Regensburg 2013 – scientific programme

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MM: Fachverband Metall- und Materialphysik

MM 22: Computational Materials Modelling - Phase Stability II

MM 22.4: Talk

Tuesday, March 12, 2013, 12:30–12:45, H24

Ab-initio study of kappa-carbide precipitates in an austenitic Fe matrix — •Poulumi Dey, Roman Nazarov, Martin Friak, Tilmann Hickel, and Jörg Neugebauer — Max-Planck-Institut für Eisenforschung GmbH, D-40237, Düsseldorf, Germany

The quaternary system Fe-Mn-Al-C exhibits interesting physical properties and is highly relevant for a new class of steels with high strength and toughness. Depending on the composition, experiments show the precipitation of kappa-carbides, (Fe,Mn)3AlC in these steels, which significantly influence the microstructure. In order to theoretically predict the formation of these precipitates, we perform a thorough investigation of the structure, composition and magnetism of kappa-carbides in an austenitic Fe-based matrix with the aid of density functional theory. The formation energy of kappa-carbides is computed as a function of the chemical potentials of its constituents, including the effect of different magnetic structures. For both aspects the constraints posed by an austenitic Fe-Mn-Al matrix have been taken into account. Our results show that the Mn-free Fe3AlC is energetically most favorable over a wide range of chemical potentials and hence most abundant as coherent precipitate in the matrix. An increase in Mn concentration results in a monotonic increase in the lattice constant of kappa-carbides and therefore a growing lattice mismatch between the kappa-carbide and the matrix. The results can be used to design strategies to adjust the amount of kappa-carbides in Fe-Mn-Al steels.