Damage Tolerant Oxide Ceramics Using Pure Fiber and Matrix Laminates

摘要

A fiber-reinforced ceramic composite was developed using matrix-infiltrated and non-infiltrated fiber layers. Processed layers were hot-pressed together resulting in an oxide-fiber (Nexte1720), oxide-matrix (mullite) composite. Matrix slurries were prepared using submicron-sized alpha-Al2O3 powder coated with amorphous SiO2, along with additives to decrease mullite-formation temperature. Room temperature 3-point bend tests were conducted on as-received samples and samples exposed to long-term, high- temperature oxidation. Composites demonstrate both reasonable fracture strength and damage tolerance. The favorable thermo-mechanical behavior can be explained by the composite's laminate-type structure. Matrix-infiltrated fiber layers provide strength but behave in a brittle, quasi-monolithic manner. Non-infiltrated fiber layers connect intiltrated layers, and provide damage tolerance through in-plane crack deflection and crack bridging. Varying inatrix-to-fiber ratio allows tailoring of composite properties, trading off strength for damage tolerance. These composites provide damage tolerant behavior in the absence of fiber interface coatings, and when using a matrix which bonds strongly to fibers.