Grain boundaries amplify local chemical ordering in CrCoNi

Abstract: Local chemical ordering plays an important role in the behavior of complex concentrated alloys, yet its characterization remains challenging due to the nanoscale dimensions and scattered spatial distribution of the ordered domains. This study explores the potential of grain boundaries as microstructural anchor points that amplify chemical ordering and enable the formation of compositional nanopatterns in CrCoNi. Using hybrid Monte Carlo/molecular dynamics simulations, we reveal the development of distinct compositional waves with ordering vectors normal to grain boundaries, extending to lengths greater than 6 nm. These waves manifest as periodic enrichment and depletion patterns, with strong Ni depletion near the Ni-segregated grain boundary accompanied by Co and Cr enrichment. Analogous to surface-driven phase separation, the concentration waves emanating from the boundaries gradually attenuate as they propagate into the grain interior. This behavior highlights the interplay between boundary-dictated directional ordering and the isotropic, untemplated domain growth within the grain. This work advances our fundamental understanding of grain boundary-mediated ordering phenomena and offers a pathway for more precise experimental characterization of local chemical ordering in CCAs.