Degradation mechanisms of a SiC fiber reinforced self-sealing matrix composite in simulated combustor environments

Non-oxide ceramic matrix composites are potential candidates to replace the current nickel-based alloys for a variety of high temperature applications in the aerospace field. The durability of a SiC(f)/PyC(i)/[Si, C, B](m) composite with a multi-layered self-sealing matrix and Hi-Nicalon fibers was investigated at 1200 °C for exposure durations up to 600 h. The specimens are aged in a variety of slow-flowing air/steam gas mixtures and total pressures, ranging from atmospheric pressure with a 10–50% water content to 1 MPa with 10–20% water content. The degradation of the composite was determined from the measurement of residual strength and strain to failure on post-exposure specimens and correlated with microstructural observation of the damaged tows. The most severe degradation of the composite occurred at 1 MPa in an air/steam (80/20) gas mixture. Correlation between this degradation and the dissolving of the SiC fibers in the generated boria-containing glass, is discussed.