Thermodynamic assessment of the Mg-Ni-Gd system with a general model description the long-period stacking ordered phases

ABSTRACT The phase equilibria of the Mg-Ni-Gd ternary system were thermodynamically assessed by the CALPHAD (CALculation of PHAse Diagrams) method based on the thermodynamic descriptions of the constitutive binary systems and experimental phase equilibria data available in the literature. The substitutional model and sublattice model were employed to describe the solution phases and intermediate phases, respectively. The ternary phases τ1-τ6 were described as stoichiometric compound and the long-period stacking ordered phase 14H and 18R were described Mgx(TM, Mg)6(RE, Mg)8 model (TM = Transition Metal, RE = Rare Earth). A set of self-consistent thermodynamic parameters of the Mg-Ni-Gd system was obtained. Some representative isothermal section, liquidus projections and the related invariant reactions were calculated. Comparisons between the calculated results and experimental data show that almost all the reliable experimental data were satisfactorily reproduced by the present modeling. The reaction scheme for the whole ternary system is also presented.