Abstract: From a point of view of time-dependent and path-dependent of interface morphology development. the experimental studies of primary spacing in directionally solidified succinomitrile-1.1 wt% ethanol are carried out. It is found that for this model alloy: (1) There exists a maximum primary spacing, the solidlfica tion rate corresponding to the maximum primary spacing is much greater than that corresponding to the transition from cellular to dendritic interface; (2)The dendritic primary spacing can remain constant when the solidification rate has increased times, and cellular spacing is very sensitive to the change of solidification rate.

Key words: directional solidification, interface morphology, primary spacing