Microstructure evolution of 55Ni-23Cr-13Co nickel-based superalloy during high-temperature cyclic deformation

The cyclic deformation behavior and microstructure evolution of the 55Ni-23Cr-13Co nickel-based superalloy were studied at 750 xf0b0;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 gamma ' 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 gamma ' 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.