Temperature dependent dynamic growth of thermally grown oxide in thermal barrier coatings

Abstract

Failures in thermal barrier coatings (TBCs) are often associated with a thermally grown oxide (TGO) due to thermal mismatch and the growth stress associated with growth of TGO. Unjustifiably, existing models assume constant growth profile of the TGO and diffusivity of oxygen in both the TGO and the bond coat (BC). The objective of this paper is to overcome this deficiency by using an integrated finite volume (FV) – finite element (FE) model to account for the change in material properties during oxidation. Three aspects of the work were accordingly examined. The first is concerned with the use of a dedicated FV model to describe the diffusion of oxygen and oxidation of BC. The second is the use of coupled FE simulations to determine the induced stress state due to oxidation using the results from the FV model. The third is to examine the combined effect of thermal load and oxidation. The results reveal that the undulating interface results in an uneven oxidation profile. Conclusively, uneven oxidation leads to higher stresses at the BC-TGO interface compared with existing models. Additionally, the change in the coefficient of thermal expansion during oxidation reduces the amplitude of the undulation and out of plane stresses.