| 1. |
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| 2. |
- Adegoke, Olutayo, 1979-, et al.
(author)
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Influence of laser powder bed fusion process parameters on the microstructure and cracking susceptibility of nickel-based superalloy Alloy 247LC
- 2022
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In: Results in Materials. - : Elsevier. - 2590-048X. ; 13
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Journal article (peer-reviewed)abstract
- Microstructures of material conditions of nickel-based superalloy Alloy 247LC fabricated using laser powder bed fusion (L-PBF) were investigated. Experiments designed in a prior study revealed the L-PBF process parameters for which the material conditions displayed a reduced susceptibility to cracking. Certain process parameters produced material conditions with an increased susceptibility to cracking. In this study, the material conditions were investigated in detail to reveal their microstructure and to determine the cause of cracking. The reason for the transition between a reduced to an increased susceptibility to cracking was examined. The results revealed solidification cracking occurred at high-angle grain boundaries. Solidification cracking may have been promoted at high-angle grain boundaries because of the undercooling contribution of the grain boundary energy. Furthermore, Si segregation was observed in the cracks. Thus, the presence of Si most likely promoted solidification cracking. It was observed that a high crack density, which occurred in the high energy density material condition, was associated with a large average grain size. The fact that certain combination of process parameters produced microstructures with a low susceptibility to cracking, indicates that reliable Alloy 247LC material may be printed using L-PBF by employing improved process parameters. © 2022
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| 3. |
- Adegoke, Olutayo, 1979-, et al.
(author)
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Influence of laser powder bed fusion process parameters on the microstructure of solution heat-treated nickel-based superalloy Alloy 247LC
- 2022
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In: Materials Characterization. - : Elsevier. - 1044-5803 .- 1873-4189. ; 183
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Journal article (peer-reviewed)abstract
- In this study, Alloy 247LC samples were built with different laser powder bed fusion (L-PBF) process parameters. The samples were then subjected to solution heat treatment at 1260 °C for 2 h. The grain size of all the samples increased significantly after the heat treatment. The relationship between the process parameters and grain size of the samples was investigated by performing a design of experiment analysis. The results indicated that the laser power was the most significant process parameter that influenced the grain height and aspect ratio. The laser power also significantly influenced the grain width. The as-built and as-built + heat-treated samples with high, medium, and low energy densities were characterized using a field emission gun scanning electron microscope equipped with an electron backscatter diffraction detector. The micrographs revealed that the cells present in the as-built samples disappeared after the heat treatment. Isolated cases of twinning were observed in the grains of the as-built + heat-treated samples. The disappearance of cells, increase in the grain size, and appearance of twins suggested that recrystallization occurred in the alloy after the heat treatment. The occurrence of recrystallization was confirmed by analyzing the grain orientation spread of the alloy, which was lower and more predominantly <1° in the as-built + heat-treated conditions than in the as-built conditions. The microhardness of the as-built + heat-treated samples were high which was plausible because γ’ precipitates were observed in the samples. However, the L-PBF process parameters had a very low correlation with the microhardness of the as-built + heat-treated samples.
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| 4. |
- Adegoke, Olutayo, et al.
(author)
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Scanning electron microscopy and atom probe tomography characterization of laser powder bed fusion precipitation strengthening nickel-based superalloy
- 2023
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In: Micron. - 0968-4328 .- 1878-4291. ; 171
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Journal article (peer-reviewed)abstract
- Atom probe tomography (APT) was utilized to supplement scanning electron microscopy (SEM) characterizationof a precipitation strengthening nickel-based superalloy, Alloy 247LC, processed by laser powder bed fusion (LPBF). It was observed that the material in the as-built condition had a relatively high strength. Using both SEMand APT, it was concluded that the high strength was not attributed to the typical precipitation strengtheningeffect of γ’. In the absence of γ’ it could be reasonably inferred that the numerous black dots observed in thecells/grains with SEM were dislocations and as such should be contributing significantly to the strengthening.Thus, the current investigation demonstrated that relatively high strengthening can be attained in L-PBF even inthe absence of precipitated γ’. Even though γ’ was not precipitated, the APT analysis displayed a nanometer scalepartitioning of Cr that could be contributing to the strengthening. After heat-treatment, γ’ was precipitated and itdemonstrated the expected high strengthening behavior. Al, Ta and Ti partitioned to γ’. The strong partitioningof Ta in γ’ is indicative that the element, together with Al and Ti, was contributing to the strain-age crackingoccurring during heat-treatment. Cr, Mo and Co partitioned to the matrix γ phase. Hf, Ta, Ti and W were found inthe carbides corroborating previous reports that they are MC.
