Yield strength and tensile ductility of laser powder bed fusion-printed fcc alloys: An analysis of the scatter in the reported properties

Abstract The yield strength and tensile ductility of grade 316L austenitic stainless steel additively manufactured using powder bed fusion laser beam (PBF-LB) are reported in the literature to range from ~ 350 to ~ 600 MPa and from ~ 12 to ~ 90%, respectively. In this study, the reasons for such a large scatter in reported mechanical properties is analyzed. One key difference between reported data is the relation between the loading direction and build direction, with samples loaded parallel to the build direction showing overall lower yield strength and higher total elongation than samples loaded perpendicular to the build direction. This is attributed to the difference in strength of texture rather than differences in effective grain size. For samples loaded parallel to the build direction, a strong correlation between the yield strength and scan speed used during printing was found, with higher scan speeds leading to higher yield strengths, and is attributed to higher scan speeds creating a more randomized texture. This relationship is lost for the total elongation, with the scan speed no longer showing a strong correlation, and the energy density instead showing a stronger correlation with the total elongation. The reason is likely because the build quality is an important factor for the total elongation, and the scan speed alone does not provide any indication of whether the build quality is good or poor. Instead, the energy density gives a better indication of the build quality along with the strength of the texture, with higher energy densities generally resulting in better build quality and stronger texture, and therefore, higher total elongation. This is due to the stronger texture typically forming $$\\langle {{11}}0\\rangle$$ ⟨ 110 ⟩ grains, providing a lower Taylor factor and better activation of deformation twins. However, the correlation between energy density and both strength and ductility is not perfectly linear with some samples showing a simultaneous increase in both strength and ductility. This is likely due to the samples having more randomized textures, increasing the contribution of dislocation strengthening (work hardening), as well as, having a higher quantity of $$\\langle {{11}}1\\rangle$$ ⟨ 111 ⟩ oriented grains over a stronger $$\\langle {{10}}0\\rangle$$ ⟨ 100 ⟩ texture, increasing the amount of deformation twinning induced plasticity. Impact statement This article attempts to explain the large scatter reported in the mechanical properties of powder bed fusion laser beam (PBF-LB) 316L stainless steel. In the literature, PBF-LB-printed 316L has been reported with yield strengths varying from ~ 350 to ~ 600 MPa, and tensile ductility varying from ~ 12 to ~ 90 percent. The reason for such a range has not been studied before and is critical to understand for PBF-LB to be used as a standard of manufacturing. The underlying mechanism for the differences was determined to be from differences in dislocation densities and textures. Samples with more randomized textures along with higher dislocation densities had combinational increases in the dislocation strengthening providing the largest difference in yield strength compared to other strengthening mechanisms. Differences in grain size had negligible effects on the strength, even when accounting for loading and build directions. The strength of the texture also played a pivotal role in the ductility, with more randomized textures allowing for higher amounts of twin induced plasticity (TWIP) increasing the ductility of those samples. With these conclusions, build parameters during printing can be more carefully chosen to provide more consistent mechanical behavior of not only PBF-LB printed 316L, but also many other metal alloys.