  High-entropy alloys (HEAs) composed of multiple principal elements have been
shown to offer improved radiation resistance over their elemental or
dilute-solution counterparts. Using NiCoFeCrMn HEA as a model, here we
introduce carbon and nitrogen interstitial alloying elements to impart chemical
heterogeneities in the form of the local chemical order (LCO) and associated
compositional variations. Density functional theory simulations predict
chemical short-range order (CSRO) (nearest neighbors and the next couple of
atomic shells) surrounding C and N, due to the chemical affinity of C with (Co,
Fe) and N with (Cr, Mn). Atomic-resolution chemical mapping of the elemental
distribution confirms marked compositional variations well beyond statistical
fluctuations. Ni+ irradiation experiments at elevated temperatures demonstrate
a remarkable reduction in void swelling by at least one order of magnitude
compared to the base HEA without C and N alloying. The underlying mechanism is
that the interstitial-solute-induced chemical heterogeneities roughen the
lattice as well as the energy landscape, impeding the movements of, and
constraining the path lanes for, the normally fast-moving self-interstitials
and their clusters. The irradiation-produced interstitials and vacancies
therefore recombine more readily, delaying void formation. Our findings thus
open a promising avenue towards highly radiation-tolerant alloys.
