Abstract
The site occupation of binary Fe-Cr, Co-Cr, Re-W and Fe-V sigma phases is studied in the present work with a first-principles-based single-site mean field theory. We show that the alloy components in these systems exhibit similar site preferences except for the Re-W system, where the occupation of two sites is reversed in agreement with previously published works. In case of the FeV sigma phase, for which the size mismatch between the alloy components is large, we also include into our consideration the effect of local lattice relaxations. The obtained results are found in good agreement with the experimental data and previous theoretical studies.
Highlights
In 1923 the σ-phase was first observed by Bain as a hard non-magnetic intermediate phase which was formed during a long-time high-temperature annealing in the Fe-Cr alloy with a nearly equiatomic composition
The V site occupancies in the Fe-V system calculated for different alloy compositions xV = {0.40; 0.60} with parameters obtained for the fixed Fe0.5 V0.5 composition or taking into account concentration and structural effects as described in the text within the disordered local moment (DLM)-longitudinal spin fluctuations (LSF) model at T = 1,000 K
In present work we gave a short overview of a single-site mean field theory for calculating of the atomic site occupancies in the σ-phase
Summary
In 1923 the σ-phase was first observed by Bain as a hard non-magnetic intermediate phase which was formed during a long-time high-temperature annealing in the Fe-Cr alloy with a nearly equiatomic composition. Some preferences in the site occupation could be estimated for some binary σ-phases, the knowledge of the atomic site distribution in a wide temperature and composition range is still missing. Such information is useful for studying the σ-phase stability and its precipitation. Hard to obtain these data experimentally due to sluggish kinetics of the transformation, difficulties in getting high purity samples and satisfying some other technological requirements In this context, an accurate theoretical study based on state-of-the-art first-principles methods combined with a proper statistical model can be used in order to determine the site preferences of the alloy components in the σ-phase. In this paper we briefly describe this method and apply it to study the distribution of alloy components in other binary σ-phase, namely, Co-Cr, Re-W and Fe-V, for which experimental and theoretical information is available
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