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The particular roles of grain morphology and defects, controlled using laser‐scan strategies, on the mechanical properties and the fatigue behavior of 316L stainless steel are investigated. Microstructural characterization and X‐ray tomography analysis was performed to understand the genesis of polycrystalline microstructure and defects. Tensile and fatigue tests were performed to analyze the effect of defect population and microstructural properties on plasticity and damage mechanisms during monotonic and cyclic loading. The effect of the grain‐size and shape and type of defect was carefully investigated to evaluate the mechanisms driving the mechanical behavior under quasi‐static and fatigue loading. It is shown that the laser‐scan strategy determines the anisotropy in the plane perpendicular to the building direction. Moreover, contrary to the existing literature, for 316L obtained by AM, the grain size and shape does not affect the mechanical properties, and LoF defects drive the fatigue life, independent of the defect/grain size ratio. [ABSTRACT FROM AUTHOR]

The main subject of this study is to investigate the correlations between the evolution of mechanical behavior and the multiscale microstructure of 316 L stainless steel obtained by laser powder bed fusion process (LPBF) after various post-manufacturing heat treatments across a wide temperature range. The microstructure of 316 L LPBF parts exhibits a hierarchical microstructure based on unique grain structures, chemical segregations, dislocation arrangements at the microscopic scale and fine nano-oxides at the nanoscopic scale. These microstructural elements play a crucial role in determining the material's mechanical and corrosion properties. To understand how different microstructural features contribute to the material's behavior, the researchers conduct post-manufacturing heat treatments to isolate and study these components. The results show that dislocation and/or micro-segregation networks significantly influence the high tensile properties of 316 L LPBF steel in its as-built state and after heat treatments above 900 ∘ C. Despite their disappearance during heat treatments, the material maintains high tensile strength due to an increase in strain-hardening capabilities. The study also examines the impact of nano-oxides and the σ phase on the material's properties. The contribution of nano-oxides to yield strength diminishes with increasing temperature. Interestingly, the σ phase does not necessarily lead to a detrimental effect on failure elongation for 316 L LPBF steel. Overall, this research provides insights into the relationship between microstructure and mechanical properties for additively manufactured stainless steel. By understanding these relationships, it becomes possible to tailor the microstructure to achieve desired mechanical properties for specific applications and extend the use of 316 L LPBF to higher temperatures compared to conventional methods. [Display omitted] • Remarkable stability of grain boundaries over a wide temperature range. • Sigma phase precipitates (800 °C–1000 °C) due to low nitrogen and thermal cycling. • Nano-oxides grow significantly between 900 °C and 1200 °C. • Dislocations and nano-oxides are primarly contributor to strengthening up to 800 °C. [ABSTRACT FROM AUTHOR]

Additive manufacturing (AM) offers distinct advantages in terms of complexity, reduced material waste, and shorter production times. However, the microstructures of AM alloys differ significantly from conventionally manufactured ones, and their impact on grain behavior remains uncertain. This study employs neutron diffraction, coupled with Crystal Plasticity Finite Element (CPFE) modeling, to investigate microstructural effects on cyclic behavior in 316L LPBF alloys. Neutron diffraction provides high-resolution strain and stress data at the polycrystalline level during loading, offering valuable insights into grain behavior. The CPFE model is initially validated at the grain scale using neutron diffraction, demonstrating its ability to predict local mechanical behavior in additively manufactured materials. This methodology holds promise for broader applications in various AM alloys, particularly when macroscopic identification of mechanical behavior is insufficient. Furthermore, the comparison between neutron diffraction and CPFE predictions allows to identify the influence of dendrites and dislocation substructures on the mechanical behavior at the grain scale. Notably, the micromechanical anisotropy resulting from dislocation organization along dendritic structures with specific orientations is highlighted. This study shows that despite the observed anisotropy, experimental measurement of intragranular strain distribution are correctly captured with a quantification of the deviation observed on some specific orientations due to the above cited microstructure sub-structures. • Elastic anisotropy remains independent of microstructure variations in LPBF alloys. • Neutron diffraction validates CPFE model predictions at the grain scale. • Neutron diffraction vs. CPFE reveals dendrite's role in grain mechanical anisotropy. [ABSTRACT FROM AUTHOR]