Impact of magnetism on screw dislocations in body-centered cubic chromium

The influence of magnetism on the properties of screw dislocations in body-centered cubic chromium is investigated by means of ab initio calculations. Screw dislocations having Burgers vectors 1/2 < 111 > and < 100 > are considered, following experimental observations showing activity for both slip systems. At low temperature, chromium has a magnetic order close to antiferromagnetism along < 100 > directions, for which 1/2 < 111 > is not a periodicity vector. Hence, dislocations with Burgers vectors 1/2 < 111 > generate magnetic faults when shearing the crystal, which constrain them to coexist and move pairwise, leading to dissociated < 111 > super-dislocations. On the other side, < 100 > is a periodicity vector of the magnetic order of chromium, and no such magnetic fault are generated when < 100 > dislocations glide. Dislocation properties are computed in the magnetically ordered and non magnetic phases of chromium for comparison purposes. We report a marginal impact of magnetism on the structural properties and energies of dislocations for both slip systems. The Peierls energy barrier opposing dislocation glide in {110} planes is comparable for both 1/2 (111) {110} and (100) {110} slip systems, with lower Peierls stresses in the magnetically ordered phase of chromium. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.