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1.
  • Amin Yavari, S., et al. (författare)
  • Layer by layer coating for bio-functionalization of additively manufactured meta-biomaterials
  • 2020
  • Ingår i: Additive Manufacturing. - : Elsevier BV. - 2214-8604 .- 2214-7810. ; 32
  • Tidskriftsartikel (refereegranskat)abstract
    • Additive manufacturing has facilitated fabrication of complex and patient-specific metallic meta-biomaterials that offer an unprecedented collection of mechanical, mass transport, and biological properties as well as a fully interconnected porous structure. However, applying meta-biomaterials for addressing unmet clinical needs in orthopedic surgery requires additional surface functionalities that should be induced through tailor-made coatings. Here, we developed multi-functional layer-by-layer coatings to simultaneously prevent implant-associated infections and stimulate bone tissue regeneration. We applied multiple layers of gelatin- and chitosan-based coatings containing either bone morphogenetic protein (BMP)-2 or vancomycin on the surface of selective laser melted porous structures made from commercial pure Titanium (CP Ti) and designed using a triply periodic minimal surface (i.e., sheet gyroid). The additive manufacturing process resulted in a porous structure and met the the design values comparatively. X-ray photoelectron spectroscopy spectra confirmed the presence and composition of the coating layers. The release profiles showed a continued release of both vancomycin and BMP-2 for 2–3 weeks. Furthermore, the developed meta-biomaterials exhibited a very strong antibacterial behavior with up to 8 orders of magnitude reduction in both planktonic and implant-adherent bacteria and no signs of biofilm formation. The osteogenic differentiation of mesenchymal stem cells was enhanced, as shown by two-fold increase in the alkaline phosphatase activity and up to four-fold increase in the mineralization of all experimental groups containing BMP-2. Eight-week subcutaneous implantation in vivo showed no signs of a foreign body response, while connective tissue ingrowth was promoted by the layer-by-layer coating. These results unequivocally confirm the superior multi-functional performance of the developed biomaterials.
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2.
  • Ananthanarayanan, Durga, et al. (författare)
  • Modelling columnar-to-equiaxed transition during fusion-based metal additive manufacturing
  • 2023
  • Ingår i: Additive Manufacturing. - : Elsevier BV. - 2214-8604 .- 2214-7810. ; 78
  • Tidskriftsartikel (refereegranskat)abstract
    • During fusion-based metal additive manufacturing, there is an inherent directionality in heat transfer, which leads to columnar grain growth. This may result in cracking and anisotropic mechanical properties in many alloy systems. Therefore, it is important to study the conditions under which columnar-to-equiaxed transition in grain structure occurs. The grain morphology is determined by several factors such as process conditions, local alloy composition, and number density of nucleating sites. In the present work, a model for simulating columnar-to-equiaxed transition is formulated, considering nucleating site size distribution, rapid solidification and constitutional undercooling in multicomponent alloys. Furthermore, the model is coupled with multicomponent Calphad-based thermodynamic and diffusion mobility descriptions. It is demonstrated that including the above aspects is important in accurately predicting the columnar-to-equiaxed transition by comparing with experimental data for an additively manufactured TiB2-reinforced AlSi10Mg alloy. The framework developed in this work may be used to predict columnar-to-equiaxed transition in additively manufactured technical alloys consisting of multiple elements.
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3.
  • Andersson, Henrik, Dr, 1975-, et al. (författare)
  • Variable low-density polylactic acid and microsphere composite material for additive manufacturing
  • 2021
  • Ingår i: Additive Manufacturing. - : Elsevier BV. - 2214-8604 .- 2214-7810. ; 40
  • Tidskriftsartikel (refereegranskat)abstract
    • Thermally expandable microspheres are extensively used in industry as a lightweight filler for many products. The spheres can expand up to 60 times the initial size and are used for different purposes, including material reduction and surface modification. In fused filament fabrication (FFF), a material is deposited in a layer-by-layer process. Typically, FFF objects need not be solid because such objects are typically used for applications with low mechanical stress. Low material infill percentages are commonly used inside a solid outer shell to reduce material usage, weight, and manufacturing time. This paper proposes a new composite filament for FFF consisting of polylactic acid (PLA) and thermally expandable Expancel microspheres in the form of masterbatch granules. These filaments contain unexpanded microspheres that can be expanded during printing by heating. Two types of filaments containing 2 wt% and 5 wt% of masterbatch granules were manufactured and tested. The filaments were successfully used with a commercial 3D printer to manufacture objects with a density of 45% compared to objects manufactured using standard PLA. The tensile strength of these objects changed linearly with density and was comparable to that of PLA objects of the same density prepared using infill patterns. The composite filaments are advantageous in that they can reduce the amount of material used, as is currently done by using different amounts of infill in a pattern. Further, by varying the nozzle temperature, their density can be adjusted directly during printing as well as during fabrication to produce layers of different densities in the same object. 
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4.
  • Brandau, Benedikt, et al. (författare)
  • Proof-of-concept of an absorbance determination of a powder bed by high resolution coaxial multispectral imaging in laser material processing
  • Ingår i: Additive Manufacturing. - 2214-8604 .- 2214-7810.
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • Imaging techniques are very popular for process monitoring in laser material processing due to their high information content. At the same time, coaxial systems focused by passive laser optics still present a major challenge, because most laser optics cause imaging errors for the monitoring channel. In this paper, the design, methodology and procedure are shown to be able to acquire coaxial image data by standard laser components, which is demonstrated by components for a laser powder bed fusion system and their use on a powder bed. The focus is on the correction of the image data to produce a high-resolution, geometrically accurate and gap-free overview image of the entire processing area. For this purpose, optical simulations of the system are performed to detect aberrations, distortions and chromatic errors and to correct them by hardware elements or in software post-processing. Over the entire 114 mm by 114 mm working area, objects can be captured geometrically accurate with a maximum deviation of 22 μm - 49 μm, depending on the detection wavelength. By capturing images atPaper C: Coaxial multispectral imaging Benedikt Brandau148wavelengths of 405 nm, 450 nm, 520 nm, 580 nm, 625 nm and 850 nm, multispectral information is gained over the entire working area. In addition, an absorbance of the powder bed is derived from the images. To qualify this methodology, tests are performed on 20 different powders. These include different particle sizes, aged and oxidized powders of different metals. The ability to determine absorbance is simulated by ray tracing powder surfaces. This allows the determination of in-line absorbances from the powder bed with a maximum deviation of 2.5 % compared to absorbance spectra of established methods. The origins of component defects such as foreign particles, powder oxidation, spatter and uncoated areas were able to be identified down to a diameter of 20 μm.
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5.
  • Cantoni, Federico, et al. (författare)
  • Round-robin testing of commercial two-photon polymerization 3D printers
  • 2023
  • Ingår i: Additive Manufacturing. - : Elsevier. - 2214-8604 .- 2214-7810. ; 76
  • Tidskriftsartikel (refereegranskat)abstract
    • Since its introduction in the 1980s, 3D printing has advanced as a versatile and reliable tool with applications in different fields. Among the available 3D printing techniques, two-photon polymerization is regarded as one of the most promising technologies for microscale printing due to its ability to combine a high printing fidelity down to submicron scale with free-form structure design. Recently, the technology has been enhanced through the implementation of faster laser scanning strategies, as well as the development of new photoresists. This paves the way for a wide range of applications, which has resulted in an increasing number of available commercial systems. This work aims to provide an overview of the technology capability by comparing three commercial systems in a round-robin test. To cover a wide range of applications, six test structures with distinct features were designed, covering various aspects of interest, from single material objects with sub-micron feature sizes up to multi-material millimeter-sized objects. Application-specific structures were printed to evaluate surface roughness and the stitching capability of the printers. Moreover, the ability to generate free-hanging structures and complex surfaces required for cell scaffolds and microfluidic platform fabrication was quantitatively investigated. Finally, the influence of the numerical aperture of the fabrication objective on the printing quality was assessed. All three printers successfully fabricated samples comprising various three-dimensional features and achieved submicron resolution and feature sizes, demonstrating the versatility and precision of two-photon polymerization direct laser writing. Our study will facilitate the understanding of the technology maturity level, while highlighting specific aspects that characterize each of the investigated systems.
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6.
