First Principles Study on Effect of Al-O Element Aggregation on Oxidation of a Ni-based Single Crystal Superalloy

Ni-based single crystal superalloys have been widely used as materials for aircraft engine turbine blades due to their excellent high-temperature mechanical properties. The harsh service environment can lead to severe oxidation of the superalloys for turbine blades. In contrast to the high-temperature mechanical properties, further research is needed on the oxidation behavior of the Ni-based single crystal superalloys. Herein, the evolution mechanism of the oxide scale on Ni-based single crystal superalloy has been studied through first-principles calculations and oxidation experiments. By analyzing the interface adhesion energy and charge distribution, while taking the impact of O and Al atoms on the interface stability into account, it is determined that the Al-O structure has been identified as the most stable NiAl/NiO interface model. The aggregation of O and Al atoms at the interface may weaken the bonding strength of the NiAl/NiO interface, which means that the interface tends to be separated easily. The oxidation behavior of the alloy was examined using XRD, EDS, SEM, etc., in terms of the oxidation kinetics of the alloy, as well as the morphology and phase composition of the oxide scales. Results indicate that NiO forms initially during the alloy oxidation, followed by Al₂ O₃ beneath NiO. As O and Al atoms aggregate at the interface, NiO tends to separate from the alloy surface. By combining first-principles calculations with the oxidation test results, the mechanism of evolution of the oxide scale on the alloy was ultimately elucidated.