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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. [ABSTRACT FROM AUTHOR]

Metal additive manufacturing (MAM) offers an excellent capability for designing complex geometries with topology-optimized and near-net-shaped structures. The optimization-designed MAM parts with constrained volume require superior mechanical properties to broaden their utilization in the industry. However, the intrinsic defects generated during the building process deteriorate the mechanical functionality and limit utilization in various industrial applications. In this study, we propose a new strategy to reduce generated defects using ultrasonic nanocrystal surface modification (UNSM) on laser powder bed fusion (LPBF) processed 316L stainless steel. Subsurface pores and high surface roughness in MAM parts were significantly improved through the impact of UNSM treatment, and a gradient structure with mechanical incompatibility was developed. Consequently, the LPBF-processed samples after UNSM treatment show the excellent combination of strength and ductility, which is attributed to the high synergistic hardening from the gradient microstructure and the suppression of damage evolution by controlling built defects. • The 316L stainless steel was fabricated by laser powder bed fusion (LPBF). • The LPBF-processed samples were treated using ultrasonic nanocrystalline surface modification (UNSM). • The UNSM-affected surface showed a high dislocation density and grain refinement, contributing to high strength. • The UNSM treatment effectively controlled building defects intrinsic in LPBF, suppressing damage evolution. • The UNSM treatment improved the combination of strength and ductility in LPBF-processed parts. [ABSTRACT FROM AUTHOR]

Heterostructured materials produced by surface modification have attracted considerable attention owing to their exceptional mechanical properties. Laser-cladding is one of the promising processes to achieve heterostructures by creating a sandwich structure through a simple process. Herein, we propose a new strategy for designing heterostructured laser-clad materials containing dynamically reinforceable heterogeneity introduced through texture-engineering. The specific processing parameters for laser-cladding of 316L stainless steel were selected to induce a predominant crystallographic orientation favorable for twinning. The textured laser-clad alloy showed different textures between the coating and substrate regions, which exhibited a preferential orientation of <111> and <100>, respectively, along the loading direction. Plastic incompatibility was intensified due to the heterogeneous structure caused by the high dislocation density and localized deformation twinning in the coating region. Consequently, the present laser-clad alloys exhibited superior strength-ductility synergy compared to the other homogeneous materials, owing to the substantial hetero-deformation-induced hardening. [Display omitted] [ABSTRACT FROM AUTHOR]