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  • 51.
    Granbom, Ylva
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Structure and mechanical properties of dual phase steels: An experimental and theoretical analysis2010Doktoravhandling, monografi (Annet vitenskapelig)
    Abstract [en]

    The key to the understanding of the mechanical behavior of dual phase (DP) steels is to a large extent to be found in the microstructure. The microstructure is in its turn a result of the chemical composition and the process parameters during its production. In this thesis the connection between microstructure and mechanical properties is studied, with focus on the microstructure development during annealing in a continuous annealing line. In-line trials as well as the lab simulations have been carried out in order to investigate the impact of alloying elements and process parameters on the microstructure. Further, a dislocation model has been developed in order to analyze the work hardening behavior of DP steels during plastic deformation. From the in-line trials it was concluded that there is an inheritance from the hot rolling process both on the microstructure and properties of the cold rolled and annealed product. Despite large cold rolling reductions, recrystallization and phase transformations, the final dual phase steel is still effected by process parameters far back in the production chain, such as the coiling temperature following the hot rolling. Lab simulations showed that the microstructure and consequently the mechanical properties are impacted not only by the chemical composition of the steel but also by a large number of process parameters such as soaking temperature, cooling rate prior to quenching, quench and temper annealing temperature. Studying the behavior of DP steels under deformation it was observed that the plastic deformation proceeds inhomogeneously. This was taken into account when developing a dislocation model accurately describing the work hardening behavior for this type of steel. By fitting the dislocation model to experimental stress-strain data it is possible to obtain information about the material’s behavior, e.g. it was observed that only a fraction of the ferrite phase takes part in the initial plastic deformation, which explains the high initial deformation hardening rate in DP steels. Another finding was that the flow stress ferrite grain size sensitivity in DP steels is much larger than that in ferritic steels. Further, the deformation hardening part of the flow stress experiences a ferrite grain size dependence, which is in glaring contrast to that found for ferritic steels.

  • 52.
    Granbom, Ylva
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Ryde, Lena
    Jeppsson, Johan
    Simulation of the soaking and gas jet cooling in a continuous annealing line using dilatometry2010Inngår i: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 81, nr 2Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The present study concerns the simulation of a continuous annealing line (CAL), using dilatometry. Simulations of CAL have been performed on four commercial steel grades with different chemical compositions in order to investigate how the alloying elements C, Mn, Si and B affect the microstructure and hardness of dual phase (DP) and martensitic steels. Three annealing cycles corresponding to those used in a CAL have been applied. When annealing intercritically, as is the case in DP-steel production, the materials do not reach equilibrium during soaking. Mn and C increase the austenite content and consequently the hardness of the materials. Higher levels of Si (0.4?wt %) are required to retard the formation of new ferrite during cooling in the gas jet section, prior to quenching. B increases hardenability effectively when annealing in the austenite region but is not as efficient during intercritical annealing, which implies that boron restrains ferrite nucleation rather than impeding ferrite growth. Results from DICTRA calculations show that it is possible to simulate the phase transformations during soaking, gasjet cooling and quenching.

  • 53.
    Grehk, Mikael
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Berger, Robert
    Bexell, Ulf
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Investigation of the drying process of linseed oil using FTIR and ToF-SIMS2008Inngår i: Proceedings of the 17th International Vacuum Congress/13th International Conference on Surface Science/Internatinal Conference on Nanoscience and Technology, Stockholm, 2008, Vol. 100Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The drying process of linseed oil, oxidized at 80 oC, has been investigated with rheology measurements, Fourier transformation infrared spectroscopy (FTIR), and time of flight secondary ion mass spectrometry (ToF-SIMS). The drying process can be divided into three main steps: initiation, propagation and termination. ToF-SIMS spectra show that the oxidation is initiated at the linolenic (three double bonds) and linoleic fatty acids (two double bonds). ToF-SIMS spectra reveal peaks that can be assigned to ketones, alcohols and hydroperoxides. In this article it is shown that FTIR in combination with ToF-SIMS are well suited tools for investigations of various fatty acid components and reaction products of linseed oil.

  • 54.
    Grehk, Mikael
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Engkvist, Josefin
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Bexell, Ulf
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Richter, Jan H
    Karlsson, Patrik G
    Sandell, Anders
    Initial stages of metal-organic chemical-vapor deposition of ZrO2 on a FeCrAl alloy2007Inngår i: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 516, nr 6, s. 875-879Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The initial stages of metal-organic chemical-vapor deposition of ZrO2 on a model FeCrAl alloy was investigated using synchrotron radiation photoelectron spectroscopy, X-ray absorption spectroscopy, scanning Auger microprobe, and time of flight secondary mass spectrometry. The coatings were grown in ultra-high vacuum at 400 °C and 800 °C using the single source precursor zirconium tetra-tert-butoxide. At 400 °C the coatings mainly consist of tetragonal ZrO2 and at 800 °C amixed ZrO2/Al2O3 layer is formed. The Almetal diffuses from the FeCrAl bulk to themetal/coating interface at 400 °C and to the surface of the coating at 800 °C. The result indicates that the reactionmechanism of the growth process is different at the two investigated temperatures.

  • 55.
    Gustafsson, Emil
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. Luleå tekniska universitet.
    Experiments on Sheet Metal Shearing2013Licentiatavhandling, med artikler (Annet vitenskapelig)
  • 56.
    Gustafsson, Emil
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Marth, Stefan
    Luleå University of Technology.
    Karlsson, Lars
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Oldenburg, Mats
    Luleå University of Technology.
    Strain and stress conditions at crack initiation during shearing of medium- and high-strength steel sheet2017Inngår i: International Journal of Mechanical and Materials Engineering, ISSN 2198-2791, Vol. 12, nr 1, s. 10-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Strain and stress conditions in sheet metal shearing are of interest for calibration of various fracture criteria. Most fracture criterion are governed by effective strain and stress triaxiality. This work is an attempt to extend previous measurements of strain fields in shearing of steel sheets with the stress state calculated from the measured displacement fields. Results are presented in terms of von Mises stress and stress triaxiality fields, and a comparison was made with finite element simulations. Also an evaluation of the similarities of the stress conditions on the sheet surface and inside the bulk material were presented. Strains and von Mises stresses were similar on the surface and the bulk material, but the stress triaxiality was not comparable. There were large gradients in strain and stress around the curved tool profiles that made the results resolution dependent and comparisons of maximum strain and stress values difficult. The stress state on the sheet surface calculated from displacement field measurements is still useful for validation of a three dimensional finite element model.

  • 57.
    Gustafsson, Emil
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Oldenburg, Mats
    Jansson, Anders
    Design and validation of a sheet metal shearing experimental procedure2014Inngår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 214, nr 11, s. 2468-2477Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Throughout the industrial processes of sheet metal manufacturing and refining, shear cutting is widely used for its speed and cost advantages over competing cutting methods. Industrial shears may include some force measurement possibilities, but the force is most likely influenced by friction losses between shear tool and the point of measurement, and are in general not showing the actual force applied to the sheet. Well defined shears and accurate measurements of force and shear tool position are important for understanding the influence of shear parameters. Accurate experimental data are also necessary for calibration of numerical shear models. Here, a dedicated laboratory set-up with well defined geometry and movement in the shear, and high measurability in terms of force and geometry is designed, built and verified. Parameters important to the shear process are studied with perturbation analysis techniques and requirements on input parameter accuracy are formulated to meet experimental output demands. Input parameters in shearing are mostly geometric parameters, but also material properties and contact conditions. Based on the accuracy requirements, a symmetric experiment with internal balancing of forces is constructed to avoid guides and corresponding friction losses. Finally, the experimental procedure is validated through shearing of a medium grade steel. With the obtained experimental set-up performance, force changes as result of changes in studied input parameters are distinguishable down to a level of 1%.

