CELLULAR AND DENDRITIC REGIMES IN DIRECTIONAL SOLIDIFICATION - MICROSTRUCTURAL STABILITY DIAGRAM

Experimental results on the directional solidification of the succinonitrile-acetone system are analyzed to examine the conditions at which finite cellular to deep cellular and deep cellular to dendritic transitions occur. Analytical expressions are then proposed which describe these transitions at low velocities in terms of characteristic lengths. It is also shown that these transitions can be related to the planar interface stability conditions at low velocity (Vc) and that at high velocity (Va). The finite cellular to deep cellular transition is shown to occur near 2Vc, whereas the deep cellular to dendritic transition occurs at a velocity which is proportional to V 1 5a V 4 5c. A general microstructural stability diagram is then proposed which maps these morphological transitions onto the Sekerka planar interface stability diagram. © 1990.