(482a) Mechanochemical Degradation Pathways of Protective Oxide Surfaces: Development of an Ab-Initio Informed Multiscale Corrosion Model

Protective surface coatings inhibit aluminum corrosion pathways by replacing the highly reactive metal surface with one that is more chemically stable. Chemical processes which erode these protective films render aluminum more susceptible to corrosion. Identifying the dominant chemical drivers for these erosion processes and the mechanisms by which they proceed can help to inform the design of more resilient and robust protective coatings. We use ab initio molecular dynamics to model the erosion of γ-alumina surfaces and calculate associated reaction barriers while subjecting the oxide surface to environmental stressors, including vacuum, pooled water, and mechanical stress. We find that the presence of water reduces erosion reaction barriers by over 60% with respect to vacuum. Connections with microstructure-aware micromechanics models show that localized shear stresses in these materials can develop, which can couple with an aqueous environment resulting in further erosion barrier reductions. These findings highlight the relevance of solvent and surface strain on aluminum corrosion and serve as a basis for predictive multiscale lifetime models.

This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.