the mass losses are reduced to 0.64% and 0.85%, and the flexural strength retention ratios are increased to 66.7% and 60.2%.