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| 5. |
- Borgström, Henrik, 1975, et al.
(author)
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Possibilities and constraints of implementing starch consolidated high speed steel in prototyping
- 2008
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In: Materials Science & Engineering. - : Elsevier BV. - 0921-5093 .- 1873-4936. ; 475:1-2, s. 34-38
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Journal article (peer-reviewed)abstract
- In the starch consolidation (SC) process, a water-based slurry containing powder, starch, dispersant and thickener is used to fabricate near net-shape green bodies that are de-binded and further consolidated by sintering. In this study, gas atomized M3/2 as well as high and low carbon V-rich M4 type high speed steel powder (<150 mu m) are considered, Both material types undergo high volumetric shrinkage during super-solidus liquid phase sintering enabling them to reach near full density. The analyses and the review cover different process aspects like: recipe optimisation, post-gelatinization drying, de-binding and sintering. A SC recipe consisting of 58 vol.% powder, 3 vol.% starch, 1 vol.% dispersant and a thickener solution resulted in a density of >98% than what is theoretically stated after sintering. It is found that the success of the post-gelatinization drying procedure depends on the smoothness of mould material and controlling powder oxidation. The best combination was freeze drying the slurry in a silicon rubber mould. For V-rich alloys a total or partial control of eutectic carbides in the final microstructure could be realized for vacuum and nitrogen sintering atmospheres, respectively.
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| 6. |
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| 7. |
- Chou, Chia-Ying, et al.
(author)
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Precipitation kinetics during post-heat treatment of a L-PBF processed SS446 ferritic stainless steel
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Other publication (other academic/artistic)abstract
- The microstructure response to post-heat treatments of SS446 ferritic stainless steel processed by laser powder bed fusion is investigated, with focus on the precipitation kinetics of Cr2N. Precipitation simulations are conducted using the precipitation module (TC-PRISMA) within the Thermo-Calc Software Package. The annealed microstructure is characterized by scanning electron microscopy and the results are used for model validation and calibration. The microstructure and hardness responses to post heat treatments is discussed in terms of optimal solid-solution strengthening in SS446 ferritic stainless steel alloys processed by laser-powder bed fusion.
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| 8. |
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| 9. |
- Deirmina, Faraz, et al.
(author)
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Heat Treatment And Mechanical Properties Of A Novel Ultrahigh Strength Co-free Maraging Steel Fabricated By Additive Manufacturing
- 2021
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In: Euro PM2021 Congress Proceedings. - : European Powder Metallurgy Association (EPMA).
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Conference paper (peer-reviewed)abstract
- We report on the fabrication of a Co-free ultra-high strength maraging steel designed for the laser-powder bed fusion (L-PBF) process using computational approaches. The aim was to obtain an essentially martensitic microstructure after the L-PBF process, and to achieve an ultimate tensile strength (UTS) of minimum 1700 MPa after direct ageing of the as-built microstructure. Microstructural characterization, dilatometry, and tensile and impact toughness tests were used to evaluate the employed approach.
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| 10. |
- Elbaz, Alexis, et al.
(author)
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Independent and Joint Effects of the MAPT and SNCA Genes in Parkinson Disease
- 2011
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In: Annals of Neurology. - : Wiley. - 1531-8249 .- 0364-5134. ; 69:5, s. 778-792
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Journal article (peer-reviewed)abstract
- Objective: We studied the independent and joint effects of the genes encoding alpha-synuclein (SNCA) and microtubule-associated protein tau (MAPT) in Parkinson disease (PD) as part of a large meta-analysis of individual data from case-control studies participating in the Genetic Epidemiology of Parkinson's Disease (GEO-PD) consortium. Methods: Participants of Caucasian ancestry were genotyped for a total of 4 SNCA (rs2583988, rs181489, rs356219, rs11931074) and 2 MAPT (rs1052553, rs242557) single nucleotide polymorphism (SNPs). Individual and joint effects of SNCA and MAPT SNPs were investigated using fixed- and random-effects logistic regression models. Interactions were studied on both a multiplicative and an additive scale, and using a case-control and case-only approach. Results: Fifteen GEO-PD sites contributed a total of 5,302 cases and 4,161 controls. All 4 SNCA SNPs and the MAPT H1-haplotype-defining SNP (rs1052553) displayed a highly significant marginal association with PD at the significance level adjusted for multiple comparisons. For SNCA, the strongest associations were observed for SNPs located at the 30 end of the gene. There was no evidence of statistical interaction between any of the 4 SNCA SNPs and rs1052553 or rs242557, neither on the multiplicative nor on the additive scale. Interpretation: This study confirms the association between PD and both SNCA SNPs and the H1 MAPT haplotype. It shows, based on a variety of approaches, that the joint action of variants in these 2 loci is consistent with independent effects of the genes without additional interacting effects. ANN NEUROL 2011; 69: 778-792
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| 11. |
- Harlin, Peter, et al.
