Evolution of Sliver Defect in Ni-Based Single Crystal Superalloy

The evolution of sliver defect in a Ni-based single crystal superalloy was explored by casting samples with a similar geometry of the airfoil section of a turbine blade using optical microscope and electron backscattered diffraction. It was found that the sliver generally initiated from 1 to 2 tertiary dendrites at the diverging boundary between the mold wall and matrix. All slivers were tilt from matrix along the [001] and some of them rotated relative to the matrix on the plane perpendicular to the solidification direction. During solidification sliver in most castings grew with a fixed orientation. All slivers can extend along the solidification direction to the top of the casting. Most of the sliver defects showed constant width and did not extend on the casting surface. However, the sliver with large misorientation to matrix on the cross section perpendicular to the solidification direction extended on the casting surface and into the casting quickly.