Coupled mechanical-oxidation modeling during oxidation of thermal barrier coatings

Abstract

The durability of thermal barrier coatings (TBCs) is controlled by the thermally grown oxide (TGO) growth, which is sustained by continuous diffusion of oxygen in TBCs. At the same time, stresses are induced due to volumetric change when TBCs are oxidized. Such stress may in return affect the diffusion of oxygen in the TGO layer, thus changing the TGO growth kinetics. In the present research, a continuum thermodynamic model is developed to account for such stress–diffusion interaction in the oxidation of TBCs. Then we numerically implement our chemo-mechanically-coupled constitutive theory into the widely used finite element software to simulate the oxidation behavior of TBCs. The results demonstrate that the maximum tensile stresses locate at the peak regions of bond coating (BC) layer and the valley region of top coating, respectively. It implies that the failure of the TBCs may occur at the peak of BC/TGO and the valley of TC/TGO interface, which is consistent with the experimental observations. It is also found the stress significantly slows down the rate of oxidation. Consequently, the TGO growth kinetic is not strictly parabolic.