Morphological evolution of thermal barrier coatings induced by cyclic oxidation

High temperature oxidation behavior of EB-PVD thermal barrier coatings (TBC) deposited on a single-crystal nickel-base superalloy with platinum aluminide bond coat has been studied using optical microscopy and luminescence spectroscopy. Examination of the TBC morphology in the course of cyclic oxidation at 1150 °C reveals that the TBC surface may develop undulations, which grow with oxidation time and eventually link together leading to TBC failure. The undulations are shown to be associated with local separations near the interface between the TBC and the thermally grown alumina scale. The observations of the pre-failure TBC evolution made by a low-magnification optical microscopy can serve as a reliable method of non-destructive evaluation of the coating. The relationship between residual stress in the thermally grown oxide and morphological evolution occurring at the TBC-bond coat interface is discussed.