Oxidation behavior of 4774DD1 Ni-based single-crystal superalloy at 980 °C in air

The oxidation behavior of a novel Ni-based single-crystal 4774DD1 superalloy for industrial gas turbine applications was investigated by the isothermal oxidation at 980 °C and discontinuous oxidation weight gain methods. The phase constitution and morphology of surface oxides and the characteristics of the cross-section oxide film were analyzed by XRD, SEM and EDS. Results show that the oxidation kinetics of the 4774DD1 superalloy follows the cubic law, indicating its weak oxidation resistance at this temperature. As the oxidation time increases, the composition of the oxide film evolves as following: One layer consisting of a bottom Al2O3 sublayer and an upper (Al2O3+NiO) mixture sublayer after oxidized for 25 h. Then, two layers composed of an outermost small NiO discontinuous grain layer and an internal layer for 75 h. This internal layer is consisted of the bottom Al2O3 sublayer, an intermediate narrow CrTaO4 sublayer, and an upper (Al2O3+NiO) mixture sublayer. Also two layers comprising an outermost relative continuous NiO layer with large grain size and an internal layer as the oxidation time increases to 125 h. This internal layer is composed of the upper (Al2O3+NiO) mixture sublayer, an intermediate continuous (CrTaO4+NiWO4) mixture sublayer, and a bottom Al2O3 sublayer. Finally, three layers consisting of an outermost (NiAl2O4+NiCr2O4) mixture layer, an intermediate (CrTaO4+NiWO4) mixture layer, and a bottom Al2O3 layer for 200 h.