Abstract
The Ag-Cu-Se ternary system is widely used in thermoelectric materials. The liquidus projection and the 300 °C isothermal section were determined based on the experimental results of this study and the phase diagrams of their constituent binary systems. For the liquidus projection, there are eight primary solidification phases. These phases include (Ag), (Cu), Ag2Se, Cu2Se, CuSe, CuSe2, (Se) and a ternary compound, AgCuSe. Additionally, based on the thermal analysis results, there are nine invariant reactions, including four Class I reactions, four Class II reactions and one Class III reaction. Interestingly, two wide compositional range of liquid miscibility gaps are observed in liquidus projection. Various kinds of interesting microstructures were observed in alloys solidified through miscibility gaps, which resulted from compositional differences, density differences, and surface tension. For the 300 °C isothermal section, the sample alloys were quenched and equilibrated at 300 °C for six months. There are seven three-phase regions in the Ag-Cu-Se system, including Cu2Se + Ag + Cu, AgCuSe + Cu2Se + CuSe, AgCuSe + CuSe + Ag2Se, CuSe + Ag2Se + CuSe2, Ag2Se + CuSe2 + Liquid, AgCuSe + Ag2Se + Ag, and AgCuSe + Cu2Se + Ag. Furthermore, Ag, Cu and Ag + Cu mixed whiskers were observed along the Cu-Cu2Se-Ag2Se-Ag section, which overlaps the miscibility gap.
•The liquidus projection of the Ag-Cu-Se ternary system is experimentally determined for the first time. Eight primary solidification phases and eight invariant reactions are identified, including a ternary AgCuSe phase.•Two extensive liquid miscibility gap regions are observed in the ternary system.•Core-shell and dispersion microstructures are found in alloys solidified through the liquid miscibility gap regions.•At 300 °C, seven three-phase regions are established in the isothermal section.•Ag, Cu, and Ag + Cu whiskers are observed in regions overlapping the liquid miscibility gap.