Thermodynamic assessment of the Me-Co-C systems (Me = Ti, Ta, or Nb)

The thermodynamic properties of the Me-Co-C (Me = Ti. Ta, or Nb) systems ar e of interest for cemented carbide applications. The model parameters for t he Gibbs energy of the individual phases have been evaluated using the CALP HAD method. The reassessment of the Ti-Co-C system was based on the recent evaluations of the Ti-C and Ti-Co binary systems. The Ta-Co-C and Nb-Co-C s ystems have been reviewed and the thermodynamic properties have been evalua ted. Due to the large scattering of the experimental data, DTA investigatio ns of the eutectic temperature in the Co-MeC sections have been carried out in the present work and the results were used in the optimization. The imp ortance of controlling the carbon activity during the experiments is emphas ized. Various isothermal and vertical sections in the Me-Co-C systems and a projection of the liquidus surface of the Ti-Co-C are reported. Most of th e experimental information is satisfactorily accounted for by the present t hermodynamic description.