Structure and energetics of Y-Ti-O nanoclusters in bcc Fe: A combined DFT and Monte Carlo Study

Oxide Dispersion Strengthened (ODS) steels consist of a ferritic matrix with dispersed oxide particles having a size of few nanometers. Due to this nanostructure ODS materials exhibit remarkable properties such as high-temperature stability and radiation tolerance. The detailed structure and composition of the nanoclusters containing Y, Ti, O, along with other alloying and impurity elements, is still under discussion. In this work simulated annealing based on the Metropolis Monte Carlo method on a rigid lattice is used in order to determine the structure of the oxide nanoclusters with the lowest formation energy. The ferritic matrix of ODS steels is modeled by bcc-iron. Extensive DFT calculations of point defects and small clusters containing Y, Ti, O and vacancies were performed to obtain the parameters describing the atomic interactions on the rigid lattice. In this work, apart from simple pairwise atomic interactions, many body interactions such as triple interactions are determined from extensive DFT calculations of the oxide clusters. Triple interactions are found to be important additions in order to correctly reproduce the experimentally observed structure of nanoclusters.