  • Cederberg, Emil, et al. (författare)
  • Physical simulation of additively manufactured super duplex stainless steels : microstructure and properties
  • 2020
  • Ingår i: Additive Manufacturing. - : Elsevier. - 2214-8604 .- 2214-7810. ; 34
  • Tidskriftsartikel (refereegranskat)abstract
    • The behavior of high performance super duplex stainless steel (SDSS) during additive manufacturing (AM) has been investigated using a novel arc heat treatment technique. Tungsten inert gas (TIG) arc pulses were applied on a disc shaped sample mounted on a water-cooled chamber to physically simulate AM thermal cycles. SDSS base metal and a duplicated additively manufactured structure (DAMS) were used as initial microstructures. Samples were melted one, five, or 15 times by arc heat treatment. Samples were also produced with a controlled slope down of the current to create slower cooling compared to pulsing. Microstructure characterization and modelling were performed to study the evolution of microstructure and properties with successive AM cycles. Microstructural changes were dependent on the number of reheating cycles, cooling rate, and peak temperature. In particular, the DAMS austenite morphology and fraction changed after reheating to peak temperatures above 700 °C. Nitrides and sigma were observed in the high and low temperature heat affected zones, respectively. Sensitization to corrosion was more pronounced in reheated DAMS than in the base metal. Hardness was increased more by multiple remelting/reheating than by slow cooling. It was found that AM thermal cycles significantly affect SDSS properties especially for an initial microstructure similar to that produced by AM. © 2020 Elsevier B.V.
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7.
  • Chinga-Carrasco, Gary, et al. (författare)
  • Bagasse—A major agro-industrial residue as potential resource for nanocellulose inks for 3D printing of wound dressing devices
  • 2019
  • Ingår i: Additive Manufacturing. - : Elsevier B.V.. - 2214-8604 .- 2214-7810. ; 28, s. 267-274
  • Tidskriftsartikel (refereegranskat)abstract
    • Sugarcane bagasse, an abundant residue, is usually burned as an energy source. However, provided that appropriate and sustainable pulping and fractionation processes are applied, bagasse can be utilized as a main source of cellulose nanofibrils (CNF). We explored in this study the production of CNF inks for 3D printing by direct-ink-writing technology. The CNF were tested against L929 fibroblasts cell line and we confirmed that the CNF from soda bagasse fibers were found not to have a cytotoxic potential. Additionally, we demonstrated that the alginate and Ca 2+ caused significant dimensional changes to the 3D printed constructs. The CNF-alginate grids exhibited a lateral expansion after printing and then shrank due to the cross-linking with the Ca 2+ . The release of Ca 2+ from the CNF and CNF-alginate constructs was quantified thus providing more insight about the CNF as carrier for Ca 2+ . This, combined with 3D printing, offers potential for personalized wound dressing devices, i.e. tailor-made constructs that can be adapted to a specific shape, depending on the characteristics of the wound healing treatment.
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8.
  • Da Silva, Adrien, et al. (författare)
  • The effects of laser irradiation on an aluminium powder stream in Directed Energy Deposition
  • 2021
  • Ingår i: Additive Manufacturing. - : Elsevier. - 2214-8604 .- 2214-7810. ; 41
  • Tidskriftsartikel (refereegranskat)abstract
    • Additive Manufacturing with aluminium alloys is a subject of increasing industrial interest. Directed Energy Deposition using high power lasers and a powder feed is a useful option but the interactions between the powder stream and the laser beam are not completely understood. It is well known that the powder particles heat up in the laser beam and some theoretical models predict that they can reach their vaporisation temperature and have their flight path altered by the associated recoil pressure. In order to learn more about these phenomena, powder streams were observed with a high-speed camera at different laser powers (up to 6 kW) and with three batches of powder (AlSi10Mg) of different particle sizes. The results showed an increase of powder focussing with increased laser power. In addition, some particles were found to disintegrate in the laser beam. It is demonstrated that particle disintegration is most likely to be caused by the momentum induced by the recoil pressure.
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9.
  • Dadbakhsh, Sasan, et al. (författare)
  • Heat treatment possibilities for an in situ βTi-TiC composite made by laser powder bed fusion
  • 2020
  • Ingår i: Additive Manufacturing. - : Elsevier. - 2214-8604 .- 2214-7810. ; 36
  • Tidskriftsartikel (refereegranskat)abstract
    • After laser powder bed fusion (LPBF) of an ultra-strong in situ TiC whisker reinforced β-Ti composite, this paper investigates the evolution of microstructure and mechanical properties in response to heat treatment at different temperatures. Using in depth nano-SEM and TEM analyses, it is shown that ageing at 400 °C rounds the whiskers, annihilates the strain fields and grows Mo segregated nano-cells, but without improving the ductility. In contrast, ageing at 600 °C enables the transformation of metastable β to a lamellar β + α, leading to a dual phase matrix embedding TiC particles. This is in such a manner that extra ageing at 600 °C coalesces the nano-lamellar α + β microstructure to form a coarser micro-lamellar α + β matrix. This microstructure achieves 66 % of the compressive deformation of Cp-Ti, and over 1400 MPa compressive strength after 1 h of ageing at 600 °C. Despite this success under compression, hard and stiff TiC particles may still cause large spherical fractured voids, severely limiting the plastic deformation under tension.
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10.
  • Fedina, Tatiana, et al. (författare)
  • A comparative study of water and gas atomized low alloy steel powders for additive manufacturing
  • 2020
  • Ingår i: Additive Manufacturing. - : Elsevier. - 2214-8604 .- 2214-7810. ; 36
  • Tidskriftsartikel (refereegranskat)abstract
    • This work reports a study of the differences between laser processing of water and gas atomized low alloy steel powders with a focus on powder behavior and performance in additive manufacturing. Material packing densities were measured to establish a relationship between powder packing and track formation. The results showed that the track height when using water atomized powder was 15% lower than the value achieved for the gas atomized powder. High-speed imaging was utilized to observe the material behavior and analyze the powder particle movement under laser irradiation. It was found that water atomized powder has less particle entrainment due to its tendency towards mechanical interlocking. The occurrence of powder spattering and melt pool instabilities was also studied. More frequent spatter ejection is believed to be due to the higher amount of oxygen in the water atomized powder.
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11.
  • Flodberg, Göran, et al. (författare)
  • Pore analysis and mechanical performance of selective laser sintered objects
  • 2018
  • Ingår i: Additive Manufacturing. - : Elsevier B.V.. - 2214-8604 .- 2214-7810. ; 24, s. 307-315
  • Tidskriftsartikel (refereegranskat)abstract
    • In this work, systematic studies were carried out on SLS (selective laser sintering) printed samples, with two different geometries, standard test samples dumb-bells (dog bones) and tubes (Ø 30 mm and 150 mm long), consisting of two different materials, viz. PA12 (polyamide) with and without the addition of carbon fibres (CFs). These samples were tested according to their respective ISO standards. The standard test samples exhibited relatively small differences with regards to printing directions when PA12 was used alone. Their tensile strengths (σm) were approx. 75%–80% of the injection-moulded sample. The addition of carbon fibres significantly enhanced the tensile strengths, namely 50% greater for the vertically printed test sample and more than 100% greater for the horizontally printed samples, compared to the respective objects consisting of PA12 alone. The strong difference in printing directions can be attributed to the orientation of the carbon fibres. Mechanical tests on the SLS printed tubes confirmed the trends that were found in the standard test samples. Porosity and pore structure inside the SLS printed tubes were studied by combining optical microscopy and X-ray microtomography with image analysis. It was found that porosity was a general phenomenon inside the SLS printed samples. Nevertheless, there were significant differences in porosity, which probably depended on the properties of the materials used, both with and without carbon fibres, thus causing significant differences in light absorption and heat conductivity. The printed samples made of PA12 alone possessed quite a high level of porosity (4.7%), of which the size of the biggest pore was hundreds of microns. The twenty biggest pores with an average size of 75*104 ÎŒ m3 accounted for 43% of the total porosity. However, the porosity of the printed samples made from PA12 + CF was only 0.68%, with the biggest pore being only tens of microns. The corresponding average pore size of the 20 biggest pores was 72*103 ÎŒ m3, which was one order of magnitude smaller than the printed samples made from PA12 alone. Pores inside the SLS printed samples were probably responsible for a spread in the mechanical properties measured, e.g. tensile strengths, tensile (Young’s) modulus, strain at break, etc. The ratios of their standard deviations to their corresponding mean values in the standard test samples could probably be used as an indicator of porosity, i.e. the bigger the ratio, the higher the porosity.
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12.
  • Goel, Sneha, 1993-, et al. (författare)
  • Effect of post-treatments under hot isostatic pressure on microstructural characteristics of EBM-built Alloy 718
  • 2019
  • Ingår i: Additive Manufacturing. - : Elsevier BV. - 2214-8604 .- 2214-7810. ; 28, s. 727-737
  • Tidskriftsartikel (refereegranskat)abstract
    • Electron beam melting (EBM) has emerged as an important additive manufacturing technique. In this study, Alloy 718 produced by EBM was investigated in as-built and post-treated conditions for microstructural characteristics and hardness. The post-treatments investigated were hot isostatic pressing (HIP) and combined HIP + heat treatment (HIP + HT) carried out as a single cycle inside the HIP vessel. Both the post-treatments resulted in significant decrease in defects inevitably present in the as-built material. The columnar grain structure of the as-built material was found to be maintained after post-treatment, with some sporadic localized grain coarsening noted. Although HIP led to complete dissolution of δ and γ′′ phase, stable NbC and TiN (occasionally present) particles were observed in the post-treated specimens. Significant precipitation of γ′′ phase was observed after HIP + HT, which was attributed to the two-step aging heat treatment carried out during HIP + HT. The presence of γ′′ phase or otherwise was correlated to the hardness of the material. While the HIP treatment resulted in drop in hardness, HIP + HT led to ‘recovery’ of the hardness to values exceeding those exhibited by the as-built material.
