Screw dislocation mobility in BCC metals: the role of the compact core on double-kink nucleation

In this work, we examine the kink-nucleation process in BCC screw dislocations using atomistic simulation and transition pathway analysis, with a particular focus on the compact core structure. We observe the existence of a threshold stress, which results in an abrupt change in the minimum energy path of the kink-nucleation process, and hence, a discontinuity in the activation energy versus stress for the process. The magnitude of the discontinuity is found to be related to the degree of metastability of an intermediate split-core structure. This feature appears to be a direct consequence of the so-called 'camel-hump' nature of the Peierls potential, which manifests itself in the existence of a metastable, intermediate split-core structure. The effect is observed in a number of empirical EAM potentials, including Fe, Ta, V, Nb and Mo, suggesting a generality to the observations.