| 1. |
- Borgenstam, Annika, et al.
(författare)
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On the Symmetry Among the Diffusional Transformation Products of Austenite
- 2011
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Ingår i: Metallurgical and Materials Transactions. A. - : Springer Science and Business Media LLC. - 1073-5623 .- 1543-1940. ; 42A:6, s. 1558-1574
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Tidskriftsartikel (refereegranskat)abstract
- Information on the diffusional transformation products of austenite in high-carbon steels is reviewed and supplemented with new microscopic studies. A comparison with transformation products in low-carbon steels indicates that there is a symmetry with pearlite in the middle, where ferrite and cementite are equal partners, and with acicular ferrite or cementite on each side. They both form with a surface relief, and at lower temperatures, each one is the leading phase in a eutectoid microstructure, bainite and inverse bainite, respectively. However, there is an asymmetry because at low temperatures bainite appears in high-carbon steels but inverse bainite never appears in low-carbon steels. At a constant high carbon content, there is another kind of symmetry, which is related to temperature. At intermediate temperatures the eutectoid reaction results in spherical nodules in which the cementite constituent originates from Widmanstatten plates. It turns spiky at both higher and lower temperatures with the leading phase in the spikes being cementite at higher temperatures and ferrite at lower temperatures. In the first kind of symmetry, there is an abrupt change among the three reaction products; in the second kind of symmetry, there is a gradual change. Accepting that all the eutectoid microstructures form by diffusion of carbon, one may explain the existence of both symmetries by the variation of the ratio of the supersaturations of ferrite and cementite with carbon content and with temperature.
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| 2. |
- Cain, Peter A, et al.
(författare)
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Age and gender specific normal values of left ventricular mass, volume and function for gradient echo magnetic resonance imaging: a cross sectional study.
- 2009
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Ingår i: BMC medical imaging. - : Springer Science and Business Media LLC. - 1471-2342. ; 9:2
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Tidskriftsartikel (refereegranskat)abstract
- Knowledge about age-specific normal values for left ventricular mass (LVM), end-diastolic volume (EDV), end-systolic volume (ESV), stroke volume (SV) and ejection fraction (EF) by cardiac magnetic resonance imaging (CMR) is of importance to differentiate between health and disease and to assess the severity of disease. The aims of the study were to determine age and gender specific normal reference values and to explore the normal physiological variation of these parameters from adolescence to late adulthood, in a cross sectional study.
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| 3. |
- Cain, Peter, et al.
(författare)
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Physiological determinants of the variation in left ventricular mass from early adolescence to late adulthood in healthy subjects
- 2005
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Ingår i: Clin Physiol Funct Imaging. - 1475-0961. ; 25:6, s. 332-9
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: The physiological determinants of left ventricular mass (LVM) measured by cardiac magnetic resonance (CMR) imaging are not well defined as prior investigators have studied either adults or adolescents in isolation or have not strictly excluded hypertension or accounted for the effects of exercise habits, haemodynamic, demographic, or body shape characteristics. METHODS: A total of 102 healthy volunteers (12-81 years, 53 males) underwent CMR. All parameters [unstandardized and adjusted for body surface area (BSA)] were analysed according to gender and by adolescence versus adulthood (adolescents <20 years, adults > or = 20 years). The influence of haemodynamic factors, exercise, and demographic factors on LVM were determined with multivariate linear regression. Results: LVM rose during adolescence and declined in adulthood. LVM and LVMBSA were higher in males both in adults (LVM: 188 +/- 22 g versus 139 +/- 21 g, P < 0.001; LVMBSA: 94 +/- 11 g m(-2) versus 80 +/- 11 g m(-2), P < 0.001) and in adolescents when adjusted for BSA (LVM: 128 +/- 29 g versus 107 +/- 20 g, P = 0.063; LVMBSA: 82 +/- 8 g m(-2) versus 71 +/- 10 g m(-2), P = 0.025). In adults, systolic blood pressure (SBP) and self-reported physical activity increased while meridional and circumferential wall stress were constant with age. Multivariate regression analysis revealed age, gender, and BSA as the major determinants of LVM (global R2 = 0.69). CONCLUSIONS: Normal LVM shows variation over a broad age range in both genders with a rise in adolescence and subsequent decline with increasing age in adulthood despite an increase in SBP and physical activity. BSA, age, and gender were found to be major contributors to the variation in LVM in healthy adults, while haemodynamic factors, exercise, and wall stress were not.
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| 4. |
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| 5. |
- Croné, Philip, et al.
(författare)
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Continuum plasticity modelling of work hardening for precipitation-hardened martensitic steel guided by atom probe tomography
- 2022
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Ingår i: Materials & design. - : Elsevier BV. - 0264-1275 .- 1873-4197. ; 215
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Tidskriftsartikel (refereegranskat)abstract
- An analytical flow stress model, based on isotropic strain gradient plasticity theory, for precipitation hardened materials, is proposed and evaluated against tensile data on a 15 wt% Cr - 5 wt% Ni (15-5) PH stainless steel. The 15-5 PH material was aged at 500 °C for 1 h, 2 h, 5 h and 50 h to obtain a wide range of precipitate sizes. Detailed characterisation of precipitates was obtained using atom probe tomography (APT). A second material, a 15-5 stainless steel without added Cu was heat treated to obtain a similar matrix microstructure as in the 15-5 PH, but without Cu precipitates. Tensile testing revealed that the heat treated 15-5 PH material covered the full range from under- to overaged conditions. The analytical model, which accounts for stress reducing effects of plastic relaxation around particles, manages to capture the experimental data in a very satisfying manner using only a total of three tunable parameters. It is believed that the proposed model can offer an alternative to the much more commonly used work hardening models based on the internal variable approach.
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| 6. |
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| 7. |
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| 8. |
- Ioannidou, Chrysoula, et al.
(författare)
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In-situ synchrotron X-ray analysis of metal Additive Manufacturing : Current state, opportunities and challenges
- 2022
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Ingår i: Materials & design. - : Elsevier BV. - 0264-1275 .- 1873-4197. ; 219, s. 110790-
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Tidskriftsartikel (refereegranskat)abstract
- Additive Manufacturing (AM) is becoming an important technology for manufacturing of metallic materials. Laser-Powder Bed Fusion (L-PBF), Electron beam-Powder Bed Fusion (E-PBF) and Directed Energy Deposition (DED) have attracted significant interest from both the scientific community and the industry since these technologies offer great manufacturing opportunities for niche applications and complex geometries. Understanding the physics behind the complex and dynamic phenomena occurring during these processes is essential for overcoming the barriers that constrain the metal AM development. Insitu synchrotron X-ray characterization is suitable for investigating the microstructure evolution during processing and provides new profound insights. Here, we provide an overview of the research on metal PBF and DED using in-situ synchrotron X-ray imaging, diffraction and small-angle scattering, highlighting the state of the art, the instrumentation, the challenges and the gaps in knowledge that need to be filled. We aim at presenting a scientific roadmap for in-situ synchrotron analysis of metal PBF and DED where future challenges in instrumentation such as the development of experimental stations, sample environments and detectors as well as the need for further application oriented research are included.
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| 9. |
- Kolmskog, Peter, et al.
(författare)
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Direct Observation that Bainite can Grow Below M-S
- 2012
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Ingår i: Metallurgical and Materials Transactions. A. - : Springer Science and Business Media LLC. - 1073-5623 .- 1543-1940. ; 43A:13, s. 4984-4988
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Tidskriftsartikel (refereegranskat)abstract
- In situ simultaneous synchrotron X-ray diffraction and laser scanning confocal microscopy have confirmed that bainite in steels can grow below the martensite start temperature. This observation suggests that the formation curves for bainite in time-temperature-transformation diagrams should be extended below the martensite start temperature. Furthermore, the implication of this observation on the growth mechanism of bainitic ferrite is discussed.
