Multiple eutectic orientation relationships in undercooled Ni−38wt.%Si eutectic alloy

Abstract Eutectic orientation relationships (EORs) in an undercooled Ni−38wt.%Si alloy were analyzed by electron backscatter diffraction. A total of seven EORs were identified, and three of them were found at the under-cooling degree ΔT≈31 K. It is found that their orientations of the primary NiSi phase are same but the misorientation between the neighboring NiSi2 grains can be either 50° or 60°. The multiple EORs were ascribed to a possible change in the growth direction of the primary phase, the change of the primary phase from the NiSi phase to the NiSi2 phase, and the transition from coupled to uncoupled eutectic growth. The current work shows that epitaxial growth of the second eutectic phase on the primary eutectic phase can obey either a single EOR or multiple EORs, which is a unique phenomenon.