Castability and Recrystallization Behavior of γ′-Strengthened Co-Base Superalloys

Abstract

Casting of single-crystalline superalloys is known to be difficult due to a variety of challenges. Co-based superalloys, however, promise to show quite good castability compared to Ni-based superalloys, as documented in this manuscript. Therefore, an alloy series, which is designed by changing only the Co-to-Ni ratio, is used to address this topic. In addition to the casting behavior, segregation and recrystallization behavior were also investigated, since these are closely related to casting challenges. It was found that in the as-cast state, all alloying elements distribute more homogeneously in the Co-rich alloys which is beneficial for casting. Casting of directionally solidified tubes revealed that the Co-rich alloys show a lower susceptibility to hot tearing and predominantly develop cold cracks. Since cold cracking can be addressed by component design, Co-base superalloys are suggested to show a better castability compared to Ni-based superalloys. Recrystallization, however, is more pronounced for the Co-rich alloys. This might become a problem during casting of single-crystalline Co-base components, if high deformation is introduced in the solidified component.