Mechanisms of self and impurity diffusion in Fe-Al intermetallic compounds

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The diffusion data of alloys, such as vacancy formation energies, migration energies, diffusion activation energies and attempt frequencies, are basic information for materials design and materials processing. For several pure metals the involved mechanisms have already been studied using both experimental and theoretical methods. However, for intermetallic compounds the investigation of the mechanism of self- and impurity diffusion is challenging from experimental and theoretical point of view. Consequently, only limited knowledge exists in particular about atomic diffusion along grain boundaries in these materials. The proposed joint project is devoted to the investigation of self- and impurity diffusion mechanisms in Fe-Al alloys. On the one hand, the defect types and the defect micro-structures will be characterized by XRD, resistivity measurements and positron lifetime spectroscopy. On the other hand, the concentration and stable configurations of point defects in Fe-Al intermetallic compounds will be derived from first-principles calculations and will be used to optimize EAM interatomic potentials. Furthermore, first principles methods will also be used to determine self- and impurity diffusion activation energies/coefficients. The corresponding data will be compared with empirical results obtained from EAM based molecular dynamics calculations. Based on these extensive validity checks, the diffusion behavior of different atoms along typical grain boundaries within the investigated compounds will be simulated employing the empirical potentials. The resulting kinetic data for iron aluminides will be used to derive a diffusion model, which incorporates the effects of diffusion within a perfect lattice structure and along selected grain boundaries. In this way the project aims at understanding and quantifying the relevant diffusion mechanisms as a function of temperature and composition and at providing ideas to optimize atomic mobilities of various elements in iron aluminides.