Evolution of crystallographic orientation and microstructure in the triangular adapter of grain continuator of a 3rd-generation single crystal superalloy casting during directional solidification

Highlights: • The misorientation between two corners of triangular GCs was increased as the increase of flare angle and withdrawal rate. • The freckle chains formed at the inside corner of triangular GCs with a low flare angle under a low withdrawal rate. • The freckle defect formed at the start position of thick triangular GCs with high flare angle under a low withdrawal rate. • Under 3 mm/min withdrawal rate, 2 mm triangular GCs with 46–68° flare angle were expected to prepare high quality casting. -- Abstract: The evolution of the crystallographic orientation and the microstructures in triangular adapters of grain continuators (GCs) with different flare angles and thicknesses prepared by a 3rd-generation single crystal (SX) superalloy were investigated under different withdrawal rates. The microstructures were observed by an optical microscope and the crystallographic orientation of the GCs was measured by electron backscatter diffraction (EBSD). The directional solidification process was simulated by a commercial simulation software ProCAST. The experimental results showed that the [001] misorientation between both sides of the GCs at top cross section increased with the increasing of the flare angle, the thickness of specimens, and the withdrawal rate. These phenomena were attributed to the changing of the isotherm morphology in the mushy zones and the velocity of the solidification front. As for a low flare angle, the freckle defect formed at one side of specimens under the withdrawal rate of 1 mm/min. With the increasing of flare angle, the freckle defect cannot be found at the same position of the specimens. The formation mechanisms of freckle defect in the triangular adapters of GCs were further discussed.