Experimental Investigation and Thermodynamic Modeling of the Ag-Cu-Ge System

The liquidus surface projection was re-investigated using scanning electron microscopy with energy dispersive spectrometer and differential thermal analysis. The invariant reactions, liq. → fcc(Ag) + diam(Ge) + η at 810 K (537 °C), and liq. + ε → η + fcc(Ag) at ~848 K (575 °C) were confirmed, and θ →liq. + η + diam(Ge) at 859 K (586 °C) was inferred in the present work. On the basis of the experimental data in the present work and literature, the Ag-Cu-Ge system was modeled using the CALPHAD (CALculation of PHAse Diagram) method. Solution phases, liquid, hcp, and fcc, were modeled as (Ag, Cu, Ge) using the substitutional solution model in the Ag-Cu-Ge ternary system. The compounds, ε, η, and θ, in the Cu-Ge system, were treated as line compounds (Ag, Cu) _m Ge _n in the Ag-Cu-Ge system. A set of self-consistent thermodynamic parameters was obtained. Using these thermodynamic parameters, the experimental isothermal sections at 763 K, 793 K, 863 K, and 923 K (490 °C, 520 °C, 590 °C, and 650 °C), the vertical section at 38.0 at. pct Cu, the liquidus surface projection, and the invariant reactions in the Ag-Cu-Ge system were well reproduced.