Fatigue Behavior of Hi-Nicalon Type-S/BN/SiC Ceramic Matrix Composites in a Combustion Environment



The fatigue behavior of Hi-Nicalon Type-S/BN/SiC ceramic matrix composites (CMCs) was investigated in a combustion environment. Two versions of this CMC were tested. The first version was manufactured by a slurry casting process using woven fiber architecture and the matrix was densified by melt-infiltration (MI) of silicon. The other was a cross-ply laminate prepared by a traditional lamination process from unidirectional prepreg followed by the MI processing. Several tests were conducted at a frequency of 1 Hz and a stress ratio of 0.05 to develop the fatigue life diagrams for both material systems. The Prepreg MI CMC exhibited higher fatigue strength, especially for cycles-to-failure >10,000, in comparison with the slurry cast MI CMC. Micrographic analysis was conducted to document the oxidation and embrittlement, which was observed to be dependent upon the applied stress level and cycles-to-failure. Overall, the prepreg MI CMC was less prone to oxidation and had better fatigue properties, demonstrating the potential for long-term use as a structural high-temperature material for high-temperature oxidative service environments, such as those found in gas turbine engines.