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13.
  • Goulas, Athanasios, et al. (författare)
  • Additive manufacturing of physical assets by using ceramic multicomponent extra-terrestrial materials
  • 2016
  • Ingår i: Additive Manufacturing. - Amsterdam : Elsevier. - 2214-8604 .- 2214-7810. ; 10, s. 36-42
  • Tidskriftsartikel (refereegranskat)abstract
    • Powder Bed Fusion (PBF) is a range of advanced manufacturing technologies that can fabricate three-dimensional assets directly from CAD data, on a successive layer-by-layer strategy by using thermal energy, typically from a laser source, to irradiate and fuse particles within a powder bed.The aim of this paper was to investigate the application of this advanced manufacturing technique to process ceramic multicomponent materials into 3D layered structures. The materials used matched those found on the Lunar and Martian surfaces. The indigenous extra-terrestrial Lunar and Martian materials could potentially be used for manufacturing physical assets onsite (i.e., off-world) on future planetary exploration missions and could cover a range of potential applications including: infrastructure, radiation shielding, thermal storage, etc.Two different simulants of the mineralogical and basic properties of Lunar and Martian indigenous materials were used for the purpose of this study and processed with commercially available laser additive manufacturing equipment. The results of the laser processing were investigated and quantified through mechanical hardness testing, optical and scanning electron microscopy, X-ray fluorescence spectroscopy, thermo-gravimetric analysis, spectrometry, and finally X-ray diffraction.The research resulted in the identification of a range of process parameters that resulted in the successful manufacture of three-dimensional components from Lunar and Martian ceramic multicomponent simulant materials. The feasibility of using thermal based additive manufacturing with multi-component ceramic materials has therefore been established, which represents a potential solution to off-world bulk structure manufacture for future human space exploration. © 2016 Elsevier B.V.
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14.
  • Götz, Inga Katharina, 1992-, et al. (författare)
  • Reactive metal additive manufacturing : Surface near ZrN - metallic glass composite formation and mechanical properties
  • 2023
  • Ingår i: Additive Manufacturing. - : Elsevier. - 2214-8604 .- 2214-7810. ; 66
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • ZrN formation in a Zr-based bulk metallic glass is observed after processing using reactive laser powder bed fusion. Two processing routes employing nitrogen as a reactive process gas are explored: (1) Standard inert processing in argon followed by reactive remelting in nitrogen and (2) reactive processing in nitrogen. Incorporation of nitrogen is depth-dependent and both approaches result in a dispersion of ZrN nanocrystals in the amorphous matrix close to the surface. The process parameters can be adjusted to control the volume fraction of crystalline phases formed. Hence, it is shown that reactive additive manufacturing can be utilised to form bulk metallic glass-ceramic composites in surface near regions. Thereby we demonstrate that the reactive gas atmosphere utilised during additive manufacturing enables local tailoring of structure, composition, and mechanical properties in the vicinity of the surface.
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15.
  • Hauser, Tobias, et al. (författare)
  • Material transitions within multi-material laser deposited intermetallic Iron Aluminides
  • 2020
  • Ingår i: Additive Manufacturing. - : Elsevier. - 2214-8604 .- 2214-7810. ; 34
  • Tidskriftsartikel (refereegranskat)abstract
    • Laser Metal Deposition is a near-net-shape processing technology, which allows remarkable freedom in multi-material processing. In the present work, the multi-material processing of two intermetallic iron aluminides, Fe28Al(at.%) and Fe30Al5Ti0.7B(at.%), was investigated. It has been shown that multi-material processing of the two alloys via discrete as well as via gradual material transition is possible without any cracks for manufacturing small cubes. Cross-sections of manufactured parts and tracks showed that a preheating temperature of at least 400 °C is necessary to process crack free samples. EDX-analyses indicated that if a discrete material transition is required in multi-material processing, the material transition should be implemented in the vertical build-up direction because the mixing zone in this direction is significantly smaller than the mixing zone in the horizontal direction. Due to the stronger mixing effects in the horizontal direction, a gradual material transition by a linear progression should be implemented in this direction rather than in the vertical direction. The mixing effects are mainly caused by melt flow, while diffusion effects can be neglected.
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16.
  • Hauser, Tobias, et al. (författare)
  • Oxidation in wire arc additive manufacturing of aluminium alloys
  • 2021
  • Ingår i: Additive Manufacturing. - : Elsevier. - 2214-8604 .- 2214-7810. ; 41
  • Tidskriftsartikel (refereegranskat)abstract
    • Wire Arc Additive Manufacturing is a near-net-shape machining technology that enables low-cost production of large and customised metal parts. In the present work, oxidation effects in Wire Arc Additive Manufacturing of the aluminium alloy AW4043/AlSi5(wt%) were investigated. Two main oxidation effects, the surface oxidation on aluminium parts and the oxidation anomalies in aluminium parts were observed and analysed. The surface oxidation on aluminium parts changed its colour during Wire Arc Additive Manufacturing from transparent to white. In the present work, it was shown by high-speed imaging that this change in the surface oxidation took place in the process zone, which was covered by inert gas. Since the white surface oxidation formed in an inert gas atmosphere, it was found that the arc interacts with the existing amorphous oxide layer of the previously deposited layer and turns it into a white duplex (crystalline and amorphous) oxide layer. In addition to the analysis of the white surface oxidation, oxidation anomalies, which occur at low shielding from the environment, were investigated. It was shown by physical experiments and Computational Fluid Dynamics simulations, that these oxidation anomalies occur at inadequate gas flow rates, too big nozzle-to-work distances, process modes with too high heat input, or too high wire feed rates. Finally, a monitoring method based on light emission spectroscopy was used to detect oxidation anomalies as they create peaks in the spectral emission when they occur.
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17.
  • Hauser, Tobias, et al. (författare)
  • Porosity in wire arc additive manufacturing of aluminium alloys
  • 2021
  • Ingår i: Additive Manufacturing. - : Elsevier. - 2214-8604 .- 2214-7810. ; 41
  • Tidskriftsartikel (refereegranskat)abstract
    • Wire Arc Additive Manufacturing is a near-net-shape processing technology which allows cost-effective manufacturing of large and customized metal parts. Processing of aluminium in Wire Arc Additive Manufacturing is quite challenging, especially in terms of porosity. In the present work, pore behaviour in Wire Arc Additive Manufacturing of AW4043/AlSi5(wt%) was investigated and a post-process monitoring approach was developed. It has been observed that as the shielding gas flow rate increases, the porosity in aluminium parts also increases due to the rapid solidification of the melt pool by forced convection. The higher convection rate seems to limit the escape of gas inclusions. Furthermore, gas inclusions escaping from the melt pool leave cavities on the surface of each deposited layer. Process camera imaging is used to monitor these cavities to acquire information about the porosity in the part. The observations were supported by Computational Fluid Dynamics simulations which show that the gas flow rate correlates with the porosity in aluminium parts manufactured by Wire Arc Additive Manufacturing. Since a lower gas flow rate leads to reduced convective cooling, the melt pool remains liquid for a longer period allowing pores to escape for a longer period and thus reducing porosity. Based on these investigations, a monitoring approach is presented.
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18.
  • Jadhav, Suraj Dinkar, et al. (författare)
  • Surface Modified Copper Alloy Powder for Reliable Laser-based Additive Manufacturing
  • 2020
  • Ingår i: Additive Manufacturing. - : Elsevier BV. - 2214-8604 .- 2214-7810. ; 35
  • Tidskriftsartikel (refereegranskat)abstract
    • Owing to the high optical reflectivity of copper, silver, and gold in the infrared region, high laser power is required for laser-based additive manufacturing (L-AM). This increases the risk of damaging the laser optics due to sustained back-reflections and renders L-AM of reflective metals an unsustainable technology. To tackle this issue, a novel, industrially upscalable powder surface modification method is proposed and validated using a CuCr1 alloy. The surface of CuCr1 powder is modified by the outward diffusion of chromium in a nitrogen atmosphere, forming a rim around the powder particles. This doubled the optical absorption of the powder. Consequently, a mere 20% of the laser energy is required to process the surface-modified powder by laser powder bed fusion compared to the virgin CuCr1 powder. The fabricated parts demonstrate a very high thermal conductivity of 370 ± 15 W/(m·K) and tensile strength of 439 ± 19 MPa, after applying a suitable post-heat treatment.
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19.
