Effect of dendrite arrays near grain boundary on the competitive growth of converging Ni-based bi-crystal superalloys

Abstract

The relationship between the arrangement of dendrite array near grain boundary (GB) and the competitive converging dendrites growth in Ni-based superalloys was characterized by the minimum spanning tree method. The results show that the primary dendrite arm spacing near and far away from GB region is different. The dendrite spacing near GB affects the interlacing of convergent dendrites, thus affecting the competitive growth. At the early solidification stage when the spacing is small, the increasing spacing near GB allows the interlacing of convergent dendrites, which leads to the continuous overgrowth of unfavorably oriented (UO) dendrites to favorably oriented (FO) dendrites. However, at the later stage of solidification when the dendrite spacing become larger, the concomitant growth of developed side-branches will hinder the interlacing of convergent dendrites. Consequently, FO-dendrites with superior growth blocks UO-dendrites with directional growth, and even overgrows UO-dendrites.