Thermodynamic evaluation of the Fe-Nb system

An optimized set of thermodynamic functions consistent with the phase diagram was derived for the Fe-Nb system from information on phase equilibria and thermodynamic data available in the literature. The thermodynamic properties of the intermediate ε (Fe2Nb) phase were described using the sublattice model. A Redlich-Kister equation was used to describe the excess thermodynamic functions of the liquid, bcc and fcc phases. For the μ phase, the enthalpy of formation was estimated from Miedema's model. The interaction coefficients were evaluated using an optimization procedure employing a conjugate gradient method. The phase diagram and the thermodynamic functions calculated from the evaluated parameters are in good agreement with experimental data.