Effect of local chemical order on the irradiation- induced defect evolution in CrCoNi medium- entropy alloy

High- (and medium- ) entropy alloys have emerged as potentially suitable structural materials for nuclear applications, particularly as they appear to show promising irradiation resistance. Recent studies have provided evidence of the presence of local chemical order (LCO) as a salient feature of these complex concentrated solid- solution alloys. However, the influence of such LCO on their irradiation response has remained uncertain thus far. In this work, we combine ion irradiation experiments with large- scale atomistic simulations to reveal that the presence of chemical short- range order, developed as an early stage of LCO, slows down the formation and evolution of point defects in the equiatomic medium- entropy alloy CrCoNi during irradiation. In particular, the irradiation- induced vacancies and interstitials exhibit a smaller difference in their mobility, arising from a stronger effect of LCO in localizing interstitial diffusion. This effect promotes their recombination as the LCO serves to tune the migration energy barriers of these point defects, thereby delaying the initiation of damage. These findings imply that local chemical ordering may provide a variable in the design space to enhance the resistance of multi- principal element alloys to irradiation damage.