| 1. |
- Westraadt, J. E., et al.
(författare)
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A high-resolution analytical scanning transmission electron microscopy study of the early stages of spinodal decomposition in binary Fe-Cr
- 2015
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Ingår i: Materials Characterization. - : Elsevier BV. - 1044-5803 .- 1873-4189. ; 109, s. 216-221
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Tidskriftsartikel (refereegranskat)abstract
- Spinodal decomposition (SD) is an important phenomenon in materials science and engineering. For example, it is considered to be responsible for the 475 degrees C embrittlement of stainless steels comprising the bcc (ferrite) or bct (martensite) phases. Structural characterization of the evolving minute nano-scale concentration fluctuations during SD in the Fe-Cr system is, however, a notable challenge, and has mainly been considered accessible via atom probe tomography (APT) and small-angle neutron scattering. The standard tool for nanostructure characterization, viz, transmission electron microscopy (TEM), has only been successfully applied to late stages of SD when embrit-dement is already severe. However, we here demonstrate that the structural evolution in the early stages of SD in binary Fe-Cr, and alloys based on the binary, are accessible via analytical scanning TEM. An Fe-36 wt% Cr alloy aged at 500 degrees C for 1, 10 and 100 h is investigated using an aberration-corrected microscope and it is found that highly coherent and interconnected Cr-rich regions develop. The wavelength of decomposition is rather insensitive to the sample thickness and it is quantified to 2, 3 and 6 nm after ageing for 1, 10 and 100 h, which is in reasonable agreement with prior APT analysis. The concentration amplitude is more sensitive to the sample thickness and acquisition parameters but the TEM analysis is in good agreement with APT analysis for the longest ageing time. These findings open up for combinatorial TEM studies where both local crystallography and chemistry is required.
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| 2. |
- Korzhavyi, Pavel A., 1966-, et al.
(författare)
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Electronic structure and effective chemical and magnetic exchange interactions in bcc Fe-Cr alloys
- 2009
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 79:5, s. 054202-
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Forskningsöversikt (refereegranskat)abstract
- Electronic structure calculations are employed in order to investigate the cohesive properties (lattice parameter, enthalpy of formation, and bulk modulus) of random Fe-Cr alloys as a function of composition and magnetic state, as well as to derive the chemical and magnetic exchange interactions of the constituent atoms. The calculations predict certain anomalies in the cohesive properties of ferromagnetic alloys at a concentration of about 7 at % Cr; these anomalies may be related to the changes in Fermi-surface topology that occur with composition in this alloy system. The obtained interatomic interactions are used as parameters in the configurational (Ising) and magnetic (Heisenberg) Hamiltonians for modeling finite-temperature thermodynamic properties of the alloys. We discuss the approximations and limitations of similar modeling approaches, investigate the origin of existing difficulties, and analyze possible ways of extending the theoretical models in order to capture the essential physics of interatomic interactions in the Fe-Cr or similar alloys where magnetism plays a crucial role in the phase stability.
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| 3. |
- Zhou, J., et al.
(författare)
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Quantitative Evaluation of Spinodal Decomposition in Fe-Cr by Atom Probe Tomography and Radial Distribution Function Analysis
- 2013
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Ingår i: Microscopy and Microanalysis. - : Oxford University Press (OUP). - 1435-8115 .- 1431-9276. ; 19:3, s. 665-675
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Tidskriftsartikel (refereegranskat)abstract
- Nanostructure evolution during low temperature aging of three binary Fe-Cr alloys has been investigated by atom probe tomography. A new method based on radial distribution function (RDF) analysis to quantify the composition wavelength and amplitude of spinodal decomposition is proposed. Wavelengths estimated from RDF have a power-law type evolution and are in reasonable agreement with wavelengths estimated using other more conventional methods. The main advantages of the proposed method are the following: (1) Selecting a box size to generate the frequency diagram, which is known to generate bias in the evaluation of amplitude, is avoided. (2) The determination of amplitude is systematic and utilizes the wavelength evaluated first to subsequently evaluate the amplitude. (3) The RDF is capable of representing very subtle decomposition, which is not possible using frequency diagrams, and thus a proposed theoretical treatment of the experimental RDF creates the possibility to determine amplitude at very early stages of spinodal decomposition.