  • 58.
    Gustafsson, Emil
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Oldenburg, Mats
    Jansson, Anders
    Experimental study on the effects of clearance and clamping in steel sheet metal shearing2016Inngår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 229, s. 172-180Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Shear cutting is common within several sheet metal industry processing steps, e.g. in cut to length lines, slitting lines, end cropping. Shearing is fast and cheap relative to competing cutting methods like laser and plasma cutting, but involves large forces on the equipment that increase with increased sheet material strength. Accurate shear experiments are a prerequisite to increase the knowledge of shearing parameters, improve industrial shearing, and provide data for validation of numerical shear models. Here, the two shear parameters clearance and clamp configuration, identified as important to the shear results, were studied in an experimental set-up with well defined tool movement and high measurability of tool position and force. In addition to force measurements, the sheared edge geometry was characterized. Steels of low, medium, and high strength were selected for the study. Throughout the experimental study, the shear tool penetration before fracture decreased with increased material strength. The required shear force decreased and the force attempting to separate the two shear tools increased when one side of the sheet was left unclamped and free to move. Further, the maximum shear force increased with decreased clearance. Clearance changes were small and moreover continuously measured during all shear experiments.

  • 59. Gustavsson, Fredrik
    et al.
    Svahn, Fredrik
    Bexell, Ulf
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Jacobson, Staffan
    Nanoparticle based and sputtered WS2 low-friction coatings: differences and similarities with respect to friction mechanisms and tribofilm formation2013Inngår i: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 232, s. 616-626Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    MoS2 and WS2 are widely known intrinsic low-friction materials that have been extensively used and thoroughly investigated in literature. They are commonly produced in the form of sputtered coatings and show extremely low friction coefficients in non-humid environments, but rapidly degrade in humid conditions. Close nested fullerene-like nanoparticles of these materials have been proposed to have better oxidation resistance due to their closed form with the absence of dangling bonds. In the present study, an electrochemically deposited coating consisting of fullerene-like nanoparticles of WS2 embedded in a Ni-P matrix is tested under various loads and humidity conditions and compared with a sputtered WS2 coating with respect to their tribological behavior. The formation of a tribofilm on both surfaces is known to be crucial for the low-friction mechanism of WS2 and the different mechanisms behind this formation for the two types of coatings are investigated. It is shown that despite the completely different transformation processes, the resulting tribofilms are very similar. This is analyzed thoroughly using SEM, AES and TEM. The friction coefficient is known to be lower at higher normal loads for these materials and in the present study the mechanical and chemical responses of the tribofilm to higher normal loads during sliding are investigated. It was observed that the basal planes become aligned more parallel to the surface at higher loads, and that the tribofilm is less oxidized. It is suggested that these mechanisms are connected and are crucial keys to the wear life of these materials. (C) 2013 Elsevier B.V. All rights reserved.

  • 60.
    Gyhlesten Back, Jessica
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. Luleå tekniska universitet, Material- och solidmekanik.
    Modelling and Characterisation of the Martensite Formation in Low Alloyed Carbon Steels2017Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The current work contains experimental and theoretical work about the formation of martensite from the austenitic state of the steel Hardox 450. Simulation of rolling and subsequent quenching of martensitic steel plates requires a model that can account for previous deformation, current stresses and the temperature history, therefore dilatometry experiments were performed, with and without deformation. Two austenitization schedules were used and in the standard dilatometry the cooling rates varied between 5-100 °C/s, in order to find the minimum cooling rate that gives a fully martensitic microstructure. Cooling rates larger than 40°C/s gave a fully martensitic microstructure. The cooling rate of 100 °C/s was used in the deformation dilatometry tests where the uniaxial deformation varied from 5-50 %. The theoretical work involved modelling of the martensite formation and the thermal/transformation strains they cause in the steel. Characterizations were done using light optical microscopy, hardness tests and electron backscatter diffraction technique. The parent austenite grains of the martensitic structure were reconstructed using the orientation relationship between the parent austenite and the martensite. Kurdjumov-Sachs orientation relationships have previously been proven to work well for low-carbon steels and was therefore selected.

    The standard implementation of the Koistinen-Marburger equation for martensite formation and a more convenient approach were compared. The latter approach does not require the storage of initial austenite fraction at start of martensite formation. The comparison shows that the latter model works equally well for the martensite formation. The results showed that the use of martensite start and finish temperatures calibrated versus experiments for Hardox 450 works better when computing thermal expansion than use of general relations based on the chemistry of the steel.

    The results from deformation dilatometry showed that deformation by compressive uniaxial stresses impedes the martensite transformation. The simplified incremental model works well for deformation with 5 % and 10 %. However, the waviness in the experimental curve for deformation 50 % does not fit the model due vi to large barrelling effect and the large relative expansion for the material that the sample holders are made of.

    Crystallographic reconstruction of parent austenite grains were performed on a hot-rolled as-received reference sample and dilatometry samples cooled with 60 °C/s and 100 °C/s. The misorientation results showed that the samples match with the Kurdjumov-Sachs orientation relationship in both hot rolled product and dilatometry samples. When misorientation between adjacent pixels are between 15° and 48°, then the boundary between them was considered as a parent austenite grain. The austenitic grain boundaries of the sample cooled at 100 °C/s is in general identical with the hot rolled sample when considering high angle boundaries (15°-48°). The results from the hardness tests showed that the rolled product exhibits higher hardness as compared to samples cooled by 100 °C/s and 60 °C/s. This can be attributed to the formation of transition-iron-carbides in the hot rolled product due to longer exposure of coiling temperature.

  • 61.
    Gyhlesten Back, Jessica
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. Luleå tekniska universitet.
    Simplified Implementation of the Koistinen-Marburger Model for Use in Finite Element Simulations2016Inngår i: Proceedings of the 11th international congress on thermal stresses, Severino: Edizioni Paguro , 2016, s. 107-110Konferansepaper (Annet vitenskapelig)
  • 62.
    Gyhlesten Back, Jessica
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. Research and Development, SSAB Europe, Borlänge.
    Engberg, Göran
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Investigation of parent austenite grains from martensite structure using EBSD in a wear resistant steel2017Inngår i: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 10, nr 5, artikkel-id 453Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Crystallographic reconstruction of parent austenite grain boundaries from the martensitic microstructure in a wear resistant steel was carried out using electron backscattered diffraction (EBSD). The present study mainly aims to investigate the parent austenite grains from the martensitic structure in an as-rolled (reference) steel sample and samples obtained by quenching at different cooling rates with corresponding dilatometry. Subsequently, this study is to correlate the nearest cooling rate by the dilatometer which yields a similar orientation relationship and substructure as the reference sample. The Kurdjumov-Sachs orientation relationship was used to reconstruct the parent austenite grain boundaries from the martensite boundaries in both reference and dilatometric samples using EBSD crystallographic data. The parent austenite grain boundaries were successfully evaluated from the EBSD data and the corresponding grain sizes were measured. The parent austenite grain boundaries of the reference sample match the sample quenched at 100 °C/s (CR100). Also the martensite substructures and crystallographic textures are similar in these two samples. The results from hardness measurements show that the reference sample exhibits higher hardness than the CR100 sample due to the presence of carbides in the reference sample.

