Thermodynamic description of the systems Co-Nb, Al-Nb and Co-Al-Nb

The Co-Al-Nb ternary system and its two binary subsystems Co-Nb and Al-Nb were thermodynamically modeled by the Calphad method based on own experimental results and critically assessed literature data. A characteristic of the Co-Nb and Co-Al-Nb system is the coexistence of three polytypes of Laves phases: hexagonal C14 and C36 as well as cubic C15. Two-sublattice models were used for the three Laves phases to enable a realistic description of their homogeneity ranges in the Co-Nb and Co-Al-Nb system. A re-assessment was needed for the Al-Nb system to obtain a better description of the homogeneity range of Nb2Al and the liquidus projection of the Co-Al-Nb system. The comparison between calculated and experimental values shows that the optimized set of thermodynamic parameters gives a very good description of most of the experimental data resulting in a complete, consistent thermodynamic description of the three systems Co-Nb, Al-Nb and Co-Al-Nb. (C) 2015 Elsevier B.V. All rights reserved.