CONTROLLED SHEAR STRENGTH OXIDATION-RESISTANT INTERFACIAL FIBER COATINGS

Continuous fiber-reinforced ceramic matrix composites represent an enabling technology for the next generation of aircraft engines and power generating equipment. The current state-of-the-art in ceramic matrix composites (CMC) for use in oxidizing environments is a silicon carbide (SiC) matrix material reinforced with low-oxygen Nicalon (SiC) fibers, both of which exhibit good oxidation resistance. The interfacial materials currently used, boron nitride (BN) and pyrolytic carbon (pyC), both posses weakly bonded graphitic planes that are able to slip, and their crystallographic orientation and thickness can be manipulated to optimize the interfacial properties. Unfortunately, both of these materials have very poor oxidation resistance at temperatures above approximately 800 and 600¿C, respectively. Thus, when used in a high temperature oxidizing environment, the interfacial coatings are severely attacked, thereby causing the mechanical properties of the composite to be degraded. In this Phase I project, Ultramet will develop an oxidation-resistant interfacial coating system that will allow CMCs to be used in aggressive, oxidizing atmospheres. The coating will not only provide the necessary weak bond between the fibers and the matrix, it will also be chemically compatible with both the fibers and the matrix at elevated temperatures.