(author)
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Abrasive wear resistance of starch consolidated and sintered high speed steel
- 2009
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In: Wear. - : Elsevier. - 0043-1648 .- 1873-2577. ; 267:9-10, s. 1482-1489
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Journal article (peer-reviewed)abstract
- The abrasive wear resistance of starch consolidated (SC) and super solidus liquid phase sintered (SLPS) M3/2 high speed steel (HSS) samples have been evaluated by a two-body micro-abrasion test (low stress abrasion), using 6 µm diamond abrasive particles, and a three-body abrasion test (high stress abrasion), using significantly larger abrasive particles of blast furnace slag (600 HV) and silicon carbide (2400 HV), respectively. In the tests a commercial powder metallurgical (PM) HSS was used as a reference material. The results show that the microstructure of the SC and SLPS HSS samples is strongly dependent on the sintering temperature used. With increasing temperature the microstructure ranges from a porous (5% porosity) relatively fine grained low temperature sintered microstructure to a fully dense relatively coarse grained high temperature sintered microstructure with eutectic carbides/carbide networks. However, despite the pronounced microstructural differences displayed by the as-sintered HSS microstructures these show a relatively high abrasive wear resistance, comparable with that of a HIPed HSS reference, both under low and high stress abrasion contact conditions. The characteristic features of the low and high temperature sintered microstructures, i.e. the pores and coarse eutectic carbides/carbide networks, only show a limited impact on the wear rate and the wear mode (dominant wear mechanism). The results obtained imply that near net shaped components manufactured by starch consolidation and super solidus liquid phase sintering might be of interest in tribological applications.
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| 12. |
- Harlin, Peter, et al.
(author)
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Influence of surface roughness of PVD coatings on tribological performance in sliding contacts
- 2006
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In: Surface & Coatings Technology. - : Elsevier BV. - 0257-8972 .- 1879-3347. ; 201:7, s. 4253-4259
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Journal article (peer-reviewed)abstract
- The influence of surface roughness on the tribological performance, i.e. friction, wear and material pick-up tendency, of two different commercial PVD coatings, TiN and WC/C, in sliding contact with ball bearing steel has been evaluated using two different types of sliding wear laboratory tests. Post-test characterisation using SEM/EDS, AES, ToF-SIMS and XPS was used to evaluate the prevailing friction and wear. The results show that the surface roughness of the coating is of importance in order to control the initial material pick-up tendency and thus the friction characteristics in a sliding contact. Once initiated, the material pick-up tendency will increase, generating a tribofilm at the sliding interface. For steel–TiN sliding couples a FeO-based tribofilm is generated on the two surfaces and FeO/FeO becomes the sliding interface (interfilm sliding) resulting in a high friction coefficient. For steel–WC/C sliding couples the WC/C displays a pronounced running-in behaviour which generates a WO3-based tribofilm on the steel surface while a carbon rich surface layer is formed on the WC/C surface, i.e. WO3/C becomes the sliding interface (interface sliding) resulting in a low friction coefficient.
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| 13. |
- Harlin, Peter, et al.
