Dresden 2014 – scientific programme

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MM: Fachverband Metall- und Materialphysik

MM 41: Computational Materials Modelling VI - Dislocations

MM 41.1: Talk

Wednesday, April 2, 2014, 11:30–11:45, IFW D

Dislocation mediated diffusion mechanisms of carbon in α-iron — •Gh.Ali Nematollahi, Blazej Grabowski, Dierk Raabe, and Jörg Neugebauer — Max-Planck Institut für Eisenforschung, D-40237 Düsseldorf, Germany

Experimental observations have revealed that dislocations can provide "diffusion short circuits", i.e., impurities can use the distorted lattice around dislocations to diffuse faster than in the perfect bulk region. This phenomenon is usually referred to as pipe diffusion. These accelerated diffusion paths help to redistribute impurities faster, especially in heavily deformed materials that contain high dislocation densities. This has important consequences e.g. for carbon redistribution in severely deformed pearlite - a steel with the highest strength among nanostructured materials. In the present study, empirical potentials in conjunction with the nudged elastic band method are used to study carbon diffusion in the vicinity of edge, screw and mixed dislocation in bcc iron. Our results show that there are low carbon diffusion barriers of *0.2 eV (vs. 0.8 eV in bulk) for all three dislocation types. For edge dislocations the results are not fully conclusive as it is technically difficult to stabilize such a dislocation due to the low Peierls barrier. For screw dislocations the low diffusion barrier is perpendicular to the dislocation line prohibiting pipe diffusion. Finally, for mixed dislocations, the low diffusion barrier is parallel with the dislocation line and is the only type that explains the experimentally proposed accelerated short circuit diffusion.