Berlin 2018 – scientific programme
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MM: Fachverband Metall- und Materialphysik
MM 13: Topical session (Symposium EPS and MM, joint session with MA): Magnetism in Materials Science: Thermodynamics, Kinetics and Defects (joint session MM/MA)
MM 13.4: Talk
Monday, March 12, 2018, 16:45–17:00, TC 010
Energetics of non-stoichiometric stacking faults in Fe-Nb alloys: An ab initio study — •Ali Zendegani1, Michaela Šlapáková Poková2, Christian Liebscher2, Frank Stein2, Alvin Noe Collado Ladines3, Thomas Hammerschmidt3, Ralf Drautz3, Fritz Körmann1, Tilmann Hickel1, and Jörg Neugebauer1 — 1Max-Planck-Institut für Eisenforschung GmbH, Düsseldorf, Germany — 2Charles University, Prague, Czech Republic — 3ICAMS, Ruhr-Universität Bochum, Bochum, Germany
The microstructure in structural materials plays an essential role for their mechanical properties. In Fe-Nb alloys a hardening via TCP phases (e.g. Laves Fe2Nb and Fe7Nb6) can be achieved. At the same time, various types of stacking faults occur during deformation. In the present work, we investigate the correlation of both features in the C14 Fe2Nb Laves phase. For this purpose, density functional theory calculations are combined with thermodynamics concepts. Particular care has been taken to take atomic relaxation effects and magnetic degrees of freedom into account. We proof that excess Nb will segregate to these planar defects and result in a local phase transformation next to it. The energetics of these structures are compared to the phase separation as predicted by the bulk phase diagram. Comparing our results with high-quality TEM measurements has revealed that some of the complex crystal structures next to basal and pyramidal stacking faults are in a constrained state.