Attractive interaction between interstitial solutes and screw dislocations in bcc iron from first principles

Plasticity in steels depends largely on how dislocations interact with solute atoms. We consider here typical interstitial solutes (B, C, N, O) in body-centered cubic (bcc) Fe and show using ab initio calculations that, systematically, when a row of interstitial solutes is in the vicinity of a 1/2〈111〉 screw dislocation, the dislocation adopts a hard core, forming regular prisms of Fe atoms centered on the solute atoms. This low-energy configuration, previously known only for C atoms, induces attractive dislocation-solute interaction energies ranging from −1.3 to −0.2 eV, depending on the nature of the solutes and their separation distance along the dislocation line. This attractive reconstruction is explained by the larger Voronoi volume of the prismatic sites in the dislocation core compared to bulk octahedral sites. Moreover, an analysis of the local density of states gives a first insight into the chemical contribution responsible for the solute dependence of the interaction energy.