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  • 51.
    Fallqvist, Mikael
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    M’Sauobi, R
    Seco Tools.
    Andersson, J
    Seco Tools.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Mechanical and tribological properties of PVD-coated cemented carbide as evaluated by a new multi-pass scratch testing method2012In: Advances in Tribology, ISSN 1687-5915, E-ISSN 1687-5923, no 305209Article in journal (Refereed)
    Abstract [en]

    A new test method based on multipass scratch testing has been developed for evaluating the mechanical and tribological properties of thin, hard coatings. The proposed test method uses a pin-on-disc tribometer and during testing a Rockwell C diamond stylus is used as the “pin” and loaded against the rotating coated sample. The influence of normal load on the number of cycles to coating damage is investigated and the resulting coating damage mechanisms are evaluated by posttest scanning electron microscopy. The present study presents the test method by evaluating the performance of Ti0.86Si0.14N, Ti0.34Al0.66N, and (Al0.7Cr0.3)2O3 coatings deposited by cathodic arc evaporation on cemented carbide inserts. The results show that the test method is quick, simple, and reproducible and can preferably be used to obtain relevant data concerning the fatigue, wear, chipping, and spalling characteristics of different coating-substrate composites. The test method can be used as a virtually nondestructive test and, for example, be used to evaluate the fatigue and wear resistance as well as the cohesive and adhesive interfacial strength of coated cemented carbide inserts prior to cutting tests.

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  • 52.
    Fallqvist, Mikael
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    The influence of surface defects on the mechanical and tribological properties of VN-based arc-evaporated coatings2013In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 297, no 1-2, p. 1111-1119Article in journal (Refereed)
    Abstract [en]

    The influence of surface defects, i.e., droplets and craters, on the mechanical and tribological properties of arc-evaporated VxN coatings deposited on cemented carbide has been investigated in a scratching contact using a diamond stylus and a sliding contact using a stainless steel pin. Post-test characterisation using 3D optical surface profilometry and scanning electron microscopy was performed in order to investigate the mechanical and tribological response of the coatings. The results show that scratch induced coating cracking mainly is restricted to larger droplets showing a low interfacial bonding to the adjacent coating matrix. The influence of coating defects on the cohesive strength, i.e., the tendency to chipping of small coating fragments, was found to be relatively small. In contrast, the presence of defects may have a significant impact on the interfacial adhesive strength, increasing the tendency to spalling. In sliding contact, surface defects such as droplets and craters have a strong impact on the tribological behaviour of the coatings causing abrasive wear of the less hard counter material surface and material transfer to the coating, both mechanisms affecting the friction characteristics of sliding contact tribo systems.

  • 53.
    Fallqvist, Mikael
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Ruppi, S
    Abrasive wear of textured-controlled CVD a-Al2O3 coatings2007In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 202, no 4-7, p. 837-843Article in journal (Refereed)
    Abstract [en]

    In the present study the wear resistance of some CVD alpha-Al2O3 coatings with different growth textures, i.e. <0001>, <10<(1)over bar>2> and <10<(1)over bar>4>, and a kappa-Al2O3 coating have been investigated using a micro-abrasion test with diamond particles as the abrasive medium. The results show that the softer kappa-Al2O3 coating shows a higher wear rate as compared with the textured alpha-Al2O3 coatings. Of the latter coatings, the 101¯4 textured a-Al2O3 coating shows the lowest wear rate while the <0001> and <10<(1)over bar>2> textured alpha-Al2O3 coatings show similar wear rate. Two different dominant wear mechanisms, i.e. micro cutting and micro chipping, were observed and the latter mechanism is believed to control the wear rate of the Al2O3 coatings investigated. The results obtained are discussed in relation to the dominant wear mechanisms of the coatings identified using scanning electron microscopy.

