69 巻 (2005) 2 号 p. 241-244
The relationships between the microstructure and the amount of alloying elements, Ru, Ta and Nb, in the 5th generation Ni-base single crystal superalloy TMS-173 (TMS-138++), which was developed by the authors, were investigated. TMS-173 was employed as the master alloy and three types of alloys were produced; one with 1 mass%Ru, another with a reduction of 0.6 mass%Ta and an addition of 0.5 mass%Nb, and another with a reduction of 0.4 mass%Ta. Using these alloys, the effects of the alloying elements on microstructure and the creep strength were investigated.
Under 900°C-392 MPa creep test condition, all three alloys had longer rupture lives than the master alloy TMS-173. In particular, the alloy with 0.4 mass% reduction in Ta content exhibited an increase of approximately 35%, and under 1100°C-137 MPa condition, the alloy with a reduction of 0.6 mass%Ta and an addition of 0.5 mass%Nb exhibited approximately 50% increase in the creep rupture life. From the microstructural analysis, it is suggested that the increased creep strength at 900°C was achieved because the precipitation of TCP phases was inhibited through the increased microstructural stability, and the creep strength at 1100°C was governed mainly by the spacing of γ/γ′ interfacial dislocation network.