Liquid-liquid demixing and microstructure of Co-Cu-Zr alloys with low Zr content

► Transition from metastable to stable miscibility gap for small additions of Zr. ► Heats of mixing drive separation into Co/Zr-rich and Cu-rich liquids. ► Zr modifies surface tension energies and wetting behavior compared to binary Co-Cu. ► Co/Zr-rich phase always encloses the Cu-rich liquid phase for Co-Cu-Zr. ► Macrosegregation morphologies proceed on a very short time scale.