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| 10. |
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| 11. |
- König, Hans-Henrik, et al.
(författare)
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MiniMelt : An instrument for real-time tracking of electron beam additive manufacturing using synchrotron x-ray techniques
- 2023
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 94:12
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Tidskriftsartikel (refereegranskat)abstract
- The development of a sample environment for in situ x-ray characterization during metal Electron Beam Powder Bed Fusion (PBF-EB), called MiniMelt, is presented. The design considerations, the features of the equipment, and its implementation at the synchrotron facility PETRA III at Deutsches Elektronen-Synchrotron, Hamburg, Germany, are described. The equipment is based on the commercially available Freemelt ONE PBF-EB system but has been customized with a unique process chamber to enable real-time synchrotron measurements during the additive manufacturing process. Furthermore, a new unconfined powder bed design to replicate the conditions of the full-scale PBF-EB process is introduced. The first radiography (15 kHz) and diffraction (1 kHz) measurements of PBF-EB with a hot-work tool steel and a Ni-base superalloy, as well as bulk metal melting with the CMSX-4 alloy, using the sample environment are presented. MiniMelt enables time-resolved investigations of the dynamic phenomena taking place during multi-layer PBF-EB, facilitating process understanding and development of advanced process strategies and materials for PBF-EB.
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| 12. |
- Manea Hedström, Minola, et al.
(författare)
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Podocytes express ADAMTS13 in normal renal cortex and in patients with thrombotic thrombocytopenic purpura
- 2007
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Ingår i: British Journal of Haematology. - : Wiley. - 0007-1048 .- 1365-2141. ; 138:5, s. 651-662
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Tidskriftsartikel (refereegranskat)abstract
- Congenital thrombotic thrombocytopenic purpura (TTP) is associated with ADAMTS13 mutations. The major site of ADAMTS13 synthesis is the liver. Expression in other tissues, and in TTP, has not been shown. In this study, ADAMTS13 protein expression was investigated in normal kidney and in renal tissue from two TTP patients, with a compound heterozygous mutation (P353L and P457L) and a homozygous mutation (4143insA). Real-time polymerase chain reaction demonstrated ADAMTS13 mRNA in normal kidney. ADAMTS13 was detected in the glomeruli and tubuli of normal and TTP kidney using anti-ADAMTS13 antibodies. In the glomeruli, expression was localised to podocytes (as demonstrated by counterstaining with two podocyte markers) and endothelium. Similar distribution was detected in the TTP kidneys. Electron microscopy detected ADAMTS13 in podocytes, endothelium and glomerular basement membrane. Cultured human podocytes expressed ADAMTS13 mRNA and protein, and podocyte lysate exhibited von Willebrand factor-cleaving activity. Mutation expression studies of the P353L and P457L mutations showed partially impaired secretion and lower activity of the secreted mutants. Impaired secretion has previously been shown for the 4143insA mutation. Podocyte-derived ADAMTS13 may offer local protection in the high-shear microcirculation of the glomerulus. The mutations in the two TTP patients studied enabled protein expression in the podocytes but affected protease secretion.
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| 13. |
- Neding, Benjamin, et al.
(författare)
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Correlating temperature-dependent stacking fault energy and in-situ bulk deformation behavior for a metastable austenitic stainless steel
- 2022
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Ingår i: Materials Science & Engineering. - : Elsevier BV. - 0921-5093 .- 1873-4936. ; 832, s. 142403-
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Tidskriftsartikel (refereegranskat)abstract
- In-situ high-energy synchrotron X-ray diffraction experiments during uniaxial tensile loading are performed to investigate the effect of temperature (25, 45 and 70 degrees C) on the deformation behavior of a 301 metastable austenitic stainless steel. The micromechanical behavior of the steel at the three deformation temperatures is correlated with the stacking fault energy (gamma(SF)) experimentally determined through the same in-situ X-ray experiments. The applied measurements provide a unique possibility to directly interrogate the temperature dependent gamma(SF) in relation to the active bulk deformation mechanism in a metastable austenitic stainless steel. The determined gamma(SF) is 9.4 +/- 1.7 mJ m(-2) at 25 degrees C, 13.4 +/- 1.9 mJ m(-2) at 45 degrees C and 25.0 +/- 1.1 mJ m(-2) at 70 degrees C. This relatively minor change of gamma(SF) and temperature causes a significant change of the dominant deformation mechanism in the alloy. At room temperature (25 degrees C) significant amounts of stacking faults form at 0.05 true strain, with subsequent formation of large fractions of deformation-induced alpha' and epsilon-martensite, 0.4 and 0.05, at 0.4 true strain, respectively. With increasing temperature (45 degrees C) fewer stacking faults form at low strain and thereupon also smaller alpha' - and epsilon-martensite fractions form, 0.2 and 0.025, at 0.4 true strain, respectively. At the highest temperature (70 degrees C) plastic deformation primarily occurs by the generation and glide of perfect dislocations at low strain, while at higher strain these dislocations dissociate to form stacking faults. The alpha'-martensite fraction formed is significantly less at 70 degrees C reaching 0.1 at 0.4 strain, whilst epsilon-martensite is not found to form at any strain at this temperature. The temperature-dependent mechanical behavior of the alloy is consistent with the observed dominant deformation mechanisms; the strong work hardening from the TRIP effect at low temperature, and low gamma(SF), decreases significantly with increasing temperature, and gamma(SF).
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| 14. |
- Tian, Ye, et al.
(författare)
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Micromechanics and microstructure evolution during in situ uniaxial tensile loading of TRIP-assisted duplex stainless steels
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Two transformation-induced plasticity (TRIP) assisted duplex stainless steels, with three different stabilities of the austenite phase, were investigated by synchrotron X-ray diffraction characterization during in situ uniaxial tensile loading. The micromechanics and the deformation-induced martensitic transformation (DIMT) in the bulk of the steels were investigated in situ. Furthermore, scanning electron microscopy supplemented the in situ analysis by providing information about the microstructure of annealed and deformed specimens. The dependence of deformation structure on austenite stability is similar to that of single-phase austenitic steels where shear bands and bcc-martensite (α’) are generally observed, and blocky α’ is only frequent when the austenite stability is low. These microstructural features, i.e. defect structure and deformation-induced martensite, are correlated with the micro- and macro-mechanics of the steels with elastoplastic load transfer from the weaker phases to the stronger α’, in particular this occurs close to the point of maximum rate of α’ formation. A clear strain-hardening effect from α’ is seen in the most unstable austenite leading to a pronounced TRIP effect.
