Thermodynamic assessment of the Bi–Zn and Bi–Sb–Zn systems

Bismuth-based alloys are considered promising candidates as environmentally friendly alternatives. This study presents a thermodynamic evaluation of the binary Bi–Zn and ternary Bi–Sb–Zn systems was performed using the CALPHAD approach, based on a critical analysis of available experimental data. Special emphasis was placed on the Bi–Zn system due to the observed discrepancies in the liquid-liquid miscibility range. The liquid and solid phases in solution were modeled using the Redlich–Kister formalism, while the Sb–Zn intermetallic compounds were described using the compound energy formalism. The thermodynamic parameters were optimized using the PARROT module of Thermo-Calc. The results show that the calculated Bi–Zn phase diagram accurately reproduces the eutectic and monotectic reactions, as well as the miscibility range, with good agreement with experimental data. For the ternary system, the isothermal sections calculated at 300°C, 425°C, and 500°C are consistent with experimental observations, and successfully reproduce the main phase equilibria. The results confirm the predominant role of the Sb–Zn subsystem and the absence of ternary compounds. Overall, this study provides a reliable thermodynamic description of the Bi–Zn and Bi–Sb–Zn systems, thus offering a basis for the design of lead-free alloys.