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

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.