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| 15. |
- Arvidsson, Martin, 1990-
(författare)
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Beyond Generative Sufficiency : On Interactions, Heterogeneity & Middle-Range Dynamics
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Explaining how properties at the level of individuals translate into properties at the level of collectives is a core objective of sociology. Because the social world is characterized by complex webs of social interdependencies, establishing how micro and macro are related to one another requires a detailed understanding of how individuals are influenced by their social environments and the consequences that such influences have for the dynamics of the social process. However, until very recently, it has been difficult to conduct detailed empirical investigations of micro-macro linkages due to the lack of large-scale data containing information on how individuals interact with one another. In the absence of such data, substantive research has tended to (a) focus its attention elsewhere: studying how social factors influence individual outcomes, rather than how actors in interaction with one another bring about collective outcomes, or (b) propose models of micro-macro linkages that—for reasons of parsimony and tractability—often assume artificially high levels of homogeneity. Against this background, this thesis sets out to investigate, first, how the data and tools that have emerged from the digital and computational revolution can help sociologists construct empirically well-founded mappings from the micro to the macro level, and second, how the conclusions about the role of social interdependencies and networks change when the analysis is informed by real-world heterogeneities.In the introductory chapter, a conceptual and analytical framework for studying micro-macro processes is proposed that integrates the theoretical principles of analytical sociology with the data and methods of computational social science. This framework constitutes the foundation of the thesis. It is used in Essays I-III, and it is methodologically built upon in Essay IV.In Essay I, the role of social networks in labor-market segregation processes is examined. Scholarship on labor-market segregation commonly assume that social networks have a segregating effect because of homophilous selection tendencies in network-based recruitment. Using large-scale register data and focusing attention on individuals’ heterogenous opportunities to form same-category ties in different workplaces, Essay I finds that opportunity structures often dominate homophilic preferences. In particular, a mechanism is identified which shows—in contradiction with the main tenet of previous research—that networks often reduce rather than increase segregation by triggering mobility events that counteract the impact of segregating mobility events.Essay II examines the conditions under which social influence can decouple adoption behaviour from individual preferences and thereby bring about unexpected collective outcomes. Prior research has shown that such decoupling can occur, but conflicting evidence and implicit assumptions of strong homogeneity mean that we still know little about the conditions under which this is likely to occur in the real world. Addressing these limitations, this study uses fine-grained, real-world behavioural data from Spotify to estimate heterogeneous social influence effects conditional on properties of individuals’ social environments, and then examine their macro-implications in empirically calibrated simulations. It is found that partial overlap in preferences and strong social ties between the senders and receivers of social influence is needed for social influence to produce decoupling.Essay III centers on the phenomenon of urban scaling and examines the relationship between within-city and between-city inequality. Previous urban scaling research has documented how cities’ total outputs increase more than proportionally with city size and has proposed theoretical models which demonstrate impressive predictive accuracy at aggregate levels. However, this research has overlooked the stark inequalities that exist within cities. Using microdata from multiple countries, it is found that between 36–80% of the previously reported scaling effects can be explained by differences in the distributional tails of cities. Providing explanatory depth to these findings, a cumulative advantage mechanism is identified which elucidates one important channel through which differences in the size of cities’ tails emerge.In Essay IV, a method is proposed for inferring theoretically meaningful dimensions from complex high-dimensional data such as text. The results show that the method captures latent semantic concepts better than or on-par with the current state of the art. For the study of social interactions, the method constitutes a new and potentially important tool for inferring theoretically meaningful dimensions about individuals and their social environments, and in so doing, improves our ability to adjust for specific types of homophily and enables richer and more precise measures of heterogeneity in social interaction processes.
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| 16. |
- Arvidsson, Martin, et al.
(författare)
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The Trojan-horse mechanism : How networks reduce gender segregation
- 2021
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Ingår i: Science Advances. - : American Association for the Advancement of Science. - 2375-2548. ; 7:16
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Tidskriftsartikel (refereegranskat)abstract
- The segregation of labor markets along ethnic and gender lines is socially highly consequential, and the social science literature has long viewed homophily and network-based job recruitments as some of its most crucial drivers. Here, we focus on a previously unidentified mechanism, the Trojan-horse mechanism, which, in contradiction to the main tenet of previous research, suggests that network-based recruitment reduce rather than increase segregation levels. We identify the conditions under which networks are desegregating, and using unique data on all individuals and all workplaces located in the Stockholm region during the years 2000-2017, we find strong empirical evidence for the Trojan-horse mechanism and its role in the gender segregation of labor markets.
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| 17. |
- Borgh, Ida, 1983-
(författare)
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Aspects of Structural Evolution in Cemented Carbide – Carbide Size, Shape and Stability
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Cemented carbide is a composite material used in applications like cutting tools and rock drilling inserts. The material commonly consists of WC grains embedded in a Co-rich binder phase and the material properties strongly depend on the WC grain size. Hence, to tailor the properties it is important to understand the fundamental mechanisms of grain coarsening. At the same time, the higher demands on material properties today also require new solutions. In the present work, some different aspects of structural evolutions in cemented carbides have been investigated.The first part of the work considers WC grain coarsening by means of size, size distribution and shape. Some efforts of the work have been to evaluate the effects of C-activity and initial WC powder size and distribution on the coarsening behavior in the material using different characterization techniques, e.g. scanning electron microscopy, and electron backscattered diffraction. Additionally, two earlier developed models are used and evaluated with the experimental data. The results indicate that the C-activity will affect size, size distribution and shape of the WC grains. It was also observed that the initial WC powder size and size distribution will have a large influence on the WC grain coarsening. The statistical shape was found to fit a spherical approximation but for individual grains both faceted and non-faceted shapes was observed. Steps and planar defects were observed supporting that the nucleation of new atomic layers is the main rate limiting mechanism for grain coarsening.The second part of this work considers the carbide phase stability in the (Ti,Zr)C system. The phase stability was investigated after synthesizing and aging a mixed (Ti,Zr)C using X-ray diffraction and different types of electron microscopy techniques. A decomposed lamellar structure was found with a composition variation of approximately 10% between the 50-75 nm thick lamellas. The experimental investigations were supported by computational work and the results were in good agreement. Additionally, two cemented carbide related systems were studied. A miscibility gap was found in the two investigated systems, (Ti,Zr,W)(C,N)-Co or Fe-graphite, and the effect of N2-gas pressure was investigated suggesting a critical N2-gas pressure below 0.1 bar.
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| 18. |
- Borgh, Ida, et al.
(författare)
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Effect of carbon activity and powder particle size on WC grain coarsening during sintering of cemented carbides
- 2014
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Ingår i: International journal of refractory metals & hard materials. - : Elsevier BV. - 0263-4368. ; 42, s. 30-35
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Tidskriftsartikel (refereegranskat)abstract
- Liquid-phase sintering is an important step in the production of cemented carbides. During sintering, the average WC grain size increases, leading to a coarser structure, which affects the performance of the final product. The coarsening occurs by dissolution of small grains and growth of large grains. In the present work, the effect of high carbon activity during sintering on the WC grain coarsening has been evaluated using electron backscattered diffraction (EBSD) and the results have been compared with a previous work where sintering was performed at a lower carbon activity. A more homogeneous grain size distribution was observed in alloys sintered at a high carbon activity. In addition, the effect of the initial powder particle size distribution was investigated. It was found that the coarsening rate of a WC powder with an initial small average grain size is significantly higher as compared to the coarsening rate for a powder with a larger initial average grain size. The results obtained emphasize the importance of considering the complete particle size distribution in order to predict coarsening.
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| 19. |
- Borgh, Ida, et al.
(författare)
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Investigation of phase separation in the (TI, ZR)C system
- 2012
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Ingår i: Advances in Powder Metallurgy and Particulate Materials - 2012, Proceedings of the 2012 International Conference on Powder Metallurgy and Particulate Materials, PowderMet 2012. - 9780985339722 ; , s. 81-810
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Konferensbidrag (refereegranskat)abstract
- The hardness of cemented carbide (WC-Co) cutting tools can be improved by the addition of TiC or ZrC to the matrix. It is possible that an even better hardness can be obtained by utilizing phase separation of a mixed (Ti, Zr)C where the mixed (Ti, Zr)C phase is stable at high temperature, but decomposes to TiC and ZrC at lower temperatures. In the present work, the decomposition is experimentally and theoretically investigated. The mixed carbide is first formed by synthesis from oxide powders at 2200°C and aging treatments are conducted at 1380 and 1450°C. X-ray diffraction analysis show that the synthesized mixed (Ti, Zr)C will decompose to TiC and ZrC. The experimental work is supplemented by thermodynamic and first-principles calculations.
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| 20. |
- Borgh, Ida, et al.
