Basic study of the relaxation volume of crystalline defects in bcc iron

Abstract

The relaxation volume (Ωrel), here determined per extra-atom or vacant site, of common crystalline defects in bcc iron (Fe) was calculated from molecular dynamics (MD) simulation cells containing defects of varying size and/or density. To this end, we used both real and reciprocal space data: for the former, the change in the MD cell volume was calculated, while for the latter, we computed X-ray diffraction reciprocal space maps to evaluate the change in the lattice parameter. We show that 〈110〉 dumbbell self-interstitial atoms have the largest Ωrel, ∼1.5atomic volume (∼1.5 Ω0). C15 clusters of size 12 and 48 atoms show Ωrel of ∼ 0.91 Ω0 and ∼ 0.98 Ω0, respectively, and similar values are found for ½〈111〉 and 〈100〉 interstitial dislocation loops, with Ωrel ∼ 0.905 Ω0 and Ωrel ∼ 0.873 Ω0, respectively. Single vacancies are characterized by a negative Ωrel, ∼−0.11 Ω0. For cavities, Ωrel rapidly increases to approach zero as the clusters grow. Using these values, we managed to predict (with an accuracy better than 2 %) the lattice strain in MD cells containing several types of defects, which indicates that the relaxation volumes can be summed up to estimate the microscopic (i.e., lattice) volume change.