Evolution mechanism of crystallographic orientation in grain continuator bars of a Ni-based single-crystal superalloy prepared by Bridgman technology during directional solidification

Abstract

Single-crystal rods with different diameters and deviation angles with respect to the solidification direction were produced by Bridgman rapid solidification method at withdrawal rates of 3 and 6 mm·min-1 and used as grain continuators. The crystallographic orientation of the rods, which cross-sections were perpendicular to the solidification direction at different solidification heights, was measured by electron backscattered diffraction, while the corresponding microstructures were observed by optical microscopy. The mushy zone morphology and the distribution of the temperature gradient were simulated by the finite element analysis software ProCAST. The experimental results indicate that the crystallographic orientation of the single-crystal rods corresponds to the statistical average value of all the dendrite orientations in cross-section. The crystallographic orientation of the primary and secondary dendrites of each single-crystal rod at different cross-sections fluctuates irregularly within a small range (less than 4°). The crystallographic orientation of the dendrite in each single-crystal rod is not exactly consistent with each other and is affected by their branching mode of dendrites in the solidification space. In addition, the simulation results show that the mushy zone shapes and the temperature gradient of single-crystal rods change with the increase of solidification height during the solidification process. Finally, the evolution mechanism of the crystallographic orientations and the corresponding influence factors were analyzed and discussed.