Strain-Dependent High-Temperature Low-Cycle Fatigue Behavior and Damage Mechanisms of GH4169 Alloy After Cold-Drawing Pre-Deformation and Short-Time Annealing

The high-temperature low-cycle fatigue (LCF) response of GH4169 (Inconel 718) is sensitive to the initial microstructural state, yet the coupled effects of cold-drawing pre-deformation and subsequent annealing remain insufficiently understood. A direct-aged condition was used as the reference, while specimens subjected to 14% and 20% cold drawing were tested either without annealing (Z) or after short-time annealing at 930 °C for 10 min (T). Strain-controlled LCF tests were conducted at 650 °C at total strain amplitudes of 0.4%, 0.6%, and 0.8%, with EBSD, SEM, and TEM used to characterize microstructures and fatigue damage. The highest recorded Nf values were 13,679 cycles for 20%-Z at 0.4%, 1095 cycles for the direct-aged reference at 0.6%, and 289 cycles for 20%-T at 0.8%. Retained deformation substructures and low-angle grain boundaries may contribute to local slip accommodation at low strain amplitude. The dislocation structures observed after testing at 0.4% and 0.6% suggest more extensive localized cyclic plasticity at the higher amplitude, while partial recovery after annealing may benefit high-amplitude plastic accommodation. These results suggest that the balance between retained deformation substructures and partial recovery contributes to the strain-amplitude-dependent LCF response of GH4169.