Additive manufacturing of biomimetic layered periodic heterogeneous structures: Achieving synergistic improvement of strength and ductility in 316L stainless steel

Abstract

The inherent strength-ductility trade-off in metallic materials restricts their applications in high-end manufacturing. Inspired by nacre, this study fabricated a biomimetic layered periodic heterogeneous structure via laser powder bed fusion by alternately depositing ductile 316L stainless steel (316L SS) and high-strength 316L SS-xTi6Al4V (x = 0.5, 1, 2 wt%) layers. Notably, trace oxygen was intentionally introduced during powder preparation to promote the in-situ formation of nanoparticles. These nanoparticles, acting as potent nucleation sites, work synergistically with α stabilizing elements to facilitate α phase precipitation and trigger the columnar-to-equiaxed transition, establishing a three-level grain hierarchy (coarse, fine, and ultrafine grains). Compared with monolithic 316L SS, the layered periodic heterogeneous structure achieves a synergistic enhancement in strength and ductility. This is primarily attributed to back stress strengthening at heterogeneous interfaces and nanoparticle reinforcement involving both shearing and Orowan bypassing mechanisms. By systematically integrating phase heterogeneity, grain hierarchy, in-situ nanoparticle reinforcement, and active compositional modulation, this work achieves a four-in-one synergistic effect. This study provides a new paradigm for the active design of high-performance metallic materials through the construction of layered periodic heterostructures.