Abstract:The cyclic deformation behavior and microstructure evolution of the 55Ni-23Cr-13Co nickel-based superalloy were studied at 750 °C under the strain amplitudes from 0.35% to 0.6%. Coffin-Manson-Basquin and Smith-Watson-Topper relationships were employed, which satisfactorily predicted the fatigue life of the alloy under various strain amplitudes. The superalloy showed an initial cyclic hardening as a result of the interaction between the dislocations and the precipitates, and following cyclic softening behavior mainly due to the shearing of the γ′ phase by dislocations and dislocations recovery under all strain amplitudes. Microstructure analyses showed that the M₂₃C₆ carbides exhibited a continuous-chain distribution at lower strain amplitudes, while they showed a discontinuous distribution at higher strain amplitudes. As the strain amplitude increased, the size of the γ′ phase decreased as the consequence of repeated shearing by dislocations. Fracture mechanisms were analyzed. Under higher strain amplitudes, cavities preferred to form around grain boundaries.

Key words: nickel-based superalloy; microstructure; low cycle fatigue; precipitate