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

Abstract

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 ≈26 μm are transformed into a recrystallized zone with equiaxed grains having a size of ≈8 μm. 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.