| 1. |
- Leicht, Alexander, 1987, et al.
(författare)
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Effect of part thickness on the microstructure and tensile properties of 316L parts produced by laser powder bed fusion
- 2021
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Ingår i: Advances in Industrial and Manufacturing Engineering. - : Elsevier BV. - 2666-9129. ; 2
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Tidskriftsartikel (refereegranskat)abstract
- Additive manufacturing provides a unique possibility to manufacture parts with advanced design and thin-walled structures. To explore thin-wall capacity, laser powder bed fusion was employed to fabricate 316L samples with different section thicknesses. A detailed microstructure characterization was then carried out, and tensile properties were assessed. It was found that reducing the part thickness did not affect the microstructure but did reduce the tensile properties. Samples with 1 mm thickness exhibited the lowest yield strength of 457 ± 11 MPa and elongation to fracture of 49 ± 20%, while the tensile properties improved when the sample thickness was increased to 3 mm. The 3 mm thick samples generated tensile properties comparable to those of standard dimensions. The results emphasize that part thickness must be considered when assessing mechanical properties and must be adjusted when performing design optimization and simulations of samples produced with laser powder bed fusion.
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| 2. |
- Leicht, Alexander, 1987, et al.
(författare)
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Increasing the Productivity of Laser Powder Bed Fusion for Stainless Steel 316L through Increased Layer Thickness
- 2021
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Ingår i: Journal of Materials Engineering and Performance. - : Springer Science and Business Media LLC. - 1059-9495 .- 1544-1024. ; 30:1, s. 575-584
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Tidskriftsartikel (refereegranskat)abstract
- Additive manufacturing (AM) is able to generate parts of a quality comparable to those produced through conventional manufacturing, but most of the AM processes are associated with low build speeds, which reduce the overall productivity. This paper evaluates how increasing the powder layer thickness from 20 µm to 80 µm affects the build speed, microstructure and mechanical properties of stainless steel 316L parts that are produced using laser powder bed fusion. A detailed microstructure characterization was performed using scanning electron microscopy, electron backscatter diffraction, and x-ray powder diffraction in conjunction with tensile testing. The results suggest that parts can be fabricated four times faster with tensile strengths comparable to those obtained using standard process parameters. In either case, nominal relative density of > 99.9% is obtained but with the 80 µm layer thickness presenting some lack of fusion defects, which resulted in a reduced elongation to fracture. Still, acceptable yield strength and ultimate tensile strength values of 464 MPa and 605 MPa were obtained, and the average elongation to fracture was 44%, indicating that desirable properties can be achieved.
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| 3. |
- Riabov, Dmitri, 1990, et al.
(författare)
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Investigation of the strengthening mechanism in 316L stainless steel produced with laser powder bed fusion
- 2021
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Ingår i: Materials Science & Engineering A: Structural Materials: Properties, Microstructure and Processing. - : Elsevier BV. - 0921-5093. ; 822
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Tidskriftsartikel (refereegranskat)abstract
- Of the many benefits of the additive manufacturing process, laser powder bed fusion (L-PBF) has specifically been shown to produce hierarchical microstructures that circumvent the common strength-ductility trade-off. Typically, high strength materials have limited ductility, and vice versa. The L-PBF microstructure, consisting of fine cells, is formed during the rapid solidification of the laser powder bed fusion process. The cell boundaries are often characterized by the segregation of alloying elements and a dislocation network. While there are a number of works describing the strengthening mechanisms in L-PBF-produced 316L, there are still some gaps in understanding the effect of stress-relief and annealing at various annealing temperatures (400, 800 and 1200 °C) on the plastic strain accumulation during deformation. In this study, the authors evaluated strain partitioning using electron backscatter diffraction and kernel average misorientation maps. The results show strain partitioning to be dependent on both the annealing temperature and the pre-straining of samples. Further, the results indicated that the dislocation structure was stable until 400 °C, whereas at 800 °C strain was no longer detected at the cell boundaries. Similarly, after the heat treatment at 800 °C, elemental segregation at the cell walls was no longer detectable. Upon straining, the boundaries of as-built and annealed samples at 400 and 800 °C registered accumulation of additional strain as compared to the unstrained states. The results demonstrate that even a weak array of dislocations along the cell walls can successfully pin dislocations, albeit at a reduced capability relative to the co-existent dislocation and segregate structures found in microstructures of the as-built and annealed samples at 400 °C.
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| 4. |
- Yu, Cheng-Han, 1992-, et al.
(författare)
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Low cycle fatigue of additively manufactured thin-walled stainless steel 316L
- 2021
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Ingår i: Materials Science & Engineering A: Structural Materials: Properties, Microstructure and Processing. - : Elsevier BV. - 0921-5093 .- 1873-4936. ; 821
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Tidskriftsartikel (refereegranskat)abstract
- To ensure the robust design freedom of metallic additive manufacturing, the fatigue properties and the dimensional limitation of as-built components by laser powder bed fusion (PBF-LB) are investigated. Fully reversed and strain-controlled fatigue tests were carried out on tubular specimens with different wall thicknesses, 1 mm and 2 mm, for the purpose of studying the thin-wall effect without having risk of buckling problem during compression. Two wrought conditions are also enclosed as a comparison, which are the cold worked (CW) and solution annealed condition (SA). In the as-built PBF-LB tubular specimens, deformed microstructure and deformation twins are discovered close to the surface region, together with a higher roughness of the inner surface due to the heat accumulation. The surface roughness is evaluated as micro-notches, and a higher fatigue notch factor, Kf, at lower applied strain range is revealed. The factors influencing Kf include, the non-conductive inclusions serving as crack initiation sites at the surface region, and the deformation twins formed by the local stress concentration. The strain-life of PBF-LB samples is comparable with the wrought samples. However, the fatigue strength of the responding mid-life stress shows greater difference and is in the following order, CW wrought > PBF-LB > SA wrought. Secondary cyclic hardening owing to deformation induced martensitic transformation is found in both of the wrought samples. Yet, only cyclic softening exhibits in the PBF-LB samples, which is the result of the suppressed martensitic transformation and the dislocation unpinning from the cell boundaries.
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