Thermal properties of the plasma-sprayed gradient thermal barrier coatings

Two layer thermal barrier coatings failed by the thermal expansion mismatches between metallic substrate and ZrO2 ceramic coat. Therefore, in this study, NiCr-ZrO2 (Y2O3) composite coat layers were introduced between substrate and ZrO2 ceramic coat in order to increase the durability by reducing the thermal expansion mismatches and by improving the bond strength. The NiCr alloy within composite coat oxidized prior to oxidation of NiCrAlY bond coat and the specimen failed within the composite coat layer. Oxidation products in composite coat layer were NiO and Cr2O3. The efficiency of the thermal barrier coatings increased with temperature up to 800 deg C. The temperature of the substrate decreased by about 110 deg C when the surface of ZrO2 ceramic coat was heated to 800 deg C. (Author)