Ternary Eutectic Growth in a Highly Undercooled Liquid Alloy

The crystal nucleation and growth mechanism during the formation of Ag_42.4Cu_21.6Sb₃₆ ternary eutectic are investigated under substantial undercooling conditions. The x-ray diffraction analysis shows that the solidified eutectic phases are not involved (Ag) within a wide undercooling range of 6-114K. This indicates that under high undercooling condition, the phase constitution of Ag-Cu-Sb eutectic is different from that in the equilibrium phase diagram. With the increase of undercooling, the crystalline morphology of Ag_42.4Cu_x21.6Sb₃₆ alloy transforms from the mixed structure of primary θ(Cu₂Sb), two pseudobinary eutectics and (ε+θ+Sb) ternary eutectic into a unique (ε+θ+Sb) ternary eutectic. The calculated results indicate that θ(Cu₂Sb) is the leading nucleating phase among the three eutectic phases. In addition, the growth morphology of primary ε(Ag₃Sb) compound in Ag₆₀Cu₆Sb₃₄ alloy exhibits the characteristics of solid solution and its orthorhombic dendrite grows along the <111> directions.