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The low-cycle fatigue(LCF)behavior of a nickel-based single crystal superalloy with[001]orientation was studied at an intermediate temperature of T_0℃and a higher temper- ature of T_0+250℃under a constant low strain rate of 10~(-3)s~(-1)in ambient atmosphere.The superalloy exhibited cyclic tension-compression asymmetry which is dependent on the temper- ature and applied strain amplitude.Analysis on the fracture surfaces showed that the surface and subsurface casting micropores were the major crack initiation sites.Interior Ta-rich carbides were frequently observed in all specimens.Two distinct types of fracture were suggested by frac- togaphy.One type was characterized by Mode-I cracking with a microscopically rough surface at T_0+250℃.Whereas the other type at lower temperature T_0℃favored either one or several of the octahedral{111}planes,in contrast to the normal Mode-I growth mode typically observed at low loading frequencies(several Hz).The failure mechanisms for two cracking modes are shearing ofγ′precipitates together with the matrix at T_0℃and cracking confined in the matrix and theγ/γ′interface at T_0+250℃.
The low-cycle fatigue (LCF) behavior of a nickel-based single crystal superalloy with [001] orientation was studied at an intermediate temperature of T_0 ° C and a higher temper- ature of T_0 + 250 ° C under a constant low strain rate of 10 ~ (-3) s ~ (-1) in ambient atmosphere. The superalloy exhibited cyclic tension-compression asymmetry which is dependent on the temper- ature and applied strain amplitude. Analysis on the fracture surfaces showed that the surface and subsurface casting micropores were the major crack initiation sites. In vitro Ta-rich carbides were frequently observed in all specimens. Two distinct types of fracture were suggested by frac-togaphy. One type was characterized by Mode-I cracking with a microscopically rough surface at T_0 + 250 ° C. Whereas the other type at lower temperature T_0 ° C favored either one or several of the octahedral {111} planes, in contrast to the normal Mode-I growth mode typically observed at low loading frequencies (several Hz). The failure mechanisms for two crack ing modes are shearing of γ’precipitates together with the matrix at T_0 ° C and cracking confined in the matrix and the γ / γ’interface at T_0 + 250 ° C.