Anomalous overgrowth of converging dendrites during directional solidification

Competitive growth of converging dendrites in directional solidification was investigated by in situ observation in a succinonitrile-acetone alloy. The specific dendrite growth behavior was analyzed and compared with the results of phase field simulations. It is found that the growth of the well aligned grain boundary dendrite is retarded and the spacing between this dendrite and its immediate neighbors (λGB1) decreases continuously as the misaligned dendrites get to the grain boundary, one by one. The anomalous overgrowth only happens when the spacing λGB1 decreases to certain level. Under the same solidification condition, smaller initial primary spacing makes the anomalous overgrowth take place earlier and more frequently.