  • 63.
    Gyhlesten Back, Jessica
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Lindgren, Lars-Erik
    Luleås tekniska universitet.
    Modelling of the influence of prior deformation of austenite on the martensite formation in a low-alloyed carbon steel2018Inngår i: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 941, s. 95-99Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The current work aims at developing models supporting design of the rolling and quenching processes. This requires a martensite formation model that can account for effect of previous plastic deformation as well as evolution of stress and temperature during the quenching step. The effect of deformation prior to the cooling on the transformation is evaluated. The experimental result shows that prior deformation impedes the martensite transformation due to the mechanical stabilisation of the austenite phase. Larger deformation above 30% reduces the effect of the mechanical stabilisation due to increase in martensite nucleation sites. The computed transformation curves, based on an extended version of the Koistinen-Marburger equation, agree well with experimental results for pre-straining less than 30 %. 

  • 64.
    Gyhlesten Back, Jessica
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Surreddi, Kumar Babu
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Microstructure analysis of martensitic low alloy carbon steel samples subjected to deformation dilatometry2019Inngår i: Materials Characterization, ISSN 1044-5803, E-ISSN 1873-4189, Vol. 157, artikkel-id 109926Artikkel i tidsskrift (Fagfellevurdert)
  • 65. Habainy, J.
    et al.
    Iyengar, S.
    Surreddi, Kumar Babu
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Lee, Y.
    Dai, Y.
    Formation of oxide layers on tungsten at low oxygen partial pressures2018Inngår i: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 506, nr SI, s. 26-34Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This work focuses on the oxidation of tungsten in inert gas atmospheres containing oxygen and moisture. It is particularly relevant for the European Spallation Source where the tungsten target is cooled by purified helium gas and the 5 MW proton beam can raise the maximum target temperature beyond the threshold for oxidation. Tungsten discs were oxidized isothermally at 400° to 900 °C for 2 h in pure helium and helium mixed with oxygen and water vapor, with varying partial pressures up to 500 Pa. Tungsten was oxidized even with a small amount of oxygen (≤5 ppm) present in industrially pure helium. Non-isothermal oxidation of tungsten foils was carried out in water vapor (∼100 Pa), in situ in an environmental scanning electron microscope. On specimens oxidized in inert gas containing water vapor (2 h, pH2O" role="presentation" style="box-sizing: border-box; margin: 0px; padding: 0px; display: inline-block; line-height: normal; font-size: 14.4px; word-spacing: normal; word-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; position: relative;">pH2O ∼790 Pa), Auger electron spectroscopy studies confirmed the presence of a thin oxide layer (40 nm) at 400 °C. At 500 °C the oxide layer was 10 times thicker. A dark, thin and adherent oxide layer was observed below 600 °C. Above this temperature, the growth rate increased substantially and the oxide layer was greenish, thick and porous. Oxide layers with varying stoichiometry were observed, ranging from WO3 at the surface to WO2 at the metal-oxide interface. For comparison, oxidation of tungsten alloysin He-5%O2 was studied. The implications of this work on the design and operation of the helium loop for cooling the target are discussed.

  • 66. Habainy, J.
    et al.
    Lee, Y.
    Surreddi, Kumar Babu
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Prosvetov, A.
    Simon, P.
    Iyengar, S.
    Dai, Y.
    Tomut, M.
    Study of heavy ion beam induced damage in tungsten for high power target applications2019Inngår i: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, ISSN 0168-583X, E-ISSN 1872-9584, Vol. 439, s. 7-16Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The spallation material at ESS is pure tungsten, which is cooled by gaseous helium flow. To study the behaviour of tungsten under dynamic beam conditions at ESS, pure tungsten specimens have been irradiated at the M3-beamline of the UNILAC facility at GSI Helmholtz Centre for Heavy Ion Research. Tungsten specimens of two thicknesses, 26 μm and 3 mm, were exposed to pulsed uranium and gold ion beams for fluences up to 7.5 · 1013 ions·cm−2 at 4.8 MeV/nucleon. Nanoindentation tests were performed on the cross section of the irradiated 3 mm sample, and microhardness was measured on the top surface. The measured data are compared with the calculated damage values, and a correlation between the radiation induced damage and the observed mechanical property is presented. Thermal diffusivities of foil samples irradiated up to four different fluences were measured with a Laser Flash Apparatus (LFA). The observed changes in the mechanical and thermal properties of irradiated tungsten were used to estimate the changes of operational temperature and mechanical stresses in the ESS target material with the progress of radiation damage, using coupled thermal and mechanical simulations. From the pulsed beam induced dynamic oscillations of thin tungsten specimens, information on fatigue properties of tungsten under irradiation was drawn. In addition to pure tungsten, oxidised tungsten samples were irradiated. This is to investigate the stability of the adhesive oxide layer under pulsed beam conditions, which would be formed due to oxygen impurities in the helium cooling loop. The irradiated oxide scale was examined using Auger Electron Spectroscopy (AES) and Scanning Electron Microscopy (SEM). 

  • 67.
    Hall, Josefin
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Beglund, Tomas
    Bexell, Ulf
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Influence of microstructure and hard phase content on the mechanisms of deformation and wear of HIP:ed Stellite® 190 composites2015Konferansepaper (Fagfellevurdert)
  • 68.
    Hall, Josefin
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Bexell, Ulf
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Fletcher, J. S.
    Canovic, S.
    Malmberg, Per
    Comparing depth profiling of oxide scale on SOFC interconnect-materials using ToF-SIMS with 69Ga+, Bi3+/Cs+ and C60+/C602+ as primary and sputter ions2015Inngår i: Materials at High Temperatures, ISSN 0960-3409, Vol. 32, nr 1-2, s. 133-141Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Oxide scale cross-sections of CeO2 coated FeCr based solid oxide fuel cell interconnect materials were examined using secondary ion mass spectrometry (SIMS) depth profiling. A duplex spinel∶chromia scale was formed after 1 h at 850°C. Ti and ceria were observed between these layers. Additionally, minor concentrations of Mn, Si and Nb were observed at the oxide/metal interface. Furthermore, Al and Ti were concentrated primarily in the metal surface close to the oxide/metal interface. Secondary ion mass spectrometry sputter depth profiles using different ion sources; 69Ga+, Bi3+/Cs+ and C60+/C602+ were compared with TEM oxide scale cross-section and field emission gun–Auger electron spectroscopy depth profiling. Secondary ion mass spectrometry depth profiling with 69Ga+, Bi3+/Cs+ showed decreased secondary ion yields in the metallic matrix. This decrease could be avoided using oxygen flooding. The C60cluster ion depth profiles were less sensitive to type of matrix and gave the best correspondence to the TEM cross-section. However, the impact energy has to be high enough to avoid carbon deposition.

  • 69.
    Hall, Josefine
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Berglund, Tomas
    Bexell, Ulf
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Influence of Microstructure and Hard Phase Content on the Mechanisms of Deformation and Wear of HIP:ed Stellite® 190 Composites2015Inngår i: Proceedings of 2015 European powder metallurgy congress, Euro PM 2015, Reims, France, 4-7 October 2015, 2015Konferansepaper (Fagfellevurdert)
  • 70.
    Halldén, Helena
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Planhet efter skärande bearbetning av formatplåt – en jämförelse mellan laserskärning och gradsaxklippning2017Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave
    Abstract [sv]

    Under de senaste åren har SSAB haft ett växande kvalitetsproblem gällande restspänningar i formatklippt plåt. Problemet innebär att oplanhet uppstår i samband med kundens bearbetning, främst laserskärning, trots att företaget har levererat ett till synes plant material.

