Hybrid Additive Manufacturing for Site-Specific Tensile Response in 316L Stainless Steel

Herein, an alternative way of achieving site-specific mechanical properties is explored-the hybridization of a directed energy deposition technology with a secondary deformation process (hammer peening (HP)) which acts between deposited layers. By applying the peening in a selective manner, microstructure and hence mechanical properties can be locally varied. Microstructural characterization reveals recrystallization in the HP-induced deformation zone. The columnar grains of as-built regions with a grain size of approximate to 26 mu m are transformed into a recrystallized zone with equiaxed grains having a size of approximate to 8 mu m. There is also a highly strain-hardened region below this recrystallized zone where the dislocation density is more than two times higher than in the as-built condition. Subsequent tensile testing reveals that these microstructural zones corresponded to local enhancement in tensile strength normal to the build direction. The strengthening mechanisms are identified as Hall-Petch and dislocation (Taylor) strengthening, and their relative contributions are studied. The local strength enhancement comes at the expense of ductility in the build direction, which is studied via finite element modeling and attributed to strain localization into non-strengthened areas. The results from this work show the possibility of achieving site-specific properties via interlayer processing. This study explores the site-specific tensile response when deformation is selectively applied to layers in a laser-based additive manufacturing process. Deformed regions show a microstructure significantly different from the non-deformed regions. This leads to spatially varying tensile properties with the deformed regions having a higher yield and ultimate tensile strength.image (c) 2024 WILEY-VCH GmbH