A physics-based model of temperature-exposure-dependent interfacial fracture toughness of thermal barrier coatings

Abstract

A physics-based model of temperature-exposure-dependent interfacial fracture toughness of thermal barrier coatings was developed using Arrhenius-type formulae and experimentally measured interfacial toughness at ambient temperature. The crack delamination occurring at the thermally grown oxide (TGO)/bond coat (BC) interface was assumed in the interfacial fracture toughness evaluation. To evaluate the interfacial toughness at elevated temperatures, the interfacial plastic zone, the interface crack tip opening displacement (ICTOD) and the interface crack density at the thermally grown oxide (TGO)/bond coat interface were specified. The temperature-exposure-dependent Young’s modulus of the topcoat was formulated using the experimentally measured data, and its effect on the interfacial toughness at elevated temperature was investigated. As an application, the proposed interfacial toughness model was then used to study toughness variation versus exposure temperature and time. The trend of interfacial toughness versus temperature and exposure was explained in terms of microstructural changes of topcoat and TGO.