Modeling Fracture in Protective Aluminum Surface Materials Exposed to Crystal Defects

Aluminum metal reacts readily with the environment to form protective oxide or hydroxide surface films, which inhibit further corrosion by shielding the bare metal underneath. Fracturing of the protective film due to stress corrosion cracking can expose the metal, accelerating corrosion chemistry. Film fracture is further complicated by the presence of defects that may be present in the protective layer. Determination of the fracture tendency of these materials subjected to defects can be leveraged by component-scale predictive lifetime models to make more refined predictions about net reaction kinetics. In this work, we use molecular dynamics with a reactive force field to predict the response of bulk γ-Al₂O₃ and γ-Al(OH)₃ under tensile loading up to the point of fracture for a range of high strain rate conditions. The effects of crystal defects such as grain boundaries and porosity are also considered. We find that while defects in γ-Al₂O₃ can dramatically increase fracture tendency, they are typically insufficient to reduce fracture strains to those observed for perfect single crystal γ-Al(OH)₃.



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