A THERMODYNAMIC EVALUATION OF THE FE-NB SYSTEM

An optimised set of thermodynamic functions consistent with the phase diagram was derived for the Fe-Nb system from information on phase equ ilibria and thermodynamic data available in the literature. The thermo dynamic properties of the intermediate epsilon (Fe2Nb) phase were desc ribed using the sublattice model. A Redlich-Kister equation was used t o describe the excess thermodynamic functions of the liquid, bcc and f cc phases. For the mu phase, the enthalpy of formation was estimated f rom Miedema's model. The interaction coefficients were evaluated using an optimisation procedure employing a conjugate gradient method. The phase diagram and the thermodynamic functions calculated from the eval uated parameters are in good agreement with experimental data.