Prediction of site occupancy of C15 Laves phase at finite temperature based on quasi-harmonic approximation model

The site occupy behaviors of NbCr2-based C15 Laves phase alloyed with M (M = Ti, V, Mo and W) and Hf0.25V0.6Nb0.15 C15 Laves phases at finite temperature were predicted using sublattice model, where the Gibbs free energies at finite temperature were obtained by quasi-harmonic approximation(QHA) model. The predicted results were compared with the available experimental results and other calculated results. The prediction was improved compared with early thermodynamic model, where the enthalpies of formation of the end-members at 0 K were accounted only. For NbCr2-based C15 Laves phases, Nb atom prefers to occupy 8a subattices, Cr atom prefers to occupy 16d subattices, and the third alloying element Ti prefers to occupy 8a subattices, which is not affected by the chemical composition and temperature, on the contrary, the site preferences of the third alloying elements Mo, V and W depend sensitively on the chemical composition and temperature. For the selected ternary Hf0.25V0.6Nb0.15 C15 phase with available experimental data, the site fraction of Nb element occupying the 8a sublattices decreases slowly with the increase of temperature, the calculated site occupying configuration at 1473 K is (Hf0.750Nb0.240V0.001)8a(Nb0.105V0.895)16d, which is close to the available experimental result.