Formation of Slivers in the Extended Cross-Section Platforms of Ni-Based Single Crystal Superalloy

A model with rejoined platforms is designed to study the casting defects in the platforms of Ni-based single crystal superalloy. The results of this study indicate the formation of sliver defects in different regions of the platforms. In the platforms, the dendrite deviation started at the section extension region and the misoriented dendrites could continue to grow into the platform to form sliver defects through the competitive growth with the adjacent dendrites. Furthermore, sliver defects formed as a result of the deformation of secondary dendrites induced by the thermal contraction stress based on the polar diagram analysis and the finite element simulation results. Finally, three different factors contributing to the formation of sliver defects in the extended cross-section platforms are speculated as follows: the orientation of the deformed dendrites, the local thermal field condition, and the sufficient growth space.