Formation of Stray Grains in Directionally Solidified Ni-Based Superalloy with Cross-Section Change Regions

The formation mechanism of stray grains in cross-section change region of casting clusters for single crystal superalloy DD483 were investigated experimentally during the conventional directional solidification. The results showed that the stray grains formation was different on the two sides of the platform. Indeed, stray grains formation in the region of the cross-section change on the shadow side showed a high probability, while the heater side, no stray grains appeared. Additionally, the cooling curves at the cross-section change region also showed that the distribution of temperature was different on the two side of the platform. The formation of stray grain can be attributed to the local undercooling at the cross-section change region is exceed the critical undercooling for nucleation, led to the heterogeneous nucleation, while the asymmetric temperature distribution should be responsible for asymmetrical formation of stray grains on the two sides of the platform.