Modeling of yttrium, oxygen atoms and vacancies in γ-iron lattice

Development of the oxide dispersion strengthened (ODS) steels for fission and fusion reactors requires a deep understanding of the mechanism and kinetics of Y2O3 nanoparticle precipitation in the steel matrix. Therefore, it is necessary to perform a large-scale theoretical modeling of the Y2O3 formation. In the current study, a series of first-principles calculations have been performed on different elementary clusters consisting of pair and triple solute atoms and containing: (i) the Y–Fe-vacancy pairs, (ii) the two Y atoms substituted for Fe lattice atoms and (iii) the O impurity atoms dissolved in the steel matrix. The latter is represented by a face-centered cubic γ-Fe single crystal. This structure is relevant because a transition to γ-phase occurs in low Cr ferritic–martensitic steels at typically hot isostatic pressing temperatures. The results clearly demonstrate a certain attraction between the Y substitute and Fe vacancy whereas no binding has been found between the two Y substitute atoms. Results of calculations on different Y–O–Y cluster configurations in lattice show that not only a presence of oxygen atom favors a certain binding between the impurity atoms inside the γ-Fe lattice but also the increased concentration of Fe vacancies is required for the growth of the Y2O3 precipitates within the iron crystalline matrix.