Exploring structural origins responsible for the exceptional mechanical property of additively manufactured 316L stainless steel via in-situ and comparative investigations.

• In-situ observation of the dislocation-scaled and grain-scaled microstructures evolution in the additively manufactured 316L stainless steel. Revealing of emission of abundant stacking faults from cellular structures at the yielding stage, for the first time, in the bulk samples. • Quantification of the total dislocation density (∼1015 m−2), the geometrically necessary dislocation density (1.5–2 × 1014 m−2) and the misorientation angle (0.05–0.1°) of the cellular structures using high-resolution electron backscatter diffraction combined with electron channeling contrast imaging. • Identification of the intrinsic dislocation configurations of cellular structures as faulted dipoles, which significantly modulating the dislocation/twining behaviors of additively manufactured 316L sample. • The extremely fine slip band spacing rising high passing stress, playing a decisive role in the high macroscopic yield strength of additively manufactured 316L sample. • Instead of work hardening capability, the maintained ductility of additively manufactured 316L sample attributed to a complex interplay of several modulated plastic deformation mechanisms regulated by the hierarchical microstructure. The laser beam powder-bed-fusion (PBF-LB) technique offers the possibility to fabricate metallic materials with unparalleled mechanical properties. However, due to the complexity of nonequilibrium solidification structures, untangling the role of specific structural features in influencing mechanical properties through post-mortem analysis remains a significant challenge. Here, we tracked the complete evolution of deformation microstructures in PBF-LB 316L stainless steel (SS) and conventionally manufactured (CM) counterparts using in-situ electron channeling contrast imaging (ECCI) in conjunction with high-angular resolution electron backscatter diffraction (HR-EBSD). Our findings underscore the importance of the intrinsic dislocation configuration, i.e. , faulted dipole, in modulating the plastic deformation behaviors of the PBF-LB sample. The periodic arrangement of faulted dipoles triggers a widespread activation of stacking faults (SFs) with extremely fine spacing at the yielding stage, resulting in a high passing stress (∼433 MPa) that is responsible for the high yield strength. Meanwhile, such configuration facilitates uniform plastic deformation and mediates twinning propensity, thereby alleviating stress concentrations and enhancing ductility. Moreover, by correlating the mechanical response with microstructural evolution, we establish a modified model for multiple strengthening mechanisms in the PBF-LB sample. Additionally, we examine the effect of nonequilibrium solidification structures on the strain rate sensitivity of PBF-LB samples. Taking 316L SS as an exemplar, our results extend the current understanding of the structural origins responsible for the exceptional mechanical properties of metals manufactured by PBF-LB. [Display omitted] [ABSTRACT FROM AUTHOR]