A novel Re-free Ni-based single-crystal superalloy with enhanced creep resistance and microstructure stability

Rhenium (Re) is a paramount strengthening element in nickel-based single crystal superalloys because of its low diffusion coefficient, high melting point and high partition coefficient between γ and γ' phases. However, its detrimental influence on phase stability has remained a long-standing problem to be solved. In this paper, we report a new design strategy to improve creep resistance and phase stability of nickel-based single crystal superalloys by replacing Re by osmium (Os), which contradicts the common belief. The experimental observations clearly show that the creep rate of newly designed CSU-Os-2 alloy is lower than that of commercial CMSX-4 alloy at 980 °C/200 MPa/100 h. Moreover, the CSU-Os-2 alloy also owns the better phase stability after exposure at 1100 °C for 1000 h, compared with CMSX-4 alloy. The striking properties can be well explained by higher partition coefficient between γ and γ' phases and very likely lower diffusion coefficient of Os in γ matrix than Re.