Thermal stability of C/Mullite composites in different environments

In the present study, the mechanical properties and microstructure of C/Mullite composites with a PyC-SiC double-layer interfacial coating after annealing were systematically studied to evaluate the evolution of thermal stability in an inert atmosphere and a vacuum. The C/Mullite composites annealed in the inert atmosphere exhibited better thermal stability than those annealed under the vacuum. The main factor for failure of the composites was carbothermal reduction. The activation temperature of carbothermal reduction in composites in the inert atmosphere was ～100 °C higher than that in the vacuum. Once carbothermal reduction was activated, the microstructure of composites was destroyed, resulting in a significant weight loss and mechanical property degeneration. The degeneration of mechanical properties was unrecoverable.