Thermodynamic re-assessment of the Al–Gd and Gd–Zr systems

• The C15_laves phase Al2Gd was optimized to have a negligible homogeneity range.
• Mixing enthalpy of Gd–Zr hcp phase was calculated by the first-principles method.
• The inverse liquid miscibility in previous work was either reduced or eliminated.
• Reasonable thermodynamic parameters were obtained for these two binary systems.

Both Al–Gd and Gd–Zr binary systems were re-assessed using the CALPHAD (calculation of phase diagram) method to ensure a multi-component system containing them can be accurately described. Compared with previous assessments, the features of this work are reflected from the following aspects. Firstly, the C15_laves phase Al2Gd was treated as an intermetallic compound with a negligible homogeneity range using the two-sublattice model (Al, Gd)2(Al, Gd), meanwhile the liquid phase being described with the substitutional solution model. Secondly, first-principles calculations were carried out to provide theoretical information for optimization. The enthalpies of mixing of Gd1−xZrx (x = 0.25, 0.5, 0.75) hcp_A3 solid solutions were calculated by applying the Special Quasirandom Structure containing 16 atoms (SQS_16). Finally, the inverse liquid miscibility appearing at high temperatures in previous studies was reduced for the Al–Gd system and eliminated for the Gd–Zr system. The calculated results for both binary systems reproduce the experimental and theoretical data satisfactorily, evidencing the reliability of the thermodynamic descriptions established in this work.