  • 54.
    Fallqvist, Mikael
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Material Science.
    Ruppi, Sakari
    Abrasive wear of multilayer kappa-Al2O3-Ti(C,N) CVD coatings on cemented carbide2007In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 263, no 1-6, p. 74-80Article in journal (Refereed)
    Abstract [en]

    In the present study the wear resistance of kappa-Al2O3–Ti(C,N) multilayer CVD coatings with different multilayer structures (8, 15, 32 layers of kappa-Al2O3 separated by thin Ti(C,N) layers) have been investigated using a micro-abrasion and a cutting test. The results show that the wear rate of the kappa-Al2O3 multilayer coatings tend to decrease with decreasing layer thickness in the micro-abrasion test and decrease with increasing layer thickness in the cutting tests. The reason for this is mainly due to the difference in wear behaviour depending on temperature. The results obtained are discussed in relation to the dominant wear mechanisms of the coatings which have been identified using scanning electron microscopy and energy dispersive X-ray spectroscopy. The potential of the micro-abrasion test in the characterisation of thin CVD coatings for cutting tool applications is discussed.

  • 55.
    Fallqvist, Mikael
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Ruppi, S
    Seco Tools.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Ottosson, M
    Uppsala Universitet.
    Grehk, Mikael
    Dalarna University, School of Technology and Business Studies, Materials Technology. Sandvik Materials Technology.
    Nucleation and growth of CVD α-Al2O3on TixOy template2012In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 207, p. 254-261Article in journal (Refereed)
    Abstract [en]

    The microstructure, phase and chemical composition of TixOy templates used to nucleate α-Al2O3 on Ti(C,N) coated cemented carbide have been elucidated using scanning electron microscopy, X-ray diffraction, Auger electron spectroscopy and Time-of-Flight Secondary Ion Mass Spectrometry. Further, the adhesive strength of the α-Al2O3–TixOy–Ti(C,N) interfaces was investigated using scratch adhesion testing.

    The present study confirmed that the as-deposited template consisted of a Ti4O7 phase which during subsequent deposition of the Al2O3 layer transformed to a Ti3O5 phase and that the grown Al2O3 layer consisted of 100% α-Al2O3. Furthermore, the results showed that the lowest interfacial strength within the multilayer structure was exhibited by the Ti(C,N)–TixOy interface and that the transformation of Ti4O7 to Ti3O5 in the template resulted in formation of pores in the Ti(C,N)-template interface lowering the interfacial strength even more. The use of surface analysis techniques such as Auger electron spectroscopy and especially Time-of-Flight Secondary Ion Mass Spectrometry enabled trace element analyses using depth profiling to characterise the thin interfacial layers in detail.

  • 56.
    Fallqvist, Mikael
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Schultheiss, F
    Lunds Universitet.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    M’Sauobi, R
    Seco Tools.
    Ståhl, J E
    Lunds Universitet.
    Influence of CVD Al2O3 coated tool surface micro topography on the tribological characteristics in metal cutting: part I2013In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, p. 87-98Article in journal (Refereed)
    Abstract [en]

    The influence of surface micro topography of CVD α-Al2O3 coatings, deposited on cemented carbide inserts, on tribological characteristics in sliding contact and in metal cutting has been investigated using quenched and tempered steel as counter/work material. Pin-on-disc and turning tests were carried out and post-test characterization using 3D optical surface profilometry and scanning electron microscopy was performed in order to investigate the tribological response of the coatings. The results show that surface micro topography can have a significant impact on the tribological performance of Al2O3 coatings under initial and cutting contact conditions. For both kinds of tests the tendency for transfer of workpiece material strongly increases with increasing coating micro topography. In the pin-on-disc tests, a smooth coating surface significantly reduces the friction coefficient. In the turning tests the contact conditions at the flank face increase with decreasing micro topography. In contrast, no general conclusions can be drawn regarding the influence of coating micro topography on the contact conditions at the rake face. The resulting topography of the turned surface was found to increase with increasing coating topography.

  • 57. Farahani, Sara
    et al.
    Worrell, Ernst
    Bryntse, Göran
    Dalarna University, School of Technology and Business Studies, Graphic/Arts Technology.
    CO2-free paper?2004In: Resources, Conservation and Recycling, ISSN 0921-3449, E-ISSN 1879-0658, Vol. 42, p. 317-336Article in journal (Refereed)
    Abstract [en]

