Dendritic morphologies of directionally solidified single crystals along different crystallographic orientations

Pb-2.2 wt%. Sb alloy was directionally solidified along [1 0 0]. [1 1 0] and [1 1 1] crystallographic orientations using pure lead single crystal seeds. with a positive thermal gradient of 140 Kcm(-1) and growth rate of 10mums(-1), and then quenched. Longitudinal (parallel to the growth direction) and transverse microstructures in the mushy region and in the quenched portion ahead of the solidification front were examined to investigate the morphology of primary dendrites solidified along different crystallographic orientations. Transverse microstructures showed that for growth along [1 0 0] the primary dendrites had the usual four-fold symmetry due to side-branching: for [11 0] orientation, they appeared plate like. while for [1 1 1] orientation. a uniform distribution of nodes was observed. Thew observations confirm that side-branches in FCC metal alloys grow along <1 0 0> crystallographic directions irrespective of heat-extraction direction. (C) 2002 Elsevier Science B.V. All rights reserved.