    SSAB har i nuläget gradsaxklippning inom företaget som utvärderingsmetod för att bestämma inre spänningar i formatplåt efter riktning i formatsträcka 3. Dock är det en stor skillnad mellan gradsaxklippning och processen laserskärning, som oftast är kundens verkliga bearbetning. Man kan följaktligen därför anta att resultat från de båda operationerna kan skilja sig åt. Därav ifrågasätts gradsaxklippning som provmetod för restspänningar.

    I examensarbetet jämförs de två operationerna gradsaxklippnings och laserskärnings påverkan på planhet hos riktade plåtar, och att därefter utvärdera gradsaxklippning som provmetod för oplanhet. Arbetes syfte är även att bestämma hur olika riktningsparametrar eventuellt påverkar resultatet av jämförelsen.

    I arbetet utfördes tre olika produktionsförsök. Första försöket innebar riktning och klippning till formatplåt i formatsträcka. Därefter skars en del av plåtarna i lasermaskin medan resterande klipptes i gradsax. Resultatet i båda fallen blev rimpor (mindre plåtbitar). Rimpornas oplanhet uppmättes för hand och mätresultaten sammanställdes därefter för att tolka resultaten och göra relevanta jämförelser skärmetoderna emellan.

    Resultaten visar att gradsaxklippning som utvärderingsmetod för att förutsäga oplanhet efter laserskärning inte är en bra metod. Dåligt inställda riktningsparametrar ökar dessutom osäkerheten hos utvärderingsmetoden. Dock kan en kombination av gradsaxklippning i två olika utföranden av rimpor ge viss information om oplanheten hos motsvarande laserskuren plåt riktade med samma riktinställningar.

  • 71.
    Hansson, Sofia
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    A three-dimensional finite element simulation of stainless steel tube extrusion using a physically based material model2006Konferansepaper (Fagfellevurdert)
  • 72.
    Hansson, Sofia
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Modeling of the Stainless Steel Tube Extrusion Process2010Doktoravhandling, monografi (Annet vitenskapelig)
    Abstract [en]

    Seamless tubes of stainless steel can be extruded using glass as a lubricant in the Ugine-Sejournet process. The process is performed at high temperature and is associated with large deformations and high strain rates. The use of finite element modeling (FEM) in the analysis and design of extrusion and other metal forming processes is constantly increasing. Computer models that with adequate accuracy can describe the material behavior during extrusion can be very useful for product and process development. The process development in industrial extrusion today is, to a great extent, based on trial and error. This often involves full size experiments which are expensive, time consuming and interfere with the production. It would be of great value if these experiments could be performed in a computer. In this work, FE models of the stainless steel tube extrusion process were developed and used. Simulations were carried out for different tube dimensions and three different materials: two austenitic stainless steels and one duplex (austenitic/ferritic) stainless steel. The models were validated by comparing the predicted values of extrusion force with measurements from production presses. A large number of input parameters are used in a FE analysis of extrusion. This includes boundary conditions, initial conditions and parameters that describe the mechanical and thermal properties of the material. The accuracy of the extrusion simulation depends, to a large extent, on the accuracy of these parameters. Experimental work, both in the form of material testing and production trials, was performed in order to give an accurate description of the input parameters in these extrusion models. A sensitivity analysis was performed for one of the models and the results showed that the initial billet temperature is the parameter that has the strongest impact on the extrusion force. In order to study the temperature evolution in the billet during manufacturing, the entire process chain at extrusion of stainless steel tubes was simulated using FEM. This process flow model includes sub-models of induction heating, expansion and extrusion. The work includes the use of a dislocation density-based material model for the AISI type 316L stainless steel. It is expected that this physically based model can be extrapolated to a wider range of strains, strain rates and temperatures than an empirical model, provided that the correct physical processes are described by the model and that no new phenomena occur. This is of interest for steel extrusion simulations since this process is carried out at higher strains and strain rates than what are normally used in mechanical laboratory tests. The developed models have given important contributions to the understanding of different phenomena that occur during extrusion of stainless steel tubes, and can be used to analyze how different process parameters affect the extrusion process.

  • 73.
    Hansson, Sofia
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Domkin, Konstantin
    Physically based material model in finite element simulation of extrusion of stainless steel tubes2005Konferansepaper (Fagfellevurdert)
  • 74.
    Hansson, Sofia
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap. Sandvik Mat Technol, R&D Ctr, Sandviken.
    Fisk, Martin
    Simulations and measurements of combined induction heating and extrusion processes2010Inngår i: Finite elements in analysis and design (Print), ISSN 0168-874X, E-ISSN 1872-6925, Vol. 46, nr 10, s. 905-915Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The manufacturing process chain at glass-lubricated extrusion of stainless steel tubing is simulated using the finite element method. The developed model includes sub-models of induction heating, expansion and extrusion. An in-house mapping tool is used to transfer the temperature fields between the electromagnetic-thermal and thermo-mechanical analyses. Using the combined model it is possible to study the influence of different process parameters on the temperature distribution in the billet, and how this affects the final extrusion properties. In this study, the model is applied to two cases of tube extrusion, one using an austenitic stainless steel and one using a duplex, austenitic/ferritic, stainless steel. It is shown that the induction heating model successfully predicts the temperatures obtained experimentally from thermocouples placed in the steel billets during heating. The agreement between models and experiments regarding extrusion force and expansion force is satisfactory.

  • 75.
    Hansson, Sofia
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap. Sandvik Mat Technol, R&D Ctr, SE-81181 Sandviken.
    Jansson, Tomas
    Sensitivity analysis of a finite element model for the simulation of stainless steel tube extrusion2010Inngår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 210, nr 10, s. 1386-1396Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this work, a sensitivity analysis has been performed on a finite element model of glass-lubricated extrusion of stainless steel tubes. Fifteen model parameters, including ram speed, billet and tool temperatures, friction coefficients and heat transfer coefficients, were considered. The aim of the study was to determine the parameters that are most important for the response of the extrusion force. The relationship between the model parameters and the responses was analyzed by a calculation of two different regression models: one linear polynomial model and one model that includes interaction terms. Additional simulations were then carried out to validate the regression models. The results show that the initial billet temperature is the factor that has the strongest impact on the extrusion force within the parameter ranges studied in this work. The goodness of prediction and goodness of fit are very good for both regression models.

  • 76.
    Harfouche, Sara
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Dimensionsmätning av varma ämnen iLIMAB och undersökning avkrympfaktorer2014Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave
    Abstract [sv]

    I valsverket på Ovako i Hofors varmvalsas det stänger i olika dimensioner. Efter det sista valsparet installerades en dimensionsmätare av märket LIMAB. Dimensionsmätaren mäter stängernas dimension i varmt tillstånd vid ca 900oC.

    När stängerna av olika stålsorter sedan svalnar till rumstemperatur krymper de olika mycket. Hittills har man använt ett schablonvärde på krympfaktorn i Hofors. Exakt hur mycket stängerna krymper är av intresse då kunderna vill ha specifika mått på sina produkter.

