Effects of moisture on fatigue behavior of SiC/SiC composite at elevated temperature

The effects of moisture on fatigue performance of a ceramic matrix composite (CMC) at an elevated temperature were investigated. CMC consisted of silicon carbide fiber reinforced in silicon carbide matrix with boron nitride (BN) interphase. Two series of tension-tension fatigue tests at a frequency of 10 Hz with a stress ratio of 0.1 were conducted at 750 °C: (1) under dry environment test condition (with 0% moisture content) and (2) under humid environment test condition (with 60% moisture content). Fatigue life diagrams were developed under these two conditions. Moisture decreased the fatigue life at a prescribed stress level relative to that without moisture. A detailed microscopic analysis showed that moisture caused embrittlement of the interphase between fiber and matrix, which in turn caused the degradation of fatigue performance of the tested CMC system.