(författare)
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Microstructure, grain size distribution and grain shape in WC-Co alloys sintered at different carbon activities
- 2014
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Ingår i: International journal of refractory metals & hard materials. - : Elsevier BV. - 0263-4368 .- 0958-0611. ; 43, s. 205-211
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Tidskriftsartikel (refereegranskat)abstract
- The properties of cemented carbides strongly depend on the WC grain size and it is thus crucial to control coarsening of WC during processing. The aim of this work was to study the effect of sintering at different carbon activities on the final microstructure, as well as the coarsening behavior of the WC grains, including the size distribution and the shape of WC grains. These aspects were investigated for five WC-Co alloys sintered at 1410 degrees C for 1 h at different carbon activities in the liquid, in the range from the graphite equilibrium (carbon activity of 1) to the eta (M6C) phase equilibrium (carbon activity of 0.33). The grain size distribution was experimentally evaluated for the different alloys using EBSD (electron backscatter diffraction). In addition, the shape of the WC grains was evaluated for the different alloys. It was found that the average WC grain size increased and the grain size distribution became slightly wider with increasing carbon activity. Comparing the two three-phase (WC-Co-eta and WC-Co-graphite) alloys a shape change of the WC grains was observed with larger grains having more planar surfaces and more triangular shape for the WC-Co-graphite alloy. It was indicated that in alloys with a relatively low volume fraction of the binder phase the WC grain shape is significantly affected by impingements. Moreover, after 1 h of sintering the WC grains are at a non-equilibrium state with regards to grain morphology. (C) 2013 Elsevier Ltd. All rights reserved.
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| 21. |
- Borgh, Ida, et al.
(författare)
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On the three-dimensional structure of WC grains in cemented carbides
- 2013
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Ingår i: Acta Materialia. - : Elsevier BV. - 1359-6454 .- 1873-2453. ; 61:13, s. 4726-4733
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Tidskriftsartikel (refereegranskat)abstract
- In the present work, the size distribution and shape of WC grains in cemented carbides (WC-Co), with different Co contents, have been investigated in three dimensions. Direct three-dimensional (3-D) measurements, using focused ion beam serial sectioning and electron backscattered diffraction (EBSD), were performed and a 3-D microstructure was reconstructed. These measurements were supplemented by two-dimensional (2-D) EBSD and scanning electron microscopy on extracted WC grains. The data from 2-D EBSD collected on planar sections were transformed to three dimensions using a recently developed statistical method based on an iterative inverse Saltykov procedure. This stereological analysis revealed that the assumed spherical shape of WC grains during the Saltykov method is reasonable and the estimated 3-D size distribution is qualitatively in good agreement with the actual distribution measured from 3-D EBSD. Although the spherical assumption is generally fair, the WC grains have both faceted and rounded surfaces. This is a consequence of the relatively low amount of liquid phase during sintering, which makes impingements significant. Furthermore, the observed terraced surface structure of some WC grains suggests that 2-D nucleation is the chief coarsening mechanism to consider.
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| 22. |
- Borgh, Ida, et al.
(författare)
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Synthesis and phase separation of (Ti,Zr)C
- 2014
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Ingår i: Acta Materialia. - : Elsevier BV. - 1359-6454 .- 1873-2453. ; 66, s. 209-218
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Tidskriftsartikel (refereegranskat)abstract
- Synthesis and phase separation of (Ti,Zr)C were investigated in the present work. The (Ti,Zr)C phase was synthesized at 2200 C and subsequently aged at 1300 C for different times. The microstructure was investigated using X-ray diffraction and electron microscopy, and supplemented by first-principles calculations. The (Ti,Zr)C phase separates into a lamellar nanostructure with alternating Ti- and Zr-rich face-centered cubic domains as well as non-stoichiometric TiC and ZrC. The lamellar structure is a consequence of phase separation within the miscibility gap that is directionally constrained by high coherency stresses, as indicated by the first-principles calculations. Moreover, the increased hardness due to the phase separation suggests that the mixed carbide could be used as a strengthening constituent in, for example, cemented carbides.
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| 23. |
- Borrajo-Pelaez, Rafael, et al.
(författare)
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Recent Developments of Crystallographic Analysis Methods in the Scanning Electron Microscope for Applications in Metallurgy
- 2018
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Ingår i: Critical reviews in solid state and materials sciences. - : TAYLOR & FRANCIS INC. - 1040-8436 .- 1547-6561. ; 43:6, s. 455-474
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Forskningsöversikt (refereegranskat)abstract
- The field of metallurgy has greatly benefited from the development of electron microscopy over the last two decades. Scanning electron microscopy (SEM) has become a powerful tool for the investigation of nano- and microstructures. This article reviews the complete set of tools for crystallographic analysis in the SEM, i.e., electron backscatter diffraction (EBSD), transmission Kikuchi diffraction (TKD), and electron channeling contrast imaging (ECCI). We describe recent relevant developments in electron microscopy, and discuss the state-of-the-art of the techniques and their use for analyses in metallurgy. EBSD orientation measurements provide better angular resolution than spot diffraction in TEM but slightly lower than Kikuchi diffraction in TEM, however, its statistical significance is superior to TEM techniques. Although spatial resolution is slightly lower than in TEM/STEM techniques, EBSD is often a preferred tool for quantitative phase characterization in bulk metals. Moreover, EBSD enables the measurement of lattice strain/rotation at the sub-micron scale, and dislocation density. TKD enables the transmitted electron diffraction analysis of thin-foil specimens. The small interaction volume between the sample and the electron beam enhances considerably the spatial resolution as compared to EBSD, allowing the characterization of ultra-fine-grained metals in the SEM. ECCI is a useful technique to image near-surface lattice defects without the necessity to expose two free surfaces as in TEM. Its relevant contributions to metallography include deformation characterization of metals, including defect visualization, and dislocation density measurements. EBSD and ECCI are mature techniques, still undergoing a continuous expansion in research and industry. Upcoming technical developments in electron sources and optics, as well as detector instrumentation and software, will likely push the border of performance in terms of spatial resolution and acquisition speed. The potential of TKD, combined with EDS, to provide crystallographic, chemical, and morphologic characterizations of nano-structured metals will surely be a valuable asset in metallurgy.
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| 24. |
- Chang, Tingru, et al.
(författare)
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High-Resolution Microscopical Studies of Contact Killing Mechanisms on Copper-Based Surfaces
- 2021
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 13:41, s. 49402-49413
-
Tidskriftsartikel (refereegranskat)abstract
- The mechanisms of bacterial contact killing induced by Cu surfaces were explored through high-resolution studies based on combinations of the focused ion beam (FIB), scanning transmission electron microscopy (STEM), high-resolution TEM, and nanoscale Fourier transform infrared spectroscopy (nano-FTIR) microscopy of individual bacterial cells of Gram-positive Bacillus subtilis in direct contact with Cu metal and Cu5Zn5Al1Sn surfaces after high-touch corrosion conditions. This approach permitted subcellular information to be extracted from the bioinorganic interface between a single bacterium and Cu/Cu5Zn5Al1Sn surfaces after complete contact killing. Early stages of interaction between individual bacteria and the metal/alloy surfaces include cell leakage of extracellular polymeric substances (EPSs) from the bacterium and changes in the metal/alloy surface composition upon adherence of bacteria. Three key observations responsible for Cu-induced contact killing include cell membrane damage, formation of nanosized copper-containing particles within the bacteria cell, and intracellular copper redox reactions. Direct evidence of cell membrane damage was observed upon contact with both Cu metal and Cu5Zn5Al1Sn surfaces. Cell membrane damage permits copper to enter into the cell interior through two possible routes, as small fragmentized Cu2O particles from the corrosion product layer and/or as released copper ions. This results in the presence of intracellular copper oxide nanoparticles inside the cell. The nanosized particles consist primarily of CuO with smaller amounts of Cu2O. The existence of two oxidation states of copper suggests that intracellular redox reactions play an important role. The nanoparticle formation can be regarded as a detoxification process of copper, which immobilizes copper ions via transformation processes within the bacteria into poorly soluble or even insoluble nanosized Cu structures. Similarly, the formation of primarily Cu(II) oxide nanoparticles could be a possible way for the bacteria to deactivate the toxic effects induced by copper ions via conversion of Cu(I) to Cu(II).