    Två typer av stål med olika kolhalter analyserades i detta arbete. Genom att ta värden på diametern i varmt tillstånd från dimensionsmätaren och jämföra med de uppmätta måtten i rumstemperatur kan en krympfaktor räknas fram.

    Flera stycken krympfaktorformler sammanställdes och i rapporten visas det en uppställning av alla undersökta formler och hur värdena på krympfaktorn skiljer sig sinsemellan.

    För våra försök ger formeln från ringproduktionen högst värde på krympfaktorn. Efter ringproduktionen är värdena på krympfaktorn från LIMAB AB näst högst och lägst är värdena från rörproduktionen.

    I nuläget är det svårt att bestämma nya krympfaktorer eftersom det krävs fler försök och kapabilitetsmätningar.

  • 77. Harfouche, Sara
    et al.
    Padam, Benita
    Dimensionsmätning av varma ämnen i LIMAB och undersökning av krympfaktorer2014Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave
    Abstract [sv]

    I valsverket på Ovako i Hofors varmvalsas det stänger i olika dimensioner. Efter det sista valsparet installerades en dimensionsmätare av märket LIMAB. Dimensionsmätaren mäter stängernas dimension i varmt tillstånd vid ca 900oC.

    När stängerna av olika stålsorter sedan svalnar till rumstemperatur krymper de olika mycket. Hittills har man använt ett schablonvärde på krympfaktorn i Hofors. Exakt hur mycket stängerna krymper är av intresse då kunderna vill ha specifika mått på sina produkter.

    Två typer av stål med olika kolhalter analyserades i detta arbete. Genom att ta värden på diametern i varmt tillstånd från dimensionsmätaren och jämföra med de uppmätta måtten i rumstemperatur kan en krympfaktor räknas fram.

    Flera stycken krympfaktorformler sammanställdes och i rapporten visas det en uppställning av alla undersökta formler och hur värdena på krympfaktorn skiljer sig sinsemellan.

    För våra försök ger formeln från ringproduktionen högst värde på krympfaktorn. Efter ringproduktionen är värdena på krympfaktorn från LIMAB AB näst högst och lägst är värdena från rörproduktionen.

    I nuläget är det svårt att bestämma nya krympfaktorer eftersom det krävs fler försök och kapabilitetsmätningar.

  • 78. Harlin, P.
    et al.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Starch consolidation of M3/2 high speed steel powder: Influence of microstructure on mechanical properties2007Inngår i: Powder Metallurgy, ISSN 0032-5899, E-ISSN 1743-2901, Vol. 50, nr 3, s. 232-238Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The influence of microstructure on the mechanical properties of starch consolidated super solidus liquid phase sintered AISI type M3/2 high speed steel powder has been evaluated. Hardness measurements, Rockwell C indentation and scratch testing were used to evaluate the mechanical properties and light optical microscopy and scanning electron microscopy were used for post-test characterisation. The results show that it is possible to starch consolidate and sinter large particle size high speed steel powder to obtain microstructures with high mechanical strength. However, the results show a strong correlation between the as sintered microstructure and the resulting mechanical properties and illuminate the importance of having a dense and isotropic microstructure in order to meet engineering requirements in demanding applications. Consequently, the failure mechanisms observed during indentation and scratch testing can be related to residual pores, present in the low temperature sintered samples, and a coarse microstructure with eutectic carbides, present in the high temperature sintered samples. 

  • 79.
    Harlin, Peter
    et al.
    Sandvik Materials Technology.
    Bexell, Ulf
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Influence of surface topography of arc-deposited TiN and sputter-deposited WC/C coatings on the initial material transfer tendency and friction characteristics under dry sliding contact conditions2009Inngår i: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 203, nr 13, s. 1748-1755Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The influence of surface topography of PVD coatings on the initial material transfer tendency and friction characteristics in dry sliding contact conditions has been investigated. A modified scratch test was used to evaluate the material transfer tendency between ball bearing steel and two different PVD coatings, TiN and WC/C, under dry sliding contact conditions. Post test characterisation of the contact surfaces was performed using SEM/EDS and AES in order to map the initiation points and mechanisms for material transfer. The results show that the resulting topography of the PVD coated surfaces is strongly dependent on both the substrate material topography and the topography induced by the coating deposition process used. In sliding contact with a softer surface the coating topography results in a significant material pick-up tendency of the PVD coated surfaces. The material pick-up is mainly controlled by the abrasive action of hard coating asperities and as a result a polishing post treatment of the as-deposited PVD coatings significantly reduces the material pick-up tendency. For the WC/C coating, showing intrinsic low friction properties, the post treatment inhibits the material pick-up and results in a low and stable friction coefficient (mu similar to 0.1). For the TiN coating, that lacks intrinsic low friction properties, the post treatment reduces the material pick-up tendency but has no significant influence on the friction characteristics. This is mainly due to the presence of metallic Ti originating from the macroparticles on the TiN coating which results in a reactive surface that promotes a strong adhesion between the mating surfaces.

  • 80.
    Harlin, Peter
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Carlsson, Per
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Bexell, Ulf
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Influence of surface roughness of PVD coatings on tribological performance in sliding contacts2006Inngår i: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 201, nr 7, s. 4253-4259Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The influence of surface roughness on the tribological performance, i.e. friction, wear and material pick-up tendency, of two different commercial PVD coatings, TiN and WC/C, in sliding contact with ball bearing steel has been evaluated using two different types of sliding wear laboratory tests. Post-test characterisation using SEM/EDS, AES, ToF-SIMS and XPS was used to evaluate the prevailing friction and wear. The results show that the surface roughness of the coating is of importance in order to control the initial material pick-up tendency and thus the friction characteristics in a sliding contact. Once initiated, the material pick-up tendency will increase, generating a tribofilm at the sliding interface. For steel–TiN sliding couples a FeO-based tribofilm is generated on the two surfaces and FeO/FeO becomes the sliding interface (interfilm sliding) resulting in a high friction coefficient. For steel–WC/C sliding couples the WC/C displays a pronounced running-in behaviour which generates a WO3-based tribofilm on the steel surface while a carbon rich surface layer is formed on the WC/C surface, i.e. WO3/C becomes the sliding interface (interface sliding) resulting in a low friction coefficient.

  • 81.
    Harlin, Peter
    et al.
    Sandvik Materials Technology.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Abrasive wear resistance of starch consolidated and sintered high speed steel2009Inngår i: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 267, nr 9-10, s. 1482-1489Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The abrasive wear resistance of starch consolidated (SC) and super solidus liquid phase sintered (SLPS) M3/2 high speed steel (HSS) samples have been evaluated by a two-body micro-abrasion test (low stress abrasion), using 6 µm diamond abrasive particles, and a three-body abrasion test (high stress abrasion), using significantly larger abrasive particles of blast furnace slag (600 HV) and silicon carbide (2400 HV), respectively. In the tests a commercial powder metallurgical (PM) HSS was used as a reference material. The results show that the microstructure of the SC and SLPS HSS samples is strongly dependent on the sintering temperature used. With increasing temperature the microstructure ranges from a porous (5% porosity) relatively fine grained low temperature sintered microstructure to a fully dense relatively coarse grained high temperature sintered microstructure with eutectic carbides/carbide networks. However, despite the pronounced microstructural differences displayed by the as-sintered HSS microstructures these show a relatively high abrasive wear resistance, comparable with that of a HIPed HSS reference, both under low and high stress abrasion contact conditions. The characteristic features of the low and high temperature sintered microstructures, i.e. the pores and coarse eutectic carbides/carbide networks, only show a limited impact on the wear rate and the wear mode (dominant wear mechanism). The results obtained imply that near net shaped components manufactured by starch consolidation and super solidus liquid phase sintering might be of interest in tribological applications.

