Electrolytic Al2O3/Y2O3 double-layer coating on IN617 superalloy

In this study, IN-617 superalloy was coated with Al2O3/Y2O3 double-layer films by electrolytic deposition in Al(NO3)3 and Y(NO3)3 aqueous solutions. Characterization of coated specimens was conducted by thermo-gravitational analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM), aqueous corrosion tests in 3.5% NaCl, hot corrosion test in 2 mg/cm2 Na2SO4 contained environment at 850 °C, and high temperature oxidation test at 1000 °C in air. The Y2O3/Al2O3 double layer coating revealed the composite crystal structures of Y2O3, Al2O3 and yttrium–aluminum garnet (YAG). Also YAG powders can be prepared by collecting and annealing the coating film. The Y2O3/Al2O3 coating film revealed the efficient retarding effects on the oxidation (NiO) of In617 superalloy in air at 1000 °C, since the coating film prohibited the formation of NiO and promoted the growth of Cr2O3. Also, it revealed more corrosion resistance in 3.5% NaCl aqueous solution and more hot corrosion resistance in Na2SO4 contained environment at 850 °C.