    Black liquor gasification–combined cycle (BLGCC) is a new technology that has the potential to increase electricity production of a chemical pulping mill. Increased electricity generation in combination with the potential to use biomass (e.g. bark, hog fuel) more efficiently can result in increased power output compared to the conventional Tomlinson-boiler. Because the BLGCC enables an integrated pulp and paper mill to produce excess power, it can offset electricity produced by power plants. This may lead to reduction of the net-CO2 emissions. The impact of BLGCC to offset CO2 emissions from the pulp and paper industry is studied. We focus on two different plant designs and compare the situation in Sweden and the US. The CO2 emissions are studied as function of the share of recycled fibre used to make the paper. The study shows that under specific conditions the production of “CO2-free paper” is possible. First, energy efficiency in pulp and paper mills needs to be improved to allow the export of sufficient power to offset emissions from fossil fuels used in boilers and other equipment. Secondly, the net-CO2 emission per ton of paper depends strongly on the emission reduction credits for electricity export, and hence on the country or grid to which the paper mill is connected. Thirdly, supplemental use of biomass to replace fossil fuel inputs is important to reduce the overall emissions of the pulp and paper industry.

  • 58. Fazakas, E.
    et al.
    Heczel, A.
    Molnar, David
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Varga, B.
    Zadorozhnyy, V.
    Vida, A.
    Comparative microstructural and corrosion development of VCrNiCoFeCu equiatomic multicomponent alloy produced by induction melting and spark plasma sintering2018In: IOP Conference Series: Materials Science and Engineering, 2018, Vol. 329, no 1, article id 012016Conference paper (Refereed)
    Abstract [en]

    The present study focuses on the corrosion behavior of a single-phase FCC high entropy alloy (VCrNiCoFeCu) casted by two different methods: induction melting and spark plasma sintering. The corrosion resistance has been evaluated using immersion tests in 3.5% NaCl solution, the potentiodynamic polarization measurements and the results are compared how is dependent the corrosion rate as a function of the production methods. Our results show that induction melted sample is stable in salty environment. On the other hand, based on the changes of polarization curves, there must be an evolution of oxide films on the SPSed sample until reaching the stable oxide layer. 

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  • 59. Ferritsius, Olof
    et al.
    Ferritsius, Rita
    Rundlöf, Mats
    Reyier Österling, Sofia
    Dalarna University, Verksamhetsstödet.
    Engberg, Birgitta A.
    Heterogeneity of Thermomechanical and Chemi-thermo-mechanical Pulps Described with Distributions of an Independent Common Bonding Factor on Particle Level2022In: BioResources, ISSN 1930-2126, E-ISSN 1930-2126, Vol. 17, no 1, p. 763-784Article in journal (Refereed)
    Abstract [en]

    Particles in mechanical pulp show a wide variety but are commonly described using averages and/or collective properties. The authors suggest using distributions of a common bonding factor, BIND (Bonding INDicator), for each particle. The BIND-distribution is based on factor analysis of particle diameter, wall thickness, and external fibrillation of several mechanical pulps measured in an optical analyser. A characteristic BIND-distribution is set in the primary refiner, depending on both wood and process conditions, and remains almost intact along the process. Double-disc refiners gave flatter distributions and lower amounts of fibres with extreme values than single-disc refiners. More refining increased the differences between fibres with low and high BIND. Hence, it is more difficult to develop fibres with lower BIND. Examples are given of how BIND-distributions may be used to assess energy efficiency, fractionation efficiency, and influence of raw material. Mill scale operations were studied for printing-grade thermomechanical pulp (TMP), and board-grade chemi-thermomechanical pulp (CTMP), both from spruce.

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  • 60.
    Finnkvist Penttinen, Anna
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Nötningsbeständighet av bestrykningsschaber2015Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    A study of the type of wears Böhler‐Uddeholms coating blades are subjected to when

    they are considered to be consumed to handle usage. Their own devices on the

    company in order to determine the abrasion resistance on the coater blades was

    comparable to the pin‐on‐disc application.

    This is to possibly find a standard way to measure the wear of the different blades

    with the currently available application. If one were to succeed in finding a way this

    will result in that one can give customers with more information on the blades and

    give a better customer service.

    Two end‐used coater blades were used to determine the wear that has occurred.

    For the investigation between Böhler‐Uddeholms device and the pin‐on‐disc

    application three different steel blades were used, named Steel |, steel || and

    steel ||| in this rapport.

    The final wear that occurred on the blades was three body abrasion and corrosive

    wear. It will also, because of the basic coating mass, build an adhesive border along

    the edge of the coating blade.