  • 82.
    Harlin, Peter
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Starch consolidation of M3/2 high speed steel powder: influence of process parameters on resulting microstructure2007Inngår i: Powder Metallurgy, ISSN 0032-5899, E-ISSN 1743-2901, Vol. 50, nr 4, s. 345-353Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The possibility to produce near net shape high speed steel components with an adequate microstructure by the combination of starch consolidation (SC) and super solidus liquid phase sintering (SLPS) has been evaluated using a gas atomised M3/2 high speed steel (HSS) powder. Characterisation of the green body and as sintered microstructures using light optical microscopy (LOM), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX) reveals that both the SC and SLPS processes strongly influence the resulting microstructure and thus the properties of the high speed steel material. The results obtained show that the morphology and distribution of starch to a high extent affect the green body surface strength and that the large pores remaining after sintering originates from entrapped air introduced in the fabrication process of the green body. The results illuminate the possibility to combine SC and SLPS to produce HSS components with fully dense microstructures and retained green body geometry from a powder with particle size distribution 50 - 150 mu m.

  • 83. Hatami, S.
    et al.
    Armada, S.
    Laurent, A.
    Nyborg, L.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Tribological properties of powder metallurgical tool steels used in powder compaction pressing dies2011Inngår i: Lubrication Science, ISSN 0954-0075, E-ISSN 1557-6833, Vol. 23, nr 3, s. 139-152Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The tribological properties of two powder metallurgical (PM) tool steels, high and low nitrogen containing, are investigated by means of three different wear tests: ball-on-disc, rubber wheel and scratch test. The ball-on-disc tests showed two distinct friction curves corresponding to each material. In order to simulate the tribosystem existing in metal powder compaction dies, the rubber wheel and the scratch test were modified. The rubber wheel test was performed using ferrous powder instead of sand, and scratch testing was carried out by sliding a powder compact over the tool steels. The scratch tests indicated a higher steady-state coefficient of friction for the low nitrogen containing PM steel as compared with the high nitrogen containing alloy. Additionally, the results from the rubber wheel tests were in agreement with industrial experiences, showing the low nitrogen containing tool steel to suffer from severe galling.

  • 84.
    Hedman, Fanny
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Inverkan av processparametrar i varmvalsverket på planhet efter formatklippning2015Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave
    Abstract [sv]

    Efter varmvalsningen kan banden, obehandlade eller betade, riktas och klippas upp i de olika formatsträckorna som finns på SSAB i Borlänge.

    Planhetsresultaten efter riktning och klippning i formatsträcka 4 skiftar trots att banden är av samma stålsort. Många faktorer påverkar planheten och detta examensarbete undersöker om bandgeometrin efter varmvalsningen har någon påverkan på planheten efter formatsträcka 4. Undersökningarna har begränsats så att ett fåtal stålsorter och dimensioner undersökts.

    För att samband skulle kunna kopplas mellan varmvalsverket och formatsträckan samlades information in angående historiska band från databaser kopplade till de olika produktionslinjerna.

    Sambanden som hittades var att vid en lägre profil på banden så blir planhetsresultaten bättre. Snedheten på de bra och de defekta banden varierar och en tjockare drivsida ger ett bättre planhetsresultat än vad en tjockare frisida ger. Formen på bandens tvärprofiler har också betydelse för planhetsresultaten.

    För att verifiera dessa samband gjordes två produktionsförsök, ett där ett antal band valsades och klipptes utan att några parametrar bestämdes och ett där några parametrar bestämdes innan valsning och klippning. Produktionsförsöken styrkte sambanden då de godkända banden hade den lägsta profilen.

  • 85. Heinrichs, J.
    et al.
    Gerth, J.
    Bexell, Ulf
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Larsson, M.
    Wiklund, U.
    Influence from surface roughness on steel transfer to PVD tool coatings in continuous and intermittent sliding contacts2012Inngår i: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 56, s. 9-18Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A sliding test is used in order to evaluate the influence of tool surface roughness on the material transfer in intermittent and continuous sliding of PVD coated HSS against case hardening steel (20NiCrMo2). Two cutting tool coatings, TiN and AlCrN, and three different surface roughnesses are tested. For polished surfaces the same types of material transfer are obtained irrespective of sliding mode and coating type. If the surfaces are too rough, the tribofilms do not grow thick enough to separate the surfaces and the work material is abrasively worn in both sliding modes. With increased sliding distance, cracking of the TiN coating occurs while the AlCrN coating remains intact. (C) 2012 Elsevier Ltd. All rights reserved.

  • 86. Heinrichs, J.
    et al.
    Norgren, S.
    Jacobson, S.
    Yvell, Karin
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Influence of cemented carbide binder type on wear initiation in rock drilling – Investigated in sliding wear against magnetite rock2019Inngår i: International journal of refractory metals & hard materials, ISSN 0958-0611, E-ISSN 2213-3917, Vol. 85, artikkel-id 105035Artikkel i tidsskrift (Fagfellevurdert)
  • 87.
    Heinrichs, J
    et al.
    Uppsala Universitet.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Jacobson, S
    Uppsala Universitet.
    Influence of tool steel microstructure on initial material transfer in metal forming: in situ studies in the SEM2013Inngår i: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 302, nr 1-2, s. 1249-1256Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Metal forming constitutes a group of industrially important processes to form metallic components to net shape. When forming aluminium and other materials that tend to stick to the tools, problems associated with material transfer, e.g. galling, may occur. In a previous study by the present authors, in situ observations of aluminium transfer during sliding contact in the SEM revealed that the surface topography and chemical composition of the tool steel counter surface have a strong impact on the initial material transfer tendency. Even if carefully polished to a very smooth surface (Ra<50 nm), transfer of aluminium was found to immediately take place on a very fine scale and preferentially to the surface irregularities presented by the slightly protruding M(C,N) particles (height 15 nm) in the tool steel. In contrast, the less protruding M6C carbides, as well as the martensitic steel matrix exhibited very little initial transfer. The mechanism behind the preferential pick-up tendency displayed by the M(C,N) particles was not fully understood and it was not possible to determine if the decisive mechanism operates on the microstructural scale, the nanoroughness scale or the chemical bonding scale. In the present study, these mechanisms have been further investigated and analysed by comparing the very initial stages of material transfer onto different types of tool steels in sliding contact with aluminium in the SEM. The tool steels investigated cover conventional ingot cast and powder metallurgy steel grades, selected to possess a range of different types, amounts and sizes of hard phase particles, including MC, M(C,N), M7C3 and M6C. The transfer mechanisms are investigated using high resolution SEM, and the differences between the different microstructures and carbide types are carefully analysed. The implications for real metal forming are discussed.

