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.