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| 25. |
- Claesson, Erik, et al.
(författare)
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Carbide Precipitation during Processing of Two Low-Alloyed Martensitic Tool Steels with 0.11 and 0.17 V/Mo Ratios Studied by Neutron Scattering, Electron Microscopy and Atom Probe
- 2022
-
Ingår i: Metals. - Basel, Switzerland : MDPI AG. - 2075-4701. ; 12:5
-
Tidskriftsartikel (refereegranskat)abstract
- Two industrially processed low-alloyed martensitic tool steel alloys with compositions Fe-0.3C-1.1Si-0.81Mn-1.5Cr-1.4Ni-1.1Mo-0.13V and Fe-0.3C-1.1Si-0.81Mn-1.4Cr-0.7Ni-0.8Mo-0.14V (wt.%) were characterized using small-angle neutron scattering (SANS), scanning electron microscopy (SEM), Scanning transmission electron microscopy (STEM), and atom probe tomography (APT). The combination of methods enables an understanding of the complex precipitation sequences that occur in these materials during the processing. Nb-rich primary carbides form at hot working, while Fe-rich auto-tempering carbides precipitate upon quenching, and cementite carbides grow during tempering when Mo-rich secondary carbides also nucleate and grow. The number density of Mo-rich carbides increases with tempering time, and after 24 h, it is two to three orders of magnitude higher than the Fe-rich carbides. A high number density of Mo-rich carbides is important to strengthen these low-alloyed tool steels through precipitation hardening. The results indicate that the Mo-rich secondary carbide precipitates are initially of MC character, whilst later they start to appear as M2C. This change of the secondary carbides is diffusion driven and is therefore mainly seen for longer tempering times at the higher tempering temperature of 600◦C.
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| 26. |
- Claesson, Erik, 1988-
(författare)
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Carbides in martensitic medium carbon low alloyed tool steels studied with small angle scattering techniques, electron microscopy and atom probe tomography
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Medium carbon low alloyed tool steels are used today in various areas to shape plastics, nonferrous metals, and steels, and they are crucial in the manufacturing industry. To be effective, tool steels must be strong and tough, and have high wear resistance and temperature stability. To achievethe desired properties, materials are alloyed so that secondary phaseparticles precipitate during processing, especially during the tempering of martensitic steels. However, the hardening contribution relates to the size,volume fraction and number density of precipitates, controlled by alloy composition and heat-treating parameters. It is therefore essential to understand how, where, and when the particles nucleate and how the precipitation sequence and kinetics are affected by alloying additions,tempering temperature, and time.This work is aimed to study carbide precipitation in two commercial low-alloy tool steel using small-angle neutron and X-ray scattering. To support these methods, samples were characterized with transmission electronmicroscopy (TEM) and atom probe tomography (APT). With a combination of high-resolution techniques, it was possible to establish the precipitation sequence in these steels. It was also possible with various small angle scattering techniques to determine the evolution of volume fraction and number density of precipitates as a function of tempering parameters.First, small angle neutron scattering (SANS) was used, which is an excellent method for bulk quantification of small precipitates in steel. It was possible with SANS to broadly study the precipitation process depending on annealing temperature and time. However, it is difficult with regular small angle scattering (SAS) to distinguish particle types with overlapping size distributions. To possibly separate the scattering signal from different carbide types, measurements were carried out with polarized small angle neutron scattering (SANSPOL) and anomalous small-angle X-ray scattering(ASAXS). With ASAXS it was possible to isolate the signal from molybdenum-rich carbides from other types of carbides.With SANSPOL, it was possible to follow the enrichment of alloy elements in cementite. The appearance of cementite can be described as an iron-richcore with a chromium-enriched shell. The partitioning of substitutional elements affects the stability of cementite and the alloy carbides. It was also possible with SANSPOL, during heating, to follow the initial precipitation of particles.Results from different experimental methods have been compared with precipitation simulations using thermodynamics-based precipitationmodeling. Equilibrium calculations indicates the possible stability ofdifferent precipitates, and the kinetics are captured with tools such as TCPRISMA to simulate structure evolution during tempering. Hardness measurements were made to correlate structure evolution to mechanical properties.
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| 27. |
- Claesson, Erik, et al.
(författare)
-
Early precipitation behavior of secondary carbides in medium carbon low alloyed tool steel studied by in-situ polarized small-angle scattering and precipitation modelling
-
Tidskriftsartikel (refereegranskat)abstract
- The strength of tempered martensite in low alloyed tool steel depends on the precipitation of secondary carbides. Tempering parameters such as time and temperature together with heating rate to tempering temperature will influence the precipitation sequence and these critical process parameters must be controlled to achieve ultimate precipitation strengthening. In this work precipitation was studied in a low alloyed tool steel using in-situ polarized small angle scattering (SANSPOL) during heating and isothermal holding. It was possible with SANSPOL to study the initial precipitation of secondary Mo- and V-rich carbides. It was found that Mo- and V-rich carbides form above 500 °C, simultaneously to the formation of cementite, which started to form already at lower temperature. It was furthermore found that the cementite particles can be described as having a core-shell structure, the Mo-V-rich carbides small and were approximated as spherical. Precipitation simulations performed using TC-PRSIMA were finally performed to compare with the experimental results, and the simulations were found to describe the experimental results well.
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| 28. |
- Claesson, Erik, et al.
(författare)
-
Evolution of iron carbides during tempering of low-alloy tool steel studied with polarized small angle neutron scattering, electron microscopy and atom probe
- 2022
-
Ingår i: Materials Characterization. - : Elsevier BV. - 1044-5803 .- 1873-4189. ; 194, s. 112464-112464
-
Tidskriftsartikel (refereegranskat)abstract
- The magnetic scattering of iron carbides in low-alloy tool steel was investigated ex-situ by polarized small angle neutron scattering measurements after tempering the steel at 550 °C and 600 °C. Magnetic features could be detected in the as-quenched sample resulting in a negative interference term, believed to be either θ-Fe3C, η-Fe2C, or ε-Fe2-3C. During tempering the evolution of cementite could be studied by the variation of the interference term and in γ-ratio, which is the ratio of the magnetic to nuclear scattering length density contrast. From scanning transmission electron microscopy (STEM) and atom probe tomography, it is evident that cementite (θ-Fe3C) is present directly when reaching the tempering temperature of either 550 °C or 600 °C. At longer tempering times, cementite gets enriched with substitutional elements like chromium and manganese, forming an enriched shell on the cementite particles. STEM and energy dispersive x-ray spectrometry show that the chemical composition of small cementite particles approaches that of Cr-rich M7C3 carbides after 24 h at 600 °C. It is also seen that small non-magnetic particles precipitate during tempering and these correspond well with molybdenum and vanadium-rich carbides.
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| 29. |
- Claesson, Erik, et al.
(författare)
-
Mapping of the carbide precipitation sequence and the in-situ transformation of cementite in medium carbon low alloyed tool steel with Scanning Precession Electron Diffraction
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Precipitation of carbides after tempering at 600 °C of a medium carbon low alloyed tool steel was studied with scanning precession electron diffraction (SPED). The precipitation sequence was evaluated by mapping the carbide distribution on carbon extraction replicas. This gave detailed information about formed precipitates which could be identified based on electron diffraction. The experimental work was compared to equilibrium calculations and energy dispersive x-ray spectroscopy (EDX). It was found that precipitates ε-Fe2C within laths during quenching via auto-tempering. During reheating to tempering temperature ε-Fe2C was dissolved and replaced by cementite, θ-M3C, which predominately form on martensitic lath boundaries. Vanadium and molybdenum are known from literature to form cubic MC or hexagonal M2C carbides, respectively. In this work it was found that the small carbides in the early stage of tempering have predominantly a cubic MC structure, even if the V/Mo-ratio the studied steel was only 0.12. Later during tempering more stable carbides, such as M7C3 and M23C6, also form, and it was concluded that the M7C3 form both by separate nucleation and in-situ transformation on cementite. The latter phenomenon was seen as particles with a core of cementite and shell of M7C3 after 24 h at 600 °C of tempering.
