Thermodynamic database for the Mo–Si–Y–Hf quaternary system

CALPHAD thermodynamic database for the Mo–Si–Y–Hf quaternary system, in TDB format compatible with pycalphad, Thermo-Calc, and OpenCalphad. The database contains 20 phases (LIQUID, BCC_A2, HCP_A3, DIAMOND_A4, three Mo-silicides, six Hf-silicides, seven Y-silicides) and 65 Redlich-Kister and end-member parameters on a common SGTE basis (Dinsdale 1991). Subsystem sources: Mo-Si (Czerny et al. 2024), Mo-Hf liquid (Shao 2002) and bcc (Zhao et al. 2020), Mo-Y (Chan et al. 2010), Hf-Si (Zhao et al. 2000), Si-Y (Zhang et al. 2019). Hf-Y is approximated as ideal in the absence of a published assessment. Ternary and quaternary excess interactions are obtained by Muggianu extrapolation. Two matrix-relevant ternary interactions (Mo-Si-Y, Mo-Si-Hf) were computed from special quasirandom structure (SQS) relaxations with the SevenNet machine-learning interatomic potential and fitted in ESPEI; their inclusion shifts the predicted solidus by ≤5 K and leaves the phase assemblage unchanged. These corrections are documented in the accompanying paper but not embedded in this released database. This database accompanies the manuscript "Thermodynamic assessment of the quaternary Mo–Si–Y–Hf system, validated by machine-learning interatomic potentials, and reactive-element co-design of a refractory silicide composite" submitted to Computational Materials Science.