Influence of platform position on stray grain nucleation in Ni-based single-crystal dummy blade clusters

Stray grains are the most severe of the solidification defects that occur in the industrial single-crystal blade preparation process. In this study, a single-crystal dummy blade cluster with different crystal orientations controlled by the seeding method was prepared, and the influence of the position of the circular platform (relative to the sample and furnace body) on stray grain nucleation was investigated. Results show that the microstructure of the circular platforms could be divided into the center, expansion, and stray grain regions. The inside of the circular platform facing the center of the cluster is more prone to stray grain formation than the outside of the circular platform facing the furnace body. With an increase in the distance between the circular platform and the bottom of the dummy blade cluster, the stray grain region expands, whereas the expansion region narrows. The stray grain is slightly aggravated with increase of the misorientation. Finally, the mechanism underlying the influence of platform position on the formation of stray grains in single-crystal dummy blade clusters is discussed based on the temperature evolution during directional solidification.