An ab initio study of Ti-Y-O nanocluster energetics in nanostructured ferritic alloys

So-called oxide dispersion strengthened steels or nanostructured ferritic alloys (NFAs) contain nanoprecipitates which give them exceptional mechanical properties and resistance to radiation effects. However, the structure and composition of these nanoprecipitates are still uncertain. To help clarify the nature of the smallest nanoprecipitates, density functional theory calculations are used to investigate the most stable Ti, Y, and O nanocluster computational units in Fe. Two distinct methods for searching for stable nanoclusters are proposed: one in which nanoclusters are restricted to the body-centered cubic Fe lattice and one in which the nanocluster structures are strained variants of bulk Ti and Y oxides. We discovered that nanoclusters that are structurally similar to bulk Ti and Y oxides are significantly more stable than nanoclusters that are restricted to the Fe lattice. Consequently, the most stable nanoprecipitates in Ti-Y-O NFAs are more likely to be small oxide phases than coherent solute-enriched clusters.