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MM: Fachverband Metall- und Materialphysik
MM 35: Structural Materials II
MM 35.2: Talk
Wednesday, March 9, 2016, 12:00–12:15, H52
Origin of the off-stoichiometry of Fe-Mn-Al-C kappa carbides: An ab-initio explanation of atom probe tomography data — •Poulumi Dey1, Roman Nazarov2, Biswanath Dutta1, Mengji Yao1, Michael Herbig1, Martin Friák3, Tilmann Hickel1, Dierk Raabe1, and Jörg Neugebauer1 — 1Max-Planck-Institut für Eisenforschung GmbH, D-40237 Düsseldorf, Germany — 2Livermore National Laboratory, Livermore, CA 94550, USA — 3Institute of Physics of Materials, v.v.i., Academy of Sciences of the Czech Republic, CZ-61662 Brno, Czech Republic
Quaternary Fe-Mn-Al-C alloys have exceptional mechanical properties such as high strength and ductility. In a certain composition range these alloys show a microstructure that comprises of an austenitic Fe-based matrix along with regularly arranged nano-sized kappa carbides which strongly strengthens the material. The nominal composition of kappa carbide is (Fe,Mn)3AlC, but our atom probe tomography measurements have indicated reduced C and Al contents in these carbides. Using density functional theory calculations, we succeeded to explain the experimentally observed off-stoichiometry with respect to C as a consequence of minimizing the elastic strains emerging in coherent microstructures. The off-stoichiometric concentration of Al can also be explained to a certain extent by a strain minimization caused by Mn antisite defects on the Al sub-lattice in kappa carbide. However, this effect becomes only significant if C vacancies are present in the vicinity of the antisite. We therefore demonstrated that the phenomena of depleted interstitial C and substitutional Al are coupled.