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| 30. |
- Claesson, Erik, et al.
(författare)
-
Scanning precession electron diffraction study of carbide precipitation sequence in low alloy martensitic Cr-Mo-V tool steel
- 2023
-
Ingår i: Materials Characterization. - : Elsevier BV. - 1044-5803 .- 1873-4189. ; 202
-
Tidskriftsartikel (refereegranskat)abstract
- Precipitation of carbides after tempering of a medium carbon low alloyed Cr-Mo-V tool steel at 600 degrees C was studied with scanning precession electron diffraction (SPED) in a transmission electron microscope (TEM). The precipitation sequence was evaluated by mapping the carbide distribution on carbon extraction replicas prepared from samples tempered for different durations of up to 24 h. The SPED results were supplemented by equilibrium calculations and energy dispersive x-ray spectroscopy (EDX) measurements in a TEM. It was found that e-Fe2C precipitates within martensite laths during quenching via auto-tempering. During reheating to tempering temperature e-Fe2C was dissolved and replaced by cementite, 0-M3C, which predominately form on martensite boundaries. It was further found that the small carbides in the early stage of tempering have predominantly a cubic MC structure, even if the V/Mo-ratio of the studied steel was only 0.12, and it is known from literature that V and Mo form cubic MC or hexagonal M2C carbides, respectively. Later during tempering more stable carbides, such as M7C3 and M23C6, also form, and it was concluded that the M7C3 form both by separate nucleation and precipitation on the cementite/matrix interface. The latter phenomenon was seen as particles with a core of cementite and a shell of M7C3 after 24 h of tempering.
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| 31. |
- Claesson, Erik, et al.
(författare)
-
Selective characterization of Mo-rich secondary carbides in medium carbon low alloyed tool steel by anomalous small angle x-ray scattering
-
Tidskriftsartikel (refereegranskat)abstract
- Anomalous small angle X-ray scattering was used to study Mo (Mo) rich secondary carbides during tempering of medium carbon low alloyed tool steel. The scattering contrast of Mo-rich carbides varies systematically close to the absorption edge of Mo. No anomalous effect could be seen for the as-quenched sample. However, a clear effect could be seen for all tempered conditions. By studying the energy dependency of scattering invariant, Mo-rich carbides are believed to have a MC structure in the early stages of tempering. The -ratio is decreasing with time which is believed to be related to the formation M2C carbides. This is more pronounced for samples tempered at 600 °C as compared to 550 °C. The volume fraction was calculated using the ASAXS gradient method. At 550 °C the volume fraction of (Mo,V)C was increasing up to 24 h of tempering to 1.7·10-3. At 600 °C tempering a maximum in volume fraction was reached already after 1 h with 1.6·10-3 fraction. The size and number density of carbides are more stable at 550 °C compared to 600 °C.
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| 32. |
- Collet, Francois, et al.
(författare)
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Old friends and new acquaintances : Tie formation mechanisms in an inter-organizational network generated by employee mobility
- 2013
-
Ingår i: Social Networks. - : Elsevier. - 0378-8733 .- 1879-2111. ; 35:3, s. 288-299
-
Tidskriftsartikel (refereegranskat)abstract
- This study investigates mechanisms of tie formation in an interorganizational network generated by the mobility of employees between organizations. We analyze a data set that contains information on all organizations in the Stockholm metropolitan area between 1990 and 2003. We show that the formation of new ties is contingent upon the direction of past ties, and that most connections occur at an intermediate geodesic distance of 2 and 3. The findings highlight the importance of tie direction and indirect connections in research on network dynamics and knowledge exchanges stemming from the mobility of employees across organizations.
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| 33. |
- Dahlström, Alexander, et al.
(författare)
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An Experimental Assessment of the alpha plus alpha ' Miscibility Gap in Fe-Cr
- 2017
-
Ingår i: TMS 2017 146TH ANNUAL MEETING & EXHIBITION SUPPLEMENTAL PROCEEDINGS. - Cham : Springer. - 9783319514932 - 9783319514925 ; , s. 711-718
-
Konferensbidrag (refereegranskat)abstract
- Phase separation in the Fe-Cr system has been studied experimentally. The upper limit of the miscibility gap and phase separation kinetics during the early stages of decomposition was studied using Vickers micro-hardness tests and atom probe tomography. The results indicate that the upper limit of the miscibility gap in current thermodynamic descriptions is overestimated, but it is necessary to further analyze the transition across the upper limit of the miscibility gap before drawing conclusions. This work demonstrates the efficient combination of micro-hardness measurements and atom probe tomography to investigate the miscibility gap in the Fe-Cr system.
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| 34. |
- Dahlström, Alexander, et al.
(författare)
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Effect of Stress on Spinodal Decomposition in Binary Alloys : Atomistic Modeling and Atom Probe Tomography
- 2022
-
Ingår i: Metallurgical and Materials Transactions. A. - : Springer Nature. - 1073-5623 .- 1543-1940. ; 53:1, s. 39-49
-
Tidskriftsartikel (refereegranskat)abstract
- Self-organizing nanostructure evolution through spinodal decomposition is a critical phenomenon determining the properties of many materials. Here, we study the influence of stress on the morphology of the nanostructure in binary alloys using atomistic modeling and atom probe tomography. The atomistic modeling is based on the quasi-particle approach, and it is compared to quantitative three-dimensional (3-D) atom mapping results. It is found that the magnitude of the stress and the crystallographic direction of the applied stress directly affect the development of spinodal decomposition and the nanostructure morphology. The modulated nanostructure of the binary bcc alloy system is quantified by a characteristic wavelength, λ. From modeling the tensile stress effect on the A-35 at. pct B system, we find that λ001<λ111<λ101<λ112 and the same trend are observed in the experimental measurements on an Fe-35 at. pct Cr alloy. Furthermore, the effect of applied compressive and shear stress states differs from the effect of the applied tensile stress regarding morphological anisotropy.
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| 35. |
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| 36. |
- Dahlström, Alexander, et al.
(författare)
-
Nanostructure in Fe0.65Cr0.35 close to the upper limit of the miscibility gap
- 2020
-
Ingår i: Scripta Materialia. - : PERGAMON-ELSEVIER SCIENCE LTD. - 1359-6462 .- 1872-8456. ; 180, s. 62-65
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Tidskriftsartikel (refereegranskat)abstract
- The nanostructure of an Fe0.65Cr0.35 alloy has been investigated by atom probe tomography after high precision thermal treatments close to the upper limit of the miscibility gap (MG). It is found that the wavelength of the decomposed ferrite between Cr- and Fe-rich regions grows exponentially when approaching the upper limit of the MG. Furthermore, the nanostructure change is gradual with temperature indicating a narrow metastable region and a diffuse transition out of the spinodal regime. Atomistic modelling near the limit of instability further supports the experimental observations. The findings are discussed in relation to the Cahn-Hilliard theory.
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| 37. |
- Dahlström, Alexander, et al.
