OXIDE-FIBER-OXIDE-MATRIX COMPOSITES

A composite of matching oxide matrix and oxide fibers, such as Al2O3-A l2O3, is an attractive system for high temperature applications answer ing the problems of thermal mismatch, creep and corrosion resistance. The fracture toughness of such composites is governed by the strength and toughness of the fiber-matrix interfaces. A coating on single-crys tal Al2O3 fiber with a layered structure, allowing the control of this interfacial strength, is proposed and the method of achieving it has been developed. The layered structure of the coating is produced by th e reaction-induced formation of a void layer in the coating. A new mod ification of a previously developed laser spallation method of measuri ng the adhesive strength between the coating and the substrate is pres ented and its application to the particular coatings is discussed. The tensile strength of the interface between the coating and the fiber s ubstrate for the pairs of Al2O(3)-TiO2 and Al2O3-ZrO2 was determined b y this method. The interdiffusion of the coating and substrate in a te mperature range up to 1600 degrees C was investigated using secondary ion mass spectrometry. The statistical strength distribution of Al2O3 single-crystal fibers that are prime candidates for reinforcement of s uch composites was evaluated.