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| 4. |
- 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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| 5. |
- Hillert, M., et al.
(författare)
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Comparison between solute drag and dissipation of Gibbs energy by diffusion
- 2001
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Ingår i: Scripta Materialia. - 1359-6462 .- 1872-8456. ; 45:2, s. 221-227
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Tidskriftsartikel (refereegranskat)abstract
- The solute drag and the dissipation of Gibbs energy in a partitionless phase transformation are compared numerically. They agree if the solute drag is compared with the driving force over the interface and the solute spike in front of the interface. The dissipation can be evaluated over this whole region or over the interface alone.
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| 6. |
- Loginova, I., et al.
(författare)
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The phase-field approach and solute drag modeling of the transition to massive gamma ->alpha transformation in binary Fe-C alloys
- 2003
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Ingår i: Acta Materialia. - : Elsevier BV. - 1359-6454 .- 1873-2453. ; 51:5, s. 1327-1339
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Tidskriftsartikel (refereegranskat)abstract
- The transition between diffusion controlled and massive transformation gamma --> alpha in Fe-C alloys is investigated by means of phase-field simulations and thermodynamic functions assessed by the Calphad technique as well as diffusional mobilities available in the literature. A gradual variation in properties over an incoherent interface, having a thickness around 1 nm, is assumed. The phase-field simulations are compared with a newly developed technique to model solute drag during phase transformations. Both approaches show qualitatively the same behavior and predict a transition to a massive transformation at a critical temperature below the T-0 line and close to the alpha/alpha + gamma phase boundary. It is concluded that the quantitative difference between the two predictions stems from different assumptions on how the properties vary across the phase interface yielding a lower dissipation of Gibbs energy by diffusion in the phase-field simulations. The need for more detailed information about the actual variation in interfacial properties is emphasized.
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| 7. |
- Odqvist, J., et al.
(författare)
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A general method for calculating deviation from local equilibrium at phase interfaces
- 2003
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Ingår i: Acta Materialia. - : Elsevier BV. - 1359-6454 .- 1873-2453. ; 51:4, s. 1035-1043
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Tidskriftsartikel (refereegranskat)abstract
- A general method to calculate the deviation from local equilibrium at phase interfaces in multicomponent systems is suggested. The deviation is caused by solute drag and finite interfacial mobility. In the limit of low transformation rates the new method degenerates to the well-known local equilibrium condition. The phase interface is divided into three zones, each with a finite thickness. In each zone a variation in thermodynamic properties and diffusional mobilities is assumed.
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| 8. |
- Odqvist, J., et al.
(författare)
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Effect of alloying elements on the gamma to alpha transformation in steel. I
- 2002
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Ingår i: Acta Materialia. - 1359-6454 .- 1873-2453. ; 50:12, s. 3211-3225
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Tidskriftsartikel (refereegranskat)abstract
- A newly constructed computer program was used to simulate partitionless growth of alpha in gamma of Fe-Ni-C alloys, taking into account so-called solute drag by evaluating the dissipation of Gibbs energy due to diffusion inside the interface and in the nickel spike being pushed in front of it. It could be shown how the conditions at the alpha/gamma interface vary with the velocity. A continuous change from paraequilibrium to quasi-paraconditions could be illustrated in the phase diagram. By combination with an approximate analytical growth equation, it was possible to derive the thickness of a as function of time. The growth velocity was assumed to start at very high values but decreased due to the pile-up of carbon. For alloy compositions outside the limit for quasi-paraconditions and just inside it the growth was predicted to stop suddenly when critical conditions are approached during the reaction. For alloy compositions further inside the limit, there was no such stop, except by the action of impingement of diffusion fields for carbon. Somewhere between the lines for paraequilibrium and quasi-paraconditions there is a rather rapid drop of the final thickness of a. In order to explain experimental information on this drop one must accept an appreciable tendency of segregation of nickel to the alpha/gamma interface.
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| 9. |
- Odqvist, Maria, et al.
