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  • 1.
    Bate, Pete
    et al.
    RISE - Research Institutes of Sweden, Swerea, Swerea KIMAB AB.
    Lundin, Peter
    RISE - Research Institutes of Sweden, Swerea, Swerea KIMAB AB.
    Lindh-Ulmgren, Eva
    RISE - Research Institutes of Sweden, Swerea, Swerea KIMAB AB.
    Hutchinson, Bevis
    RISE - Research Institutes of Sweden, Swerea, Swerea KIMAB AB.
    Application of laser-ultrasonics to texture measurements in metal processing2017Inngår i: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 123, s. 329-336Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The paper describes in principle how information about textures can be obtained through the application of laser-ultrasonics (LUS) which can be carried out at elevated temperatures, for example in connection with hot rolling. The benefits from getting a measure of texture in this way are explained together with the proposed methodology which is based on the elastic anisotropic properties of the textured material. Measurements are made using only a single laser pulse and in real-time. Two approaches are presented to modelling the propagation of elastic waves, ray tracing and finite difference modelling. These give consistent results but the latter provides a more complete prediction of the ultrasonic spectrum that can be quantitatively related to measured signals through a cross-correlation procedure. Some experimental results are presented for room temperature measurements on a sheet of interstitial-free steel. Agreement between experimental data and modelling results is good and allows estimation of the 4th order coefficients of the orientation distribution function.

  • 2. Guldberg-Pedersen, H
    et al.
    Bergström, L
    YKI – Ytkemiska institutet.
    Stabilizing ceramic suspensions using anionic polyelectrolytes: adsorption kinetics and interparticle forces2000Inngår i: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 48, s. 4563-4570Artikkel i tidsskrift (Fagfellevurdert)
  • 3.
    Hosseini, Seyed
    et al.
    RISE - Research Institutes of Sweden, Swerea, Swerea IVF AB, Tillverkningsprocesser. Chalmers University of Technology, Sweden; AB SKF, Sweden.
    Thuvander, Mattias
    Chalmers University of Technology, Sweden.
    Klement, Uta
    Chalmers University of Technology, Sweden.
    Sundell, Gustav
    Chalmers University of Technology, Sweden.
    Ryttberg, Kristina
    AB SKF, Sweden.
    Atomic-scale investigation of carbon atom migration in surface induced white layers in high-carbon medium chromium (AISI 52100) bearing steel2017Inngår i: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 130, s. 155-163Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The microstructure and chemical composition of white layers (WLs) formed during hard turning of AISI 52100 steel were studied using atom probe tomography (APT) and transmission electron microscopy (TEM). APT analyses revealed a major difference in the re-distribution of the carbon (C) atoms between WLs formed above and below the Ac1 temperature, i.e. T-WL and M-WL, respectively. In T-WL, the C-atoms segregate to grain boundaries (GBs) forming interconnected or isolated C-rich clusters, ∼5 nm, with a concentration of 9.8 ± 0.3 at.%C. Apart from the GB segregation, in M-WLs, large C-rich regions were found with 24.8 ± 0.4 at.%C. Owing to the chemical composition (stoichiometry) and element partitioning of such regions, they were assigned as θ-carbides (cementite). The APT results reveal that the original θ-carbides remain un-dissolved in the M-WLs, but might be plastically deformed due to the excessive strain that exists in hard machining process. The obtained results are in good agreement with the temperatures that are reached during formation of M-WLs. The isolated nano-sized C-clusters were assigned as off-stoichiometric carbides whereas the interconnected C-rich clusters were attributed to Cottrell atmospheres, evident by the linear shape of the C-enrichment as observed in the APT reconstructions. The C-contents in the nano-sized martensitic and ferritic grains were estimated to 0.50 ± 0.06 at.%C and ∼0.46 ± 0.02 at.%C, respectively. The C-content in the ferritic grains, beyond the C-solubility limit in ferrite (<0.1 at.%) is governed by the high dislocation density inside the grains, supported by the favorable binding energy between dislocations and C-atoms compared to C-atoms and Fe in carbides. No other evidence of redistribution of the substitutional alloying elements was observed. TEM analyses showed that T-WLs comprises of an equiaxed and nano-sized grains with well-defined cell boundaries, whereas the structure in the M-WLs comprised of elongated sub-grains formed via re-orientation of the original martensite followed by breakage/partitioning into elongated sub-grains.

