The Effect of the Interface on the Impact Strength of Fiber-Reinforced Silicon Nitride Composites

Abstract

Abstract Hot-pressed silicon nitride can offer large gains in gas turbine performance when used as a blade or vane provided the limitation of low impact strength can be overcome. Through the use of fiber reinforcement, energy absorption modes not available in monolithic materials are provided, with the result that the elevated temperature (1300°C) impact strength of an Si3N4 composite reinforced with 30 volume percent tungsten wires has been shown to increase ninefold over unreinforced Si3N4.To make use of the energy absorbing mechanisms of fiber pullout and/or interfacial splitting, one needs to retain the filament strength and have a fairly weak or low modulus interface or interfacial region between the tungsten and the silicon nitride. At elevated temperatures, this is the case; however, at room temperature the tungsten silicide layer formed at the W-S13N4 interface during hot pressing has been found to render the tungsten reinforcement ineffective as a crack blunting constituent. Efforts are being mad...