    The apparatus of the company is in the current situation not quite optimal to mimic

    the actual wear that occurs. The pin‐on‐disc application gives a harder abrasive wear

    that can sees in the wear in the industries at the end use.

  • 61. Fisk, Martin
    et al.
    Hansson, Sofia
    Dalarna University, School of Technology and Business Studies, Material Science.
    FE-Simulation of combined induction heating and extrusion in manufacturing of stainless steel tubes2009In: Computational Plasticity (COMPLAS) X: Fundamentals and Applications: proceedings of the tenth International Conference on Computational Plasticity held in Barcelona, Spain, 2th-4th September 2009 / [ed] E. O˜nate and D.R.J. Owen, Barcelona: International Center for Numerical Methods , 2009Conference paper (Refereed)
    Abstract [en]

    The manufacturing process chain for extrusion of AISI 316L tubes is simulatedusing the finite element method. Models of induction heating and expansion is included and thetemperature field in the billet before extrusion is calculated. It is shown that a correct initialtemperature of the billet is needed in order to predict the extrusion force curve in the initialstage of the process.

  • 62. Fleury, E.
    et al.
    Jayamani, Jayaraj
    Kim, Y. C.
    Seok, H. K.
    Kim, K. Y.
    Kim, K. B.
    Fe-based amorphous alloys as bipolar plates for PEM fuel cell2006In: Journal of Power Sources, ISSN 0378-7753, E-ISSN 1873-2755, Vol. 159, no 1, p. 34-37Article in journal (Refereed)
    Abstract [en]

    Two compositions of Fe-based Fe50Cr18Mo8Al2Y2C14B6 and Fe44Cr15Mo14Y2C15B6N4 amorphous alloys were developed as alternative bipolar plate material for polymer electrolyte membrane fuel cell (PEMFC). In this paper, we present results of an investigation on the electrical, mechanical, corrosion properties and processing ability of these amorphous alloys. The combination of excellent properties indicated that Fe-based amorphous alloys could be potential candidate materials as bipolar plates in PEMFC.

  • 63.
    Gorella, Nagaraju
    Dalarna University, School of Information and Engineering.
    Characterization of as prepared and exposed Perovskitesolar cells by microscopic and spectroscopic techniques2021Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Studying the microstructural features, optical, and electrical properties of the thin-filmperovskite solar cells (PSC) is the main objective of this thesis work. All the PSCs used in thisthesis work were prepared by spin coating assisted with gas quenching process and the samplesreceived from Interuniversity Microelectronics Centre (IMEC), Belgium.Microstructural and architectural details of the stagewise prepared PSCs were investigatedusing a Scanning Electron Microscope (SEM) - Focused Ion Beam (FIB) technique. With thereference to the given specification from IMEC, the SEM-FIB examinations of the as-preparedPSCs confirmed the presence of different layers such as hole transport layer (HTL), perovskitelayer, and electron transport layer (ETL). Further, the thickness of the perovskite layers wasmeasured and found to be 400 and 500 nm which validates the specification of the as-preparedsamples 1 and 2, respectively. The observed average grain size of the perovskite of the asprepared samples 1 and 2 are significantly different and the values are approximately 83 and169 nm, respectively. The average surface roughness values of perovskite layers (as-preparedsamples 1 and 2) and electron transport layer (as-prepared samples 3) were evaluated by atomicforce microscopy (AFM) and the values are 10, 19, and 12 nm, respectively. Furthermore, theconductive-AFM was performed to evaluate the electrical properties of the perovskite layers,and the results confirmed that the as-prepared sample 2 showed a higher mean current value of4.1 nA, than sample 1 resulted in 2.9 nA. The higher electrical performance of the as-preparedsample 2 could be correlated to the larger grain size, higher thickness, and higher surfaceroughness values of the perovskite layer.Moreover, the performance evaluation of a complete perovskite solar device with a similarconfiguration was evaluated between the as-prepared (newly fabricated) and the exposedsamples (tested under sunlight for ten weeks), and their behavior was studied. The optical andelectrical characteristics of the solar cell at the device level were examined with the help ofphotoluminescence (PL), electroluminescence (EL), and solar simulator techniques. The peakand fullwidth half maximum (FWHM) values of the PL emission spectra of the as-prepareddevice are in line with IMEC specification, whereas these values are slightly decreased for theexposed perovskite solar device. Also, during the EL examination, predominantly uniformluminescence was observed for the as-prepared device, whereas discontinuity in the emissionof electrons, and in some parts absence of luminescence-effect was observed for the exposedsolar cell. The current-voltage characteristics obtained from the solar simulator resultsconfirmed that the power conversion efficiency of the as-prepared device is at least 6 timeshigher than the exposed device. Based on the PL, EL, and PCE results it could be confirmedthat the perovskite solar cell exposed to sunlight for 10 weeks has started to degrade.