(author)
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Influence of surface topography of arc-deposited TiN and sputter-deposited WC/C coatings on the initial material transfer tendency and friction characteristics under dry sliding contact conditions
- 2009
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In: Surface & Coatings Technology. - : Elsevier. - 0257-8972 .- 1879-3347. ; 203:13, s. 1748-1755
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Journal article (peer-reviewed)abstract
- The influence of surface topography of PVD coatings on the initial material transfer tendency and friction characteristics in dry sliding contact conditions has been investigated. A modified scratch test was used to evaluate the material transfer tendency between ball bearing steel and two different PVD coatings, TiN and WC/C, under dry sliding contact conditions. Post test characterisation of the contact surfaces was performed using SEM/EDS and AES in order to map the initiation points and mechanisms for material transfer. The results show that the resulting topography of the PVD coated surfaces is strongly dependent on both the substrate material topography and the topography induced by the coating deposition process used. In sliding contact with a softer surface the coating topography results in a significant material pick-up tendency of the PVD coated surfaces. The material pick-up is mainly controlled by the abrasive action of hard coating asperities and as a result a polishing post treatment of the as-deposited PVD coatings significantly reduces the material pick-up tendency. For the WC/C coating, showing intrinsic low friction properties, the post treatment inhibits the material pick-up and results in a low and stable friction coefficient (mu similar to 0.1). For the TiN coating, that lacks intrinsic low friction properties, the post treatment reduces the material pick-up tendency but has no significant influence on the friction characteristics. This is mainly due to the presence of metallic Ti originating from the macroparticles on the TiN coating which results in a reactive surface that promotes a strong adhesion between the mating surfaces.
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| 14. |
- Harlin, Peter, 1974-
(author)
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Metal powders for additive manufacturing of superalloys and titanium alloys
- 2023. - 1
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In: Additive Manufacturing of High-Performance metallic Materials. - : Elsevier. - 9780323918855 - 9780323913829 ; , s. 41-82
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Book chapter (peer-reviewed)abstract
- This chapter explores the fundamentals of powders for metaladditive manufacturing and includes descriptions of powdermanufacturing processes, powder properties, and how theproperties affect the powder performance in metal additivemanufacturing processes. The powder manufacturing processeswill be restricted to processes used for titanium alloys andsuperalloys. Related to the powder properties, the reader will beintroduced to both characteristics of discrete particles and as avolume of a larger amount of powder particles and some of themost used standards.
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| 15. |
- Harlin, Peter, 1974
(author)
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On the processing of starch consolidated high speed steel - Microstructure and tribological properties
- 2008
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Doctoral thesis (other academic/artistic)abstract
- This thesis focuses on processing of high speed steel (HSS) powder into components using starch consolidation (SC) and supersolidus liquid phase sintering (SLPS). The work consists of four parts. First, the possibilities and constrains of the SC process are investigated and the role of starch in the green body fabrication clarified. Secondly, the possibility to sinter green bodies to full density using SLPS is investigated and the influence of sintering temperature on the as-sintered microstructures evaluated. Further, the mechanical and tribological properties of the as-sintered microstructures were evaluated using hardness indentation, scratch testing and three different wear tests. Finally, the use of physical vapour deposited (PVD) coatings, TiN and WC/C, for improved tribological performance of HSS components in sliding contacts was investigated and the importance of pre- and post-surface treatment illuminated. Also, the mechanisms of material transfer and tribo film formation and how these influences the tribo contact was investigated.The results show that it is possible to combine SC and SLPS in order to produce HSS components with fully dense microstructure and retained green body geometry from coarser HSS powder. The strength of the green bodies is mainly controlled by the morphology and distribution of starch and green bodies easy to handle can be obtained. The sintering temperature has a strong impact on the resulting microstructures, i.e. microstructures sintered at low temperatures show a porous microstructure while microstructures sintered at high temperatures show a coarser more inhomogeneous microstructure. The mechanical and tribological properties of SC HSS are in different extent controlled by the microstructure. The presence of a residual porosity will result in lower hardness but also in increased cracking tendency if porous areas are loaded. In contrast, microstructures sintered at high temperatures result in lower hardness and a more plastic behaviour. The abrasive wear resistance is, as compared with HIPed HSS, surprisingly good both under low and high stress abrasion conditions and the influence of any residual porosity is relatively small. Under sliding wear conditions a porous microstructure should be avoided since it will increase the wear of a softer counter surface. However, the deposition of a PVD coating will significantly improve the performance also of a porous microstructure.Evaluation of the sliding wear characteristics of PVD coated HSS shows that, besides a correct choice of the coating material, the control of surface structure topography is of outmost importance in order to obtain low friction and stable contact conditions.In summary, the obtained results are positive regarding the near net shape manufacturing (based on SC and SLPS) of PVD-coated HSS components for tribological applications.
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| 16. |
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| 17. |
- Harlin, Peter, et al.
