Determination of the Structure and Chemistry of Thermally Grown Oxides in Thermal Barrier Coatings

Abstract Thermal barrier coatings (TBCs) insulate gas turbine hot section components from the hot (∽1200 - 1450°C) combustion gas exhaust stream. An airline company can save millions of dollars per year by using TBCs to protect vital engine components and to improve fuel efficiency. TBCs typically consist of an 8 wt.% yttria-partially-stabilized zirconia (YPSZ) ceramic topcoat deposited on a platinum-nickel-aluminide (Pt-Ni-Al) bondcoat covering a nickel-based superalloy substrate. Thermal exposure during YPSZ electron beam-physical vapor deposition (EB-PVD) and engine operation promotes the formation of a thermally grown oxide (TGO) between the Pt-Ni-Al and the YPSZ layers. Stresses can develop at the Pt-Ni-Al/TGO and TGO/YPSZ interfaces due to TGO growth and thermal expansion coefficient mismatch. These stresses eventually cause spallation of the YPSZ, leaving the metallic substrate vulnerable to high temperature degradation since exhaust temperatures are often higher than the melting temperature of most nickel-based superalloys (∽1200 - 1450°C).