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  • 64.
    Granbom, Ylva
    Dalarna University, School of Technology and Business Studies, Material Science.
    Structure and mechanical properties of dual phase steels: An experimental and theoretical analysis2010Doctoral thesis, monograph (Other academic)
    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.

  • 65.
    Granbom, Ylva
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Ryde, Lena
    Jeppsson, Johan
    Simulation of the soaking and gas jet cooling in a continuous annealing line using dilatometry2010In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 81, no 2Article in journal (Refereed)
    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.

  • 66.
    Grehk, Mikael
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Berger, Robert
    Bexell, Ulf
    Dalarna University, School of Technology and Business Studies, Material Science.
    Investigation of the drying process of linseed oil using FTIR and ToF-SIMS2008In: Proceedings of the 17th International Vacuum Congress/13th International Conference on Surface Science/Internatinal Conference on Nanoscience and Technology, Stockholm, 2008, Vol. 100Conference paper (Refereed)
    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.

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  • 67.
    Grehk, Mikael
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Engkvist, Josefin
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Bexell, Ulf
    Dalarna University, School of Technology and Business Studies, Material Science.
    Richter, Jan H
    Karlsson, Patrik G
    Sandell, Anders
    Initial stages of metal-organic chemical-vapor deposition of ZrO2 on a FeCrAl alloy2007In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 516, no 6, p. 875-879Article in journal (Refereed)
    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.

  • 68.
    Gustafsson, Emil
    Dalarna University, School of Technology and Business Studies, Materials Technology. Luleå tekniska universitet.
    Experiments on Sheet Metal Shearing2013Licentiate thesis, comprehensive summary (Other academic)
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  • 69.
    Gustafsson, Emil
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Marth, Stefan
    Luleå University of Technology.
    Karlsson, Lars
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Oldenburg, Mats
    Luleå University of Technology.
    Strain and stress conditions at crack initiation during shearing of medium- and high-strength steel sheet2017In: International Journal of Mechanical and Materials Engineering, ISSN 2198-2791, Vol. 12, no 1, p. 10-Article in journal (Refereed)
    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.

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  • 70.
    Gustafsson, Emil
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Oldenburg, Mats
    Jansson, Anders
    Design and validation of a sheet metal shearing experimental procedure2014In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 214, no 11, p. 2468-2477Article in journal (Refereed)
    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%.

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  • 71.
    Gustafsson, Emil
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Oldenburg, Mats
    Jansson, Anders
    Experimental study on the effects of clearance and clamping in steel sheet metal shearing2016In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 229, p. 172-180Article in journal (Refereed)
    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.

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  • 72. Gustavsson, Fredrik
    et al.
    Svahn, Fredrik
    Bexell, Ulf
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Jacobson, Staffan
    Nanoparticle based and sputtered WS2 low-friction coatings: differences and similarities with respect to friction mechanisms and tribofilm formation2013In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 232, p. 616-626Article in journal (Refereed)
    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.

  • 73.
    Gyhlesten Back, Jessica
    Dalarna University, School of Technology and Business Studies, Materials Technology. Luleå tekniska universitet, Material- och solidmekanik.
    Modelling and Characterisation of the Martensite Formation in Low Alloyed Carbon Steels2017Licentiate thesis, comprehensive summary (Other academic)
    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.

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  • 74.
    Gyhlesten Back, Jessica
    Dalarna University, School of Technology and Business Studies, Materials Technology. Luleå tekniska universitet.
    Simplified Implementation of the Koistinen-Marburger Model for Use in Finite Element Simulations2016In: Proceedings of the 11th international congress on thermal stresses, Severino: Edizioni Paguro , 2016, p. 107-110Conference paper (Other academic)
  • 75.
    Gyhlesten Back, Jessica
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology. Research and Development, SSAB Europe, Borlänge.
    Engberg, Göran
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Investigation of parent austenite grains from martensite structure using EBSD in a wear resistant steel2017In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 10, no 5, article id 453Article in journal (Refereed)
    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.

