Abstract
The effects of H segregation to a Σ11 symmetric tilt Al grain boundary are investigated using atomistic simulations, as part of a wider study on cracking in 7xxx series alloys. Density functional theory based simulations of uniaxial straining of grain boundaries containing 11 different concentrations of H were performed under the cohesive zone fracture mechanics framework. The theoretical strength of grain boundaries is shown to be supressed by H segregation, and the cause of this is attributed to the prevention of the formation of Al ligaments across grain boundaries. Segregated concentrations of relevant alloying elements (Zn, Mg, and Cu) show minimal impact on the H embrittlement process investigated, namely H enhanced decohesion (HEDE). Further modelling, of H transport and grain boundary precipitates, is required to confirm the validity of the HEDE mechanism in the case of 7xxx alloys.
Highlights
The effects of H segregation to a Σ11 symmetric tilt Al grain boundary are investigated using atomistic simulations, as part of a wider study on cracking in 7xxx series alloys
Energy curves do not follow the smooth path found in rigid grain shift (RGS) simulations, which can be explained by discrete structural changes such as the formation of ligament structures, and by sudden changes in the arrangement of surface H atoms
We have presented results which simulate decohesion of a cohesive zone (CZ) model of fracture in Al alloys, using a broad range of segregated H concentrations on a Σ11 symmetric tilt grain boundaries (GBs)
Summary
The effects of H segregation to a Σ11 symmetric tilt Al grain boundary are investigated using atomistic simulations, as part of a wider study on cracking in 7xxx series alloys. Segregated concentrations of relevant alloying elements (Zn, Mg, and Cu) show minimal impact on the H embrittlement process investigated, namely H enhanced decohesion (HEDE). Hydrogen-enhanced local plasticity (HELP) is a complex phenomenon involving high localised H concentrations increasing dislocation mobility by shielding dislocation interactions Another related model of HE involves adsorbed H (i.e. external H) inducing the emission of dislocations [8]. The fourth mechanism is hydrogen-enhanced decohesion (HEDE) which posits that segregated H at the GB compromises cohesive forces between grains by disrupting bonds across the interface [9]. The energy of decohesion as a function of displacement χ(u) is evaluated in (1)
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