Interaction of a 1/2⟨111⟩ screw dislocation with Cr precipitates in bcc Fe studied by molecular dynamics

The appearance of Cr-rich precipitates (alpha' prime) after thermal aging or irradiation is a typical feature of high-Cr ferritic/martensitic steels. alpha' particles, obstructing the motion of dislocations, are long known to be the cause of hardening and embrittlement, observed in steels and Fe-Cr binary alloys. In this work, we consider the interaction of a screw dislocation with Cr precipitates in a bcc Fe matrix using a molecular dynamics technique. We derive an interatomic potential, based on the existing two band formalism, specifically accounting for information about screw dislocation properties in the Fe-Cr system available from the first-principles calculations. The derived potential was accordingly benchmarked and successfully applied to study the interaction of a moving 1/2 < 111 > screw dislocation with Cr precipitates. The results obtained suggest that two principally different interaction mechanisms may operate depending on the interatomic potential applied. The improved potential predicts stable glide of a screw dislocation, whereas the potential predicting an incorrect core structure shows the bypass movement of the dislocation around the precipitate without shearing of the latter. The bypass movement involves the glide of the dislocation under the precipitate in the plane inclined to the maximum resolved shear stress plane. The reasons for this were rationalized in terms of the compact-to-degenerate transformation of the structure occurring at the precipitate matrix interface. This study emphasizes the importance of the atomic scale features and dislocation core effects in the process of the interaction of a dislocation with secondary phase particles.