Evolution of local lattice distortion under irradiation in medium- and high-entropy alloys

A major challenge for future nuclear reactors is to design nuclear materials that can sustain extremely prolonged radiation damage. Local lattice distortion, considered as a core effect of high-entropy alloys (HEAs), can suppress the growth of radiation defects to control radiation performance. However, local lattice distortion in HEAs is rarely quantitatively measured. Here we employed total scattering technique to study the local structure of the face-centered cubic (fcc) equiatomic FeCoNiCr MEA, and FeCoNiCrMn and FeCoNiCrPd HEAs before and after ion irradiation. Their local lattice distortions were quantitatively evaluated based on the difference of lattice constant between the local structure and the average structure. We revealed that the mean local lattice distortion in the pristine samples varies in the following order: FeCoNiCr < FeCoNiCrMn < FeCoNiCrPd. Density functional theory (DFT) calculations further unveiled that the fluctuation of local distortions in FeCoNiCr and FeCoNiCrMn is less than 5%, whereas the highest bond-length fluctuation in FeCoNiCrPd can approach to 8%. Under irradiation the mean local lattice distortion in FeCoNiCr and FeCoNiCrMn evolves differently from FeCoNiCrPd by showing a relaxation behavior at low dose. And the impact of local lattice distortion on dislocation loops after a prolonged ion-irradiation was investigated by transmission electron microscope (TEM) and the underlying mechanism was discussed.