A combined first-principles/CALPHAD modeling of the Al–Ir system Original Research Article

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 Al2.7Ir, 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 Al1−xIrx 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.