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 tau(1) (Al9FeNi) and tau(2) (Al10Fe3Ni) compounds. The previous thermodynamic model for describing the disorder/order transition (fcc_A1/L1(2)) 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 L1(2) 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. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.