Takao Murakumo, Toshiharu Kobayashi and Hiroshi Harada
High Temperature Materials Group, Materials Engineering Laboratory, National Institute for Materials Science, Tsukuba 305-0047
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.
nickel-base superalloys, creep, volume fraction, superdislocation, super stacking fault, TEM(transmission electron microscopy)
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