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.