Numerical investigation of thermal stresses induced interface delamination in plasma-sprayed thermal barrier coatings

Abstract

Thermal barrier coatings (TBCs) are designed to be able to withstand a severe environment with coupled conditions including high temperature and thermal stresses. However, the complexity of their microstructure and the severity of these conditions give rise to premature TBCs failure and consequently reduce their service lifetime. This work aims to investigate the mechanisms of failure in plasma-sprayed TBCs and one of the most important failure mechanisms is related to thermal residual stresses developed in TBCs which leads to coating delamination at the interface contact between layers. A discrete element-based model has been developed to investigate thermal stresses generated at the interface on either side of the thermally grown oxide (TGO) layer due to the mismatch of coefficients of thermal expansion (CTE) between layers, and their material properties are assumed to vary with temperature. Thermal stresses induced in local areas due to the TGO interface irregularities are considered as well in the model by using the image analysis, which consists of a segmentation processing on actual microstructure images of TBCs, thereof allow to account for the undulation of the TGO interface which has been found to be associated with the failure of TBCs.