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Implementation of an effective bond energy formalism in the multicomponent Calphad approach

N. J. Dupin, U. R. Kattner, B. Sundman, M. Palumbo, S. G. Fries.

Journal of Research of National Institute of Standards and Technology, 123, 123020, (2018)

Entropy of the sigma phase calculate for Mo-Ni binary system 500 K, 1500 K and 2500 K using the CEF with 30 stoichiometric compounds from DFT results compared to the EBEF using 20 effective bond energies. The upper figure shows the isothermal section in the Mo-Ni-Re system calculated for 500 K with the EBEF using 20 effective bond energies from each binary system calculated with OpenCalphad.

Most models currently used for complex phases in the calculation of phase diagrams (Calphad) method are based on the compound energy formalism. The way this formalism is presently used, however, is prone to poor extrapolation behavior in higher-order systems, especially when treating phases with complex crystal structures. In this paper, a partition of the Gibbs energy into effective bond energies, without changing its confgurational entropy expression, is proposed, thereby remarkably improving the extrapolation behavior. The proposed model allows the use of as many sublattices as there are occupied Wyckoff sites and has great potential for reducing the number of necessary parameters, thus allowing shorter computational time. Examples for face centered cubic (fcc) ordering and the σ-phase are given.

Keyword(s): Calphad; compound energy formalism; effective bond energy formalism
DOI: 10.6028/jres.123.020
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