A chemo-thermo-mechanical coupled phase field framework for failure in thermal barrier coatings

The failure process in a thermal barrier coating (TBC) system can be complicated due to complex microstructure, material property mismatch, high temperature change, chemical reactions during the failure process, etc. It brings considerable difficulties to the modeling technique. A complete failure process in TBC contains multiple failure types, e.g., bulk fracture, delamination of TC (top coating)/TGO (thermally grown oxide) interface and TGO/BC (bond coating) interface, and the interaction among them. However, existing approaches mainly focus on a single failure type and thus are faced with limits on exploring the complete failure mechanism. In this work, we propose a chemo-thermo-mechanical coupled phase field model based on thermodynamic laws, such that the complete TBC fracture process can be captured. The present contribution provides a step forward in comparison with the existing phase field models. Couplings among thermal conduction, material oxidation and damage are considered, and the fundamental differential equations are derived strictly follow the thermodynamic laws. The proposed model is first validated through several benchmarks, and then followed by several simulations of the failure process of a TBC system. The simulations and experiments show that the bulk fracture occurs when the TGO is thin at the cooling process, the growth effect of TGO layer causes damage initiation at the interface and finally transformed into the interfacial delamination, the interaction of interface cracking and bulk material cracking is captured. The proposed model is proven to be a powerful tool in solving the failure process of a TBC system and is promising to handle other similar problems.