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

Abstract

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.

Deformation mechanisms in high entropy alloys: a minireview of short-range order effects

“…This hinders the migration of radiation-induced defects, restricting their movement to local areas and void creation is delayed by easier recombination of interstitials and vacancies. 95 This recombination-based mechanism for improved irradiation resistance is also reported in an experimental irradiation study of the CrCoNi MEA from Zhang et al 96 Here, the investigators measure significantly lower defect densities (but similar defect sizes) over a wide range of irradiation dosing for samples with SRO relative to an RSS reference (see Fig. 6f and g).…”

Defect properties of a body-centered cubic equiatomic TiVZrTa high-entropy alloy from atomistic simulations

“…Thus, 3D diffusion of interstitials is slower than vacancy diffusion in TiVZrTa and SRO TiVZrTa. The closer mobility between interstitials and vacancies can significantly result in high fractions of defect recombination [68]. From figure 8, we can conclude that the mobility between interstitials and vacancies in TiVZrTa and SRO TiVZrTa is closer than that in pure Ta and V. In addition, Ti, Zr, and Ta defects have closer mobility compared to Ta interstitial and vacancy.…”

Recent advances in computational design of structural multi-principal element alloys

“… 49 , 50 , 51 Recently, a combination of classical MD simulations with scanning transmission electron microscopy (STEM) imaging identified SFTs in CoCrNi medium entropy alloy. 52 It should be noted that the tetra-vacancy clusters have a positive binding energy in CoCrFeMnNi, suggesting that these vacancy clusters can form when cascade damage is caused by high-energy ion or neutron irradiation. 49 …”