Effect of micro removal amounts in laser shock peening with post-low stress milling on surface integrity and fatigue life of GH4169 superalloy

Laser shock peening (LSP) markedly enhances the fatigue life of metallic materials but can degrade near-surface topography. This study develops a hybrid route that applies LSP followed by low-stress milling (LSP-LSM). The micro-removal depth (\({\delta }_{LSM}\)) is treated as a design variable for GH4169 to balance surface roughness reduction and retention of compressive residual stress (CRS). Guided by the indentation depth analysis of LSP, we experimentally quantify how the \({\delta }_{LSM}\) in LSP-LSM affects the surface integrity and high-cycle fatigue life of GH4169. LSP produces a CRS field extending to approximately 1 mm, with a maximum of approximately − 700 MPa within a subsurface layer near 300 μm, while increasing the surface roughness \({S}_{\text{a}}\) to 3.72 μm, a 68.3% increase compared with the untreated surface. In contrast, LSP-LSM reduces the minimum \({S}_{\text{a}}\) by 74.7% compared with LSP and by 57.4% compared with the untreated surface, increases the surface CRS by 287.4% and the maximum CRS by 37.0%, and shifts the stress peak toward the surface (CRS depth of approximately 700 μm). The fatigue life increases by 86.8% compared with LSP and by 192.2% compared with the untreated condition. LSP refines the surface grain size from approximately 254 μm to approximately 24 μm; LSP-LSM effectively retains this refinement at approximately 30 μm. Overall, an optimum \({\delta }_{LSM}\) of approximately 100 μm is identified under the present conditions. Building on these findings, the LSP-LSM route provides engineering guidance for GH4169 components and can be extended to curved and thin-walled geometries; evaluation of broader LSP/LSM settings and fatigue conditions will support component-level implementation.

Graphical Abstract