| 1. |
- Holmberg, Max, et al.
(author)
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On Surface Losses in Direct Metal Laser Sintering Printed Millimeter and Submillimeter Waveguides
- 2018
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In: Journal of Infrared, Millimeter and Terahertz Waves. - : SPRINGER. - 1866-6892 .- 1866-6906. ; 39:6, s. 535-545
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Journal article (peer-reviewed)abstract
- Different lengths of WR3 (220-330 GHz) and WR10 (75-110 GHz) waveguides are fabricated through direct metal laser sintering (DMLS). The losses in these waveguides are measured and modelled using the Huray surface roughness model. The losses in WR3 are around 0.3 dB/mm and in WR10 0.05 dB/mm. The Huray equation model is accounting relatively good for the attenuation in the WR10 waveguide but deviates more in the WR3 waveguide. The model is compared to finite element simulations of the losses assuming an approximate surface structure similar to the resulting one from the DMLS process.
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| 2. |
- Larsson, Lisa, et al.
(author)
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Biocompatibility of a Zr-Based Metallic Glass Enabled by Additive Manufacturing
- 2022
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In: ACS Applied Bio Materials. - : American Chemical Society (ACS). - 2576-6422. ; 5:12, s. 5741-5753
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Journal article (peer-reviewed)abstract
- The present work explored the use of the selective laser melting (SLM) technique to develop a Zr-based bulk metallic glass (BMG) and investigate the influence of the process parameters on obtaining different levels of surface roughness. Moreover, the potential of the additively manufactured BMG Zr59.3Cu28.8Al10.4Nb1.5 (trade name AMLOY-ZR01) as an implant material was studied by evaluating the osteoblastic cell response to the alloy and its stability under simulated biological environments. The materials were characterized in terms of degree of crystallinity, surface roughness, and morphology, followed by a systematic investigation of the response of the MC3T3-E1 preosteoblastic cell line to the as-printed samples. The materials supported cell proliferation and differentiation of the preosteoblastic cells, with results comparable to the reference material Ti-6Al-4V. The surface microroughness and surface morphology (porous or groove-type laser tracks) investigated in this study did not have a significant effect on modulating the cell response. Ion release experiments showed a large increase in ion release under inflammatory conditions as compared to regular physiological conditions, which could be attributed to the increased local corrosion under inflammatory conditions. The findings in this work showed that the surface roughness of the additively manufactured BMG AMLOY-ZR01 can be tailored by controlling the laser power applied during the SLM process. The favorable cell response to the as-printed AMLOY-ZR01 represents of a significant advancement of the investigation of additively manufactured BMGs for orthopedic applications, while the results of the ion release study highlights the effect that inflammatory conditions could have on the degradation of the alloy.
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| 3. |
- Lindwall, Johan, et al.
(author)
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Simulation of phase evolution in a Zr-based glass forming alloy during multiple laser remelting
- 2022
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In: Journal of Materials Research and Technology. - : Elsevier. - 2238-7854 .- 2214-0697. ; 16, s. 1165-1178
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Journal article (peer-reviewed)abstract
- Additive manufacturing by laser-based powder bed fusion is a promising technique for bulk metallic glass production. But, reheating by deposition of subsequent layers may cause local crystallisation of the alloy. To investigate the crystalline phase evolution during laser scanning of a Zr-based metallic glass-forming alloy, a simulation strategy based on the finite element method and the classical nucleation theory has been developed and compared with experimental results from multiple laser remelting of a single-track. Multiple laser remelting of a single-track demonstrates the crystallisation behaviour by the influence of thermal history in the reheated material. Scanning electron microscopy and transmission electron microscopy reveals the crystalline phase evolution in the heat affected zone after each laser scan. A trend can be observed where repeated remelting results in an increased crystalline volume fraction with larger crystals in the heat affected zone, both in simulation and experiment. A gradient of cluster number density and mean radius can also be predicted by the model, with good correlation to the experiments. Prediction of crystallisation, as presented in this work, can be a useful tool to aid the development of process parameters during additive manufacturing for bulk metallic glass formation.
