Modelling of dislocation-solute interaction in ODS steels: Analytic bond-order potential for the iron-yttrium system

An interatomic potential for iron-yttrium is presented that allows to investigate the diffusion of yttrium in iron. The potential provides a complete description of the elastic and thermal properties of yttrium. The iron-yttrium interaction is fitted with focus on yttrium point defects in an iron matrix, as the interaction and diffusion of point defects is the crucial part of the formation of precipitates in ODS steels. The formation energy of substitutional yttrium atoms, the binding energy to vacancies and the migration barriers are very well reproduced. The potential is used to investigate the interaction between substitutional yttrium atoms and edge dislocations. It shows a significant attraction between yttrium atoms and the stress field of the dislocation which leads to yttrium segregation and pinning of dislocation motion. Pipe diffusion of yttrium atoms within the edge dislocation core is investigated by calculating migration barriers. The potential predicts a significant reduction of the activation barriers in the tensile part of the stress field around an edge dislocation. We conclude that yttrium pipe diffusion is relevant for the precipitate formation in ODS steels. (C) 2018 Elsevier B.V. All rights reserved.