Influence of non-uniform feature of thermally grown oxide thickness on the local stress state and cracking behavior in TBC

Abstract

The growth of thermally grown oxide (TGO) at high temperatures is the main reason for inducing the cracking near the YSZ/bond coat interface in the thermal barrier coating (TBC). The non-uniform thickening of TGO can change the local stress state and crack evolution. In this work, a TBC model including non-uniform TGO is established to explore the effect of non-uniform feature of TGO on the local cracking behavior. The continuous growth of TGO is simulated by applying a stress-free strain. The arbitrary path propagation of cracks in YSZ and TGO is realized by the XFEM method. The influences of TGO non-uniform degree and lateral growth rate on the stress variation and crack evolution are discussed. The results show that the non-uniform growth of TGO increases the local oxide film thickness and decreases the amplitude of TGO/bond coat interface, which leads to a greater crack driving force than TGO uniform growth. The increase of TGO non-uniform degree will induce longer TGO crack. The coating life predicted by the uniform TGO model is overestimated. The increase of TGO lateral growth strain leads to the improvement of YSZ crack driving force and TGO crack length, which is independent of TGO non-uniform degree. The results in this study indicate that obtaining uniform TGO with a low growth rate by process optimization will be an important option to improve the durability of TBC.