Thermodynamic assessment of the Fe–Hf binary system

The Fe–Hf system was critically assessed by means of the Calphad approach. The solution phases (liquid, BCC, FCC and HCP) were described with the sublattice formalism and the excess model with the Redlich–Kister equation by imposing additional constraints to avoid the appearance of unwanted inverted miscibility gap in the liquid phase during the phase diagram calculation up to 6000 K. The λ sub-stoichiometric intermetallic compound, which melts congruently and has an homogeneity range, was treated as the usual C14 Laves phases, with the formula (Fe)0.6667(Hf,Fe)0.3333, by a two-sublattice model with Fe alone in the first sublattice and Fe and Hf in the second one. The others polytypes Fe2Hf_HT, Fe2Hf_LT as well as FeHf2 were treated as stoichiometric compounds. The calculated phase diagram and thermodynamic properties are in good agreement with the experimental data.