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Based on a fourth generation single crystal (SC) superalloy, TMS-138, we designed new SC alloys that contain higher amount of refractory elements, Nb, Ta, Mo, or Re, for strengthening. The Ru content was also increased to improve the phase stability. The creep strength and microstructure of these alloys were examined and compared with those of the base alloy TMS-138 and a third generation SC superalloy, CMSX-10K. As predicted by our alloy design program, TMS-162 (Mo and Ru addition) and TMS-173 (Re and Ru addition) exhibited excellent creep properties. Their times to 1% creep deformation at 1100 C/137MPa were about 2.5 times as long as that of TMS-138 and 5 times as long as that of CMSX-10K. The temperature capability of TMS-162 has reached a project target of 1100 C under stress at 137MPa and a creep rupture life as long as 1000 h, which is the highest ever reported.

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