The growth and influence of thermally grown oxide in a thermal barrier coating

The growth of a thermally grown oxide (TGO) layer and its influence on cracking was studied in an air-plasma sprayed (APS) thermal barrier coating (TBC) following thermal cycling. The TGO that formed upon thermal exposure in air was comprised predominantly of layered chromia and spinels, as well as some oxide clusters of chromia, spinel and nickel oxide. The increase in thickness of the TGO exhibited a three-stage growth phenomenon. Cracks formed mostly at oxide clusters as well as at the opening of discontinuities. Crack propagation during cyclic oxidation appeared to be related to TGO growth, with a nearly linear relationship between crack length and TGO thickness.