Critical aerospace components like turbine blades and landing gears are increasingly produced using additive manufacturing (AM), especially laser powder bed fusion (LPBF) due to its design flexibility and material efficiency. However, LPBF inherently results in high surface roughness, primarily due to AM-induced features such as spatter, partially melted particles, and scan tracks. These AM-deterministic features consist of significant surface slope gradients and additional textural area, acts as stress concentrators and compromise part performance and service life. Additionally, high temperature gradient during the layer-by-layer manufacturing technique generates large tensile stresses. These promote the formation of sub-cellular grain structures and microscopic strain localization zones, especially near melt-pool boundaries. Internal misfit strain and dislocation pile-up destabilize the microstructure. Moreover, the non-uniform distribution of thermal strains across the build results in macroscopic shape distortions (warping and/or residual bowing) which ultimately degrade structural reliability. In-process mitigation of these issues by optimizing printing parameters has limited improvements. Therefore, shot peening is implemented as a post-processing method.

 

Shot peening, a mechanical surface work-hardening process that induces severe plastic deformation through repeated high-velocity impacts of spherical metallic media enhancing surface integrity and strength while retaining bulk ductility. This study investigates the influence of shot peening on the surface integrity of LPBF-fabricated IN718, 316SS, and Ti64, across surface orientations from 0–90°.

 

Specifically, the research objective is to understand the surface strengthening and homogenization effect from grain boundary reorientation and shear band formation (suppressing crystal sliding) generated by inhomogeneous elastic-plastic deformation in AM parts. Furthermore, material- and orientation-specific peening optimization is

 

performed to achieve uniform roughness reduction by elimination of AM-deterministic features across different surface orientations. This work considers two specific peening techniques, gravity-assisted shot peening and pneumatic shot peening, targeting surface modification under controlled low (έ ≈ 103 s-1) and high (έ ≈ 105 s-1) strain rate conditions, respectively.

 

Optimized peening conditions effectively reduced average areal roughness (Sa) by ≈ 70%, and generated significant compressive stresses (≈ -400 MPa), thereby increasing surface strength and hardness (≈ 35%). Comparative evaluation of shot peening on three LPBF-manufactured IN718, 316SS, and Ti64 materials are performed for broader applicability. As the industry applies AM for complex performance-critical parts, these analyses provide a pathway to achieve industry standard surface quality (Ra ≈ 1.6 μm) through shot peening. The anisotropic nature of LPBF (bottom-up material addition approach) is critically evaluated through comparative analysis of areal and hybrid roughness metrics for upskins and downskins.