Short Term Oxidation in HT-SEM of the Pt-containing TROPEA Single Crystal Ni-based Superalloy from 680 to 1000°C

Abstract Short-time oxidation of the Ni-based TROPEA single-crystal superalloy was implemented to determine the nature and quantities of transient oxides in the 680–1000°C temperature range. Experiments were carried out in situ in the SEM with reduced air pressure (150 Pa, \(\:{P}_{{O}₂}\) ∼ 31.5 Pa) compared to atmospheric conditions (10⁵ Pa, \(\:{P}_{{O}₂}\) ∼ 2.1 10⁴ Pa). TEM characterization after oxidation showed the complexity of the oxidation products developed. Aluminum underwent internal oxidation between 680 and 1000°C. During the limited duration of oxidation, the TROPEA alloy only formed a continuous alumina layer at 1000°C. At 680 and 850°C, the low diffusion rate and small amount of Al in the Ni-based single crystal led to the formation of a significant amount of transient oxides such as (Ni,Co)O, compared to the desired chromia or alumina protective oxides. The lower the temperature, the smaller the size of the internal Al₂O₃ precipitates and the larger the transient oxide crystals, which would lower the resistance of TROPEA to Type II hot corrosion. In contrast after a transient period shorter than 22 hours, during which multiple transient oxide developed, the oxidation resistance would be ensured at 1000°C by the formation of a continuous Al₂O₃ scale.