Interfacial stability and grain diameter of the metal phase of directionally solidified Al‐Si‐type eutectics

The morphology of the solid‐liquid interface and the metal phase grain diameter of Al—Si‐type eutectics (Al—Si, Ag—Si, Ag—Ge, Zn—Ge) were investigated in the range of a growth rate R = 0.2 … 20 mm/h and of a temperature gradient at the solid‐liquid interface G = 2 … 25 K/mm. Three types of interfacial morphologies depending on the G / R ratios were found out. The G / R ratio of the transition from a planar to a nonplanar solid‐liquid interface corresponds to the critical G / R | c ratio, which can be calculated by the criterion of the constitutional undercooling. The grain diameter of the metal phase depends on growth parameters as follows: d K ∼ R —r G —g with r = 0.33 … 0.43 and g = −0.37 … 0.03.