(author)
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Starch consolidation of M3/2 high speed steel powder : influence of process parameters on resulting microstructure
- 2007
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In: Powder Metallurgy. - 0032-5899 .- 1743-2901. ; 50:4, s. 345-353
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Journal article (peer-reviewed)abstract
- The possibility to produce near net shape high speed steel components with an adequate microstructure by the combination of starch consolidation (SC) and super solidus liquid phase sintering (SLPS) has been evaluated using a gas atomised M3/2 high speed steel (HSS) powder. Characterisation of the green body and as sintered microstructures using light optical microscopy (LOM), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX) reveals that both the SC and SLPS processes strongly influence the resulting microstructure and thus the properties of the high speed steel material. The results obtained show that the morphology and distribution of starch to a high extent affect the green body surface strength and that the large pores remaining after sintering originates from entrapped air introduced in the fabrication process of the green body. The results illuminate the possibility to combine SC and SLPS to produce HSS components with fully dense microstructures and retained green body geometry from a powder with particle size distribution 50 - 150 mu m.
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| 18. |
- Harlin, Ulrika, et al.
(author)
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Flexible balancing of assembly systems and its impact on performance and human factors – a scenario-based analysis
- 2013
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In: Proceedings of NES 2013, 45th Nordic Ergonomics & Human Factors Society conference, Iceland, August 2013. - 9789979723974
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Conference paper (peer-reviewed)abstract
- Increased production complexity challenges traditional methods for planning and preparation of assembly. This paper addresses alternative approaches for assembly line balancing and an assembly plant area was studied in a cross-disciplinary scenario-based analysis. Results show that the complexity in products, operations, flow, and organisation increases setting new demands on developing line balancing methods, including meeting the requirements and understanding the impact, e.g. competences, organization, support functions. Further research is suggested for increase knowledge of what impact different line balancing concepts has on performance, human work and working conditions as well as development of strategies and guiding principles for dynamic planning.
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| 19. |
- Hassila Karlsson, Carl Johan, et al.
(author)
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Influence of carbon content on microstructure and mechanical properties of Inconel 718 processed with Powder Bed Fusion – Laser Beam
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Other publication (other academic/artistic)abstract
- Additive manufacturing of alloys belonging to the Inconel family is today a hot research topic. Given that these alloys were developed with casting and forging as the main manufacturing route, the possibilities of adjusting their composition to make them better suited for the additive manufacturing processes should be investigated. In this work we study two different versions of Alloy 718 with different carbon content; one having a normal carbon content and one having a very low carbon content. Test pieces from these alloys were produced using the Powder Bed Fusion – Laser Beam process. TEM and SEM with EDS/EBSD was used to study the resulting microstructures both in the as-built and after heat treatment. Mechanical properties were evaluated for samples printed in different build directions using tensile and impact testing. The achieved materials in the as-built condition were very similar to one another in both the microstructure and the displayed mechanical properties. After heat treatment, differences in the microstructures could be identified as secondary carbides were found to precipitate exclusively in the alloy with a normal carbon content. Additionally, the different carbon contents affected the number of annealing twins that formed in the respective alloys, where more twins formed in the alloy with a low carbon content. This was attributed to the alloy’s lower stacking-fault energy. As annealing twins facilitate the transformation of the anisotropic as-built grain structure, effectively making the materials more isotropic, only the low carbon content alloy showed isotropic material properties after heat treatment.
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| 20. |
- Heckman, Michael G., et al.
(author)
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Population-specific Frequencies for LRRK2 Susceptibility Variants in the Genetic Epidemiology of Parkinson's Disease (GEO-PD) Consortium
- 2013
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In: Movement Disorders. - : Wiley. - 0885-3185. ; 28:12, s. 1740-1744
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Journal article (peer-reviewed)abstract
- BackgroundVariants within the leucine-rich repeat kinase 2 gene are recognized as the most frequent genetic cause of Parkinson's disease. Leucine-rich repeat kinase 2 variation related to disease susceptibility displays many features that reflect the nature of complex, late-onset sporadic disorders like Parkinson's disease. MethodsThe Genetic Epidemiology of Parkinson's Disease Consortium recently performed the largest genetic association study for variants in the leucine-rich repeat kinase 2 gene across 23 different sites in 15 countries. ResultsHerein, we detail the allele frequencies for the novel risk factors (p.A419V and p.M1646T) and the protective haplotype (p.N551K-R1398H-K1423K) nominated in the original publication. Simple population allele frequencies not only can provide insight into the clinical relevance of specific variants but also can help genetically define patient groups. ConclusionsEstablishing individual patient-based genomic susceptibility profiles that incorporate both risk factors and protective factors will determine future diagnostic and treatment strategies. (c) 2013 International Parkinson and Movement Disorder Society
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| 21. |
- Isoaho, Jerry, et al.