(författare)
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High-Sensitivity Troponins and Outcomes After Myocardial Infarction
- 2018
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Ingår i: Journal of the American College of Cardiology. - : Elsevier BV. - 0735-1097 .- 1558-3597. ; 71:23, s. 2616-2624
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND It remains unknown how the introduction of high-sensitivity cardiac troponin T (hs-cTnT) has affected the incidence, prognosis, and use of coronary angiographies and revascularizations in patients with myocardial infarction (MI). OBJECTIVES The aim of this study was to investigate how the incidence of MI and prognosis after a first MI was affected by the introduction of hs-cTnT. METHODS In a cohort study, the authors included all patients with a first MI from the Swedish National Patient Registry from 2009 to 2013. Cox regression was used to calculate hazard ratios (HRs) with 95% confidence intervals (CIs) for risk of all-cause mortality, reinfarction, coronary angiographies, and revascularizations in patients with MI diagnosed using hs-cTnT compared with those diagnosed using conventional troponins (cTn). RESULTS During the study period, 47,133 MIs were diagnosed using cTn and 40,746 using hs-cTnT. The rate of MI increased by 5% (95% CI: 0% to 10%) after the introduction of hs-cTnT. During 3.9 +/- 2.8 years of follow-up, there were 33,492 deaths, with no difference in the risk of all-cause mortality (adjusted HR: 1.00; 95% CI: 0.97 to 1.02). There were, in total, 15,766 reinfarctions during 3.1 +/- 2.3 years of follow-up, with the risk of reinfarction reduced by 11% in patients diagnosed using hs-cTnT (adjusted HR: 0.89; 95% CI: 0.86 to 0.91). The use of coronary angiographies (adjusted HR: 1.16; 95% CI: 1.14 to 1.18) and revascularizations (adjusted HR: 1.13; 95% CI: 1.11 to 1.15) increased in the hs-cTnT group. CONCLUSIONS In a nationwide cohort study including 87,879 patients with a first MI, the introduction of hs-cTnT was associated with an increased incidence of MI, although with no impact on survival. We also found a reduced risk of reinfarction alongside increased use of coronary angiographies and revascularizations. (C) 2018 The Authors. Published by Elsevier on behalf of the American College of Cardiology Foundation.
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| 10. |
- Odqvist, Maria, et al.
(författare)
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Outcomes in patients with chest pain in emergency departments using high-sensitivity versus conventional troponins
- 2023
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Ingår i: Scandinavian Cardiovascular Journal. - : Taylor & Francis. - 1401-7431 .- 1651-2006. ; 57:1
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Tidskriftsartikel (refereegranskat)abstract
- Objectives. There is a paucity of data regarding the association between the use of high-sensitivity troponin (hs-cTn) compared with conventional troponin (cTn) and outcomes in chest pain patients in emergency departments (EDs). This study examined the impact of hs-cTnT on prognosis in chest pain patients in EDs. Design. In an observational cohort study, we included chest pain patients visiting the EDs of 14 hospitals in Sweden from 2011 to 2016. The study population was retrieved from each hospital, and information on characteristics and outcomes was collected from nationwide registries. Cox regression was used to estimate adjusted hazard ratios with 95% confidence intervals (HR, 95% CI) for (1) 1-year all-cause mortality, (2) missed acute coronary syndromes (ACSs), (3) use of coronary angiography, and (4) revascularizations within 30 days. Results. We included 170461 patients with chest pain where 62669 patients were tested with cTn while 107792 patients were tested with hs-cTnT. We found 4149 (4.6%) deaths in the cTn group and 6087 (3.7%) deaths in the hs-cTnT group. Patients in the hs-cTnT group had 9% lower mortality (0.91, 0.87-0.94), and were 14% more likely to undergo coronary angiography (1.14, 1.10-1.17), and 12% more likely to be revascularized (1.12, 1.08-1.17) than patients in the cTn group. Conclusions. Patients with chest pain visiting EDs using hs-cTnT had lower mortality and a higher likelihood of undergoing coronary angiographies and revascularizations than those using cTn. There may be a survival benefit of being tested with hs-cTnT compared with cTn in patients seeking medical attention for chest pain.
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