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  • 76.
    Gyhlesten Back, Jessica
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Lindgren, Lars-Erik
    Luleås tekniska universitet.
    Modelling of the influence of prior deformation of austenite on the martensite formation in a low-alloyed carbon steel2018In: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 941, p. 95-99Article in journal (Refereed)
    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 %. 

  • 77.
    Gyhlesten Back, Jessica
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Surreddi, Kumar Babu
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Microstructure analysis of martensitic low alloy carbon steel samples subjected to deformation dilatometry2019In: Materials Characterization, ISSN 1044-5803, E-ISSN 1873-4189, Vol. 157, article id 109926Article in journal (Refereed)
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  • 78. Habainy, J.
    et al.
    Iyengar, S.
    Surreddi, Kumar Babu
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Lee, Y.
    Dai, Y.
    Formation of oxide layers on tungsten at low oxygen partial pressures2018In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 506, no SI, p. 26-34Article in journal (Refereed)
    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.

  • 79. Habainy, J.
    et al.
    Lee, Y.
    Surreddi, Kumar Babu
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Prosvetov, A.
    Simon, P.
    Iyengar, S.
    Dai, Y.
    Tomut, M.
    Study of heavy ion beam induced damage in tungsten for high power target applications2019In: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, ISSN 0168-583X, E-ISSN 1872-9584, Vol. 439, p. 7-16Article in journal (Refereed)
    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). 

  • 80.
    Hall, Josefin
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Beglund, Tomas
    Bexell, Ulf
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Influence of microstructure and hard phase content on the mechanisms of deformation and wear of HIP:ed Stellite® 190 composites2015Conference paper (Refereed)
  • 81.
    Hall, Josefin
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Bexell, Ulf
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    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 ions2015In: Materials at High Temperatures, ISSN 0960-3409, Vol. 32, no 1-2, p. 133-141Article in journal (Refereed)
    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.

  • 82.
    Halldén, Helena
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Planhet efter skärande bearbetning av formatplåt – en jämförelse mellan laserskärning och gradsaxklippning2017Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    In recent years, SSAB has had a growing quality problem regarding residual stresses in sheet metal. The problem means that unevenness arises in connection with the customer processing, mainly during laser cutting, although the company has delivered a seemingly flat material.

    SSAB currently has power shearing within the company as an evaluation method for determining the internal stresses in metal sheet after leveling in sheet cutting line 3. However, there is a big difference between power shearing and the process laser cutting, which usually is the customer´s actual process method. Consequently, results from evaluating the two operations can differ. For that reason power shearing is questioned as a test method of residual stresses.

    The thesis compares the two operations power shearings and laser cuttings impact on flatness of leveled sheet metal, and thereafter to evaluate power shearing as a test method of unevenness. The intention of the thesis is also to determine how different leveling parameters may affect the results of the comparison.

    The work was performed by three different production trials. The first trial was leveling and cutting sheet metal. Thereafter some of the sheets were cut in a laser cutting machine and the rest with a power shearing machine. The result was in both cases smaller plates. The unevenness of the plates was measured by hand and then the results were compiled in order to read the results and make relevant comparisons between the cutting methods.

    The results show that power shearing, as an evaluation method to predict unevenness after laser cutting, is not a good method. Poor set leveling parameters also increases the uncertainty of the valuation method. However, a combination of power shearing into two different versions of plates, can provide some information about the unevenness of a corresponding laser cut sheet leveled with the same leveling settings.

  • 83.
    Hansson, Sofia
    Dalarna University, School of Technology and Business Studies, Material Science.
    A three-dimensional finite element simulation of stainless steel tube extrusion using a physically based material model2006Conference paper (Refereed)
  • 84.
    Hansson, Sofia
    Dalarna University, School of Technology and Business Studies, Material Science.
    Modeling of the Stainless Steel Tube Extrusion Process2010Doctoral thesis, monograph (Other academic)
    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.

