Effect of Strain Amplitude on Cyclic Deformation Behavior of Nickel-Based Single Crystal Superalloy DD11 in Low Cycle Fatigue

The cyclic stress response behavior and failure modes of nickel-based single crystal superalloys DD11 with [001] orientation in low cycle fatigue at 980 degrees C and strain amplitude range of 0.5%similar to 1.2% were investigated. The relationship between deformation microstructure and fatigue behavior was established. The results show that cyclic softening occurs and the softening degree decreases with increasing the strain amplitude. The coarsening of gamma' and the broadening of transverse channels of gamma are liable to cause the movement of dislocation in the gamma channel and result in cyclic softening. Moreover, the dislocation recovery occurs at the low strain amplitude, which also causes cyclic softening. The pilling-up of dislocation occurs at the gamma/gamma' interfaces as the degree of coarsening gamma' and broadening transverse channels of gamma decreases when the strain amplitude is large than 0.8%, which results in a decrease in the degree of cyclic softening. The fatigue failure mode changes from normal fracture to shear fracture, corresponding to the transition of crack from stable propagation to the instant fracture.