Thickness effect on the microstructures, mechanical properties, and anisotropy of laser-powder bed fusion processed 316L stainless steel

Thin-wall structures are promising for lightweighting with widened applications in topology-optimized lattice structures. Also, they are extensively used in heat exchangers because of their rapid heat transfer rate. This work presents the effects of thin-wall thickness on the microstructures, property, and anisotropy of the laser-powder bed fusion processed thin-walled structures with varied wall thicknesses of 0.3 mm, 0.5 mm, 1.0 mm, and 1.5 mm. The epitaxial columnar growth is favored, and the columnar grain aspect ratio increases with the wall thickness. Further, the columnar grain size increases and the geometrically necessary dislocation density decreases with increasing thickness. These microstructural differences significantly affected the tensile properties; the yield and the tensile strengths reduced, and the elongation increased with the wall thickness increase. Further, the L-PBF processed thin walls presented anisotropic properties. The samples tested along the build direction showed lower strength than those across the build direction. Moreover, the drop in strength with increasing thickness is less in the samples taken across the build direction than that along the build direction. Importantly, the degree of anisotropy increased with increasing wall thickness.