(author)
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Applications of additive manufacturing : Selected case studies and future prospects
- 2023. - 1
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In: Additive Manufacturing of High-Performance metallic Materials. - : Elsevier. - 9780323918855 - 9780323913829 ; , s. 676-716
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Book chapter (peer-reviewed)abstract
- From an industrial standpoint, cost is of one of the most important drivers for utilizing new technologies such as additive manufacturing (AM). Other important drivers for why AM can be an advantageous technology for component manufacturing is decreased manufacturing lead time, rapid demonstration capability, freedom of design/geometry, advancing technology development, and not least sustainability in terms of both material utilization and improved part/system performance. In this chapter, six selected “case studies” are compiled, in which AM techniques have been used to manufacture components for actual applications. In some case studies, a comparison between the additive manufacturing route and the corresponding conventional manufacturing route is also included.
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| 22. |
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| 23. |
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| 24. |
- Karlsson, Dennis, et al.
(author)
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Additive manufacturing of the ferritic stainless steel SS441
- 2020
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In: Additive Manufacturing. - AMSTERDAM, NETHERLANDS : Elsevier BV. - 2214-8604 .- 2214-7810. ; 36
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Journal article (peer-reviewed)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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| 25. |
- Karlsson, Dennis, et al.
(author)
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Structure and phase transformations in gas atomized AlCoCrFeNi high entropy alloy powders
- 2022
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In: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388 .- 1873-4669. ; 893
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Journal article (peer-reviewed)abstract
- In this study, the crystal structure and phase stability of gas atomized equiatomic AlCoCrFeNi powder was investigated. This alloy is usually described as a high entropy alloy forming a solid solution phase stabilized by a high mixing entropy. However, thermodynamic calculations show that the high entropy phase is stable only at very high temperatures close to the melting point and that a mixture of several phases are the most stable state at lower temperatures. This suggest that kinetic effects may influence the phase composition of atomized powder. The unique features of X-ray diffraction, neutron diffraction as well as transmission electron microscopy were used to study the atomic structure of the atomized powder in detail. The results show that the powder crystallises in an ordered B2 (CsCl-type) structure with a preferred site occupation of Al and Fe on the (1/2 1/2 1/2) position and Co and Ni on the (0 0 0) position. During heat-treatment of the powder, the B2 phase decomposes into fcc and sigma phases and the final phase composition is highly dependent on the heating rate. The effect of heat-treatment on the atomized powder was also investigated and revealed a significant phase transformation with e.g. the formation of sigma phase preferably at the surface of the powder particles. The phase content was also dependent on the size fraction of the powder particles. Sintering of green bodies made with different heat cycles showed that the phase composition of the starting material had a significant impact on the final phase composition and microstructure of the sintered components. The results illustrate the importance of well-defined powder materials for powder consolidation, especially additive manufacturing (binder jetting) of high entropy alloys.
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| 26. |
- Ross, Owen A., et al.
