Low Cycle Fatigue Damage Mechanism of GH4169 Nickel-based Superalloy at Elevated Temperature

Low cycle fatigue tests at elevated temperature of 650℃ were conducted on GH4169 nickel-based superalloy after solid solution and double aging treatments. The cyclic response characteristics at different stress amplitudes (550, 600, 650 MPa) were studied. The morphology of fatigue fracture and secondary cracks was observed. The damage mechanism at different stress amplitudes was analyzed. The results show that the tested alloy showed cyclic softening characteristics at different stress amplitudes, and the degree of softening increased with the increase of stress amplitude. The crack propagation showed the transgranular propagation mode at the stress amplitude of 550 MPa, and the secondary cracks were mainly generated at inclusions and slip bands. When the stress amplitude reached 650 MPa, the crack propagation mode became transgranular-intergranular mixed propagation, and the secondary cracks were mainly generated at grain boundaries and slip bands. The deformation mechanism of the tested alloy changed from planar slip at a low stress amplitude to cross slip at a high amplitude.