Infiltration/Pyrolysis Processing of Fiber-Reinforced Silicon Nitride

While its high-temperature strength, resistance to oxidation, and other properties make silicon nitride an attractive candidate for many advanced structural applications, its propensity for brittle failure has hindered its widespread adoption. One approach to avoiding brittle failure is through incorporation of continuous fiber-reinforcement; however, conventional (powderbased) methods of silicon nitride fabrication can degrade fibers and are not amenable to the production of complex shapes. The Southwest Research Institute has developed a number of polymeric precursors to silicon nitride which are available as thermosetting liquids, and we have shown that these materials can be used in combination with near net-shape manufacturing techniques to produce fiber-reinforced silicon nitride composites. Mechanical property tests conducted at room temperature suggest that these polymer-derived composites exhibit fracture behavior comparable to those produced through conventional techniques; micromechanical investigations conducted at 800°C indicate that non-brittle failure is maintained at elevated temperature.