Enhanced surface integrity and fatigue properties of laser powder bed fused GH4169 superalloy processed by femtosecond laser shock peening

The fatigue resistance of laser powder bed fused (LPBFed) GH4169 superalloy is critically limited by surface defects, residual tensile stresses, and coarse columnar γ grains with 〈001〉 crystallographic texture. To overcome these limitations, we implement the femtosecond laser shock peening (Fs-LSP) as a post-processing strategy, systematically investigating its pulse energy effects (100–300 μJ) on surface integrity and high-cycle fatigue behavior. Results showed that the optimal pulse energy was determined to be 200 μJ, which resulted in excellent surface integrity: 1) complete elimination of irregular ablation features and near-surface micropores; 2) generation of high-magnitude compressive residual stresses (−395 MPa) with effective penetration depth (70 μm); 3) grain refinement (66.1 → 34.56 μm) through dynamic recrystallization, coupled with dense dislocation networks, and 4) suppression of Laves phase segregation at grain boundaries. These coordinated modifications fundamentally alter fatigue failure mechanisms: 1) crack initiation sites migrate from surface defects to subsurface regions; 2) randomized grain orientations and refined microstructure deflect crack propagation paths; 3) compressive stress fields and dislocation barriers synergistically decelerate crack growth. Consequently, the fatigue strength demonstrates a remarkable 26.7 % improvement (from 378 to 516 MPa). This work establishes a process-microstructure-property correlation framework and provides actionable guidelines for fatigue-resistant additive manufacturing of nickel-based superalloy.