Regensburg 2013 – wissenschaftliches Programm

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MM: Fachverband Metall- und Materialphysik

MM 12: Computational Materials Modelling - Mechanical Properties

MM 12.3: Vortrag

Montag, 11. März 2013, 16:15–16:30, H24

Interaction of dislocations with carbon interstitials in α-iron — •Gholamali Nematollahi, Blazej Grabowski, Johann von Pezold, Chris Race, Jörg Neugebauer, and Dierk Raabe — Max-Planck Institut für Eisenforschung, D-40237 Düsseldorf, Germany

The interaction of carbon with dislocations gives rise to the formation of Cottrell atmospheres in α-Fe. This does not only directly affect the mechanical properties of the matrix, but may also result in an indirect effect due to a dislocation-driven rearrangement of the C distribution during severe plastic deformation. Recent experimental studies of severely deformed pearlitic wires reveal a considerable refinement of the cementite layers and a substantial accumulation of C in the ferrite. It was tentatively suggested that the accumulation of C in the ferritic layers proceeds via the co-migration of C atoms with mobile dislocations gliding from the ferrite/cementite interface into the ferrite phase. In the present study, we provide molecular statics calculations addressing the proposed mechanism in detail. In particular, nudged elastic band (NEB) calculations are used to determine the effective migration barrier for an interstitial C atom in the vicinity of an edge and screw dislocation in α-Fe, using a semi-empirical EAM potential. Carbon diffusion barriers of 0.2 eV are found in the core of the dislocation suggesting that carbon is more mobile than in bulk iron (barrier: 0.9 eV). The Portevin-le Chatelier effect that suggests the mobile solute atoms can diffuse with the moving dislocation at high temperature and moderate strain rate. These conditions are satisfied about C in the dislocation core already at room temperature.