Dendrite growth in undercooled DD3 single crystal superalloy

Crystal growth in the undercooled DD3 single crystal super-alloy is investi gated in this paper. With the increase of undercooling, two kinds of dendri tes are obtained. When DeltaT < 30 K, dendrite growth is dominantly control led by solutal diffusion, and the as-solidified morphologies are similar to the conventional as-cast highly branched dendrites. In the undercooling ra nge of 78-150 K, the severe solute trapping that originates from high dendr ite growth velocity weakens the effect of solutal diffusion on the dendrite growth. Thermal diffusion, controlled by heat gradient, instead of solutal diffusion, is found to become the key factor in determining the formation of largely developed fine dendritic morphologies. Furthermore, the measured dendrite arm spacing are explained by employing the current dendrite growt h theories. (C) 2001 Elsevier Science Ltd. All rights reserved.