2004 Volume 45 Issue 2 Pages 380-383
The phase equilibria in the Sn-Ag-Bi-Cu quaternary system have been studied experimentally and using thermodynamic calculations. The phase boundaries in some vertical sections of the Sn-Bi-Cu and Sn-Ag-Bi-Cu systems were determined using differential scanning calorimetry. The experimental values of the thermodynamic parameters were used in the calculations of the phase diagrams for the quaternary system. Thermodynamic evaluation of the Sn-Bi-Cu system was performed by considering a two-phase separation of the liquid phase. The phase diagram calculations showed that the Cu-Sn-based compounds form as the primary crystals, even for low Cu concentrations, and accordingly, the melting point of the alloys rises markedly. The microstructure of the solidified alloys was observed using a scanning electron microscope. We observed that coarsened Bi particles existed alongside the Cu-Sn-based primary crystals. Based on these results, a non-equilibrium solidification process using the Scheil model was simulated and compared with the observed structures. Our calculations reasonably explain the Bi-enrichment in the final solidification zone.