First-principles aluminum database: Energetics of binary Al alloys and compounds

Abstract

Using an extensive series of first-principles density functional calculations, we have constructed a ``first-principles aluminum database'' of thermodynamic properties of binary Al-based alloys with 26 different solute elements, $X$. In all cases, first-principles results are critically compared to experimental data for observed Al-rich ordered compounds, dilute impurities in Al, disordered $\mathrm{Al}\text{\ensuremath{-}}X$ solid solutions, and pure elements, $X$, in a variety of structure types. We find the following: (i) In all $\mathrm{Al}\text{\ensuremath{-}}X$ systems, first-principles formation enthalpies of ordered compounds are in excellent agreement with experimental data. Impurity energetics for $X$ in Al also agree rather well with thermodynamically assessed values from the COST507 database. (ii) Formation enthalpies of ordered compounds and energies of dilute impurities for elements from the $3d$ series are most negative at the beginning and the end of the series, and reach a maximum near the middle of the series for Cr. The ordering tendency decreases dramatically in the Al-Cu system with filled $d$ bands. (iii) The special quasirandom structure approach has been used to obtain mixing energies of disordered solid solutions across the whole composition range for all systems. We find that mixing energies follow the same general trend across the $3d$ series as the ordered and impurity formation enthalpies. Asymmetry in the mixing energies is also similar in all systems, giving less negative mixing energies for Al-rich compositions. (iv) Calculation of the solubility enthalpy, which is the difference in the formation energy per solute atom between the ordered and dilute solid solution phases, shows that the observed low solubility in $\mathrm{Al}\text{\ensuremath{-}}X$ systems is due to very negative values of the ordered formation enthalpies in comparison with those for the dilute solid solution.