Experimental Investigation and Thermodynamic Assessment of Phase Equilibria in the Al-Ta-V Ternary System

The phase equilibria in the Al-Ta-V ternary system at 1000 °C and 1200 °C have been studied by using electron probe microanalysis and x-ray diffraction. τ-Al2.9Ta2.7V1.4 phase was found in the Al-Ta-V ternary system in both isothermal sections. The addition of V stabilizes the Al69Ta39 phase at 1000 °C. The line compound Al3(V,Ta) (D022-type) forms a continuous phase region from the Al-V side to the Al-Ta side at the two temperatures. Based on our experimental results, reported liquidus projection of the ternary Al-Ta-V system and thermodynamic data of the binary systems of Al-V, Al-Ta and V-Ta, a thermodynamic evaluation of Al-Ta-V system was carried out by CALPHAD method. A set of reliable thermodynamic parameters for the Al-Ta-V system was obtained. The current calculation results agree well with the available experimental data. The invariant reaction scheme of Al-Ta-V ternary system was presented. The present study could provide essential experimental and thermodynamic data for establishing a comprehensive Co-based superalloy database.