Temperature and exposure-dependent interfacial fracture toughness model for thermal barrier coatings

Abstract

An interfacial fracture toughness model for thermal barrier coatings (TBCs) is proposed in which model parameters not only include the effect of high temperature and exposure period of TBCs but also demonstrate the mode mixity characteristics. The model is expressed in terms of the Arrhenius-type form showing a temperature-dependent feature and also exhibits a dependence of microcrack density distributed along the coating interface. Two scaling parameters are used in formulating the model, one is introduced to link dislocation Burgers vector to the crack tip opening displacement (CTOD), the other is utilized to describe the crack tip energy release rate associated with the P-N force responsible for dislocation movement. These scaling parameters can be obtained by fitting to the interfacial fracture toughness data at ambient temperature and the CTOD, respectively. Since the experimentally measured microcrack density exhibits thermal cycle dependent behavior, an attempt is made to explain the experimentally obtained toughness values using the proposed interfacial crack toughness model. The model predicts an increase in fracture toughness with exposure temperature and mode mixity. The limitation of the model and possible improvement scheme are discussed.