CALPHAD modelling of the unmixing of transition metal carbide phases

Phase separation in a pseudo-binary solid solution of the form (M1,M2)C where M1 and M2 are chosen among minor addition in 9% Cr, martensitic-ferritic steels such as Nb, V, Ta and other transition elements such as Hf and Zr has been studied using the Calphad-Thermocalc approach. Ternary excess parameters accounting for phase equilibria in pseudo-binary sections have been optimised using suitable combinations of already published excess parameters which have been calculated on a physical basis. The ternary parameters obtained by optimisation were checked, when possible, with experimental information on isothermal ternary sections.