  • 4.
    Hutchinson, Bevis
    et al.
    RISE - Research Institutes of Sweden, Swerea, Swerea KIMAB AB.
    Bate, Pete
    RISE - Research Institutes of Sweden, Swerea, Swerea KIMAB AB.
    Lindell, David
    RISE - Research Institutes of Sweden, Swerea, Swerea KIMAB AB.
    Malik, Amer
    RISE - Research Institutes of Sweden, Swerea, Swerea KIMAB AB.
    Barnett, Matthew
    Deakin University, Australia.
    Lynch, Peter
    Deakin University, Australia.
    Plastic yielding in lath martensites – An alternative viewpoint2018Inngår i: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 152, s. 239-247Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In recent literature the gradual yielding of quenched martensitic steels has been attributed to either heterogeneous microstructures having different strength levels or to the presence of small scale, Type II, residual stresses. Using in-situ tensile testing in synchrotron diffraction experiments in combination with crystal plasticity finite element modelling (CPFEM) we show that the dominant influence on yielding derives from the residual stresses which are a product of the displacive transformation from austenite during quenching. As plastic straining proceeds, the measured diffraction peaks become narrower and asymmetric, as predicted by the CPFEM calculations. The model predictions are generally in good agreement with published results showing large variations in local strains in different microstructural elements.

  • 5.
    Hutchinson, Bevis
    et al.
    RISE, Swerea, Swerea KIMAB AB.
    Hagström, Joacim
    RISE, Swerea, Swerea KIMAB AB.
    Karlsson, Oskar
    RISE, Swerea, Swerea KIMAB AB.
    Lindell, David
    RISE, Swerea, Swerea KIMAB AB.
    Tornberg, Malin
    RISE, Swerea, Swerea KIMAB AB.
    Lindberg, Fredrik
    RISE, Swerea, Swerea KIMAB AB.
    Thuvander, M.
    Chalmers University of Technology.
    Microstructures and hardness of as-quenched martensites (0.1-0.5%C)2011Inngår i: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 59, nr 14, s. 5845-5858Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Four commercial steels with carbon contents in the range 0.1-0.5 wt.% have been examined in the as-quenched condition using electron microscopy, X-ray diffraction and atom probe tomography. The austenite had been deformed 0%, 10% and 30% prior to brine quenching. No influence of this deformation was evident on the martensite hardness or in any of the microstructure measurements. Increasing carbon content showed a well-known marked effect on the hardness but resulted in little refinement in the grain structure of the martensite. All crystal structures were cubic; no evidence of tetragonality was seen even at the highest carbon level but some systematic changes in grain boundary misorientations existed. The content of carbon in true interstitial solid solution deduced from X-ray line shifts was small (∼0.02 wt.%), and was independent of the total carbon content in the steel. Atom probe tomography showed that carbon was almost completely segregated to lath boundaries and dislocations but with an increasing density of segregates in the higher carbon steels. Calculations of diffusion distances confirmed that the segregation patterns were compatible with autotempering of the martensite during quenching. Analysis of different possible contributions to strength leads to the conclusion that segregated carbon atoms at defects behave similarly to carbon in true solid solution and that this is the largest single factor controlling the strength of as-quenched martensite. © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

  • 6.
    Hutchinson, Bevis
    et al.
    RISE, Swerea, Swerea KIMAB AB.
    Jain, J.
    Deakin University.
    Barnett, M.R.
    Deakin University.
    A minimum parameter approach to crystal plasticity modelling2012Inngår i: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 60, nr 15, s. 5391-5398Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Plastic deformation processes in hexagonal metals are complex and are best analyzed using procedures such as visco-plastic self-consistent crystal plasticity modelling. These involve a large number of adjustable parameters and make limited use of independent input data. Using physical arguments, the authors show that several of the parameters can be replaced by experimentally measured values of critical resolved shear stresses from the literature. A further simplification derives from the argument that all deformation modes interact with the same substructure, and so a common work-hardening behaviour can be assumed as a reasonable first approximation. Furthermore, many microstructural contributions to the strength can be introduced through a single constant term. In these ways, the twelve or more adjustable parameters in the model are reduced to only three. This new approach is tested critically by applying it to a sheet magnesium alloy for which the plastic strain ratio varies markedly during the test. Its complex plastic behaviour, which arises from changes among the active deformation modes, is successfully predicted. A benefit of the present approach is that the effect of metallurgical variables such as grain size or precipitation strengthening can be readily investigated. Although tested here for a magnesium alloy, the same principles should be applicable to other hexagonal close-packed materials. © 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

  • 7.
    Lillbacka, Robert
    et al.
    RISE., SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, SP – Sveriges Tekniska Forskningsinstitut / Hållfasthet (BMh).
    Johnson, Erland
    RISE., SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, SP – Sveriges Tekniska Forskningsinstitut / Hållfasthet (BMh).
    Cyclic Stress-Strain Behavior and Load-sharing in duplex Stainless Steels - Aspects on Modeling and Experiments2007Inngår i: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 55, nr 16, s. 5359-5368Artikkel i tidsskrift (Fagfellevurdert)
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