Just another WordPress site - Ruhr-Universität Bochum

Abstract

The body-centered cubic metals represent a technologically highly relevant material class including Fe and the refractory metals W and Mo. A major drawback of this material class is given by the brittle-to-ductile transition which for some metals, e.g. W occurs above room temperature. A dominant role in this connection is assigned to the ½ screw dislocation which, due to a non-planar core, has low mobility and limits plastic deformation. However, it has been proposed recently that mixed ½ dislocations, which are of predominantly edge character and therefore expected to be glissile, possess unexpectedly high Peierls stress. Therefore, such dislocations might play an equally important role for the limited plastic deformation at low temperature. So far the issue has not been systematically investigated for the class of bcc transition metals Nb, Ta, Mo, W and Fe. In this study, we investigate the core structures and mobilities of mixed ½ dislocations in five BCC transition elements Nb, Ta, Mo, W and Fe using atomistic simulations. The simulations were carried out with different models of interatomic interactions, ranging from classical potentials via tight-binding-based bond order potentials to first-principles methods based on density functional theory. We find pronounced differences for the structure of the dislocation core in terms of width and dissociation into fractionals. As a result, Peierls barriers vary strongly between the different transition metals. By comparing mobility of the mixed dislocation with the one of the screw dislocation we provide hints to what extent mixed dislocations matter in the different metals and discuss the implications of our findings for thermal activation of dislocation glide and shape of dislocation loops.