Contribution to a thermodynamic database and phase equilibria calculations for low activation Ta-containing steels

In the framework of the Calphad-Thermocalc approach, a first attempt is presented to update the TCFe2000 steel database by introducing existing and recently optimized thermodynamic parameters of Ta-containing binary and ternary systems. The ultimate aim of the work is to develop a self-consistent thermodynamic description of low-activation steels. In a first stage, we performed a complete modeling and optimization of the Fe–Ta binary system in order to provide a description of its intermediate phases coherent with that existing for other systems in the TCFe2000 database. In doing such a modeling, we have also taken into account experimental data of higher order systems such as Fe–Ta–C and Fe–Ta–N. After considering the reported interactions of Ta with other alloying elements of low-activation steels, we have carried out phase diagram calculations in the austenite region of the Eurofer 97 (9CrWVTa) alloy. A reasonable agreement was found with the available experimental information.