Synergistic effect of rhenium and ruthenium in nickel-based single-crystal superalloys

The microstructures of ternary Ni-Al-Re and quaternary Ni-Al-Re-Ru single-crystal alloys were investigated at atomic and electronic levels to clarify the synergistic effect of Re and Ru in nickel-based single-crystal superalloys. In the Ni-Al-Re alloy, it was directly observed that Re atom occupied the Al site of γ′ phase. In the Ni-Al-Re-Ru alloy, the mechanisms of Re repartition between γ and γ′ phases were proposed. In the dendritic cores, high concentrations of Re exceeded the solubility limit of γ′ phase and partitioned to γ phase, which led to the homogenization. In the interdendritic regions, Ru resulted in the repartitioning of Re to γ phase which was proved by transmission electron microscopy and first-principles calculations.