The origin of surface discoloration on Thermal Barrier Coatings (TBCs) of land-based industrial gas turbine hot gas path vanes has been investigated. Three ex-service row one (R1) vanes have been examined. Dense black colour deposits were observed on the pressure side leading edge and trailing edge, whereas red and brown deposits were present on the pressure side surface. Energy dispersive spectroscopy (EDS) analyses reveal a significant amount of iron oxide present with smaller amount of calcium, magnesium, aluminium, and silicon. X-ray diffraction revealed that the surface film was mixture of hematite (Fe2O3) and magnetite (Fe3O4) phases. This research aims to characterise these surface oxides with the aim of understanding the TBC surface condition whilst in service.
