Microstructure and orientation variation during cell/dendrite transition in directional solidification of a single crystal nickel-base superalloy

The crystallographic orientation and microstructure variation during cell/dendrite transition of a nickel-base single crystal superalloy have been analyzed. The crystal with the off-<0 1 1> orientation grew with a cellular interface at 6 μm s−1 while with a dendrite interface at 100 μm s−1. The crystal kept the orientation of bottom seed in the dendritic growth stage, and there was a short transitional zone. The deviation angle between the cellular orientation and the heat flow direction became small in the cellular growth stage. The cellular growth direction was in accordance with the heat flow direction and was independent of the crystallographic orientation. At the same crystallographic orientation, the dendrites had a large primary dendrite arm spacing during the cell/dendrite transition. The cellular crystal with a smaller orientation deviation from the cylindrical axis showed a larger primary arm spacing.