68 巻 (2004) 2 号 p. 138-141
In this study, the partitioning behavior of alloying elements into γ matrix and γ′ precipitates in Ruthenium (Ru)-bearing γ′ precipitation hardening Ni-base superalloys has been investigated using electron probe X-ray micro-analyzer (EPMA). The third generation single crystal (SC) superalloy TMS-121 (Ni-16Co-3Cr-3Mo-6W-6Al-6Ta-5Re-0.1Hf: mass%) and three alloys with the addition of Ru in the range of 2 to 6 mass% into TMS-121 alloy were used. It is shown that Ru addition into Ni-base superalloys is effective in suppressing the topologically close packed (TCP) phase formation. Ru is preferentially partitioned into the γ matrix with the partitioning ratio of about 3:1 at 900°C, and 1.5:1 at 1200°C. Furthermore, it seems that the partitioning behavior of alloying elements is not affected by the Ru addition. For example, Re is preferentially partitioned into the γ matrix in any of the superalloys investigated, and the partitioning ratio of Re at 900°C in TMS-121 alloy is 13.5:1, and 9.5:1 for the alloy with 6 mass%Ru addition. The effect of Ru addition to suppress the TCP formation should not be attributed to a ‘Reverse partition’, which was reported by O'hara, et al.