Strain hardening and embrittlement of Al crystal with a surface oxidized void

YH Wu and WS Yu and SP Shen, MECHANICS OF MATERIALS, 148, 103531 (2020).

DOI: 10.1016/j.mechmat.2020.103531

Although metal failure has been extensively investigated, the impact of oxidation on the failure of ductile metals involving defects is relatively unclear. In this study, reactive molecular dynamics simulations are performed to observe the change in the mechanical properties (e.g., strength and ductility) of a voided Al crystal when the void surface is oxidized. For a preoxidized void surface, as the oxide scale becomes thicker and denser, the microdeformation and fracture mechanisms of the Al crystal change significantly, according to which four failure modes can be identified. Furthermore, the decrease in the fracture strain indicates a transition from significant plasticity to brittle fracture of the Al slab. A simple analytical model is proposed to establish the relation between the yield strength and oxygen uptake. When the void surface oxidation continuously occurs while loading, the continuous supply of oxygen heals the oxide/metal interface, leading to a considerably enhanced ductility and the occurrence of a unique strain hardening phenomenon. The presented findings highlight the influence of the interaction between the chemical and mechanical effects on the deformation and fracture mechanisms of metallic materials.

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