Solidification process and microstructure evolution of bulk undercooled Co–Sn alloys

A series of Co–Sn alloys with Sn content ranging from 12% to 32% (mole fraction) were undercooled to different degrees below the equilibrium liquidus temperature and the solidification behaviors were investigated by monitoring the temperature recalescence and examing the solidification microstructures. A boundary clearly exists, which separates the coupled growth zone from the decoupled growth zone of eutectic phases for the alloys with Sn content ranging from 14% to 31% (mole fraction). The other Co–Sn alloys out of this content range are hard to be undercooled into the coupled growth zone in the experiment. It is found that the so-called non-reciprocal nucleation phenomenon does not happen in the solidification of undercooled Co–Sn off-eutectic alloys.