Atomic Scale Mechanisms of Multimode Oxide Growth on Nickel-Chromium Alloy: Direct In Situ Observation of the Initial Oxide Nucleation and Growth

The initial growth mode of oxide on alloy plays a decisive role in the development of protective oxide scales on metals and alloys, which is critical for their functionality for high temperature applications. However, the atomistic mechanisms dictating that the oxide growth remain elusive due to the lack of direct in situ observation of the initial oxide nucleation and growth at atomic-scale. Herein, we employed environmental transmission electron microscopy and the first-principles calculations to elucidate the initial atomic process of nickel-chromium (Ni- Cr) alloy oxidation. We directly revealed three different oxide growth modes of initial NiO islands on Ni-Cr alloy upon oxidation by O-2, which result in distinct crystallography and morphology. The multimode oxide growth leads to irregular-shaped oxides, which is shown to be sensitive to the local mass transport. This localization of oxide growth mode is also demonstrated by the identified vigorous competence in oxide growth and thus shown to be kinetically controlled. The concept exemplified here provides insights into the oxide formation and has significant implications in other material and chemical processes involving oxygen gas, such as corrosion, heterogeneous catalysis, and ionic conduction.

Automated summary

The initial growth mode of oxide on alloy is crucial for the development of protective oxide scales on metals and alloys, but the specific atomistic mechanisms governing this growth remain unclear. By using environmental transmission electron microscopy and first-principles calculations, researchers have elucidated three different oxide growth modes of initial NiO islands on Ni-Cr alloy upon oxidation by O-2, showing that oxide growth is sensitive to local mass transport and kinetically controlled. This concept provides insights into oxide formation and has significant implications in material and chemical processes involving oxygen gas.