Mohammad Dadgar

Additive manufacturing (AM) enables rapid, near-net-shape fabrication with high material efficiency, but the resulting components often exhibit surface roughness, microstructural heterogeneity, and tensile residual stresses that reduce their performance. Machine hammer peening (MHP) is a mechanical surface treatment capable of modifying the surface integrity of AM components. It can be applied either as a conventional post-processing step after fabrication or as a hybrid interlayer treatment integrated into the build process. In this study, the effects of MHP process parameters and treatment strategies on wire-based laser metal deposition (LMD-w) Inconel 718 components were investigated, including the implementation of hybrid interlayer MHP. Surface topography, hardness, microstructure, and residual stresses were examined experimentally, while numerical simulations were developed to support the measurements and to characterize local contact conditions and plastic strain evolution during peening. The results show that MHP significantly reduces surface waviness and roughness, increases near-surface hardness, refines the microstructure, and introduces deep compressive residual stresses. Furthermore, hybrid interlayer MHP enhances the depth and uniformity of the modified layer by influencing the evolving microstructure during deposition. Standard forged Inconel 718 samples were also treated with MHP as a reference, showing comparable characteristics between the forged and AM components. These findings demonstrate that MHP is a versatile and effective modification technique for improving the performance and reliability of AM components, particularly when implemented as a hybrid interlayer treatment during the AM process.

Gear systems operate under high mechanical and tribological loads, making their surfaces vulnerable to wear and fatigue. Improving surface durability requires finishing processes that improve near-surface properties and extend service life. Since machine hammer peening (MHP) offers such potential, this study investigates its influence on the performance of case-hardened spur gears and evaluates its suitability as an alternative to shot peening as a conventional finishing method. Analog specimens with simplified geometries were treated using various MHP parameters to identify effective process settings. These optimized settings were then applied to real spur gears to assess performance under practical conditions. The experiments showed that MHP can significantly modify surface integrity, achieving surface roughness reductions of up to 55%, surface hardness increases of up to 30%, and compressive residual stresses exceeding −1400 MPa with stability to depths of 200 µm. These modifications resulted in improved wear and fatigue performance, with increases in load cycle number in the tooth flank up to 99% and an increase in load amplitude in the tooth root of more than 5%. For comparison, specimens were also treated with shot peening. Although MHP induced stronger surface integrity modifications, shot peening achieved higher overall load-carrying capacity because several critical areas could not be fully accessed by MHP, limiting its effectiveness. Overall, MHP shows promise as a finishing process, but its full potential depends on overcoming accessibility limitations in complex gear geometries.