A quasi in-situ investigation of the cell to dendrite transition using Ni-W single crystal alloy

A quasi in-situ investigation of the cell to dendrite transition (CDT) was carried out by preparing Ni-W single crystal alloy with an increasing withdrawal rate. It was shown that the solidification process occurred under the convex growth interface, which produced a gradient of the drift velocity along the interface and led to a coarsening effect on the microstructures. This coarsening effect, combined with the refining effect induced by the increasing withdrawal rate, resulted in the CDT and an inconstant primary spacing. The results showed that the cell to dendrite transition for hexagonal cell was nonuniformed, and the tip splitting and lateral branching for cellular and dendritic structures were controlled by the ratio of the neighbor spacing to the average primary spacing. Two models and a rule, which separately revealed the influence factor of the drift velocity, the transition process from cell to dendrite, and the law of tip splitting and lateral branching for cellular and dendritic structures, were proposed. It was hoped that the present work could provide ideas for in-situ studies of microstructural evolution.