Thermal barrier coating crack driving force investigation on the basis of a new constitutive framework

As well known, bond-coat oxidation plays an important role in the failure of thermal barrier coating. A new constitutive framework is provided for the bond-coat oxidation within thermal barrier system under isothermal or cyclic exposure, simultaneously taking into account some accompanying nonlinearities such as phase transformation, creep and plasticity. This constitutive framework is applied to a three-dimensional finite element model of thermal barrier system to investigate the crack driving force within thermal barrier coating. It follows that the TGO film calculated numerically agrees well in crest or trough thickness with the one observed experimentally. With a three-dimensional circular crack initiated within the top-coat, the energy release rate at each point along the front of the top-coat crack is studied in the case of multiple hours of isothermal exposure or multiple times of cyclic exposure. The energy release rate is correlated to the TGO thickness and could be divided into three phases. Such correlation is helpful to investigate the dependence of thermal barrier coating crack propagation on TGO thickness and even to predict the lifetime of thermal barrier coating using TGO thickness as an important parameter.