Gelcast Reaction Bonded Silicon Nitride Composites

Abstract

Nicalon fiber-reinforced, reaction-bonded silicon nitride (RBSN) composites were made by gelcasting green bodies of Si and fibers and nitriding the composites in a 2.45-GHz microwave furnace. The bodies were prepared by casting a 48 vol % slurry of silicon into a mold containing unidirectional fibers cut to the length of the mold. The extent of nitridation and the properties of the reaction-bonded silicon nitride composites were measured. Fracture surfaces of the composites processed at 1250°C for 8 h showed significant fiber pullout; however, those nitrided at 1350°C for 4 h exhibited only limited fiber pullout indicating possibly some degree of fiber degradation and strong matrix-fiber bonding.