The vacancy mechanism of high oxygen solubility and nucleation of stable oxygen-enriched clusters in Fe

Abstract

First-principles studies have identified the atomic-level mechanism that underlies the unusually high solubility of O and nucleation of self-assembled stable O-enriched nanoclusters in defect-containing Fe. Oxygen is confined as an interstitial in Fe such that it shows an exceptionally high affinity for vacancies (an effect that is augmented by density expansion due to spin-polarization), leading to the formation of very stable O-vacancy (O:V) pairs. If vacancies pre-exist, the formation energy of an O:V pair essentially vanishes, allowing the O concentration to become as high as that of the vacancies. This vacancy mechanism based upon O-confinement enables the nucleation of O-enriched nanoclusters, that also contain solutes (Ti and Y) with high O-affinities. Fe-based alloys strengthened by these stable nanoclusters exhibit superior mechanical properties.