Dynamic multi-crack evolution and coupling TBC failure together induced by continuous TGO growth and ceramic sintering

Abstract

The thickening of oxide scale and ceramic sintering are the key factors leading to crack propagation and spallation of thermal barrier coatings (TBCs) during service. In this work, a finite element model containing both horizontal and vertical cracks is developed to explore the coupling TBC failure. The continuous growth of thermally grown oxide (TGO) and dynamic sintering of the ceramic top coat are together introduced in this model. The changes of stress state and cracking driving force in the ceramic coat are first examined. Subsequently, the dynamic propagations of multiple cracks with cycles are investigated. The effect of the thermal mismatch between bond coat and substrate on the coating failure is also studied. The results show that TGO growth leads to a ratcheting rise of the strain energy at the horizontal crack tip in the ceramic coat. Ceramic sintering mainly contributes to the accumulation of strain energy at the vertical crack tip. When the vertical crack propagates to the vicinity of the horizontal crack, both of them promote each other’s growth. Selecting a bond coat with lower thermal expansion coefficient than substrate can delay the propagation of the horizontal crack. The results in this study can contribute to the structural design and material selection of advanced TBCs with long lifetime.