Study of vacancy-(H,B,C,N,O) clusters in Al using DFT and statistical approaches: Consequences on solubility of solutes

Abstract

This article is a study of the solubility of interstitial atoms in aluminum using a multi-scale approach. We focused on hydrogen, boron, carbon, nitrogen and oxygen atoms (labeled X). We studied isolated atoms as well as the possible formation of clusters with and without vacancies (V), i.e., Xm, VXm and V2Xm (m ≥0). Formation and segregation energies are first obtained using first-principles calculations, subsequently, a statistical approach is employed in order to evaluate the concentration of impurities and defects according to the temperature. For instance, we find that, in solute solution, H, N and O atoms prefer to be located in tetrahedral sites, and C and B atoms in octahedral sites. The chemical and energetic interactions between the interstitials, the metal and the vacancies are consequently presented and analyzed in detail. Results show that certain species prefer to interact with themselves, thus forming Xm clusters, and others with vacancies, thus forming stable VXm clusters in the metal. Using a statistical approach, we finally discuss the formation of clusters according to the temperature and the X concentration. At low and intermediate temperatures (below 600 K), we found that the atoms prefer to form clusters rather than stay isolated in aluminum. We show that H and B atoms are the only elements likely to increase vacancy concentration.