Finite Element Analysis Of Delamination Cracks In Thermal Barrier Coatings

Thermal barrier coatings(TBCs) are widely used in aero turbines, especially used in the key high temperature parts inside the engine, in order to improve the ability to sustain high temperature, weaken it the elatic-viscoplastic deformation, and enhance the strength and durability of components. Thermal barrier coatings easily fail spalling at the ceramic layer, which connected to its application environment, coating structure, and coating materials. The failure mechanisms of TBCs connect mainly to the formation of thermally grown oxide(TGO), cracking behaviors and the interaction between TGO and cracking. Thermally grown oxide layer during repeatedly thermal cycling occurs the irregular deformation, and further promotes the interface between the ceramic layer and the oxide layer to form delamination, and in turn the delamination provides oxygen ions and space to grow more oxidation products. Its failure has a certain relation with the material parameters of each layers. For example, high temperature yield can relief stress within the coating to a certain extent, but during repeated thermal cycles the cycle to cycle accumulation of plastic strain in the oxidation layer can causes coatings deformation, crack initiation and propagation.In this paper, the nonlinear finite element software ABAQUS is used to create models to analyze the fracture of TBCs, which are considered the growth deformation of TGO and high yield features of bond coating(BC) and TGO. Firstly, the stress strain field of TBCs as the temperature changes was being determined to find out the failure place in the TBCs, whose interface of TGO included concave type and convex type. And focused on the analysis of the stress field of concave interface of TGO, and summary of the prone sites of coatings. And then the model were preset the delamination crack upon the TGO/BC interface to analyze its cracking rules. Finally, the three main factors to affect the growth of the oxide layer deformation were analyzed to affect the ability of the ceramic to cracking, which were the TGO growth strain rate, TGO/BC yield characteristics, thermal loading and the undulations amplitude in the TGO.The results showed that the thermal barrier coating delamination failure prone position was at the interface of TBC/TGO and TGO/BC, and the delamination crack initiation in the heating stage upon internal depression in the oxide layer, while delamination cracks easily extended in the high temperature and cooling stage and lead t oxide coating layer to promote the growth of deformation from damage. As the fluctuation amplitude increases, Delamination cracks are more easily to extend. It can give some help of the understanding of the failure mechanism of thermal barrier coatings.