Reliability and failure mechanism of ceramic matrix composites in high-temperature combustion environment

Ceramic matrix composites such as the carbon fiber reinforced silicon carbide composites have received considerable attentions in their application of hot load-carrying structures for the aero-crafts. However, the reliability, life time as well as the failure mechanism in specific environment must be understood before its use. In this paper, a carbon/silicon carbide composite with protective silicon carbide coating was prepared by chemical vapor infiltration. The thermo-mechanical properties were performed on the composites in a self-built high-temperature combustion environment. Reliability of the composites in combustion environment was estimation under tensile strength, stress-oxidation behavior, as well as the cyclic fatigue, comparing with the results at room temperature in air. Test conditions were controlled at temperatures 1300°C, 1500°C and 1800°C, and the stress was sustained at 40MPa, 80MPa, 120MPa, 160MPa and 200MPa. Fatigue tests were conducted at the same maximum stress level of 180MPa but at various temperatures and cycles. Residual strength of pre-oxidized and pre-fatigued specimen was studied respectively in controlled environments. Analysis of failure mechanisms showed that interfacial bonding and oxidation of carbon fibers was the major difference of reliability and lifetime between the room and high temperatures. Oxidizing atmosphere in combustion environment speeded and enhanced the failure of composites by decreasing the load-carrying ability of fibers suffered from oxidation damage. The strength enhancement at room temperature but the significant strength degradation in high-temperature combustion environment was obtained after cyclic fatigue.