Thermodynamic modeling of the Nb–Si system

Optimized coefficients of the Gibbs free energy expression for each stable phase of the binary Nb–Si have been obtained, using the Thermo-Calc program for this purpose. The Nb3Si, αNb5Si3, NbSi2 and Diamond (Si) have been modeled as stoichiometric phases and the liquid L, BCC (Nb) and the βNb5Si3 phases as solutions, with the excess term described using the Redlich–Kister formalism. The Si solubility in the βNb5Si3 phase has been modeled according to two possibilities: (i) Si substituting for Nb and (ii) vacancies in the Nb positions. The calculated diagrams compare well with the experimental information taken from the literature.