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MM: Fachverband Metall- und Materialphysik

MM 12: Poster session I

MM 12.16: Poster

Montag, 1. April 2019, 19:15–20:45, Poster C

Atomistic investigation of non-stoichiometric stacking faults in Fe-Nb alloys — •Ali Zendegani¹, Michaela Šlapáková Poková^1,2, Christian Liebscher¹, Frank Stein¹, Sharvan Kumar³, Thomas Hammerschmidt⁴, Fritz Körmann¹, Tilmann Hickel¹, and Jörg Neugebauer¹ — ¹Max-Planck-Institut für Eisenforschung GmbH, Düsseldorf, Germany — ²Charles University, Prague, Czech Republic — ³Brown University, Providence, USA — ⁴Ruhr-Universität Bochum, Bochum, Germany

In Fe-Nb alloys a hardening via tetrahedrally close-packed (TCP) phases (e.g. Laves Fe₂Nb and µ Fe₇Nb₆) can be achieved. At the same time, various types of stacking faults occur during deformation. To investigate the correlation of both features in a Nb-rich Laves phase, ab initio calculations are combined with thermodynamics concepts.

By performing gamma surface calculations we resolve the atomic structure of these planar faults and show that they have a surprising geometrical complexity. Introducing a new thermodynamic framework allows us to compare the stability of planar faults (2D) with bulk phases (3D) in a convex hull diagram. The resulting diagram reveals that Nb-rich crystal structures next to basal and pyramidal stacking faults can become energetically more favorable than the nucleation of an epitaxially constrained µ phase. Excess Nb results thus in an enhanced formation of 2D stacking faults rather than forming 3D Nb rich precipitates in form of the µ phase. This unexpected finding allows a direct interpretation of recent HR-TEM studies on this materials system.