Effect of Environment on the Stress‐Rupture Behavior of a Carbon‐Fiber‐Reinforced Silicon Carbide Ceramic Matrix Composite

Abstract

Stress‐rupture tests were conducted in air, under vacuum, and in steam‐containing environments to identify the failure modes and degradation mechanisms of a carbon‐fiber‐reinforced silicon carbide (C/SiC) composite at two temperatures, 600° and 1200°C. Stress‐rupture lives in air and steam‐containing environments (50–80% steam with argon) are similar for a stress of 69 MPa at 1200°C. Lives of specimens tested in a 20% steam/argon environment were about twice as long. For tests conducted at 600°C, composite life in 20% steam/argon was 30 times longer than life in air. Thermogravimetric analysis of the carbon fibers was conducted under conditions similar to the stress‐rupture tests. The oxidation rate of the fibers in the various environments correlated with the composite stress‐rupture lives. Examination of the failed specimens indicated that oxidation of the carbon fibers was the primary damage mode for specimens tested in air and steam environments at both temperatures.