To improve the creep strength of Ni-base superalloys, Re and Ru additions were investigated with using 2^nd generation single crystal superalloy TMS-82+ which contains 2.4 mass%Re, as the base alloy.
   When Re and Ru were added at the same time, creep strength was improved at lower and higher temperature. We suppose that these were caused by the solution strengthening due to Re at lower temperature, and the stabilization of γ/γ′ structure at higher temperature by Ru addition. Further more, in the case of Re addition, creep strength at lower temperature was improved, and creep strength at higher temperature became worse due to the TCP phase formation. Also, in the case of Ru addition, creep strength at lower and higher temperature became worse, although TCP phase formation was completely suppressed. This is because Ru is not an effective element for the solution strengthening at high temperature.