  • Jansson, Anton, 1986-, et al. (författare)
  • Characterisation of carbon fibre-reinforced polyamide manufactured by selective laser sintering
  • 2016
  • Ingår i: Additive Manufacturing. - Amsterdam, Netherlands : Elsevier. - 2214-8604 .- 2214-7810. ; 9, s. 7-13
  • Tidskriftsartikel (refereegranskat)abstract
    • Polymers and reinforced plastics are employed in various load-bearing applications, from household objects to aerospace products. These materials are light, strong, and relatively cheap but can be difficult to form into complex geometries. However, the development of additive manufacturing processes has made it easier to manufacture reinforced plastics in complex shapes. The aim of this work was to study the internal features and mechanical properties of carbon fibre-reinforced polyamide (CF/PA12) fabricated with the additive manufacturing technique of selective laser sintering. The test specimens were studied using computed tomography to analyse the internal geometry, and the material proved to be highly porous. Moreover, the test specimens revealed an internal layered structure, which was found to have a great effect on the tensile properties of the material. The results highlight that there is room for further optimisation of the manufacturing parameters for CF/PA12, because the layered structure makes it challenging to design end user parts with acceptable mechanical properties.
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20.
  • Kalkal, Ashish, et al. (författare)
  • Recent advances in 3D printing technologies for wearable (bio)sensors
  • 2021
  • Ingår i: Additive Manufacturing. - : ELSEVIER. - 2214-8604 .- 2214-7810. ; 46
  • Forskningsöversikt (refereegranskat)abstract
    • Wearable (bio)sensors driven through emerging three-dimensional (3D) printing technologies are currently considered the next-generation tools for various healthcare applications due to their exciting characteristics such as high stretchability, super flexibility, low cost, ultra-thinness, and lightweight. In this context, 3D printing, an emerging advanced additive manufacturing technology has revolutionized the concept of free form construction and end-user customization owing to its multifarious peculiarities that involve ease of operation, on-demand and rapid fabrication, precise and controlled deposition, as well as versatility with various soft functional materials. The customized functional structures with controllable geometry and design can be autonomously printed on the desired surfaces using the 3D printing technologies excluding the prerequisite amenities of microfabrication technologies. To accomplish this, both academics and industry experts have worked persistently to fabricate smaller, faster, and more efficient wearable devices using readily available 3D printing technologies. The contribution of 3D printing technologies in developing novel 3D structures for wearable applications using printable soft and functional materials is highlighted in this article. Moreover, the process of 3D printing along with major techniques, namely vat photopolymerization, material jetting, and material extrusion are summarized. Besides this, a number of 3D printed (bio)sensing platforms such as glucose sensors, lactate sensors, sweat sensors, strain sensors, tactile sensors, wearable oximeters, smart bandages, artificial skin, tattoo sensors, electroencephalography (EEG), electrocardiography (ECG) sensors, etc., are discussed in terms of design specifications and fabrication strategies of devices obtained via 3D printing techniques.
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21.
  • Karimi Neghlani, Paria, 1986-, et al. (författare)
  • Columnar-to-equiaxed grain transition in powder bed fusion via mimicking casting solidification and promoting in situ recrystallization
  • 2021
  • Ingår i: Additive Manufacturing. - : ELSEVIER. - 2214-8604 .- 2214-7810. ; 46
  • Tidskriftsartikel (refereegranskat)abstract
    • Columnar grain structure typically formed along the build direction in the electron beam-powder bed fusion (EBPBF) technique leads to anisotropic physical and mechanical properties. In this study, casting solidification condition was mimicked, and in situ recrystallization was promoted in EB-PBF to facilitate columnar-to-equiaxed grain structure transition in Alloy 718. This is achieved via a unique linear melting strategy coupled with a specific selection of process parameters in EB-PBF. It was found that site-specific melting using line order number (LON) function affected the cooling rate and temperature gradient, which controlled grain morphology and texture. A high LON resulted in a large equiaxed grain zone with a random texture, whereas a fixed LON with a high areal energy density led to a strong texture. The main driving force in the formation of cracks and shrinkage defects during the transition was investigated. A high LON at a fixed areal energy density reduced the average total shrinkage defects and crack length. The hardness was decreased through the transition, which was linked to the reduction in the size of the gamma ‘’ precipitates.
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22.
  • Karimi Neghlani, Paria, 1986-, et al. (författare)
  • Contour design to improve topographical and microstructural characteristics of Alloy 718 manufactured by electron beam-powder bed fusion technique
  • 2020
  • Ingår i: Additive Manufacturing. - : Elsevier BV. - 2214-8604 .- 2214-7810. ; 32
  • Tidskriftsartikel (refereegranskat)abstract
    • Additive manufacturing (AM) processes are being frequently used in industry as they allow the manufacture ofcomplex parts with reduced lead times. Electron beam-powder bed fusion (EB-PBF) as an AM technology isknown for its near-net-shape production capacity with low residual stress. However, the surface quality andgeometrical accuracy of the manufactured parts are major obstacles for the wider industrial adoption of thistechnology, especially when enhanced mechanical performance is taken into consideration. Identifying theorigins of surface features such as satellite particles and sharp valleys on the parts manufactured by EB-PBF isimportant for a better understanding of the process and its capability. Moreover, understanding the influence ofthe contour melting strategy, by altering process parameters, on the surface roughness of the parts and thenumber of near-surface defects is highly critical. In this study, processing parameters of the EB-PBF techniquesuch as scanning speed, beam current, focus offset, and number of contours (one or two) with the linear meltingstrategy were investigated. A sample manufactured using Arcam-recommended process parameters (threecontours with the spot melting strategy) was used as a reference. For the samples with one contour, the scanningspeed had the greatest effect on the arithmetical mean height (Sa), and for the samples with two contours, thebeam current and focus offset had the greatest effect. For the samples with two contours, a lower focus offset andlower scan speed (at a higher beam current) resulted in a lower Sa; however, increasing the scan speed for thesamples with one contour decreased Sa. In general, the samples with two contours provided a lower Sa (∼22 %)but with slightly higher porosity (∼8 %) compared to the samples with one contour. Fewer defects were detected with a lower scanning speed and higher beam current. The number of defects and the Sa value for thesamples with two contours manufactured using the linear melting strategy were ∼85 % and 16 %, respectively,lower than those of the reference samples manufactured using the spot melting strategy.
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23.
  • Karlsson, Dennis, et al. (författare)
  • Additive manufacturing of the ferritic stainless steel SS441
  • 2020
  • Ingår i: Additive Manufacturing. - AMSTERDAM, NETHERLANDS : Elsevier BV. - 2214-8604 .- 2214-7810. ; 36
  • Tidskriftsartikel (refereegranskat)abstract
    • In this study, the ferritic stainless steel SS441 was produced with excellent mechanical properties using laser powder bed fusion (L-PBF) compared to samples produced by conventional casting and hot-rolling. In addition, thermodynamic calculations were utilized to study the phase stability at elevated temperatures and to understand the solidification behavior. The hot-rolled sample showed a grain size up to several hundred mu m with additional precipitates of TiN and Nb(C,N). In contrast, the as-built L-PBF samples displayed a grain size in the mu m range. Spherical precipitates with a size of around 50 nm could be observed and were attributed to a corundum phase from the thermodynamic calculations. The printed material shows superior mechanical properties, with more than 30 times higher impact energy compared to the hot-rolled alloy (217 +/- 5 J vs. 7 +/- 0.5 J). Furthermore, the properties are anisotropic for the L-PBF produced alloy, with the highest tensile strength vertical to the build direction. The superior mechanical properties of the L-PBF produced sample can be attributed to a smaller grain size, giving a higher strength according to the Hall-Petch relationship. The anisotropy of the material can be eliminated by heat treatments at 900 degrees C followed by water quenching, but the absolute strength decreases slightly due to formation of intermetallic phases such as Nb(C,N) and the Fe2Nb Laves phase. The results clearly illustrates that L-PBF provides a promising manufacturing mute for enhanced strength of ferritic stainless steels.
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24.
  • Karlsson, Dennis, et al. (författare)
  • Binder jetting of the AlCoCrFeNi alloy
  • 2019
  • Ingår i: Additive Manufacturing. - : Elsevier. - 2214-8604 .- 2214-7810. ; 27, s. 72-79
  • Tidskriftsartikel (refereegranskat)abstract
    • High density components of an AlCoCrFeNi alloy, often described as a high-entropy alloy, were manufactured by binder jetting followed by sintering. Thermodynamic calculations using the CALPHAD approach show that the high-entropy alloy is only stable as a single phase in a narrow temperature range below the melting point. At all other temperatures, the alloy will form a mixture of phases, including a sigma phase, which can strongly influence the mechanical properties. The phase stabilities in built AlCoCrFeNi components were investigated by comparing the as-sintered samples with the post-sintering annealed samples at temperatures between 900 °C and 1300 °C. The as-sintered material shows a dominant B2/bcc structure with additional fcc phase in the grain boundaries and sigma phase precipitating in the grain interior. Annealing experiments between 1000 °C and 1100 °C inhibit the sigma phase and only a B2/bcc phase with a fcc phase is observed. Increasing the temperature further suppresses the fcc phase in favor for the B2/bcc phases. The mechanical properties are, as expected, dependent on the annealing temperature, with the higher annealing temperature giving an increase in yield strength from 1203 MPa to 1461 MPa and fracture strength from 1996 MPa to 2272 MPa. This can be explained by a hierarchical microstructure with nano-sized precipitates at higher annealing temperatures. The results enlighten the importance of microstructure control, which can be utilized in order to tune the mechanical properties of these alloys. Furthermore, an excellent oxidation resistance was observed with oxide layers with a thickness of less than 5 μm after 20 h annealing at 1200 °C, which would be of great importance for industrial applications.
