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MM: Fachverband Metall- und Materialphysik

MM 3: Computational Materials Modelling I

MM 3.3: Talk

Monday, March 14, 2011, 11:30–11:45, IFW B

Ab initio determination of diffusion mechanisms in FeAl — •Niko Sandschneider, Tilmann Hickel, and Jörg Neugebauer — Max-Planck-Institut für Eisenforschung GmbH, Max-Planck-Str. 1, 40237 Düsseldorf

Iron aluminides are a promising material class for industrial high temperature applications. FeAl shows a very high vacancy concentration (several percent at T>1000 K) which severely affects its mechanical properties. It is therefore crucial to understand the generation and diffusion behavior of those vacancies.

The simplest diffusion mechanism which preserves long-range order in B2-FeAl is the next-nearest neighbor (NNN) jump of a vacancy. As a first step we performed ab initio calculations to determine the formation energies of the defects in FeAl. Four defects were investigated, namely vacancies and antisite atoms on the Fe and Al sublattices. We found that the Al vacancy has a large formation energy compared to the other defects. Therefore the NNN jump was only investigated for Fe vacancies. In a second step we calculated the migration barrier of this process using the climbing image nudged elastic band method.

Several more sophisticated mechanisms are proposed in the literature. A very promising candidate is the triple defect mechanism. We also performed nudged elastic band calculations for this mechanism and found a migration barrier which is significantly lower than for the NNN jump and several other diffusion mechanisms. We therefore conclude that the triple defect mechanism is the energetically most favorable diffusion mechanism.