ORIENTATION DEPENDENCE OF PRIMARY DENDRITE SPACING

The orientation dependence of the primary dendrite spacing is examined through the solidification of a succinonitrile-3.61 wt pet acetone al loy with a Bridgman-type device. Primary dendrite spacing has been stu died as a function of the primary dendrite trunk orientation with resp ect to the thermal gradient direction under different growth rate cond itions. The observations show that the orientation dependence of the p rimary dendrite spacing can be related to the formation of new primary dendrites at divergent grain boundaries via the branching mechanism. A branching-based model is developed to study the interaction between secondary and tertiary dendrite arms. Based on this model, a simple an alytical relationship is proposed to account for the orientation depen dence of the primary dendrite spacing.