  • 88.
    Heinrichs, J
    et al.
    Uppsala Universitet.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Jacobson, S
    Uppsala Universitet.
    Initial deformation and wear of cemented carbides for rock drilling as evaluated by a sliding wear test2015Inngår i: Proceedings of International Tribology Conference 2015, 2015Konferansepaper (Fagfellevurdert)
  • 89. Heinrichs, J.
    et al.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Jacobson, S.
    Initial deformation and wear of cemented carbides in rock drilling as examined by a sliding wear test2017Inngår i: International journal of refractory metals & hard materials, ISSN 0958-0611, E-ISSN 2213-3917, Vol. 64, s. 7-13Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Due to a combination of high hardness and toughness, resulting in excellent wear resistance, cemented carbides are commonly used as the rock crushing component in rock drilling. The present paper presents a unique study where the very initial stages of deformation and wear of cemented carbide in sliding contact with rock are followed in small incremental steps. After each step, a pre-determined area within the wear mark is characterized using high resolution SEM and EDS. This facilitates analysis of the gradual deformation, material transfer, degradation and wear. The deterioration mechanisms found in this sliding test are similar to those observed in actual rock drilling. Cemented carbide grades with different microstructures show significant differences, where a higher amount of Co and a larger WC grain size both are associated to more wear. 

  • 90.
    Heinrichs, J
    et al.
    Uppsala Universitet.
    Olsson, Mikael
    Jacobson, S
    Uppsala Universitet.
    Initiation of Galling in Metal Forming: Differences Between Aluminium and Austenitic Stainless Steel Studied In Situ in the SEM2013Inngår i: Tribology letters, ISSN 1023-8883, E-ISSN 1573-2711, Vol. 50, nr 3, s. 431-438Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    High friction and transfer of work material to tool surfaces constitute important industrial problems in forming of many metals and alloys. However, it is very hard to gain a deeper understanding of these phenomena by studying real forming operations. In this paper, we have tried to gain fundamental understanding by avoiding as much as possible of the complexity of real forming. This has been realised by studying the friction and material transfer between well-defined tool material surfaces; uncoated and DLC-coated tool steel, and a needle shaped austenitic stainless steel tip, in situ in the SEM. The tool materials were tested in two conditions; well polished and well polished with local intentional scratches. It was found that work material was immediately transferred to the tool steel surface. When passing an intentional scratch, the local transfer was on a much larger scale, and the friction was higher, but the effect was mostly local. For the polished DLC-coated surface, almost no work material was transferred and the friction was low. An intentional scratch in the polished DLC surface barely influenced the galling behaviour. The present results are discussed in the light of previously published results from an analogous study with aluminium as work material.

  • 91.
    Heinrichs, J.
    et al.
    Uppsala universitet.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. Uppsala universitet.
    Jacobson, S.
    Uppsala universitet.
    Surface degradation of cemented carbides in scratching contact with granite and diamond: the roles of microstructure and composition2015Inngår i: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 342, s. 210-221Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Cemented carbides are composite materials comprising metal carbide grains in a more ductile metallic binder. This microstructure results in a combination of high hardness and toughness, making them commonly used as rock crushing parts in rock drilling, where they usually show wear on a very fine scale. The hardness and toughness can ultimately be tuned for the application by adjusting the carbide grain size, binder fraction and composition.In the present investigation, the initial micro-scale deformation and wear of polished cemented carbide surfaces is studied by micro scratching with diamond and granite styli, and also by instrumented micro and nanoindentation. The deformation and wear is evaluated on the sub-micrometer scale using high resolution FEG-SEM and FIB cross sectioning. The selected microstructures include besides four cemented carbide grades that are commonly used in rock drilling also binderless and Ni containing grades. This wider range of cemented carbides is used to gain fundamental insights into the relations between microstructure and micro-scale deformation and wear. The results are discussed with respect to their significance for wear of cemented carbides in rock drilling operations.

  • 92. Heinrichs, J.
    et al.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. Uppsala University.
    Yvell, Karin
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Jacobson, S.
    On the deformation mechanisms of cemented carbide in rock drilling: Fundamental studies involving sliding contact against a rock crystal tip2018Inngår i: International journal of refractory metals & hard materials, ISSN 0958-0611, E-ISSN 2213-3917, Vol. 77, s. 141-151Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Cemented carbide is a composite material, most commonly consisting of tungsten carbide grains in a metallic matrix of cobalt. The combination of a hard ceramic phase in a ductile metallic matrix combines high hardness and ability to withstand plastic deformation with toughness to avoid cracking and fracturing. Since these properties are very important in rock drilling, cemented carbides are frequently used in such applications. In earlier work, it was found that granite in sliding contact with considerably harder cemented carbides not only results in plastic deformation of the cemented carbide composite, but also in plastic deformation of some of the individual WC grains. The latter observation is remarkable, since even the two hardest granite constituents (quartz and feldspar) are significantly softer than the WC grains. This tendency to plastic deformation of the WC grains was found to increase with increasing WC grain size. The present investigation aims to increase the understanding of plastic deformation of cemented carbides in general, and the individual WC grains in particular, in a situation representative for the rock drilling application. The emphasis is put on explaining the seemingly paradoxical fact that a nominally softer counter material is able to plastically deform a harder constituent in a composite material. The experimental work is based on a scratch test set-up, where a rock crystal tip slides against a fine polished cemented carbide surface under well-controlled contact conditions. The deformation and wear mechanisms of the cemented carbide are evaluated on the sub-micrometer scale; using high resolution FEG-SEM, EDS, EBSD, BIB and FIB cross-sectioning. The size of the Co-pockets, together with the shape and size of WC grains, turned out to be decisive factors in determining the degree of carbide deformation. The results are discussed with respect to their industrial importance, including rock drilling.

  • 93.
    Heinrichs, J
    et al.
    Uppsala Universitet.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Yvell, Karin
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Jacobson, S
    Uppsala Universitet.
    Soft rock scratches hard cemented carbide2015Inngår i: Proceedings of Wear of Materials, 2015Konferansepaper (Fagfellevurdert)
  • 94.
    Heinrichs, Jannica
    et al.
    Tribomaterials group, The Ångström Laboratory, Uppsala University, Uppsala, Sweden.
    Gerth, Julia
    Tribomaterials group, The Ångström Laboratory, Uppsala University, Uppsala, Sweden.
    Thersleff, Thomas
    Applied Materials Science, The Ångström Laboratory, Uppsala University, Uppsala, Sweden.
    Bexell, Ulf
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Larsson, Mats
    Primateria AB, Uppsala, Sweden.
    Wiklund, Urban
    Tribomaterials group, The Ångström Laboratory, Uppsala University, Uppsala, Sweden.
    Influence of sliding speed on modes of material transfer as steel slides against PVD tool coatings2013Inngår i: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 58, s. 55-64Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    An intermittent sliding test was used in order to study the formation and build- up of tribofilms during intermittent sliding of PVD coated HSS against case hardening steel (20NiCrMo2). Two cutting tool coatings were tested, TiN and AlCrN, and the influence of sliding speed was evaluated. With moderate speed,  two tribofilms were formed separately, one consisting of Mn, Si, Al and O on an intermediate layer  of Fe and one consisting of Fe, Mn, Cr and O on an intermediate layer of Cr and Mn. At low sliding speeds an uneven transfer of steel occured while high sliding speeds resulted in thermal softening of the substrate leading to coating failure. AlCrN provided better substrate protection at high speeds than TiN did.

