Achieving ultra strain hardening of laser powder bed fusion-fabricated 316L through controlled periodic dislocation structure

Abstract

Conventional strengthening strategies for 316L stainless steel (SS) often improve strength at the cost of reduced work hardening and uniform ductility. This study proposes a dislocation architecture design strategy by adjusting laser energy density during the Laser Powder Bed Fusion (LPBF) process to tailor the spatial distribution of dislocation density. Higher energy density promotes the transition from low-to high-density dislocation regions, forming a gradient dislocation density structure. The periodic thickness of this gradient can be further tuned by varying the number of layers processed under specific parameters. The resulting Periodic Dislocation Structure (PDS) significantly enhances mechanical properties, increasing uniform elongation from 32 % to 42 % without compromising strength. Microstructural evolution shows that PDS stabilizes the strain hardening rate and reduces strain localization. Unlike homogeneous materials that primarily undergo either dislocation slip or twinning, the PDS benefits from heterogeneous deformation-induced strengthening (HDI) and high interface density, promoting twin formation and the generation of geometrically necessary dislocations (GNDs), which refine the microstructure. These effects collectively enable a superior combination of strength and ductility. This work demonstrates a promising LPBF-based approach for tailoring dislocation structures in stainless steel to overcome the traditional trade-off between strength and ductility.