Ab initio calculations of elastic properties of bcc Fe-Mg and Fe-Cr random alloys

Using the ab initio exact muffin-tin orbitals method in combination with the coherent-potential approximation, we have calculated the elastic parameters of ferromagnetic Fe1-m Mgm (0≤m≤0.1) and Fe1-c Crc (0≤c≤0.2) random alloys in the body-centered cubic (bcc) crystallographic phase. Results obtained for Fe1-c Crc demonstrate that the employed theoretical approach accurately describes the experimentally observed composition dependence of the polycrystalline elastic moduli of Fe-rich alloys encompassing maximum ∼10% Cr. The elastic parameters of Fe-Cr alloys are found to exhibit anomalous composition dependence around 5% Cr. The immiscibility between Fe and Mg at ambient conditions is well reproduced by the present theory. The calculated lattice parameter for the Fe-Mg regular solid solution increases by ∼1.95% when 10% Mg is introduced in Fe, which corresponds approximately to 11% decrease in the average alloy density, in perfect agreement with the experimental finding. At the same time, we find that all of the elastic parameters of bcc Fe-Mg alloys decrease almost linearly with increasing Mg content. The present results show a much stronger alloying effect for Mg on the elastic properties of α-Fe than that for Cr. Our results call for further experimental studies on the mechanical properties of the Fe-Mg system.