  • 85.
    Hansson, Sofia
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Domkin, Konstantin
    Physically based material model in finite element simulation of extrusion of stainless steel tubes2005Conference paper (Refereed)
  • 86.
    Hansson, Sofia
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science. Sandvik Mat Technol, R&D Ctr, Sandviken.
    Fisk, Martin
    Simulations and measurements of combined induction heating and extrusion processes2010In: Finite elements in analysis and design (Print), ISSN 0168-874X, E-ISSN 1872-6925, Vol. 46, no 10, p. 905-915Article in journal (Refereed)
    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.

  • 87.
    Hansson, Sofia
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science. 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 extrusion2010In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 210, no 10, p. 1386-1396Article in journal (Refereed)
    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.

  • 88.
    Harfouche, Sara
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Dimensionsmätning av varma ämnen iLIMAB och undersökning avkrympfaktorer2014Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    At the rolling mill in Ovako, Hofors, bars are produced in different dimensions during a hot rolled procedure. After the last rollers, a dimension gauge LIMAB was installed. LIMAB measures the bars at high temperatures, around 900 oC.

    When the bars of different steel types cool down to room temperature, they shrink differently. Exactly how much they shrink is of interest to the customers who want specific dimensions of their products.

    Two types of steels with different carbon content have been analyzed in in this project. By comparing the bars hot dimension values from the dimension gauge with the cold measured values, a shrinkage factor can be calculated.

    Several types of shrinkage formulas were compiled and the result shows a lineup of all the

    evaluated formulas and how the shrinkage factors deviate from each other.

    The production of rings formula gives us the highest value on the shrinkage factor based on our calculations. The next highest values are from LIMAB AB and the lowest values are from the production of pipes.

    Currently, it is difficult to determine new shrinkage factor values because it requires more experiments and some capability measurements.

  • 89. Harfouche, Sara
    et al.
    Padam, Benita
    Dimensionsmätning av varma ämnen i LIMAB och undersökning av krympfaktorer2014Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    At the rolling mill in Ovako, Hofors, bars are produced in different dimensions during a hot rolled procedure. After the last rollers, a dimension gauge LIMAB was installed. LIMAB measures the bars at high temperatures, around 900 oC.

    When the bars of different steel types cool down to room temperature, they shrink differently. Exactly how much they shrink is of interest to the customers who want specific dimensions of their products.

    Two types of steels with different carbon content have been analyzed in in this project. By comparing the bars hot dimension values from the dimension gauge with the cold measured values, a shrinkage factor can be calculated.

    Several types of shrinkage formulas were compiled and the result shows a lineup of all the

    evaluated formulas and how the shrinkage factors deviate from each other.

    The production of rings formula gives us the highest value on the shrinkage factor based on our calculations. The next highest values are from LIMAB AB and the lowest values are from the production of pipes.

    Currently, it is difficult to determine new shrinkage factor values because it requires more experiments and some capability measurements.

     

  • 90. Haribabu, S.
    et al.
    Sudha, C.
    Raju, S.
    Hajra, R. N.
    Mythili, R.
    Jayamani, Jayaraj
    Murugesan, S.
    Saroja, S.
    Effect of Al Addition on the Microstructure and Phase Stability of P91 Ferritic-Martensitic Steel2019In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 50, no 3, p. 1421-1436Article in journal (Refereed)
    Abstract [en]

    This paper presents the results of an experimental and computational study carried out to elucidate the effect of Al on the microstructure and phase stability of P91 F/M steel in as-cast, homogenized and normalized conditions. Al-added steels followed ‘Ferritic-Austenitic’ mode of solidification and the as-cast microstructures consisted of δ-ferrite + α′-martensite, the volume fraction of ferrite and hardness of martensite increased with Al concentration. Heat treatments and DSC experiments confirmed increased stability for δ-ferrite with Al addition. Systematic change in the phase transformations temperatures and volume fraction of equilibrium phases due to Al addition was estimated with the help of Thermo-Calc®. Al addition promoted the formation of AlN which was confirmed through electron microscopy-based investigations. AlN dissolution temperature was always above γ-loop which made it impossible to dissolve during austenization. With the help of Scheil and equilibrium simulations using Thermo-Calc®, elemental partitioning between δ-ferrite and α′ phases was found to be the reason for higher hardness of martensite. Based on experimental evidences, it is concluded that except in the case of 0.48 wt pct Al-added steel it is impossible to obtain single phase γ-field (without ferrite) at high temperature thereby a fully martensite structure on cooling.

