Measurements of interface strength and toughness in shear of environmental barrier coatings on ceramic substrates at ambient and at elevated temperature

Abstract

A new experimental method is presented in detail that is capable of measuring the interfacial strength and toughness in shear of an environmental barrier coating on a ceramic substrate at ambient and at elevated temperatures. The method also allowed for the characterization of the coating modulus at temperature. The method involved subjecting a finite length strip of coating on a substrate to an axial compressive load parallel to the interface, thus loading the interface in shear. The technique successfully caused delamination of the coating at the coating ends thereby allowing for the evaluation of the interfacial strength and toughness in conjunction with a previously derived model for the mechanics of delamination for this geometry. Monitoring of coating and substrate strains allowed also for an experimental evaluation of the coating modulus at temperature in conjunction with the mechanics model. Initial results showed that both the strength and the toughness of the interface decreased sharply around 1000 C. The same was also true of the tensile modulus of the coating. Furthermore, results indicated a much higher interfacial strength and toughness in shear when compared to the tensile mode of delamination.