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| 4. |
- Marattukalam, Jithin James, et al.
(author)
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Exploring the use of selective laser melting to control the surface roughness of a Zr-based bulk metallic glass: surface characterization, ion release and osteoblastic cell response
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Other publication (other academic/artistic)abstract
- Zr-based bulk metallic glasses (BMGs) have attracted attention as promising candidates for orthopedic applications due to their relatively low Young´s modulus, excellent corrosion and wear resistance, and high strength. The challenge for BMGs as potential biomaterials is their production in large dimensions and complex geometries, a problem that can be addressed by additive manufacturing techniques. The present work explored the use of selective laser melting to develop a Zr-based BMG (Zr59.3Cu28.8Al10.4Nb1.5, trade name AMLOY-ZR01) and investigated the influence of the process parameters on obtaining different levels of surface roughness with the ultimate aim of modulating the material biocompatibility. The materials were characterized in terms of the degree of crystallinity, surface roughness, and morphology, followed by a systematic investigation of the response of the MC3T3-E1 pre-osteoblastic cell line to the as-printed samples. The substrates supported cell proliferation and differentiation of the pre-osteoblastic cells, with results comparable to the reference material Ti6A14V. The surface microroughness and surface morphology (porous or groove-type laser tracks) under study did not have a significant effect on modulating the cell response. Ion release experiments performed under regular physiological and inflammatory test conditions showed a large increase in ion release under inflammatory conditions as compared to regular physiological conditions. The findings in this work showed that the additively manufactured AMLOY-ZR01 is a promising BMG for orthopedic applications, and highlighted the effect that inflammatory conditions could have on the degradation of the alloy.
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| 5. |
- Marattukalam, Jithin James, et al.
(author)
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Microstructure and corrosion behavior of laser processed NiTi alloy
- 2015
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In: Materials science & engineering. C, biomimetic materials, sensors and systems. - : Elsevier BV. - 0928-4931 .- 1873-0191. ; 57, s. 309-313
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Journal article (peer-reviewed)abstract
- Laser Engineered Net Shaping (LENS™), a commercially available additive manufacturing technology, has been used to fabricate dense equiatomic NiTi alloy components. The primary aim of this work is to study the effect of laser power and scan speed on microstructure, phase constituents, hardness and corrosion behavior of laser processed NiTi alloy. The results showed retention of large amount of high-temperature austenite phase at room temperature due to high cooling rates associated with laser processing. The high amount of austenite in these samples increased the hardness. The grain size and corrosion resistance were found to increase with laser power. The surface energy of NiTi alloy, calculated using contact angles, decreased from 61 mN/m to 56 mN/m with increase in laser energy density from 20 J/mm2 to 80 J/mm2. The decrease in surface energy shifted the corrosion potentials to nobler direction and decreased the corrosion current. Under present experimental conditions the laser power found to have strong influence on microstructure, phase constituents and corrosion resistance of NiTi alloy.
