On the role of TGO growth in the interface undulation in MCrAlY coating system upon thermal cycling

The bond-coat/TGO (thermally grown oxide) interface has been experimentally observed to progressively undulate upon thermal cycling. This work presents a study on the role of TGO growth in the interface undulation. An axisymmetric finite element model was built based on the ratcheting phenomenon. It is found that the interface undulation is associated with not only the compressive stresses in the TGO but also the softness of the bond-coat. The compressive stresses provide the driving force for the interface undulation. At high temperature, lengthening TGO growth is responsible for the compressive stresses and therefore plays a crucial role in the interface undulation. The bond-coat needs to be soft enough to accommodate the interface undulation. Thickening TGO growth itself almost has no effect on the interface undulation, but the variation of TGO thickness appears to affect the sensitivity of the interface undulation to the lengthening strain rate of TGO growth.