(författare)
-
Precision Thermal Treatments, Atom Probe Characterization, and Modeling to Describe the Fe-Cr Metastable Miscibility Gap
- 2021
-
Ingår i: Metallurgical and Materials Transactions. A. - : Springer. - 1073-5623 .- 1543-1940. ; 52:4, s. 1453-1464
-
Tidskriftsartikel (refereegranskat)abstract
- Abstract: The Fe-Cr metastable miscibility gap has been studied by high-precision thermal treatments, Vickers micro-hardness (HV) measurements, and atom probe tomography (APT). Thermodynamic modeling further supplements the experimental work. The results obtained show that recent thermodynamic descriptions of the metastable miscibility gap found in literature generally overestimates the consolute temperature. We can show that the source of ambiguity in previous studies is most likely a lack of clear distinction between Cr-Cr clustering and α′ formation. This distinction is here made by APT results, and it leads to a determined consolute temperature of 580 ± 1 °C for Fe0.50Cr0.50. The revised thermodynamic modeling of the metastable miscibility gap captures the experimental results and is consistent with the overall picture from the Fe-Cr data in the literature. Graphic Abstract: [Figure not available: see fulltext.]
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| 38. |
- Das, Yadunandan, et al.
(författare)
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Quantitative Nanostructure and Hardness Evolution in Duplex Stainless Steels : Under Real Low-Temperature Service Conditions
- 2022
-
Ingår i: Metallurgical and Materials Transactions. A. - : Springer Nature. - 1073-5623 .- 1543-1940. ; 53:2, s. 723-735
-
Tidskriftsartikel (refereegranskat)abstract
- Duplex stainless steels are a group of widely used stainless steels, because of their attractive combination of strength and corrosion resistance. However, these steels embrittle because of a phase separation phenomenon in the ferrite phase when exposed to temperatures within the miscibility gap. This manuscript investigates the phase separation in two commercial stainless steels, the duplex stainless steel (DSS) 22Cr-5Ni (2205 or UNS S32205), and the super-duplex stainless steel (SDSS) 25Cr-7Ni (2507 or UNS S32750), and its subsequent effect on mechanical property evolution. Long-term isothermal aging heat treatments were carried out at industrially relevant temperatures between 250 °C and 350 °C for up to 48,000 hours, and quantitative measurements of the amplitude and wavelength of the phase separated nanostructure were obtained using Small-Angle Neutron Scattering (SANS). These quantifications were used as input parameters in hardness models to predict the hardness evolution. It is concluded that the quantitative information from SANS combined with these hardness models enables the prediction of hardness evolution in DSS at low temperatures, which in turn correlates with the embrittlement of the DSS.
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| 39. |
- Das, Yadunandan, et al.
(författare)
-
Small-angle neutron scattering quantification of phase separation and the corresponding embrittlement of a super duplex stainless steel after long-term aging at 300 degrees C
- 2020
-
Ingår i: Materialia. - : ELSEVIER SCI LTD. - 2589-1529. ; 12
-
Tidskriftsartikel (refereegranskat)abstract
- Small-angle neutron scattering (SANS) was applied to quantify the nanostructural evolution during spinodal decomposition in a 25Cr-7Ni (wt.%) super duplex stainless steel isothermally aged at 300 degrees C, for up-to 48,000 h. Prior to the application on the 25Cr-7Ni alloy, the SANS methodology was validated by comparing results from SANS measurements on binary Fe-Cr alloys with atom probe tomography results. SANS results on the 25Cr-7Ni alloy indicated that decomposition wavelength decreased from 5.1 nm to 4.5 nm, whereas the amplitude increased from 15.0 to 33.4 at.%. This quantitative nanostructural evolution correlated to a hardening of the ferrite phase by 190 HV and a reduction of the sub-size Charpy-V impact toughness from 60 J to 25 J.
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| 40. |
- Ding, Wei, et al.
(författare)
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Heat treatment, microstructure and mechanical properties of a C-Mn-Al-P hot dip galvanizing TRIP steel
- 2016
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Ingår i: Materials Science & Engineering. - : Elsevier. - 0921-5093 .- 1873-4936. ; 674, s. 151-157
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Tidskriftsartikel (refereegranskat)abstract
- Heat treatments of a hot dip galvanizing TRIP (Transformation induced plasticity) steel with chemical composition 0.20C-1.50Mn-1.2Al-0.07P(mass%) were performed in a Gleeble 3500 laboratory equipment. The heat treatment process parameters were varied to investigate the effect of intercritical annealing temperature as well as isothermal bainitic transformation (IBT) temperature and time, on the microstructure and the mechanical properties. The microstructure was investigated using scanning electron microscopy, transmission electron microscopy and x-ray diffraction, while mechanical properties were evaluated by tensile testing. Furthermore, to generate a better understanding of the phase transformations during heat treatment, dilatometry trials were conducted. The desired microstructure containing ferrite, bainite, retained austenite and martensite was obtained after the heat treatments. It was further found that the IBT is critical in determining the mechanical properties of the steel, since it controls the fraction of bainite. With increasing bainite fraction, the fraction of retained austenite increases while the fraction of martensite decreases. The mechanical properties of the steel are excellent with a tensile strength above 780 MPa (expect in one case) and elongation above 22%.
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| 41. |
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| 42. |
- Engdahl, Elin, et al.
(författare)
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Increased Serological Response Against Human Herpesvirus 6A Is Associated With Risk for Multiple Sclerosis
- 2019
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Ingår i: Frontiers in Immunology. - : Frontiers Media S.A.. - 1664-3224. ; 10
-
Tidskriftsartikel (refereegranskat)abstract
- Human herpesvirus (HHV)-6A or HHV-6B involvement in multiple sclerosis (MS) etiology has remained controversial mainly due to the lack of serological methods that can distinguish the two viruses. A novel multiplex serological assay measuring IgG reactivity against the immediate-early protein 1 from HHV-6A (IE1A) and HHV-6B (IE1B) was used in a MS cohort (8,742 persons with MS and 7,215 matched controls), and a pre-MS cohort (478 individuals and 476 matched controls) to investigate this further. The IgG response against IE1A was positively associated with MS (OR = 1.55, p = 9 × 10-22), and increased risk of future MS (OR = 2.22, p = 2 × 10-5). An interaction was observed between IE1A and Epstein-Barr virus (EBV) antibody responses for MS risk (attributable proportion = 0.24, p = 6 × 10-6). In contrast, the IgG response against IE1B was negatively associated with MS (OR = 0.74, p = 6 × 10-11). The association did not differ between MS subtypes or vary with severity of disease. The genetic control of HHV-6A/B antibody responses were located to the Human Leukocyte Antigen (HLA) region and the strongest association for IE1A was the DRB1*13:01-DQA1*01:03-DQB1*06:03 haplotype while the main association for IE1B was DRB1*13:02-DQA1*01:02-DQB1*06:04. In conclusion a role for HHV-6A in MS etiology is supported by an increased serological response against HHV-6A IE1 protein, an interaction with EBV, and an association to HLA genes.
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| 43. |
- Ertug, Gokhan, et al.
(författare)
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KIN TIES AND THE PERFORMANCE OF NEW FIRMS: A STRUCTURAL APPROACH
- 2020
-
Ingår i: Academy of Management Journal. - : ACAD MANAGEMENT. - 0001-4273 .- 1948-0989. ; 63:6, s. 1893-1922
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Tidskriftsartikel (refereegranskat)abstract
- Kin ties are all but ubiquitous in new firms. However, their effects on performance are not straightforward, as they can provide new firms with advantages (enhanced coordination and cooperation) as well as disadvantages (reduced diversity, nepotism concerns, and the possible spillover of personal conflict). As kin ties may have both positive and negative implications for performance, a contingency approach to the performance of new firms is valuable. We develop such an approach by relating different structural configurations of kin ties-whether they are between founders, between founders and employees, or between employees-to the performance of new firms. We test our predictions using data on 4,967 new firms founded in Stockholm between 1998 and 2003. Our theory deepens our understanding of why kin ties have heterogeneous effects on the performance of new firms.
