Oxidation of nickel with groove defects: Cation vacancies expansion mechanism and directional layer-by-layer oxidation

In this work, we perform molecular dynamics simulations with the reactive force-field to systematically unravel the oxidation mechanism of Ni groove defects. We show that Ni atoms at the edge of groove are preferentially oxidized, and then diffuse outward with cation vacancies left. The oxidation spreads to both sides directionally by vacancies expansion. The effects of groove defect type, temperature, and oxidizing medium on oxidation kinetics are evaluated. We reveal that the oxidation degree of Ni {1 1 0} system is greater than that of Ni {1 1 1} system, owing to the different atomic arrangement. The high temperature can effectively promote oxidation. Under the oxygen environment, the oxidation directionally spread layer by layer, while the introduction of water vapor can change this mechanism, leading to the inward spreading of oxidation. We expect this work would provide theoretical guidance for the improvement of anti-corrosion measures of Ni-based superalloys.