Nonequilibrium Solute Capture in Passivating Oxide Films.

Area of Science:

• Materials Science
• Surface Science
• Physical Chemistry

Background:

• High-temperature oxidation and aqueous corrosion significantly impact the performance and longevity of NiCrMo alloys.
• Understanding the resulting oxide layers' composition and crystallography is crucial for predicting material behavior.
• Existing thermodynamic models often fail to explain observed phenomena in these complex environments.

Purpose of the Study:

• To experimentally determine the composition and crystallography of oxides formed on NiCrMo alloys.
• To develop a theoretical framework explaining the formation of unexpected oxide phases.
• To provide a predictive model for material behavior under oxidation and corrosion.

Main Methods:

• High-temperature oxidation and aqueous corrosion experiments.
• Transmission electron microscopy and diffraction for structural analysis.
• Aberration-corrected chemical analysis and atom probe tomography for compositional analysis.
• Density functional theory (DFT) for theoretical modeling.

Main Results:

• Observed unexpected combinations of oxide composition and crystallography, exceeding thermodynamic solubility limits.
• Identified a nonequilibrium solute capture mechanism driven by rapidly moving interfaces.
• Validated experimental findings with a combined thermodynamic, kinetic, and DFT theoretical framework.

Conclusions:

• The composition and crystallography of oxides are governed by nonequilibrium processes at rapidly moving interfaces.
• The developed predictive framework explains unusual phase formations and is applicable to other material systems.
• This research advances the understanding of oxidation and corrosion mechanisms in alloys and other solid-state transformations.