Effects of Shot Peening on High-Temperature Low-Cycle Fatigue Behavior of Superalloys

Surface engineering is vital for enhancing the fatigue resistance of nickel-based superalloys in aero-engine turbine disks. This study systematically evaluates the effects of shot peening (SP), laser shock peening (LSP), and hybrid treatments on the high-temperature low-cycle fatigue (HT-LCF) behavior of FGH96 and GH4169 alloys. Experimental results demonstrate that hybrid treatments introduce hierarchical gradients, combining surface nanocrystallization and deformation twinning with deep (>1000 µm) compressive residual stress (CRS) fields. At 650 °C, LCF life enhancement is primarily governed by the stability of these engineered gradients. While high-cold-work SP layers undergo rapid thermal-mechanical relaxation, the deeper, low-cold-work CRS fields introduced by LSP and hybrid processes exhibit superior stability. Specifically, the out-of-plane (transverse) CRS component retains over 50% of its initial magnitude even after fatigue, effectively suppressing crack propagation. Quantitative correlation reveals that the integrated transverse CRS depth, rather than surface magnitude, is the dominant descriptor for HT-LCF life. These findings highlight the synergy of microstructural refinement and stable stress gradients in inhibiting crack ingress, offering a robust strategy for the design of gradient surface structures to extend the service life of critical components under thermo-mechanical loading.