Impact of the clusterization on the solubility of oxygen and vacancy concentration in nickel: A multi-scale approach

Abstract

Combining thermodynamic concepts with first-principles calculations, we study the solubility of oxygen atoms (O) in nickel. In our approach, we include the possible formation of oxygen clusters (On) and vacancies-oxygens clusters (VOn and V2On). We show that the vacancy-oxygens interactions are strong (approximately 1 eV) and would induce a large concentration of clusters in fcc-Ni. The use of a thermodynamic model, within a grand canonical approach, allows calculation of the vacancy concentration, including these VOn clusters, as a function of O concentration, for different temperatures. We find that at low temperatures (below 600 K), a small content of oxygen (in appm) strongly modifies the vacancy concentration, increasing the total vacancy concentration in the metal by many orders of magnitude more than the thermal vacancy concentration. The vacancy concentration is thus directly controlled by the oxygen content in the metal. At high temperatures, the effect is reduced, becoming negligible near the melting point. These results show the strong impact of interstitial atoms on the vacancy concentration. The influence of the vacancy formation energy is also discussed.