Interface fatigue crack propagation in ceramic thermal barrier coatings

Failure of thermal barrier coating (TBC) layer, especially spalling of ceramic coating layer, results not only in degradation of thermal barrier properties but also in crucial damage to turbine components. The spalling of ceramic coating layer will follow the crack initiation and propagation along the interface between ceramic top-layer and metal bond-layer. In the present study, fatigue crack growth tests of TBCs with various porosities were carried out at room and elevated temperatures. It is found that an interface crack induced near a pre-introduced notch propagates along the interface under mixed mode condition, and its growth behavior can be well characterized by using the parameter DeltaK(i)=DeltarootK(1)(2)+K-2(2), which corresponds to the energy release rate. It is also found that the crack propagation resistance decreases with increasing of the porosity of the top ceramic coating. The crack propagation resistance at elevated temperature becomes lower compared to that at room temperature.