(author)
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Association of LRRK2 exonic variants with susceptibility to Parkinson's disease: a case-control study
- 2011
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In: Lancet Neurology. - 1474-4465. ; 10:10, s. 898-908
-
Journal article (peer-reviewed)abstract
- Background The leucine-rich repeat kinase 2 gene (LRRK2) harbours highly penetrant mutations that are linked to familial parkinsonism. However, the extent of its polymorphic variability in relation to risk of Parkinson's disease (PD) has not been assessed systematically. We therefore assessed the frequency of LRRK2 exonic variants in individuals with and without PD, to investigate the role of the variants in PD susceptibility. Methods LRRK2 was genotyped in patients with PD and controls from three series (white, Asian, and Arab-Berber) from sites participating in the Genetic Epidemiology of Parkinson's Disease Consortium. Genotyping was done for exonic variants of LRRK2 that were identified through searches of literature and the personal communications of consortium members. Associations with PD were assessed by use of logistic regression models. For variants that had a minor allele frequency of 0.5% or greater, single variant associations were assessed, whereas for rarer variants information was collapsed across variants. Findings 121 exonic LRRK2 variants were assessed in 15 540 individuals: 6995 white patients with PD and 5595 controls, 1376 Asian patients and 962 controls, and 240 Arab-Berber patients and 372 controls. After exclusion of carriers of known pathogenic mutations, new independent risk associations were identified for polymorphic variants in white individuals (M1646T, odds ratio 1.43, 95% CI 1.15-1.78; p=0.0012) and Asian individuals (A419V, 2.27, 1.35-3.83; p=0.0011). A protective haplotype (N551K-R1398H-K1423K) was noted at a frequency greater than 5% in the white and Asian series, with a similar finding in the Arab-Berber series (combined odds ratio 0.82, 0.72-0.94; p=0.0043). Of the two previously reported Asian risk variants, G2385R was associated with disease (1.73, 1.20-2.49; p=0.0026), but no association was noted for R1628P (0.62, 0.36-1.07; p=0.087). In the Arab-Berber series, Y2189C showed potential evidence of risk association with PD (4.48, 133-15.09; p=0.012). Interpretation The results for LRRK2 show that several rare and common genetic variants in the same gene can have independent effects on disease risk. LRRK2, and the pathway in which it functions, is important in the cause and pathogenesis of PD in a greater proportion of patients with this disease than previously believed. These results will help discriminate those patients who will benefit most from therapies targeted at LRRK2 pathogenic activity. Funding Michael J Fox Foundation and National Institutes of Health.
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| 27. |
- Squillaci, Linda, et al.
(author)
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Extending powder particle size distribution of laser powder bed fusion Ti-6Al-4V : investigation of single tracks and multilayer experiments
- 2023
-
Conference paper (other academic/artistic)abstract
- This paper explores the effects of varying process parameters (i.e., laser power, laser scanning speed, hatch distance) on the characteristics of single tracks, triple tracks and cubes, in order to provide answers to Research Question 1. A full factorial DoE approach was adopted to produce the experiments. Data was extracted from different sources to find correlations between tracks and multilayer geometries. A digital microscope was used to obtain height profiles, whilst polished/etched cross sections cut parallel to the build direction were imaged using a LOM to obtain measurements of track height, width, melt pool depth, subsurface porosity and residual defect content in cubes. Track height was found to exceed the recoated value of 70μm for both single and triple tracks. The width of single tracks showed a clear upward trend when displayed against VED, showing a lateral expansion as energy input increased. It was also revealed that single tracks expand laterally as they grow above the substrate, indicating swelling. The melt pool depth showed a steady upward trend when plotted against LED, though less systematic than track width. A martensitic microstructure was detected, with hierarchical α’ needles growing at prescribed crystallographic directions within vertical prior-β grains. A large portion of spatter particles and unmelted powder granules were detected on the substrate and tracks, with many accumulating on the side of the tracks forming a denudation zone.
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| 28. |
- Swaminathan, Kameshwaran, et al.
(author)
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Characterization of Laser Powder Bed Fusion of Nickel-Based Superalloy Haynes 282
- 2023
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In: Proceedings of the 10th International Symposium on Superalloy 718 and Derivatives. - : Springer. - 9783031274466 - 9783031274473 ; , s. 553-570
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Conference paper (peer-reviewed)abstract
- Nickel-based superalloy Haynes 282 specimens were manufactured using the Laser Powder Bed Fusion process with a powder layer thickness of 60 and 90 microns to study the effect of laser power, laser scan speed, and hatch distance on the melt pool dimensions and porosity. The melt pool dimensions and porosity were measured at the center of the cubes parallel to the build direction. Variation of melt pool depth and overlap exist within the same sample signifying the scatter present in the process. Laser scan speed was found to be the most significant parameter for porosity and hatch distance was found to be the most significant parameter affecting the average melt pool overlap depth in the cubes built with 60 microns layer thickness. Interaction of speed and hatch distance was found to be the most significant parameter for porosity and Laser scan speed was the most significant parameter for average melt pool overlap depth in cubes built with 90 microns layer thickness. Comparison of measured responses with individual parameters provides partial trends of melt pool dimensions and porosity. As the heat input is captured better in line energy and area energy density, a better trend of the melt pool dimensions data and marginal trend of porosity in comparison with energy densities is discussed. The ratio of maximum length to minimum length of defects such as porosity and lack of fusion is measured to determine the shape of the defects and averaged to provide insight into the dominant shape of defect for a given set of parameters.
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