Influence of Microstructural Homogenization on the Localized Deformation Behavior of Single-Crystal Ni-Based Superalloy, CMSX-4

CMSX-4 is a technically important Ni-based superalloy which is used for various niche applications in the aerospace industries, owing to its excellent strength, fatigue, and creep resistances. However, the as-cast single-crystal alloy suffers from elemental segregation and micro-scale inhomogeneities, i.e., dendritic structure along with nano-scale γ/γʹ precipitates. A 16-fold enhancement in the withdrawal rate with respect to the commonly used one shows prominent microstructural refinement. The specialized heat treatment schedule along with higher withdrawal rate leads to the successful removal of micro- and nano-scale non-uniformities and elemental partitioning. Systematic nanoindentation-based investigation indicates higher hardness for faster withdrawal rate. Furthermore, localized nanoindentation reveals distinctly higher hardness for the dendrite as compared to inter-dendritic region in the as-cast condition. Most importantly, uniformity in localized hardness as well as least effect of size dependency is achieved upon optimally heat treating the superalloy. The gradual transition from elastic to plastic deformation behavior is noted for the as-cast alloy. Aged alloys, however, show excellent resistance to plastic deformation. Overall, a detailed insight is developed on the processing-structure-property correlation for CMSX-4 superalloy. Certainly, the newly designed faster withdrawal rate with homogenized microstructure can provide a reliable approach for manufacturing of single-crystal components.