69 巻 (2005) 8 号 p. 763-768
The creep behavior of Ni-base single-crystal superalloys TMS-75 and TMS-26 with various γ′ fractions was investigated at 800°C and 735 MPa. Creep strength of two-phase alloys was superior to single phase alloys. The creep rupture lives were the longest for the 60%γ′ alloys. In contrast with creep behavior above 900°C, 40%γ′ alloys were stronger than 80%γ′ alloys at 800°C. 60%γ′ alloy of TMS-26 was much stronger than that of TMS-75 because of lower Co and Re contents and lower stacking fault energy. Changes in the microstructure after creep rupture were studied. While raft structure was observed perpendicular in 60%γ′ alloy of TMS-26, rafts were parallel in 80%γ′ alloy. Super stacking faults were often observed in γ′ precipitates in 60%γ′ alloy of TMS-75. However, super stacking faults were not frequent in the other alloys. Usual a/2 <110> dislocations were observed in γ matrix in 20 and 40%γ′ alloys, and superdislocations were observed in coarse γ′ phases in 80%γ′ alloy.