Thermodynamic evaluation of the C–Ta–Ti system and extrapolation to the C–Ta–Ti–N system

• Thermodynamic modeling for the C–Ta–Ti system is developed.
• The quaternary C–Ta–Ti–N system is extrapolated based on the modeling work of the C–Ta–Ti system.
• The miscibility gap of the fcc carbide in the C–Ta–Ti–N system is predicted.

Based on a critical review of the literature data, the C–Ta–Ti system has been thermodynamically evaluated. The CALPHAD (CALculation of PHAse Diagrams) approach is applied to assess the Gibbs energies of individual phases in this ternary system. A set of self-consistent thermodynamic parameters is obtained. Comprehensive comparisons between the calculations and literature data show that the reliable experimental information is satisfactorily accounted for by the present thermodynamic description. Based on the present work and the previous assessments of the sub-ternary systems, a thermodynamic description of the quaternary C–Ta–Ti–N system is extrapolated and used to predict the miscibility gap in the fcc carbonitride.