PIP processing, microstructure and properties of Si{sub 3}N{sub 4} fiber and Al{sub 2}O{sub 3} fiber reinforced silicon nitride

Polymer infiltration/pyrolysis (PIP) processing has the potential to become an affordable means of manufacturing continuous fiber-reinforced ceramic-matrix components. The PIP method is very similar to the well-known polymer-matrix and carbon-carbon composite manufacturing techniques, the major difference being the use of a preceramic polymer in place of the organic polymer or carbon precursor. To date, the majority of research in the field of preceramic polymers has centered on precursors to silicon carbide (SiC). The Southwest Research institute (SwRI) has focused on the development of polymeric precursors to silicon nitride (Si{sub 3}N{sub 4}) because its high-temperature strength, resistance to oxidation, and other properties make it an attractive candidate for many advanced high-temperature structural applications. PIP Si{sub 3}N{sub 4} composites with NICALON SiC fiber reinforcement have exhibited good fracture toughness (K{sub IC} {approximately} 16 MPa {center_dot} m{sup 1/2}). The authors report here processing, microstructure and preliminary mechanical properties of two new PIP Si{sub 3}N{sub 4} composites. One is reinforced with Tonen Si{sub 3}N{sub 4} fiber (plain weave) while the other is reinforced with ALMAX Al{sub 2}O{sub 3} fiber (8 Harness satin weave).