Thermodynamic properties of the Al-Fe-Ni system acquired via a hybrid approach combining calorimetry, first-principles and CALPHAD

A reaction calorimeter coupled with first-principles calculations was employed to obtain enthalpies of formation for τ₁ (Al₉FeNi) and τ₂ (Al₁₀Fe₃Ni) compounds. The previous thermodynamic model for describing the disorder/order transition (fcc_A1/L1₂) in the Al-Fe-Ni system was modified to extrapolate this model to quaternary and higher-order systems. The first-principles energy calculations for the end-members of sub-lattice models in ternary compounds and L1₂ phase were performed to facilitate subsequent modeling. The existence of the experimentally observed miscibility gap for ternary B2-ordered phase is detected by the present calculation. Such a feature cannot be identified with available thermodynamic software due to the tiny difference between the Gibbs energies associated with different phase assemblages. A set of thermodynamic parameters for the Al-Fe-Ni system was obtained via thermodynamic modeling. Numerous experimental data including phase diagram, thermodynamic properties and site occupation of Fe in B2 phase are well accounted for by the present modeling.