Interfacial delamination of double-ceramic-layer thermal barrier coating system

Thermal barrier coating system (TBCs) must withstand the most demanding high temperature conditions where state-of-the-art top coat material Y2O3-stabilized ZrO2 may undergo significant sintering and phase change. The concept of double-ceramic-layer (DCL) TBCs seems to be an effective way to meet the need for both thermal stability and transformation toughening. In this paper, a virtual crack closure technique based interface element method is introduced to study the mechanics associated with the interfacial delamination of DCL TBCs. The evolution of energy release rate of interfacial delamination is explored for DCL TBCs with various geometrical and material parameters. Analysis of fracture mechanisms of delamination reveals that considering the integrated thermal and mechanical functionalities of coatings an optimal thickness ratio of outer to inner ceramic layers exists, which can be preliminarily evaluated by running numerical calculations of fracture parameters and performing thermal life experiments over a wide range of thickness ratios of outer to inner coating layers. In addition, the influence of separation centered at the interface of two ceramic layers is also examined. It is demonstrated that the local separation between two ceramic layers makes delamination readily to form and propagate at the interface between the inner coating and the underlying layer.