Mechanisms governing the performance of thermal barrier coatings

Thermal barrier coatings (TBCs) are now used on hot section components in most commercial turbine engines. They are used to enhance the temperature differential between the gas and the underlying metal surfaces. They comprise several layers designed to simultaneously provide thermal and oxidation protection. They have microstructures which afford sufficient strain tolerance that they remain attached despite severe thermomechanical cycling. Eventually, they spall. This happens because a thin, highly stressed, thermally grown oxide (TGO) develops beneath the TBC. In this article, the specific mechanisms that contribute to failure are described, with the motivation that this understanding can be used to design TBCs having greater reliability and durability.