Chemical complexity enhances grain boundary absorption efficiency through expansion of microstate phase space

Grain boundaries (GB) are effective defect sinks and can be engineered to enhance radiation tolerance in materials. The capacity of a GB to absorb radiation damage is influenced by the material's ability to accommodate new atoms into its internal structure. This work provides a quantitative link between material composition and self-interstitial atom (SIA) absorption efficiency through GB structural rearrangements. Molecular dynamics simulations are employed to reveal GB evolution to denser structural units in a chemically complex alloy, whereas the GBs in a pure material and dilute alloy establish a steady structural state during the SIA deposition. Following, regions of structural transformation are correlated to large positive misfit volume differences and thus higher hydrostatic stress. This environment drives GB structural unit transformations to relieve stress and accommodate the absorbed defects. There is an additional driving force from chemistry which promotes structural transformations given nominally lower values of local stress. These regions are mostly rich in Co and Cr, which are also the regions where we observe more pronounced SIA absorption events. Energetically, we find that it is this balance of thermodynamics and mechanical stress which stabilizes specific GB structures. GBs in pure Ni, $\mathrm{N}{\mathrm{i}}_{95}\mathrm{C}{\mathrm{r}}_{5}$, and equiatomic CoCrNi are evaluated as a function of SIA deposition into the GB. We find that chemistry has an unequivocal role in widening the available microstate range for defect absorption, which highlights chemical tailoring as a pathway for enhanced radiation resistance due to elevated GB absorption efficiencies.