Interaction of screw and edge dislocations with chromium precipitates in ferritic iron: An atomistic study

Binary (Fe, Cr) alloys and high-chromium ferritic–martensitic steels undergo α–α′ phase separation under thermal ageing or irradiation. The resulting Cr-rich precipitates (α′ phase) are well known to cause hardening and embrittlement in such alloys and steels. In this work molecular statics (MS) and molecular dynamics (MD) simulations were applied to study the interaction between both a ½〈1 1 1〉 screw and ½〈1 1 1〉{1 1 0} edge dislocation with pure Cr precipitates in a bcc Fe matrix at various temperatures. After summarizing the interaction mechanisms for both types of dislocations, an analytical assessment of the interaction energy between a dislocation and precipitate is presented. The critical stress derived from the interaction energy is compared with MD data to reveal a possible correlation. For the edge dislocation and a precipitate of diameter less than 4 nm correlation with MD data is good, while for the screw dislocation no correlation was found.