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MM: Fachverband Metall- und Materialphysik
MM 21: Topical Session: Thermodynamics at the nano scale I - Kinetics, nucleation, grain growth, segregation
MM 21.3: Vortrag
Dienstag, 1. April 2014, 11:00–11:15, BAR 205
Segregation at and structure of iron grain boundaries using parameterized electronic description. — •Georg K. H. Madsen1, Jingliang Wang1, Nicholas Hatcher1,2, and Ralf Drautz1 — 1ICAMS, Ruhr-Universität Bochum, 44780 Bochum, Germany — 2QuesTek Innovations LLC, Evanston, IL 60201, USA
We employ a recently developed iron carbon orthogonal tight-binding model of grain boundaries (GBs) in the iron-carbon system. Bulk electron states are captured in this model as it is applied to systems containing over 5,000 ferromagnetic atoms. A strategy for a systematic screening of grain boundary energies has been applied to BCC-Fe. We show how the Fe-Fe tight binding model is able to pre-screen the rigorous coincidence site lattice GBs and apply it to calculate the stable Σ<15 GBs in α-Fe.
The properties of carbon near and on the Σ 5 (310)[001] symmetric tilt GB are calculated and it is found that a carbon atom lowers the GB energy by 0.29 eV/atom in accordance with the DFT value of 0.23 eV. Carbon segregation to the GB is analyzed, and we find an energy barrier of 0.92 eV for carbon to segregate to the carbon-free interface while segregation to a fully-filled interface is disfavored. We isolate two different mechanisms governing carbon’s behavior in iron: a volumetric strain which increases the energy of carbon in interstitial α-iron and a non-strained local bonding which stabilizes carbon at the GB.