Effect of Ceramic Cores on the Freckle Formation During Casting Ni-Based Single Crystal Superalloys
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A directional solidification experiment was carried out using CMSX-4 superalloy to investigate the effect of the ceramic core on the freckle formation. The results show that the freckle formation exhibits a strong wall-dependence regardless of the shell mold wall or the ceramic core wall. With increasing inner diameter of the ceramic core, the freckle formation on the outer surfaces of the castings is reduced, whereas it is increased on the inner surfaces. The internal freckle defect was found only on the outer convex surfaces of the castings. No freckle appeared on the inner concave surfaces of the castings. With increasing wall-thickness of the ceramic core, the occurrence of the freckle defect on the outer surfaces of the castings is reduced, while the internal freckle defect is increased. The findings in the present study will extend our understanding of the freckle formation and contribute to develop a method to minimize the freckle defect in the directional solidified Ni-based single crystal castings.
This research was supported by the German Research Foundation (DFG) (BU1072/15-1 and -2) and the National Science and Technology Major Project of China (No. 2017ZX04014001-005). The authors would like to acknowledge the aid of Elke Schaberger-Zimmermann, Ying Ma, and Can Huang.
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