A combined first-principles/CALPHAD modeling of the Al-Ir system

A combined first-principles/CALPHAD approach was employed to model the thermodynamics of the Al-Ir system. Among the six intermetallic compounds in this system, the formation enthalpies of Al₉Ir₂, Al₃Ir and AlIr were obtained from T = 0 K first-principles total energy calculations. The formation enthalpies of Al₄₅Ir₁₃, Al₁₃Ir₄ and Al_2.7Ir, whose structures are either unknown or too complicated for first-principles calculations, were estimated using a greedy algorithm developed in this study. The mixing enthalpies of Al_1-xIr_x face-centered cubic (fcc) alloys were calculated at x = 0.25, 0.5 and 0.75 using the special quasirandom structure approach. The vibrational formation entropy of AlIr was also calculated using the supercell method within the harmonic and quasi-harmonic approximation, respectively. We demonstrated that, with the incorporation of first-principles energetics, a physically meaningful thermodynamic description of the Al-Ir system can be obtained even with very scarce experimental data. The predicted B2 and fcc two-phase equilibrium in the Al-Ir-Ni ternary system was also in reasonable agreement with experiments.