Abstract
Gas turbine engines are exposed to severe oxidation and thermal shock under service conditions. Thermal barrier coatings (TBCs) are used to protect metallic components of gas turbines against such failures. Yttria stabilized zirconia (YSZ) has been the most common top coating material for TBC systems. However, rare earth zirconates such as La2Zr2O7 and Gd2Zr2O7 stand out as alternatives to YSZ top coating for TBCs. In this study, Inconel 718 substrates were coated with CoNiCrAlY using cold gas dynamic spray (CGDS) technique, which is a promising technology for bond coat spraying. All the ceramic top coats were produced by electron beam physical vapor deposition (EB-PVD) method that provides high strain tolerance under thermal loadings. To predict the lifetime of TBCs, the samples were subjected to furnace cycling tests at 1150 °C. After the tests, the microstructure of thermally grown oxide (TGO) layers, crack formations and chemical compatibility between the coating layers were investigated in detail. Results show that TBCs with double layered rare earth zirconate exhibit longer lifetime as compared to single layered TBCs.
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