Low-Cycle Fatigue Performance and Fracture Mechanism of Nickel-based Single Crystal Superalloy at 530 °C

Abstract:

The low-cycle fatigue performance and fracture damage mechanism of Ni-based single crystal superalloy were investigated at 530 °C. Results show that at 530 °C, the fatigue crack of the single crystal superalloy generally appears on the surface, sub-surface or inside of the sample. When there are casting defects on the sub-surface, fatigue crack will arise preferentially from the defects. Under the condition of large strain amplitude (>0.85%), the alloy shows obvious cyclic hardening behavior during the fatigue cycle, and the cyclic stress response curve tends to be stable when the strain amplitude is lower than 0.85%. The plastic deformation of Ni-based single crystal superalloy is mainly proceeded by slip. At 530 °C, the fracture of single crystal superalloy is mainly caused by octahedral slip mechanism, and the main slip system is {111} <110>. According to the sectional structure characteristics of the fracture, no obvious plastic deformation occurs near the source area. The characteristic of fatigue striation can be seen in the stable extension of the crack, and a lot of cross slip bands exist at the slip step in the rapid crack extension stage. By electron backscattered diffraction analysis, there are obvious plastic deformation on the fracture surface at the junction of different slip planes, and the γ matrix and cubic γ' phase near the fracture surface are seriously distorted. No obvious oxidation is observed on the surface of fatigue fracture at 530 °C .

Key words:single crystal superalloy;low cycle fatigue;octahedral slip;cyclic hardening