Abstract
Thermal barrier coatings (TBCs) are widely used in gas turbines to reduce thermal exposure of structural components and increase turbine efficiency. They typically consist of a MCrAlY bond coat and a YSZ topcoat. At high temperatures, a thermally grown oxide (TGO) layer forms between the bond coat and topcoat. If this layer is a continuous scale of alumina, it will act as a diffusion barrier to suppress the formation of other detrimental oxides, thus helping to protect the substrate from further oxidation. It has been reported, however, that other oxides, such as chromia, spinel, and NiO, may form along with the TGO layer, ultimately leading to TBC failure. To investigate such claims, coatings of comparable thickness were deposited by various spraying methods onto a superalloy substrate using a powder of the same composition. Samples were isothermally oxidized at 1273 K for different periods up to 3000 hours. The samples were examined before and after furnace tests and the results are presented and discussed.
