Comprehensive effects of TGO growth on the stress characteristic and delamination mechanism in lamellar structured thermal barrier coatings

Abstract

To clarify the role of thermally grown oxide (TGO) in the failure of thermal barrier coating system (TBCs) is beneficial to further understand coating spallation mechanism and optimize the spraying process. In this study, the influences of TGO growth on the stress state and crack growth behavior upon temperature cycling are quantitatively examined based on a novel model with lamellar structure. Three kinds of TGO growth modes are employed to explore the TGO growth effect. The non-uniform distribution of lateral growth strain through TGO thickness is included in the model. TGO growth is dynamically modeled using the material property change step by step. The successive propagation and coalescence of multi-crack are materialized by a fracture mechanics analysis. The results suggest that the continuous increase of tensile and shear stress with cycles can occur only when the lateral growth strain is considered into the TGO. Large stress concentration arises at the crack tip and near the pore, which is responsible for the early crack growth. The successive growth and linkage of multi-crack can be expected in the model with TGO lateral growth. The spallation path and the variation trend of total crack length achieved in the current model are in line with the results in experiments. The large gradient of lateral strain distribution in TGO will result in a higher cycle to failure and incubation period. However, the overall crack propagation behavior and linkage mechanism are not affected by the lateral strain distribution. The computational results in the current model can provide a theoretical foundation for developing advanced TBCs with long lifetime.