Experimental investigation and thermodynamic assessment of the phase equilibria in the Cu-Co-Si ternary system

The phase equilibria in the Cu-Co-Si ternary system at 900°C, 1000°C and 1100°C were experimentally determined using Electron Probe Micro-Analyzer (EPMA) on equilibrated alloys. Three-phase microstructures were observed, and no ternary compounds were detected. At 900 °C, four three-phase regions were identified. As the temperature increased, the (Cu) phase became less stable. At 1000 °C, the (Cu)+CoSi + Co ₂ Si region transformed into Liquid + CoSi + Co ₂ Si. At 1100 °C, the liquid phase expanded further. Thermodynamic assessments were performed using CALPHAD (Calculation of Phase Diagrams) method, yielding a consistent set of thermodynamic parameters with reasonable agreement between the calculated results and experimental data. This work demonstrates that Si addition stabilizes the metastable liquid-phase separation in the Cu-Co binary system and increases its critical temperature, providing insights for designing Cu-Co-Si-Zr-B amorphous composites.