Effect of strain on the stabilization of oxygen-enriched nanoclusters in Fe-based alloys

摘要

First-principles theory has been developed to understand the unique material state underlying the ultra stability of O-enriched (with Ti and Y solute additions) nanoclusters (NCs) observed in nanostructured Fe. We show that an essential condition for the formation of these 2-4 nm diameter NCs is the existence of their exceptionally stable interface, as manifested in a higher (i.e., more negative) O-binding energy on the interface (E_s) than in the interior (EB) of the NCs. The difference between Es and EB is due to the effect of strain, originating from the solute-solute repulsion and the presence of O in the form of O-vacancy (O: V) pair. A Friedel-type oscillation pattern is found for the distance dependence of the solute-(O: V) and (O: V)-(O: V) interaction energies. The strain is also important in controlling the size of NCs, which are predicted to exist only within a narrow O concentration range.