Solidification interface morphology pattern in the undercooled Co–24.0 at.% Sn eutectic melt

Co–24.0 at.% Sn eutectic alloy melt was undercooled to different degrees below the equilibrium eutectic temperature. The dependence of solidification behavior on undercooling was established based on the experimental results of the solidification microstructure, crystal orientation and crystal growth velocity. In the entire undercooling range studied (0–203 K), coupled eutectic growth of the α-Co and β-Co3Sn2 phases invariably takes place during the rapid solidification stage. The eutectic solidification interface advances in the alloy melt in seaweed morphologies rather than the well-known dendritic mode due to the weak interface energy anisotropy. But a critical undercooling of 175 K exists, from which the eutectic solidification interface changes from a fractal into a compact seaweed pattern, accompanied with an abrupt increase of growth velocity. At high undercoolings the enhancement of the interface tip stability with the rise of crystal growth velocity should be responsible for the growth mode transition.

► Coupled eutectic growth occurs in the undercooled Co–24 at.% Sn eutectic melt.
► The eutectic solidification interface advances in seaweed morphologies.
► A fractal to compact seaweed interface transition takes place above a critical undercooling.
► The interface morphology selection closely depends on interface energy anisotropy.