Oxidation of the single-crystal Ni-base superalloy DD32 containing rhenium in air at 900 and 1000 °C

The oxidation behavior of a single-crystal Ni-base superalloy DD32 was studied in air at 900 and 1000 °C. The oxide morphology and microstructure were analyzed by X-ray diffraction (XRD), SEM/EDS. The scales formed at 900 and 1000 °C were complicated, with an outer layer of columnar NiO, an intermediate layer mainly composed of complex oxides and a small amount of spinels, and an inner continuous layer of α-Al2O3. At 900 and 1000 °C, two oxidation steps appear in the oxidation kinetics. The first one is controlled by NiO growth and the second by Al2O3 growth once a continuous Al2O3 layer formed under the previously grown NiO layer after a critical time.