Dresden 2020 – scientific programme
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MM: Fachverband Metall- und Materialphysik
MM 51: Computational Materials Modelling - Mechanical Properties
MM 51.3: Talk
Thursday, March 19, 2020, 10:45–11:00, IFW B
Two mechanisms of anomalous slip in bcc metals — •Roman Gröger1 and Vaclav Vitek2 — 1Czech Academy of Sciences, Institute of Physics of Materials and CEITEC IPM, Brno, Czech Republic — 2University of Pennsylvania, Department of Materials Science and Engineering, Philadelphia, PA, USA
Many body-centered cubic metals and alloys exhibit anomalous slip of 1/2⟨ 111⟩ screw dislocations on {110} planes with very low Schmid factors. The origin of this phenomenon is still unknown but there is a growing pool of evidence linking it to core structures of these dislocations and their transformations under applied load. Here, we identify two possible mechanisms leading to the anomalous slip for uniaxial loading in the center of the stereographic triangle. The first originates from the glide of 1/2[111] and 1/2[111] screw dislocations on their most highly stressed planes, as proposed by the Schmid law. This inevitably leads to their intersection and formation of [100] screw junctions, as proposed previously in the co-planar double slip model. If this junction is strong, the three dislocations have to move on their common (011) plane, which results in anomalous slip. The second mechanism is based on a hypothesis that the two 1/2⟨ 111⟩ screw dislocations may move directly on the (011) plane in contradiction to the Schmid law. Using atomistic simulations, we investigate which of these two mechanisms is operative at 0 K in the five non-magnetic bcc metals (V, Nb, Ta, Mo, W), magnetically isotropic state of Cr, and in ferromagnetic α-Fe. The predictions of both models are compared with available low-temperature experiments on high-purity single crystals.