Oxidation of Ni-Cr and Ni-Cr-Mo was studied in operando with near ambient pressure x-ray photoelectron spectroscopy in the Cabrera-Mott regime. The oxidation temperature was 200°C—a severely diffusion-limited regime. The near-surface alloy is Cr-enriched after the reduction of native oxide in vacuum, and especially so for Ni-15Cr-6Mo. Mo-cations are integrated into the oxide and Mo(VI) dominates at the surface. The surface chemistry-driven promotion of chromia by Mo predicted by theory is negated by the limited surface diffusion of reactants. Preoxidation processing is proposed to control the oxide properties for the use of Ni-Cr superalloys at low temperatures.

Subject
Composition, Metal surfaces, Diffusion, Nickel based alloys, Chromia, Molybdenum alloys, Oxide layers, Metal oxides, X-ray spectroscopy, Oxide surfaces, Interfaces, Alloys, Oxidation
Keywords:
form B. (operando), form B. (XPS), mat A. (Ni), mat A. (Ni-Cr), prop C. (oxidation), prop C. (surface science)
© 2023, AMPP
2023
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