Effect of Cr atoms on the formation of double kinks in screw dislocations in Fe and its correlation with solute hardening and softening in Fe-Cr alloys

In this work, we employed atomistic simulations to study the formation of a double kink (DK) on a screw dislocation in bcc Fe and to investigate how the presence of Cr affects it, using one of the most recent and reliable interatomic potentials for Fe and Fe-Cr systems (i.e. from Refs. [G.J. Ackland, M.I. Mendelev, D.J. Srolovitz, S. Han, A.V. Barashev, J. Phys.: Condens. Mat. 16 (2004) 1, P. Olsson, J. Wallenius, C. Domain, K. Nordlund, L. Malerba, Phys. Rev. B 72 (2005) 214119]). The formation energy of a DK of different lengths and structures, as well as the formation energies of each single kink and the interaction energies between them, have been obtained by performing large scale atomistic simulations and compared with the results obtained from elasticity theory. We show that the presence of Cr atoms, particularly Cr-Cr pairs, affects, sometimes significantly, the formation energy of DKs. The obtained results suggest a strong dependence of the effect of solute Cr atoms on dislocation motion in Fe-Cr alloys, depending on the actual Cr distribution, which in turn depends strongly on concentration and temperature. A possible framework to understand solute softening and hardening experimentally observed in Fe-Cr alloys is accordingly discussed.