  • 91. Harlin, P.
    et al.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Starch consolidation of M3/2 high speed steel powder: Influence of microstructure on mechanical properties2007In: Powder Metallurgy, ISSN 0032-5899, E-ISSN 1743-2901, Vol. 50, no 3, p. 232-238Article in journal (Refereed)
    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. 

  • 92.
    Harlin, Peter
    et al.
    Sandvik Materials Technology.
    Bexell, Ulf
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    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 conditions2009In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 203, no 13, p. 1748-1755Article in journal (Refereed)
    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.

  • 93.
    Harlin, Peter
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Carlsson, Per
    Dalarna University, School of Technology and Business Studies, Material Science.
    Bexell, Ulf
    Dalarna University, School of Technology and Business Studies, Material Science.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Material Science.
    Influence of surface roughness of PVD coatings on tribological performance in sliding contacts2006In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 201, no 7, p. 4253-4259Article in journal (Refereed)
    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.

  • 94.
    Harlin, Peter
    et al.
    Sandvik Materials Technology.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Material Science.
    Abrasive wear resistance of starch consolidated and sintered high speed steel2009In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 267, no 9-10, p. 1482-1489Article in journal (Refereed)
    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.

  • 95.
    Harlin, Peter
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Material Science.
    Starch consolidation of M3/2 high speed steel powder: influence of process parameters on resulting microstructure2007In: Powder Metallurgy, ISSN 0032-5899, E-ISSN 1743-2901, Vol. 50, no 4, p. 345-353Article in journal (Refereed)
    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.

  • 96. Hatami, S.
    et al.
    Armada, S.
    Laurent, A.
    Nyborg, L.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Tribological properties of powder metallurgical tool steels used in powder compaction pressing dies2011In: Lubrication Science, ISSN 0954-0075, E-ISSN 1557-6833, Vol. 23, no 3, p. 139-152Article in journal (Refereed)
    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.

  • 97.
    Hedman, Fanny
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Inverkan av processparametrar i varmvalsverket på planhet efter formatklippning2015Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    After the hot rolling mill the coils are sent either untreated or pickled to be leveled and cut in one off the different cut to length lines in SSAB Borlänge.

    The results on the flatness after leveling and cutting in the cut to length line 4 shifts even though the coils are from the same steel type. Many factors could affect the flatness and this thesis examines if the geometry on the coil after the hot rolling mill has any impact on the flatness after the cut to length line 4. The studies have been limited to a few steel types and dimensions.

    In order to find a connection between the hot rolling mill and the cut to length line were information on historical coils gathered from data bases that are connected to the different production lines.

    The connections that were found were that with a lower crown on the coils the flatness results are better. The wedge on good and defect coils varies and a thicker drive side gives a better flatness result than a thicker free side gives. Even the shape of the cross profile is affecting the flatness results.

    To verify these connections two production experiments were done, one where some coils were rolled and cut to length without any changes on the parameters and one where some parameters were changed before the coils was rolled and cut to length. The production experiments proved the connections because the good coils had the lowest crown.

  • 98. Heinrichs, J.
    et al.
    Gerth, J.
    Bexell, Ulf
    Dalarna University, School of Technology and Business Studies, Material Science.
    Larsson, M.
    Wiklund, U.
    Influence from surface roughness on steel transfer to PVD tool coatings in continuous and intermittent sliding contacts2012In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 56, p. 9-18Article in journal (Refereed)
    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.

  • 99. Heinrichs, J.
    et al.
    Norgren, S.
    Jacobson, S.
    Yvell, Karin
    Dalarna University, School of Information and Engineering, Materials Technology.
    Olsson, Mikael
    Dalarna University, School of Information and Engineering, Materials Technology.
    Influence of binder metal on wear initiation of cemented carbides in sliding contact with granite2021In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 470-471, article id 203645Article in journal (Refereed)
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  • 100. Heinrichs, J.
    et al.
    Norgren, S.
    Jacobson, S.
    Yvell, Karin
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Influence of cemented carbide binder type on wear initiation in rock drilling – Investigated in sliding wear against magnetite rock2019In: International journal of refractory metals & hard materials, ISSN 0263-4368, Vol. 85, article id 105035Article in journal (Refereed)
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