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^—rG^—g with r = 0.33 … 0.43 and g = ?0.37 … 0.03.