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25.
  • Karlsson, Joakim, 1984-, et al. (författare)
  • Thickness dependency of mechanical properties for thin-walled titanium parts manufactured by Electron Beam Melting (EBM®)
  • 2024
  • Ingår i: Additive Manufacturing. - : Elsevier. - 2214-8604 .- 2214-7810.
  • Tidskriftsartikel (refereegranskat)abstract
    • Metal powder bed additive manufacturing technologies, such as the Electron Beam Melting process, facilitate a high degree of geometric flexibility and have been demonstrated as useful production techniques for metallic parts.  However, the EBM process is typically associated with lower resolutions and higher surface roughness compared to similar laser-based powder bed metal processes. In part, this difference is related to the larger powder size distribution and thicker layers normally use As part of an effort to improve the resolution and surface roughness of EBM fabricated components, this study investigates the feasibility of fabricating components with a smaller powder size fraction and layer thickness (similar to laser based processes). The surface morphology, microstructure and tensile properties of the produced samples were evaluated. The findings indicate that microstructure is dependent on wall-thickness and that, for thin walled structures, tensile properties can become dominated by variations in surface roughness.
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26.
  • Karlsson, Joakim, 1984-, et al. (författare)
  • Thickness dependency of surface properties for thin-walled titanium parts manufactured by Electron Beam Melting (EBM®)
  • Ingår i: Additive Manufacturing. - 2214-8604 .- 2214-7810.
  • Tidskriftsartikel (refereegranskat)abstract
    • The surface morphology of components produced by powder bed metal additive manufacturing is of interest for multiple industry sectors including biomedical and aerospace.  For some applications, improvements in surface finish can reduce or eliminate the requirement for secondary finishing processes. In this study, titanium alloy (Ti6Al4V) samples were manufactured using the Electron Beam Melting (EBM) process. The effect of variations in sample thickness, powder size distribution and layer thickness were measured with three different techniques, both for direct measurement and comparison of the techniques.  Ra-values in the range of 15 µm – 37 µm were obtained and varied depending on measurement technique. However, independent of technique, Ra values were found to be dependent on powder size distribution, build layer thickness, and wall thickness. Analytical transmission electron microscopy of cross sections prepared by focused ion beam milling revealed that the outermost surfaces consisted of an oxide layer of 5 nm -6 nm thickness.
  •  
27.
  • Kumara, Chamara, et al. (författare)
  • Microstructure modelling of laser metal powder directed energy deposition of alloy 718
  • 2019
  • Ingår i: Additive Manufacturing. - : Elsevier. - 2214-8604 .- 2214-7810. ; 25, s. 357-364
  • Tidskriftsartikel (refereegranskat)abstract
    • A multi-component and multi-phase-field modelling approach, combined with transformation kinetics modelling, was used to model microstructure evolution during laser metal powder directed energy deposition of Alloy 718 and subsequent heat treatments. Experimental temperature measurements were utilised to predict microstructural evolution during successive addition of layers. Segregation of alloying elements as well as formation of Laves and δ phase was specifically modelled. The predicted elemental concentrations were then used in transformation kinetics to estimate changes in Continuous Cooling Transformation (CCT) and Time Temperature Transformation (TTT) diagrams for Alloy 718. Modelling results showed good agreement with experimentally observed phase evolution within the microstructure. The results indicate that the approach can be a valuable tool, both for improving process understanding and for process development including subsequent heat treatment.
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28.
  • Lane, Brandon, et al. (författare)
  • Transient Laser Energy Absorption, Co-axial Melt Pool Monitoring, and Relationship to Melt Pool Morphology
  • 2020
  • Ingår i: Additive Manufacturing. - : Elsevier. - 2214-8604 .- 2214-7810. ; 36
  • Tidskriftsartikel (refereegranskat)abstract
    • Melt pool monitoring (MPM) is a technique used in laser powder bed fusion (LPBF) to extract features from insitu sensor signals that correlate to defect formation or general part fabrication quality. Various melt pool phenomena have been shown to relate to measured transient absorption of the laser energy, which in turn, can be relatable to the melt pool emission measured in MPM systems. This paper describes use of a reflectometer-based instrument to measure the dynamic laser energy absorption during single-line laser scans. Scans are conducted on bare metal and single powder layer of nickel alloy 625 (IN625) at a range of laser powers. In addition, a photodetector aligned co-axially with the laser, often found in commercial LPBF monitoring systems, synchronously measured of the incandescent emission from the melt pool with the dynamic laser absorption. Relationships between the dynamic laser absorption, co-axial MPM, and surface features on the tracks are observed, providing illustration of the melt pool dynamics that formed these features. Time-integrated measurements of laser absorption are shown to correlate well with MPM signal, as well as indicate the transition between conduction and keyhole mode. This transition is corroborated by metallographic cross-section measurement, as well as topographic measurements of the solidified tracks. Ultimately, this paper exemplifies the utility of dynamic laser absorption measurements to inform both the physical nature of the melt pool dynamics, as well as interpretation of process monitoring signals.
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29.
  • Lefebvre, L. P., et al. (författare)
  • Assessing the robustness of powder rheology and permeability measurements
  • 2020
  • Ingår i: Additive Manufacturing. - : Elsevier B.V.. - 2214-8604 .- 2214-7810. ; 35
  • Tidskriftsartikel (refereegranskat)abstract
    • Powder metallurgy processes rely on powder flowability. However, flowability is not an intrinsic property and depends on the measurement conditions. Standards have been developed to adjust measurement methods to various flow conditions but there is presently questions whether current methods are adapted to the specific requirements of powder bed additive manufacturing. Rheology has been used to assess powder flowability but there is still limited information available on the robustness of the method. This paper presents the flow characteristics measured in five laboratories with a powder rheometer. Attempts were made to understand the sources of intra and inter laboratory variations and find ways to reduce them. The variations do not seem to be associated with sampling or environmental conditions. Experimental setup, calibration and/or the modification of the powder during handling could be associated with the variations observed. However, additional tests would be required to confirm the sources and improve the repeatability of the measurements.
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30.
  • Lin, Danyang, et al. (författare)
  • A Si-containing FeCoCrNi high-entropy alloy with high strength and ductility synthesized in situ via selective laser melting
  • 2020
  • Ingår i: Additive Manufacturing. - : Elsevier. - 2214-8604 .- 2214-7810. ; 35
  • Tidskriftsartikel (refereegranskat)abstract
    • To widen the applications of new materials in additive manufacturing (AM), the traditional method of printing using pre-alloyed powders should be improved because the pre-alloying process is expensive and makes it difficult to adjust the composition of new materials. This study investigates the synthesis of a FeCoCrNi high-entropy alloy (HEA) containing 1.5 at.% Si in situ using selective laser melting (SLM). A remelting strategy and process optimization based on polynomial regression modeling allowed for the printing of almost fully dense (99.78 %) samples. The samples comprised columnar grains, each containing numerous subgrains of a single-phase face-centered cubic solid solution. No precipitation or segregation were observed. The room temperature tensile properties of the samples were excellent, with yields and tensile strengths reaching 701 +/- 14 and 907 +/- 25 MPa, respectively, and an elongation at fracture of 30.8 +/- 2%. These properties were attributed to solid solution strengthening and novel dislocation loop strengthening mechanism. These findings demonstrate that HEAs with a high relative density and good mechanical properties can be directly synthesized by SLM using inexpensive pure metal powders, thereby extending the application potential of AM to manufacture new materials.
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31.
