A CALPHAD assessment of the Ga–In–Sn liquidus for designable low-melting liquid-metal coolants

Gallium-based liquid metals combine high thermal conductivity with melting temperatures near room temperature, making the Ga–In–Sn system attractive candidate for thermal management of high heat flux electronics. Designing application specific coolants requires an accurate thermodynamic description of the liquidus surface across the full composition range. We report a CALPHAD assessment of the Ga–In–Sn liquidus calculated by combining optimized descriptions of the Ga–In, Ga–Sn, and In–Sn binary systems through the Muggianu extrapolation and introducing a single symmetric ternary interaction parameter. The Ga–Sn liquid is reassessed using experimental mixing enthalpies measured by quantitative differential thermal analysis with a root-mean-square deviation (RMSD) of 41 J/mol. The calculation workflow is confirmed against the Pb–Sn eutectic; the calculated invariant deviates by 1.1 °C and 0.1 wt% from accepted values. The resulting thermodynamic model reproduces the binary eutectics within 2 °C of the expected values and predicts the ternary eutectic at 9.85 °C. Binary extrapolation without a ternary interaction already predicts the eutectic within 1.9 °C, indicating that binary interactions account for most of the excess Gibbs energy of the ternary liquid. The resulting liquidus surface provides a computational framework for designing Ga–In–Sn alloys with application specific melting temperatures. The complete thermodynamic database, pycalphad scripts, and calculated composition grids are released to enable independent validation, reuse, and future refinement of the assessment.