A phase-field study of the pattern selection between dendrite and seaweed during directional solidification

In this paper, the dendrite-seaweed transition was studied by changing solidification conditions through a phasefiled method. Results show that with the increase of thermal gradient, the critical pulling velocity for the transition from seaweed morphology to dendrite morphology increases. And the splitting spacing of seaweeds decreases with increasing the thermal gradient. To quantitatively describe the seaweed-dendrite transition, here the fractal dimension was introduced. It is found that the fractal dimension increased with the pulling velocity in the dendritic regime and seaweed regime, while it decreased in the stage of transition from seaweed to dendrite. It indicates that the fractal dimension can be regarded as an effective tool to quantitatively describe the dendriteseaweed transition.