Oxidation-induced failure of EB-PVD thermal barrier coatings

Oxidation-induced failure of EB-PVD thermal barrier coatings (TBC) deposited on a single-crystal superalloy with a platinum aluminide bond coat has been studied in order to determine the specific mechanisms leading to TBC spallation. Cyclic oxidation tests performed at 1150°C show that failure of the TBC occurs when the alumina scale, growing at the bond coat–TBC interface, attains its critical thickness. Therefore, the oxidation rate of the bond coat is considered the major factor affecting TBC durability. The growth rate, morphology and residual stress in the alumina scale depend on the method of the bond coat surface treatment prior to TBC deposition. While the TBC failure is ultimately driven by the elastic strain energy stored in the scale on cooling, the magnitude of the compressive stress in the scale has no apparent effect on the TBC lifetime. Except for the sample edges, no significant damage in the scale under the TBC has been detected by luminescence spectroscopy prior to failure.