  • 95. Heinrichs, Jannica
    et al.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. Uppsala universitet.
    Almqvist, Bjarne
    Jacobson, Staffan
    Initial surface failure and wear of cemented carbides in sliding contact with different rock types2018Inngår i: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 408-409, s. 43-55Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The initial wear, deformation and degradation of cemented carbide in contact with different rock types are studied using a crossed cylinder sliding test. The sliding distance is limited to centimetres at a time, interrupted by successive SEM analysis. This allows for careful studies of the gradually changing microstructure of the cemented carbide during the test. Five different rock types are included; granite, metal sulphide ore, mica schist, quartzite and marble. All rock types are very different in microstructure, composition and properties. The cemented carbide grade used for the evaluation contains 6 wt% Co and fine (~ 1 µm) WC grains, a grade commonly used in rock drilling. The results show that the cemented carbide microstructure becomes altered already during the very first contact with rock. The initial wear rate and wear character is highly influenced by the rock type. The initial wear of the cemented carbide is highest against quartzite and lowest against marble.

  • 96.
    Heinrichs, Jannica
    et al.
    Uppsala University.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Jacobson, Staffan
    Uppsala University.
    Initial wear of cemented carbides in sliding contact with different rock types2016Inngår i: Proceedings of the 17th Nordic Symposium on Tribology - Nordtrib 2016, 2016Konferansepaper (Fagfellevurdert)
  • 97. Heinrichs, Jannica
    et al.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Jacobson, Staffan
    Mechanisms of material transfer studied in situ in the SEM: explanations to the success of DLC coated tools in aluminium forming2012Inngår i: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 292, s. 49-60Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Metal forming constitutes a group of industrially important processes to form metallic components to net shape. When forming aluminium and other materials that tend to stick to the tools, problems occur. The transferred work material increases the friction, which increases the forming forces. Additionally, the transferred work material becomes hardened and then scratches the softer work material in subsequent forming. This process, known as galling, compromises the surface finish of the next pieces to be formed. This paper employs a newly developed technique to investigate the initial stages of transfer at high resolution in situ in the SEM. We show that the complex microscale processes involved can be distinguished into three classes: primary transfer, secondary transfer and damage activated transfer. The damage activated transfer constitutes a new fundamental tribological phenomenon, involving the activation and healing of a soft metal in sliding contact with a harder surface. Damage activation leads to transfer onto surfaces such as the polished DLC in this investigation, which would otherwise not see any transfer. These processes are important when forming aluminium, but are expected to be of general tribological significance, in sliding involving non-perfect lubricant films, especially for soft metals with protective surface oxides. (C) 2012 Elsevier B.V. All rights reserved.

  • 98. Heinrichs, Jannica
    et al.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Jacobson, Staffan
    New understanding of the initiation of material transfer and transfer layer build-up in metal forming: in situ studies in the SEM2012Inngår i: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 292, s. 61-73Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The tribological mechanisms behind the initiation of material transfer and build-up of transfer layers in aluminium forming have been studied in situ in the SEM where a tip of aluminium is put into contact with a tool steel surface under controlled sliding contact conditions. By combining in situ observations with post-test high resolution FEG-SEM studies of the contacting surfaces we have shown that aluminium is immediately transferred onto the fine polished tool steel. It was also confirmed that the initial transfer occurs on a very fine scale and is localised to the surface irregularities presented by the slightly protruding carbonitrides. In contrast, the less protruding M6C carbides, as well as the martensitic steel matrix exhibit very little initial transfer. Intentionally made scratches (roughly 5 mu m wide and 2 mu m deep) across the tool surface immediately result in larger scale transfer, which grows upon further passages of work material causing a high coefficient of friction. The study illuminates the extreme value of combining the in situ technique with high-resolution scanning electron microscopy using low acceleration voltage as a mean to detect the very thin initial transfer layers. With the higher acceleration voltages normally used, the transferred aluminium becomes transparent and can hardly be detected. (C) 2012 Elsevier B.V. All rights reserved.

  • 99. Hooshyar, H.
    et al.
    Jonsson, T.
    Hall, Josefine
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Svensson, J. -E
    Johansson, L. G.
    Liske, J.
    The effect of H2 and H2O on the oxidation of 304L-stainless steel at 600 °C: general behaviour (part I)2016Inngår i: Oxidation of Metals, ISSN 0030-770X, E-ISSN 1573-4889, Vol. 85, nr 3-4, s. 321-342Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The effect of p(H2O) and p(H2) on the oxidation of 304L stainless steel at 600 °C has been investigated in the present study. The samples were analysed by means of X-ray diffraction, Auger spectroscopy, and scanning electron microscopy equipped with energy dispersive spectroscopy. The results showed that at fixed p(H2), the corrosion rate increased considerably with increasing p(H2O). At fixed p(H2O), the corrosion rate decreased slightly with increasing p(H2). Duplex oxide scales formed during the exposure in all environments. The outer and inner layer consisted of Fe3O4 and (Fe, Cr)3O4, respectively. The latter was mainly in the form of internal oxidation. The Cr-rich oxide formation was observed at the initial oxidation process before oxide breakdown. The Auger analysis also suggested the presence of Cr-rich oxide layer just after the breakaway oxidation. The results indicated that the rate-determining step in the corrosion attack is surface controlled or diffusion controlled through an oxide layer with fixed thickness over time.

  • 100.
    Huang, Shuo
    et al.
    Royal Inst Technol, Dept Mat Sci & Engn, Appl Mat Phys, SE-10044 Stockholm, Sweden..
    Vida, Adam
    Wigner Res Ctr Phys, Inst Solid State Phys & Opt, POB 49, H-1525 Budapest, Hungary.;Eotvos Lorand Univ, Dept Mat Phys, Pazmany Peter Setany 1-A, H-1117 Budapest, Hungary..
    Li, Wei
    Royal Inst Technol, Dept Mat Sci & Engn, Appl Mat Phys, SE-10044 Stockholm, Sweden..
    Molnar, David
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. KTH.
    Kwon, Se Kyun
    Pohang Univ Sci & Technol, Grad Inst Ferrous Technol, Pohang 37673, South Korea..
    Holmstrom, Erik
    Sandvik Coromant R&D, S-12680 Stockholm, Sweden..
    Varga, Bela
    Transylvania Univ Brasov, Fac Mat Sci, Bulevardul Eroilor 29, Brasov 500036, Romania..
    Varga, Lajos Karoly
    Wigner Res Ctr Phys, Inst Solid State Phys & Opt, POB 49, H-1525 Budapest, Hungary..
    Vitos, Levente
    Royal Inst Technol, Dept Mat Sci & Engn, Appl Mat Phys, SE-10044 Stockholm, Sweden.;Wigner Res Ctr Phys, Inst Solid State Phys & Opt, POB 49, H-1525 Budapest, Hungary.;Uppsala Univ, Div Mat Theory, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden..
    Thermal expansion in FeCrCoNiGa high-entropy alloy from theory and experiment2017Inngår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 110, nr 24, artikkel-id 241902Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    First-principle alloy theory and key experimental techniques are applied to determine the thermal expansion of FeCrCoNiGa high-entropy alloy. The magnetic transition, observed at 649 K, is accompanied by a significant increase in the thermal expansion coefficient. The phase stability is analyzed as a function of temperature via the calculated free energies accounting for the structural, magnetic, electronic, vibrational and configurational contributions. The single-and polycrystal elastic modulus for the ferro-and paramagnetic states of the face-centered and body-centered cubic phases are presented. By combining the measured and theoretically predicted temperature-dependent lattice parameters, we reveal the structural and magnetic origin of the observed anomalous thermal expansion behavior. Published by AIP Publishing.

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