  • Lindberg, Anders, et al. (författare)
  • Mechanical performance of polymer powder bed fused objects - FEM simulation and verification
  • 2018
  • Ingår i: Additive Manufacturing. - : ELSEVIER SCIENCE BV. - 2214-8604 .- 2214-7810. ; 24, s. 577-586
  • Tidskriftsartikel (refereegranskat)abstract
    • Additive manufacturing (3D printing) enables the designing and producing of complex geometries in a layer-by layer approach. The layered structure leads to anisotropic behaviour in the material. To accommodate anisotropic behaviour, geometrical optimization is needed so that the 3D printed object meets the pre-set strength and quality requirements. In this article a material description for polymer powder bed fused also or selective laser sintered (SLS) PA12 (Nylon-12), which is a common 3D printing plastic, was investigated, using the Finite Element Method (FEM). The Material Model parameters were obtained by matching them to the test results of multipurpose test specimens (dumb-bells or dog bones) and the model was then used to simulate/predict the mechanical performance of the SLS printed lower-leg prosthesis components, pylon and support. For verification purposes, two FEM designs for a support were SLS printed together with additional test specimens in order to validate the used Material Model. The SLS printed prosthesis pieces were tested according to ISO 10328 Standard. The FEM simulations, together with the Material Model, was found to give good estimations for the location of a failure and its load. It was also noted that there were significant variations among individual SLS printed test specimens, which impacted on the material parameters and the FEM simulations. Hence, to enable reliable FEM simulations for the designing of 3D printed products, better control of the SLS process with regards to porosity, pore morphology and pore distribution is needed.
  •  
32.
  • Lindgren, Lars-Erik, et al. (författare)
  • Simulation of additive manufacturing using coupled constitutive and microstructure models
  • 2016
  • Ingår i: Additive Manufacturing. - : Elsevier. - 2214-8604 .- 2214-7810. ; 12:Part B, s. 144-158
  • Tidskriftsartikel (refereegranskat)abstract
    • The paper describes the application of modeling approaches used in Computational Welding Mechanics (CWM) applicable for simulating Additive Manufacturing (AM). It focuses on the approximation of the behavior in the process zone and the behavior of the solid material, particularly in the context of changing microstructure. Two examples are shown, one for the precipitation hardening Alloy 718 and one for Ti-6Al-4V. The latter alloy is subject to phase changes due to the thermal cycling
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33.
  • Lindwall, Johan, et al. (författare)
  • Thermal simulation and phase modeling of bulk metallic glass in the powder bed fusion process
  • 2019
  • Ingår i: Additive Manufacturing. - : Elsevier. - 2214-8604 .- 2214-7810. ; 27, s. 345-352
  • Tidskriftsartikel (refereegranskat)abstract
    • One of the major challenges with the powder bed fusion process (PBF) and formation of bulk metallic glass (BMG) is the development of process parameters for a stable process and a defect-free component. The focus of this study is to predict formation of a crystalline phase in the glass forming alloy AMZ4 during PBF. The approach combines a thermal finite element model for prediction of the temperature field and a phase model for prediction of crystallization and devitrification. The challenge to simulate the complexity of the heat source has been addressed by utilizing temporal reduction in a layer-by-layer fashion by a simplified heat source model. The heat source model considers the laser power, penetration depth and hatch spacing and is represented by a volumetric heat density equation in one dimension. The phase model is developed and calibrated to DSC measurements at varying heating rates. It can predict the formation of crystalline phase during the non-isothermal process. Results indicate that a critical location for devitrification is located a few layers beneath the top surface. The peak is four layers down where the crystalline volume fraction reaches 4.8% when 50 layers are built.
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34.
  • Marattukalam, Jithin J., et al. (författare)
  • Development of process parameters for selective laser melting of a Zr-based bulk metallic glass
  • 2020
  • Ingår i: Additive Manufacturing. - : Elsevier. - 2214-8604 .- 2214-7810. ; 33
  • Tidskriftsartikel (refereegranskat)abstract
    • Parameters for selective laser melting of Zr59.3Cu28.8Al10.4Nb1.5 (trade name AMZ4), allowing crack-free bulk metallic glass with low porosity, have been developed. The phase formation was found to be strongly influenced by the heating power of the laser. X-ray amorphous samples were obtained with laser power at and below 75 W. The as-processed bulk metallic glass was found to devitrify by a two-stage crystallization process within which the presence of oxygen was concluded to play an essential role. At laser powers above 75 W, the observed crystallites were found to be a cubic phase (Cu2Zr4O). The hardness and Young’s modulus in the as-processed samples was found to increase marginally with increased fraction of the crystalline phase.
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35.
  • Marschner, David E., et al. (författare)
  • A methodology for two-photon polymerization micro 3D printing of objects with long overhanging structures
  • 2023
  • Ingår i: Additive Manufacturing. - : Elsevier BV. - 2214-8604 .- 2214-7810. ; 66
  • Tidskriftsartikel (refereegranskat)abstract
    • 3D printing by two-photon polymerization (TPP) is a well-established manufacturing approach for realizing 3D polymer structures at the micro- and nanoscale. However, an important shortcoming of 3D printing by two-photon polymerization is that it is extremely challenging to print 3D objects with long overhanging features, which severely limits the application space of this technology. Here, we introduce a methodology for 3D printing by two-photon polymerization that allows the realization of 3D objects with long overhanging structures that cannot be printed using conventional printing strategies. Our methodology combines different printing approaches for realizing the overhanging structure, including locally adjusted printing block sizes and a mix of the Shell & Scaffold and Solid printing modes. As a result, objects with long overhanging parts can be printed without the need for added support structures. Using this approach, we demonstrate successful printing of overhanging cantilevers with a quadratic cross-section of 50 µm x 50 µm and lengths of up to 1000 µm. Thus, our printing modality substantially extends the capabilities and application space of 3D printing by two-photon polymerization and removes current design limitations regarding 3D printed objects with long overhanging structures.
  •  
36.
  • Morales Lopez, Alvaro, et al. (författare)
  • Monitoring and classification of polymeric surface features for enabling the adoption of polypropylene powder bed fusion as a standard tool for bioprocessing equipment production
  • 2023
  • Ingår i: Additive Manufacturing. - : Elsevier BV. - 2214-8604 .- 2214-7810. ; 72
  • Tidskriftsartikel (refereegranskat)abstract
    • Polypropylene (PP) powder bed fusion (PBF) with subsequent mechanical postprocessing can enable the development of more efficient and effective surfaces for bioprocessing equipment. However, there is still a lack of knowledge regarding the most relevant surface differences when compared to standardized surfaces. Herein, we present a new systematic methodology, including the evaluation of relevant roughness parameters and surface wettability, which has been implemented to assess the potential of AM to produce biopharmaceutical components. Surfaces of PP components produced by PBF and mechanically postprocessed by tumble surface finishing at 5, 10 and 15 h were compared to reference surfaces produced by computer numerical control (CNC) milling manufacturing. Thirteen roughness parameters were found to be relevant, of which the arithmetic mean peak curvature (Spc) and the density of peaks (Spd) were the most significant. The results demonstrate that the reference surfaces had Spc and Spd values of 1029 ± 36 mm−1 and 67739 ± 5440 mm−2, respectively, and moderate wettability with advancing (ACA) and receding (RCA) contact angles of 89 ± 3° and 68 ± 2°, respectively. The as-printed PBF surfaces were hydrophobic, with ACA of 119 ± 2° and RCA of 107 ± 4°, and with Spc and Spd values of 1089 ± 110 mm−1 and 30078 ± 4325 mm−2, respectively. PBF surfaces switched to a hydrophilic surface of 67 ± 3° and 44 ± 4° when the tumble surface finishing time was increased to 15 h. By taking advantage of this knowledge, we could produce surfaces using PBF and 5 h of mechanical postprocessing, which mimicked surface wetting and had Spc of 1100 ± 68 mm−1 and Spd of 55702 ± 9477 mm−2, similar to that of the CNC milling manufacturing. The developed comparative method and the results are important to better understand AM surfaces and can be used to transfer manufacturing from subtractive to additive technologies.
  •  
37.
  • Moustafa, Abdel R., et al. (författare)
  • Scheil ternary projection (STeP) diagrams for designing additively manufactured functionally graded metals
  • 2020
  • Ingår i: Additive Manufacturing. - : Elsevier BV. - 2214-8604 .- 2214-7810. ; 32
  • Tidskriftsartikel (refereegranskat)abstract
    • Functionally graded metals fabricated using high-temperature additive manufacturing can form intermetallics that fracture during printing due to thermal stresses generated by the heat source. To address this problem, we introduce a new class of non-equilibrium phase diagrams, termed Scheil Ternary Projection (STeP) diagrams, for designing optimal composition gradients that avoid brittle phases. Using the Fe-Cr-Al ternary as a model system, we compare the phase fields in equilibrium and STeP diagrams to show that intermetallic phase fields are dramatically expanded under the rapid solidification conditions in melt-based additive manufacturing, an important effect that must be accounted for when designing composition gradients.
  •  
38.
