Density-functional theory (DFT) calculations have been performed to study the atomic scale energies, structures, and formation mechanisms of dissolved Y, Ti, and O solutes and small Y-Ti-O nanoclusters (NCs) in a bcc Fe lattice. Key results include the following observations. The Y and O are dissolved during mechanical alloying of ${\text{Y}}_2{\text{O}}_3$ with metal powders by ball milling, which provides the large requisite solution energy of about 4 eV per yttria atom. The solution energies of substitutional Y as well as interstitial O, which are referenced to elemental Y and solid FeO, respectively, are also high. Bound O-O, Y-O, and Ti-O pairs decrease the system energy relative to the isolated solutes and constitute the basic building blocks for NCs. The lowest energy configuration for a ${\text{Y}}_2{\text{TiO}}_3$ NC is 5.11 eV less than the total energy of the dissolved solutes. Our DFT calculations show that Y-Ti-O NC formation can take place without the energetic assistance of pre-existing vacancies. This conclusion is significant since excess vacancies are not a persistent thermodynamic-energetic constituent of the Fe-Y-Ti-O system and will quickly annihilate at dislocations during high-temperature powder consolidation.

• Received 17 October 2008

DOI:https://doi.org/10.1103/PhysRevB.79.064103