Oxidation behavior of a single-crystal Ni-based superalloy over the temperature range of 850 °C–950 °C in air.

The oxidation behavior of a single-crystal Ni-based superalloy over the temperature range of 850 °C–950 °C and under R a = 0.1–0.2 μm was investigated. The oxidation kinetics of the superalloy presented two stages. The first and second stages had activation energies of 222 and 263 KJ·mol−1, respectively. The oxide film comprised NiO, NiCr 2 O 4 , CrTaO 4 , and Al 2 O 3. The formation time of the continuous Al 2 O 3 layer corresponded to the transition point of oxidation kinetics at each temperature. Mass gain in the first stage could be attributed to the formation of an outer NiO layer and an inner alumina layer, whereas that in the second stage could be ascribed to the growth of intermediate spinel layers. • NiO was the first species formed on the surface under the R a = 0.1–0.2 μm of this alloy. • Two oxidation stages were observed at each temperature. • The evolution of outer NiO, inner Al 2 O 3 and intermediate spinels played a different role on the oxidation kinetics. • The morphology of inner Al 2 O 3 layer was responsible for the transition of oxidation kinetics. [ABSTRACT FROM AUTHOR]