  • Neikter, Magnus, 1988-, et al. (författare)
  • Alpha texture variations in additive manufactured Ti-6Al-4V investigated with neutron diffraction
  • 2018
  • Ingår i: Additive Manufacturing. - : Elsevier. - 2214-8604 .- 2214-7810. ; 23, s. 225-234
  • Tidskriftsartikel (refereegranskat)abstract
    • Variation of texture in Ti-6Al-4V samples produced by three different additive manufacturing (AM) processes has been studied by neutron time-of-flight (TOF) diffraction. The investigated AM processes were electron beam melting (EBM), selective laser melting (SLM) and laser metal wire deposition (LMwD). Additionally, for the LMwD material separate measurements were done on samples from the top and bottom pieces in order to detect potential texture variations between areas close to and distant from the supporting substrate in the manufacturing process. Electron backscattered diffraction (EBSD) was also performed on material parallel and perpendicular to the build direction to characterize the microstructure. Understanding the context of texture for AM processes is of significant relevance as texture can be linked to anisotropic mechanical behavior. It was found that LMwD had the strongest texture while the two powder bed fusion (PBF) processes EBM and SLM displayed comparatively weaker texture. The texture of EBM and SLM was of the same order of magnitude. These results correlate well with previous microstructural studies. Additionally, texture variations were found in the LMwD sample, where the part closest to the substrate featured stronger texture than the corresponding top part. The crystal direction of the α phase with the strongest texture component was [112¯3]. © 2018 Elsevier B.V.
  •  
39.
  • Noll, I., et al. (författare)
  • A micromechanically motivated multiscale approach for residual distortion in laser powder bed fusion processes
  • 2022
  • Ingår i: Additive Manufacturing. - : Elsevier BV. - 2214-7810 .- 2214-8604. ; 60
  • Tidskriftsartikel (refereegranskat)abstract
    • For the broader industrial usage of metal additive manufactured parts, especially made by laser powder bed fusion, a better prediction and understanding of the warpage and of eigenstresses within the final part are necessary. Due to the diverse and sophisticated metallurgical and thermal processes during production, physically motivated simulations are rather complex and time consuming. Therefore, various simplifications concerning the process and material models are frequently made, which leads to practicable simulation times at the expense of physical accuracy. This motivates the procedure in this contribution: A multiscale approach combining various modelling levels, in particular regarding the heat source and material model. The model is based on three finite element simulations on different levels and with different specific aims, i.e. the laser scan model, the layer hatch model and the part model. For the smallest scale considered, a sophisticated thermomechanically fully coupled model based on a phase transformation model explicitly considering the powder, molten, and re-solidified material is incorporated. The goal of this detailed simulation is to extract an effective heat source for the next level of simulation, i.e. the layer hatch model. The layer hatch model is used to extract the inherent strains for the part model. With these strains, the remaining deformation and eigenstresses of arbitrary large parts with the same material and laser parameters can be efficiently and directly computed. The capabilities of the present framework are investigated by simulations on the behaviour of a twin cantilever beam, where the effect of different process parameters on the overall material and structural response is carried out.
  •  
40.
  • Pant, Prabhat, 1990-, et al. (författare)
  • Mapping of residual stresses in as-built Inconel 718 fabricated by laser powder bed fusion : A neutron diffraction study of build orientation influence on residual stresses
  • 2020
  • Ingår i: Additive Manufacturing. - : Elsevier B.V.. - 2214-8604 .- 2214-7810. ; 36
  • Tidskriftsartikel (refereegranskat)abstract
    • Manufacturing of functional (ready to use) parts with the powder bed fusion method has seen an increase in recent times in the field of aerospace and in the medical sector. Residual stresses (RS) induced due to the process itself can lead to defects like cracks and delamination in the part leading to the inferior quality of the part. These RS are one of the main reasons preventing the process from being adopted widely. The powder bed methods have several processing parameters that can be optimized for improving the quality of the component, among which, build orientation is one. In this current study, influence of the build orientation on the residual stress distribution for the Ni-based super-alloy Inconel 718 fabricated by laser-based powder bed fusion method is studied by non- destructive technique of neutron diffraction at selected cross-sections. Further, RS generated in the entire part was predicted using a simplified layer by layer approach using a finite element (FE) based thermo-mechanical numerical model. From the experiment, the part printed in horizontal orientation has shown the least amount of stress in all three directions and a general tendency of compressive RS at the center of the part and tensile RS near the surface was observed in all the samples. The build with vertical orientation has shown the highest amount of RS in both compression and tension. Simplified simulations results are in good agreement with the experimental value of the stresses. © 2020 The Authors
  •  
41.
  • Radulov, I. A., et al. (författare)
  • Production of net-shape Mn-Al permanent magnets by electron beam melting
  • 2019
  • Ingår i: Additive Manufacturing. - : Elsevier BV. - 2214-8604 .- 2214-7810. ; 30
  • Tidskriftsartikel (refereegranskat)abstract
    • The main goal of this work is the adoption of additive manufacturing for the production of inexpensive rare-earth free MnAl-based permanent magnets. The use of more advanced binder-free additive manufacturing technique such as Electron Beam Melting (EBM) allows obtaining fully-dense magnetic materials with advanced topology and complex shapes. We focus on the feasibility of controlling the phase formation in additively manufactured Mn-Al alloys by employing post-manufacturing heat treatment. The as-manufactured EBM samples contain 8% of the desired ferromagnetic τ-MnAl phase. After the optimized annealing treatment, the content of the τ-phase was increased to 90%. This sample has a coercivity value of 0.15 T, which is also the maximum achieved in conventionally produced binary MnAl magnets. Moreover, the EBM samples are fully dense and have the same density as the samples produced by conventional melting density. 
  •  
42.
  • Rännar, Lars-Erik, 1973-, et al. (författare)
  • Hierarchical structures of stainless steel 316L manufactured by Electron Beam Melting
  • 2017
  • Ingår i: Additive Manufacturing. - : Elsevier BV. - 2214-8604 .- 2214-7810. ; 17, s. 106-112
  • Tidskriftsartikel (refereegranskat)abstract
    • One of the serious obstacles preventing wide industrial use of additive manufacturing (AM) in metals and alloys is a lack of materials available for this technology. It is particularly true for the Electron Beam Melting (EBM®) process, where only a few materials are commercially available, which significantly limits the use of the method. One of the dominant trends in AM today is developing processes for technological materials already widely used by other methods and developed for other industrial applications, gaining further advantages through the unique value added by additive manufacturing. Developing new materials specifically for additive manufacturing that can utilize the properties and specifics of the method in full is still a research and development subject, and such materials are yet far from full scale industrial usage. Stainless steels are widely used in industry due to good mechanical properties, corrosion resistance and low cost of material. Hence, there is potentially a market for this material and one possible business driver compared with casting for example is that lead times could be cut drastically by utilizing an additive approach for one-off or small series production. This paper presents results from the additive manufacturing of components from the known alloy 316L using EBM®. Previously the samples of 316L were made by laser-based AM technology. This work was performed as a part of the large project with the long term aim to use additively manufactured components in a nuclear fusion reactor. Components and test samples successfully made from 316L stainless steel using EBM® process show promising mechanical properties, density and hardness compared to its counterpart made by powder metallurgy (hot isostatic pressing, HIP). As with the other materials made by EBM® process, 316L samples show rather low porosity. Present paper also reports on the hierarchical microstructure features of the 316L material processed by EBM® characterized by optical and electron microscopy.
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43.
  • Sadeghi, Esmaeil, 1985-, et al. (författare)
  • Inclusion-induced fatigue crack initiation in powder bed fusion of Alloy 718
  • 2020
  • Ingår i: Additive Manufacturing. - : Elsevier B.V.. - 2214-8604 .- 2214-7810. ; 36
  • Tidskriftsartikel (refereegranskat)abstract
    • Fatigue crack initiation of Alloy 718 additively manufactured via electron beam-powder bed fusion (EB-PBF) process was investigated. The melt parameters were chosen to achieve sufficient energy input and minimize process-induced defects. A line offset of 200 µm with enough line energy was used, leading to the formation of wide and deep melt pools. This strategy facilitated the formation of equiaxed grains at the melt pools bottom, and short columnar grains within the melt pools aligned parallel to the build direction. The mixed grain morphology and texture were retained after various thermal post-treatments, including heat treatment (HT), hot isostatic pressing (HIP), and HIP-HT. Micron-sized non-metallic inclusions in the feedstock powder, such as Al-rich oxide and titanium nitride clustered during the EB-PBF process, and remained intact during the post-treatments. Low cycle fatigue cracks mainly originated from the non-metallic inclusions found near the surface of the test specimens. HIPing was able to remove a portion of the internal defects, including round-shaped and shrinkage pores; therefore, a small fatigue life enhancement was observed in HIP-HT compared to HT.
  •  
44.