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| 44. |
- Ertug, Gokhan, et al.
(författare)
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THE ART OF REPRESENTATION: HOW AUDIENCE-SPECIFIC REPUTATIONS AFFECT SUCCESS IN THE CONTEMPORARY ART FIELD
- 2016
-
Ingår i: Academy of Management Journal. - : ACAD MANAGEMENT. - 0001-4273 .- 1948-0989. ; 59:1, s. 113-134
-
Tidskriftsartikel (refereegranskat)abstract
- We study the effects of actors audience-specific reputations on their levels of success with different audiences in the same field. Extending recent work that has emphasized the presence of multiple audiences with different concerns, we demonstrate that considering audience specificity leads to an improved understanding of reputation effects. Using data on emerging artists in the field of contemporary art from 2001 to 2010, we investigate the manner in which artists audience-specific reputations affect their subsequent success with two distinct audiences: museums and galleries. Our findings suggest that audience-specific reputations have systematically different effects with respect to success with museums and galleries. Our findings also illuminate the extent to which audience-specific reputations are relevant for emerging research on the contingent effects of reputation. In particular, our findings support our predictions that audiences differ from one another in terms of the extent to which other signals (specifically, status and interaction with other audiences) enhance or reduce the value of audience-specific reputations. Our study thus advances theory by providing empirical evidence for the value of incorporating audience-specific reputations into the general study of reputation.
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| 45. |
- Fischer, Tim, et al.
(författare)
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Creep-fatigue properties of austenitic cast iron D5S with tension and compression dwell : A dislocation density-based crystal plasticity study
- 2022
-
Ingår i: Materials Science & Engineering. - : Elsevier BV. - 0921-5093 .- 1873-4936. ; 860, s. 144212-
-
Tidskriftsartikel (refereegranskat)abstract
- To predict and better understand the creep-fatigue behaviour of austenitic cast iron D5S under tension and compression dwell at 800 degrees C, a physics-based crystal plasticity model that describes the complex rate-and temperature-dependent deformation of the material as a function of the dislocation density is implemented. In addition to the tension and compression dwell direction, the effect of three different dwell times (30, 180 and 600 s) on the creep-fatigue properties is investigated. The dislocation density-based crystal plasticity simulations are compared to experimental tests from a prior work. While relaxation tests and low-cycle fatigue (LCF) tests without dwell assist in systematically identifying the material parameters, creep-fatigue (CF) data is used to validate the predictions. The virtual testing is performed on a large-scale representation of the actual test specimen with a polycrystalline structure. To analyse the fatigue damage mechanism, small-scale predictions are also conducted using a micromechanical unit cell approach. Here, a single graphite nodule frequently found in the material is embedded into the austenitic matrix. In the present work, a close agreement is achieved between the predicted CF behaviour and the experimental results. Consistent with the experimental findings, the simulation results show that the addition of compression dwell leads to an uplift of the overall tensile stress level, which significantly reduces the fatigue life of the material. The unit cell studies demonstrate that during this uplift, a strong localisation of stresses and strains arises at the graphite/matrix interface, triggering the nucleation and growth of cavities and/or debonding.
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| 46. |
- Fischer, Tim, et al.
(författare)
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Relating stress/strain heterogeneity to lath martensite strength by experiments and dislocation density-based crystal plasticity
- 2024
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Ingår i: International journal of plasticity. - : Elsevier BV. - 0749-6419 .- 1879-2154. ; 174
-
Tidskriftsartikel (refereegranskat)abstract
- To enhance the fundamental understanding for micromechanical lath martensite deformation, the microstructure as well as macro- and microscopic tensile properties of as -quenched 15-5 PH stainless steel are systematically analysed depending on the austenitisation temperature. Based on electron backscatter diffraction (EBSD) and backscattered electron (BSE) analysis, it is noted that the martensite morphology alters from a less defined to a more clearly defined parallel arrangement of the block and lath structure with increasing temperature. For an indepth quantification of the hierarchical boundary strengthening contributions in relation to local stress/strain heterogeneity, separate high-fidelity virtual microstructures are realised for the different scales (prior austenite grains, packets and blocks). This is consistent with the materials transformation process. The virtual microstructures are simulated employing the crystal plasticity finite element method (CPFEM) adapted for handling high dislocation density and encompassing all relevant strengthening mechanisms by boundaries, dislocations and solute atoms. While accurately capturing the measured size -dependent stress-strain behaviour, the simulations reveal in line with the experiments (Hall-Petch) that blocks are the most effective dislocation motion barrier, causing increased strain hardening and stress/strain heterogeneity. Furthermore, since strain localisation is predicted strongest in the distinct block structure, the experimentally observed early plastic material yielding is thought to be favoured here.
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| 47. |
- Fischer, Tim, et al.
(författare)
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Sensitivity of local cyclic deformation in lath martensite to flow rule and slip system in crystal plasticity
- 2023
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Ingår i: Computational materials science. - : Elsevier BV. - 0927-0256 .- 1879-0801. ; 222, s. 112106-
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Tidskriftsartikel (refereegranskat)abstract
- The prediction of the cyclic deformation behaviour in lath martensite-based high-strength steels requires constitutive models that reflect the local stress and strain fields as accurately as possible. At the same time, the constitutive models should act as efficiently as possible in order to achieve the required high number of cycles in a finite time. Only few research works have studied the sensitivity of the local cyclic deformation in lath martensite to the power law-based flow rule (Hutchinson or Chaboche-Cailletaud) and the active body-centred cubic (bcc) slip systems ({110}(111) and {112}(111)) in the crystal plasticity finite element method (CPFEM). This paper, therefore, aims to provide some guidance in the selection of suitable flow rule and slip systems. Based on full-field micromechanical modelling of a medium-carbon steel under symmetric strain-controlled cyclic loading, it can be shown that the two most commonly used flow rules according to Hutchinson and Chaboche-Cailletaud are equally capable of predicting the local stress and strain distributions within the hierarchical martensitic microstructure. However, using the Hutchinson flow rule increases the computational performance for the quasi-rate-independent problem considered here. The local distributions found differ strongly from those in the parent austenitic microstructure. If plastic deformation is assumed not only on the slip systems {110}(111), as often done, but also on the {112}(111) type, a redistribution of the bimodal distributed local stresses occurs at a significantly lower stress level. The unimodal distributed local strains are less affected by this. In addition, it is found that slightly different critical resolved shear stress (CRSS) values for both slip system types influence the local stress and strain distributions less severely than the additional plastic slip activation in the material.
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| 48. |
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Frontiers of sociology
- 2009
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Samlingsverk (redaktörskap) (övrigt vetenskapligt/konstnärligt)abstract
- The 37th World Congress of the IIS focused on theory and research at the forefront of sociology and the relationship between sociology and its neighbouring disciplines. This volume constitutes a sustained effort by prominent sociologists and other social scientists to assess the standing of sociology.
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| 49. |
- Gardelli, Åsa, et al.
(författare)
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Det behövs bättre kunskap om AKK
- 2017
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Ingår i: Intra. - : Stiftelsen Intra. - 1102-4143. ; :4
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Tidskriftsartikel (refereegranskat)abstract
- Att kommunicera är en grundläggande mänsklig rättighet och kommunikation är en förutsättning för delaktighet, medbestämmande och självständighet. Många personer med funktionsnedsättningar har kommunikationssvårigheter. För att de ska kunna utöva sin rätt till självbestämmande och inflytande bör därför personal inom Socialförvaltningens verksamheter kunna ge stöd till kommunikation. I Luleå har man utbildat all LSS-personal i AKK (Alternativ kompletterande kommunikation). Det har gett fina resultat.
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| 50. |
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