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| 6. |
- Marattukalam, Jithin James
(author)
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Tailoring structure and morphology during additive manufacturing of metallic components
- 2021
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Doctoral thesis (other academic/artistic)abstract
- The work described in this thesis explores the use of laser process parameters to functionalize the material properties by the control of microstructure and optimization of morphology in components by selective laser melting. The microstructure in amorphous and crystalline metallic alloy systems is influenced by changing the laser power density and scanning strategies respectively. A combination of X-ray/neutron diffraction and optical/electron microscopy is used to evaluate the microstructure and phase formation in SLM components. The influence of the microstructure on the mechanical properties of as-printed samples was investigated using hardness and uniaxial tensile testing methods. To begin with, the process parameters for selective laser melting of a Zr-based bulk metallic glass Zr59.3Cu28.8Al10.4Nb1.5 (trade name AMLOY-ZR01) are developed to obtain high density and crack-free bulk components. The influence of oxygen on the thermal stability and crystallization pathway in AMLOY-ZR01 was found to be significant in determining the formation of metastable crystalline phases within the amorphous matrix. It was also shown that the mechanical properties in AMLOY-ZR01 can be influenced by changing the amount of crystalline phases formed within the amorphous matrix. This was achieved by changing the laser power density during the SLM process. The alloy composition was also investigated for its biocompatibility, and the cell-material interactions under in-vitro test conditions showed no cytotoxic effect. These findings demonstrate that AMLOY-ZR01 is a promising candidate for orthopedic bio-implant applications. The latter half of this work demonstrates the influence of microstructure and crystallographic texture on the mechanical properties of 316L SS. This was achieved by changing the "laser scanning methodology" during the SLM process and a correlation between the applied scanning methodology and structure-property relation was identified. A single crystalline-like texture can be obtained using a bi-directional scanning methodology, whereas a fiber texture is achieved when rotating the laser scan vectors by 67° to melt consecutive powder bed layers. The mechanical properties of 316L SS are influenced by the type of laser scan used to fabricate the components, as it dictates the final grain orientation within the SLM samples. It is also shown that the scanning patterns can be altered during the SLM process to create position-specific crystallographic grain orientation within the component. This opens up the possibility to fabricate functionally graded components which contain a spatial variation in composition and/or microstructure for the specific purpose of controlling material properties. Finally, the functionalization of material properties through design of components by additive manufacturing was demonstrated by fabricating waveguides with the specific geometries.
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| 7. |
- Marattukalam, Jithin James, et al.
(author)
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The effect of laser scanning strategies on texture, mechanical properties, and site-specific grain orientation in selective laser melted 316L SS
- 2020
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In: Materials & design. - : Elsevier BV. - 0264-1275 .- 1873-4197. ; 193
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Journal article (peer-reviewed)abstract
- Selective laser melting has been used to demonstrate the striking effect of laser scanning strategies on the crystalline texture in 316L SS. The aligned crystal orientation along the tensile direction (Z-axis) could be varied using the scanning strategy. A strong 〈100〉 single crystalline-like texture is obtained in the direction of the laser scan and a 〈110〉 texture was observed in the build direction when using a bidirectional scan without rotation. Fiber texture was observed along the tensile direction when the bi-directional laser scanning vectors were rotated by 67° (Rot-scan) for each layer. The study highlights a correlation between laser scanning strategies with resulting textures, microstructure, and mechanical properties in as-printed bulk 316L SS. The hardness, Young's modulus, and ultimate tensile strength were significantly influenced by the final microstructure, crystallographic texture, and porosity. Furthermore, the applied laser scanning strategies made it possible to tailor crystallographic textures locally within the component. This was demonstrated by printing characters with a fiber texture, in a matrix with ⟨100⟩ texture parallel to the Z-axis.
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| 8. |
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| 9. |
- Pacheco, Victor, et al.
(author)
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On the relationship between laser scan strategy, texture variations and hidden nucleation sites for failure in laser powder-bed fusion
- 2022
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In: Materialia. - : Elsevier. - 2589-1529. ; 26
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Journal article (peer-reviewed)abstract
- While laser powder-bed fusion has overcome some of the design constraints of conventional manufacturing meth-ods, it requires careful selection of process parameters and scan strategies to obtain favorable properties. Here we show that even simple scan strategies, complex ones being inevitable when printing intricate designs, can inadvertently produce local alterations of the microstructure and preferential grain orientation over small areas - which easily remain unnoticed across the macroscale. We describe how a combined usage of neutron imaging and electron backscatter diffraction can reveal these localized variations and explain their origin within cm-sized parts. We explain the observed contrast variations by linking the neutron images to simulated data, pole figures and EBSD, providing an invaluable reference for future studies and showing that presumably minor changes of the scan strategy can have detrimental effects on the mechanical properties. In-situ tensile tests reveal that fracture occurs in a region that was re-melted during the building process.
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