Influence of TGO and Initial Crack on Crack Nucleation and Propagation in Thermal Barrier Coatings Based on Finite Element Analysis

Aiming at the change of nucleation position and propagation failure process and mechanism of cracks in thermal barrier coating system, the cohesive element was used to analyze the nucleation location and propagation of the interface cracks of the thermal growth oxide/top-coat (TGO/TC). The extended finite element method was used to analyze the effects of the thickness and roughness of TGO and the initial crack of TC on the nucleation location and propagation of the new TC crack and TGO crack. The results demonstrated that the cracks at the TGO/TC interface first appear at the off-peak after being subjected to thermal cycling loads. During the cooling process, as the initial TGO thickness increased, the nucleation position of the TC crack shifted from the peak to off-peak without significant change in the crack length. The nucleation position of the TGO crack remained unchanged but the crack length increased significantly. With the decrease of TGO roughness, the nucleation position of TC crack shifted from the off-peak to the middle and was finally constrained, however, the crack length did not change significantly. The nucleation position of TGO crack did not change significantly, but the crack length increased with the decrease of TGO roughness. Furthermore, the longer the initial transverse TC crack, the longer the TGO crack. The initial vertical TC crack near off-peak and middle can effectively constrain the nucleation and propagation of the new TC crack. It could provide the finite element model for investigation of failure mechanism of thermal barrier coatings.