First-principles theoretical and experimental studies of effects of ruthenium on precipitation behavior of μ phase and μ/matrix interface stability in Ni-based single crystal superalloys

Precipitation of deleterious topologically close-packed (TCP) phases worsens the mechanical behavior of Ni-based single crystal superalloys. It is acknowledged that Ru will inhibit precipitation of TCP phase. In this paper, precipitation behaviors of TCP in alloy with and without Ru have been investigated through experimental characterization means, combined with the first principles calculations. For the first time, the interface structure between precipitated mu phase and matrix gamma phase has been established, and stable interfacial termination types in different orientation relationships were obtained. Effects of solute atoms like Ru on interface stability and site substitution behaviors of different solute elements in two phases were further calculated, and compared with precipitation behavior and composition information of TCP phases in two alloys. It is verified that Ru is different with other elements, which can remarkably increase the interfacial energy of mu/gamma interface, decrease interface stability, and rise the difficulty of nucleation of mu phase; conversely, W will lower the interfacial energy of mu/gamma, making it easier for mu phase to nucleate; the effects of Co and Cr are not that obvious; the effects of Re and Mo on interfacial energy and nucleation of mu phase vary with orientation relationships. Also, Re, Cr, and Ru have larger trends to diffuse from matrix gamma to mu phase during growing process of mu phase. The above reasons give rise to blocking effect of Ru on the nucleation of TCP phase, but Ru has trifling influence on inhibition of precipitation growth.