Models for predicting TGO growth to rough interface in TBCs

Oxidation is often regarded as a key factor to cause the failure of thermal barrier coating system (TBCs), which arouses uneven growth of thermal grown oxide (TGO) layer. During the process of oxidation, the rough interface between TGO and bond coat (BC) influences the large growth of TGO and the stress concentration in TBCs. However, theoretical models to describe the effect are not many previously. In the present research, firstly, based on the finite deformation analysis, a three-concentric-circle model considering growth effect of TGO layer is presented to characterize stress concentration around the TGO induced by the oxidation of TBCs. Secondly, another growth model for TGO layer growth is presented based on the creep constitutive theory. From two models, the results indicate that the maximum tensile stress in the valley region locates at the interface of top coating (TC)/TGO, while the maximum normal stress locates at the BC/TGO interface in the peak region. Additionally, the thickness of TGO layer in the valley region decreases as roughness increases, while it increases as the roughness increases in the peak region. The theoretical models can be used to explain the uneven growth of TGO.