Abstract
The solid–liquid interface structures and the Al segregation in the solidifying front were investigated by directional solidification and electron probe microanalysis. The results show that the interface structure would vary greatly with solidification velocity, the morphology of which changed from planar at 1 µ m/s, dendrite at 25 µ m/s, cellular–dendrite at 50 µ m/s, to hexagon cell at 100 and 150 µ m/s and finally high-velocity cell at 200 µ m/s. The stability of the planar interface was mainly influenced by Al segregation. The narrow solidification temperature range benefited the transformation of dendrite to cell-dendrite. Regarding Fe, Cr as solvents and Al as solute, the secondary dendrite arm spacing when solidification velocity is 25 µ m/s could be predicted by the formula which was widely adopted in binary alloy system, and the predicted values fit well with the experimental results. The Al partition coefficient was found to be 0.96, and it indicated that there existed slight Al segregation when solidification velocity is 1 µ m/s, which was the main stabilizing factor of the planar interface. Al segregation is not obvious at velocities above 25 µ m/s and the interface transformed to various structures when solidification velocities were higher than 25 µ m/s.
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