Influence of the Size Effect on the Microstructures of the DWDS- and Bridgman-Solidified Single-Crystal CMSX-4 Superalloy

To evaluate the potential benefits of utilizing the downward directional solidification process (DWDS) for controlling the homogeneity of microstructures, single-crystal CMSX-4 superalloy bars having different sizes of cross sections have been directionally solidified at a withdrawal rate of 1 mm/min using the DWDS and Bridgman processes. By varying the sizes of the cross sections, the DWDS process demonstrated higher thermal gradients, with smaller microstructural variations. The higher and more uniform thermal gradients not only refined the microstructures but also improved the microstructural homogeneity. In contrast to this, the Bridgman cast bars exhibited large-sized pores and a high volume of microporosity regardless of the cross-sectional size.