  • Saeidi, Kamran, et al. (författare)
  • Ultra-high strength martensitic 420 stainless steel with high ductility
  • 2019
  • Ingår i: Additive Manufacturing. - : Elsevier. - 2214-8604 .- 2214-7810. ; 29
  • Tidskriftsartikel (refereegranskat)abstract
    • Martensitic 420 stainless steel was successfully fabricated by Selective laser melting(SLM) with >99% relative density and high mechanical strength of 1670 MPa, yield strength of 600 MPa and elongation of 3.5%. X-ray diffraction (XRD) and scanning electron microscopy disclosed that the microstructure of SLM 420 consisted of colonies of 0.5–1 μm sized cells and submicron martensitic needles with 11 wt. % austenite. Tempering of as-built SLM 420 stainless steel at 400 °C resulted in ultra-high strength material with high ductility. Ultimate tensile strength of 1800 MPa and yield strength of 1400 MPa were recorded with an elongation of 25%. Phase transformation analysis was carried out using Rietveld refinement of XRD data and electron backscattered diffraction (EBSD), which showed the transformation of martensite to austenite, and resulted in austenite content of 36 wt. % in tempered SLM 420 stainless steel. Transformation induced plasticity (TRIP), austenite formation and fine cellular substructure along with sub-micron martensite needles resulted in stainless steel with high tensile strength and ductility. The advanced mechanical properties were compared with conventionally made ultra-high-strength steels, and the microstructure-properties relationships were disclosed.
  •  
45.
  • Stenlund, Patrik, et al. (författare)
  • Osseointegration Enhancement by Zr doping of Co-Cr-Mo Implants Fabricated by Electron Beam Melting
  • 2015
  • Ingår i: Additive Manufacturing. - : Elsevier BV. - 2214-8604 .- 2214-7810. ; 6, s. 6-15
  • Tidskriftsartikel (refereegranskat)abstract
    • Direct osseous healing to prosthetic components is a prerequisite for the clinical success of uncemented treatment in total hip replacements (THR). The demands imposed on the material properties are constantly being stepped up to withstand the impact of an active lifestyle and ensure lifelong integration. Cobalt–chromium–molybdenum (Co-Cr-Mo) materials are interesting for their excellent mechanical stability, corrosion resistance and possibility to be produced by additive manufacturing into complex designs with modifiable stiffness. The bone response to Co-Cr-Mo is regarded as inferior to that of titanium and are usually cemented in THR. The hypothesis in the present study was that a low amount of Zr in the Co-Cr-Mo alloy would improve the bone response and biomechanical anchorage. The results showed significantly higher implant stability for the Co-Cr-Mo alloy with an addition of 0.04% Zr after eight weeks of healing in rabbits, while no major differences were observed in the amount of bone formed around the implants. Further, bone tissue grew into surface irregularities and in direct contact with the implant surfaces. It is concluded that additively manufactured Co-Cr-Mo alloy implants osseointegrate and that the addition of a low amount of Zr to the bulk Co-Cr-Mo further improves the bone anchorage.
  •  
46.
  • Verbelen, Leander, et al. (författare)
  • Analysis of the material properties involved in laser sintering of thermoplastic polyurethane
  • 2017
  • Ingår i: Additive Manufacturing. - : Elsevier BV. - 2214-8604 .- 2214-7810. ; 15, s. 12-19
  • Tidskriftsartikel (refereegranskat)abstract
    • As laser sintering is increasingly being used for the production of actual end-use parts, there is considerable interest in developing materials that would enable new applications for this technique. Considering their properties and current applications, elastomeric polymers such as thermoplastic polyurethanes (TPU) have a very high potential in this regard. This study investigates the material properties that are involved in TPU sintering through the analysis of four distinct TPU grades. Examined parameters include powder flow, rheology of the melt and shrinkage and hardening behavior. It is found that, even though the particle morphology is not optimum, smooth and dense powder layers can be deposited for the investigated powders. Low melt viscosity and low shrinkage upon hardening further enable these materials to be easily processed into functional parts. Remaining issues, however, are part porosity and material degradation. The findings in this study provide clear links between material properties and behavior during laser sintering, and result in guidelines for future selection of TPU grades.
  •  
47.
  • Vilardell, Anna M., et al. (författare)
  • Manufacturing and characterization of in-situ alloyed Ti6Al4V(ELI)-3 at.% Cu by laser powder bed fusion
  • 2020
  • Ingår i: Additive Manufacturing. - : Elsevier. - 2214-8604 .- 2214-7810. ; 36, s. 1-14
  • Tidskriftsartikel (refereegranskat)abstract
    • Biofunctionalization of Ti6Al4V alloy with metallic agents like Ag or Cu is a promising approach to add antibacterial properties and thus to reduce the risk of implant failure. This research investigates the in-situ alloying of Ti6Al4V(ELI) with 3 at.% Cu powders using Laser Powder Bed Fusion (L-PBF). The morphology and geometrical characteristics of the single tracks and layers were studied. Laser powers of 170 W and 340 W, and scanning speeds ranging from 0.4 to 1.4 m/s and 0.8-2.8 m/s were implemented. Single track results showed balling effect and humping at high scanning speeds, 1.4 m/s and 1.6 m/s, for each laser powder respectively. Conversely, keyhole formation occurred at lower scanning speeds of 0.4-0.6 m/s for 170 W laser power, and below and 0.8 m/s for 340 W laser power. For both laser powers, single layers resulted in smoother surfaces at lower scanning speeds. These results were used for the development of optimal process parameters for 3D cubes with 99.9 % density. Optimal process parameters were found for 170 W and 340W laser powders at 0.7-0.9 and 1.0-1.2 m/s scanning speeds, respectively.In-situ alloying by L-PBF was challenging and a homogeneous distribution of Cu within the alloy was hard to achieve. The increase in laser power from 170 to 340 W resulted in small increase in homogenization. Microstructural analyses after stress-relieving treatment showed the presence of alpha' and beta phases, as well as CuTi2 intermetallic precipitates. The finer microstructure together with CuTi2 intermetallic precipitates resulted in an increase in hardness. This study demonstrates the potential for printing in-situ alloyed Ti6Al4V(ELI)- 3 at.% Cu for biomedical applications. However, further studies are required to determine the effectiveness of antibacterial properties.
  •  
48.
  • Xu, Jinghao, 1992-, et al. (författare)
  • Effect of post-processes on the microstructure and mechanical properties of laser powder bed fused IN718 superalloy
  • 2021
  • Ingår i: Additive Manufacturing. - : Elsevier B.V.. - 2214-8604 .- 2214-7810. ; 48
  • Tidskriftsartikel (refereegranskat)abstract
    • The post-processing on the additively manufactured component is of huge interest as the key to tailor the microstructure to obtain certain mechanical properties. In this present study, the effects of hot isostatic pressing, as well as heat treatment on the microstructure, phase configuration and mechanical properties of laser powder bed fused (LPBF) IN718 superalloy were systematically investigated. Three different post-processes were studied such as hot isostatic pressing (HIP), heat treatment (HT), and HIP followed by HT (HIP+HT). The HIP process effectively eliminated the Laves phase remained in the as-built microstructure and brought uniformly distributed super fine γ″ precipitates in nano-meter size. In the heat-treated microstructure, larger γ″ precipitates were promoted directly from the as-built material. In comparison the HIP+HT process caused a moderate growth of γ″. In the latter two cases, the developed γ″ significantly strengthened the material. Yield strength of IN718 was increased from 738 MPa in as-built condition to 1015 MPa and 1184 MPa after HT and HIP+HT, respectively. On the contrary the ductility in the as-built IN718 condition was reduced by more than 40% after HT and HIP+HT. This can be compared to an increase in the ductility by almost 30% when subjected the as-built specimens to only HIPping. Finally, the correlation between microstructure evolution and mechanical properties is discussed in detail. © 2021 The Authors
  •  
49.
  •  
50.
  • Yu, Cheng-Han, 1992-, et al. (författare)
  • Thin-wall Effects and Anisotropic Deformation Mechanisms of an Additively Manufactured Ni-based Superalloy
  • 2020
  • Ingår i: Additive Manufacturing. - : Elsevier. - 2214-8604 .- 2214-7810. ; 36
  • Tidskriftsartikel (refereegranskat)abstract
    • Laser powder bed fusion (LPBF) of Ni-based superalloys shows great potential for high temperature applications, for example, as a burner repair application for gas turbines where the thin-walled structure is important. It motivates this work to investigate the evolution of microstructure and the anisotropic mechanical behavior when plate-like specimens are built with a thickness from 4 mm down to 1 mm. By performing texture analysis using neutron diffraction, a clear transition in fiber texture from <011> to <001> is indicated when the specimen becomes thinner. The residual stress shows no thickness dependence, and at the subsurface the residual stress reaches the same level as the yield strength. Due to the rough as-built surface, a roughness compensation method for mechanical properties of thin-walled structures is outlined and demonstrated. Tensile tests from room temperature up to 700 °C have been carried out. Anisotropic mechanical behavior is found at all temperatures, which is strongly related to the anisotropic texture evolution. Stronger texture evolution and grain rotations are discovered when the tensile loading is applied along the building direction. The mechanical behavior has been compared to a wrought material, where the high dislocation density and the subgrain structure of the LPBF material result in a higher yield strength. Combining the statistical texture analysis by neutron diffraction with mechanical testing, EBSD grain orientation mapping and the investigation of dislocation structures using transmission electron microscopy, this work illustrates the significance of texture for the thin-wall effect and anisotropic mechanical behavior of LPBF materials.
  •  
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