Temperature effect on low-cycle fatigue behavior of nickel-based single crystalline superalloy

The low-cycle fatigue (LCF) behavior of a nickel-based single crystal superalloy with [001] orientation was studied at an intermediate temperature of T0°C and a higher temperature of T0 + 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 temperature 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 T0 + 250°C. Whereas the other type at lower temperature T0C 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 of γ′ precipitates together with the matrix at T0°C and cracking con ned in the matrix and the γ/γ′ interface at T0 + 250°C.