Formation and Growth Behaviour of Thermally Grown Oxide Layer in Thermal Barrier Coatings with HVOF Sprayed Nickel-Chromium Bond Coats

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In this study, the oxidation behavior of thermal barrier coatings (TBCs) with a nickel–chromium (NiCr) bond coat was investigated under high-temperature atmospheric conditions. Nickel–chromium bond coats were deposited on an Inconel 718 substrate using the high-velocity oxy-fuel (HVOF) spray technique. Production of TBCs was done with deposition of topcoats from yttria-stabilized zirconia using the atmospheric plasma spray technique. After the production of coatings, isothermal oxidation tests were conducted at 900, 1000 and 1100°C in air atmosphere for different time periods up to 50 h. The formation and growth behavior of the thermally grown oxide (TGO) layer and the microstructural evolutions in the TBC system were investigated with scanning electron microscopy and elemental mapping analysis. The results showed that the TGO layer was composed of only chrome oxide at 900 and 1000°C. However, above 1000°C, this layer extremely thickened and mixed oxides formed with the oxidation of nickel in the bond coat composition. The effect of TGO layer development on the ceramic topcoat and the damage potential of the coating system were also evaluated.