Effect of Ruthenium on Precipitation Behavior of the Topologically Close-Packed Phase in a Single-Crystal Ni-Based Superalloy During High-Temperature Exposure

The precipitation behaviors of the topologically close-packed (TCP) phase in the Ru-free and Ru-containing single-crystal Ni-based superalloys have been investigated. All the TCP phases have been identified as the mu phase with large numbers of planar defects by using a scanning transmission electron microscope (STEM). The addition of 3 wt pct Ru effectively suppresses the nucleation of the mu phase because the addition of 3 wt pct Ru not only decreases the supersaturation of gamma phase but also increases the elastic strain energy for the nucleation of the mu phase. Additionally, the addition of 3 wt pct Ru makes more Re enter the mu phase during its growth and the critical nucleus radius of the mu phase becomes larger. Therefore, it is found that the addition of 3 wt pct Ru decreases the growth rate of the mu phase.