FUNCTIONAL INTERFACES FOR OXIDE OXIDE COMPOSITES

Potentially useful interfacial coatings for composites of sapphire fib ers in polycrystalline aluminum oxide matrices are discussed, subject to the constraints of phase compatibility in high temperature oxidizin g environments and low mechanical interface strength (i.e. to allow pu ll-out). Results of preliminary tests to investigate feasibility of so me candidate coatings (beta-aluminas, LaPO4 and CaF2) are presented. T hese systems exhibited interfacial debonding under certain conditions, as required for high toughness composites, although several issues re main to be resolved before they can be used successfully.