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

Abstract

The thermodynamic properties of the Me-Co-C (Me ϭ Ti, Ta, or Nb) systems are of interest for cemented carbide applications. The model parameters for the Gibbs energy of the individual phases have been evaluated using the CALPHAD 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 systems have been reviewed and the thermodynamic properties have been evaluated. Due to the large scattering of the experimental data, DTA investigations 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 importance of controlling the carbon activity during the experiments is emphasized. 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 the experimental information is satisfactorily accounted for by the present thermodynamic description.

Protection of cobalt-based refractory alloys by chromium deposition on surface

“…This {software + database} calculation tool is able to assess solidus temperatures consistent with experimental DTA measurements for tantalum-containing cobalt-based alloys [12]. The systems added to the initial SSOL database are TaC [13], CoTa [14], CrTa [15] and CoTaC [16].…”

Influence of the morphologic evolution of the eutectic carbides at high temperature on the thermal expansion behavior of refractory cast alloys

“…The theoretical stable microstructure states at 1200 • C of the two alloys were determined using the Thermo-Calc version N software and the SSOL database (SGTE) enriched with the descriptions of the following binary and ternary systems: Ta-C [10], Co-Ta [11], Ni-Ta [12], Cr-Ta [13], Co-Ta-C [14], Ni-Cr-Ta [15] (only four ternary systems were still missing in the new database: Co-Cr-Ta, Co-Ni-Ta, Ni-Ta-C and Cr-Ta-C). Calculations were carried out to specify, when the aging duration increases, the degree of convergence of the alloys towards the theoretic stable state at 1200 • C, first by comparing the microstructures of the alloys (after each of the three heat treatments) to the metallurgical stable state at 1200 • C, and second to compare the temperatures of fusion's start and fusion's end to the theoretic solidus and liquidus temperatures.…”

Thermodynamic calculations for studying high temperature oxidation of superalloys

“…Thermodynamic calculations were carried out using Thermo-Calc software [7] with the SSOL database (SGTE) [8]. For the more complex cobalt alloys, the SSOL database was completed with binary and ternary systems : Ta-C [9], Co-Ta [10], Ni-Ta [11], Cr-Ta [12], Co-Ta-C [13], Ni-Cr-Ta [14]. Thereafter, only four ternary systems were still missing in the new database : Co-Cr-Ta, Co-Ni-Ta, Ni-Ta-C and Cr-Ta-C. Thermo-Calc calculations have been performed, firstly to verify the good accordance of chemical composition and the stable microstructure at the considered high temperature.…”