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  • 151.
    Molnar, David
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. KTH, Tillämpad materialfysik.
    Generalised stacking fault energy and plastic deformation of austenitic stainless steels2018Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Austenitic stainless steels are primarily known for their exceptional corrosion resistance. They have the face centred cubic (FCC) structure which is stabilised by adding nickel to the Fe-Cr alloy. The Fe-Cr-Ni system can be further extended by adding other elements such as Mn, Mo, N, C, etc. in order to improve the properties. Since austenitic stainless steels are often used as structural materials, it is important to be able to predict their mechanical behaviour based on their composition, microstructure, magnetic state, etc.

    In this work, we investigate the plastic deformation behaviour of austenitic stainless steels by theoretical and experimental approaches. In FCC materials the stacking fault energy (SFE) plays an important role in the prediction of the deformation modes. Based on the magnitude of the SFE different deformation modes can be observed such as martensite formation, deformation twinning, dissociated or undissociated dislocation glide. All these features influence the behaviour differently, therefore it is desired to be able to predict their occurrence. Alloying and temperature have strong effect on the SFE and thus on the mechanical properties of the alloys. Several models based on the SFE and more recently on the so called generalised stacking fault energy (GSFE or γ-surface) are available to predict the alloy's affinity to twinning and the critical twinning stress representing the minimum resolved shear stress required to initiate the twinning deformation mechanism. One can employ well established experimental techniques to measure the SFE. On the other hand, one needs to resort to ab initio calculations based on density functional theory (DFT) to compute the GSFE of austenitic steels and derive parameters like the twinnability and the critical twinning stress. 

    We discuss the effect of the stacking fault energy on the deformation behaviour for two different austenitic stainless steels. We calculate the GSFE of the selected alloys and based on different models, we predict their tendency for twinning and the critical twinning stress. The theoretical predictions are contrasted with tensile tests and electron backscatter diffraction (EBSD) measurements. Several conventional and in situ tensile test are performed to verify the theoretical results. We carry out EBSD measurements on interrupted and fractured specimens and during tensile tests to closely follow the development of the microstructure. We take into account the role of the intrinsic energy barriers in our predictions and introduce a new and so far unique way to experimentally obtain the GSFE of austenitic stainless steels. Previously, only the SFE could be measured precisely by well-designed experiments. In the present thesis we go further and propose a technique that can provide accurate unstable stacking fault energy values for any austenitic alloy exhibiting twinning. 

  • 152.
    Molnar, David
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. KTH.
    Engberg, Göran
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Li, Wei
    Lu, Song
    Hedström, Peter
    Kwon, Se Kyun
    Vitos, Levente
    Experimental study of the gamma-surface of austenitic stainless steels2019Inngår i: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 173, s. 34-43Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We introduce a theory-guided experimental approach to study the γ-surface of austenitic stainless steels. The γ-surface includes a series of intrinsic energy barriers (IEBs), which are connected to the unstable stacking fault (USF), the intrinsic stacking fault (ISF), the unstable twinning fault (UTF) and the extrinsic stacking fault (ESF) energies. The approach uses the relationship between the Schmid factors and the effective energy barriers for twinning and slip. The deformation modes are identified as a function of grain orientation using in situ electron backscatter diffraction measurements. The observed critical grain orientation separating the twinning and slip regimes yields the USF energy, which combined with the universal scaling law provides access to all IEBs. The measured IEBs and the critical twinning stress are verified by direct first-principles calculations. The present advance opens new opportunities for modelling the plastic deformation mechanisms in multi-component alloys.

  • 153.
    Molnar, David
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. KTH.
    Engberg, Göran
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Li, Wei
    Vitos, Levente
    Deformation properties of austenitic stainless steels with different stacking fault energies2018Inngår i: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 941, s. 190-197Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In FCC metals a single parameter – stacking fault energy (SFE) – can help to predict the expectable way of deformation such as martensitic deformation, deformation twinning or pure dislocation glide. At low SFE one can expect the perfect dislocations to dissociate into partial dislocations, but at high SFE this separation is more restricted. The role of the magnitude of the stacking fault energy on the deformation microstructures and tensile behaviour of different austenitic steels have been investigated using uniaxial tensile testing and electron backscatter diffraction (EBSD). The SFE was determined by using quantum mechanical first-principles approach. By using plasticity models we make an attempt to explain and interpret the different strain hardening behaviour of stainless steels with different stacking fault energies.

  • 154.
    Molnar, David
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. KTH.
    Sun, Xun
    Lu, Song
    Li, Wei
    Engberg, Göran
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Vitos, Levente
    Effect of temperature on the stacking fault energy and deformation behaviour in 316L austenitic stainless steel2019Inngår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 759, s. 490-497Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The stacking fault energy (SFE) is often used as a key parameter to predict and describe the mechanical behaviour of face centered cubic material. The SFE determines the width of the partial dislocation ribbon, and shows strong correlation with the leading plastic deformation modes. Based on the SFE, one can estimate the critical twinning stress of the system as well. The SFE mainly depends on the composition of the system, but temperature can also play an important role. In this work, using first principles calculations, electron backscatter diffraction and tensile tests, we show a correlation between the temperature dependent critical twinning stress and the developing microstructure in a typical austenitic stainless steel (316L) during plastic deformation. We also show that the deformation twins contribute to the strain hardening rate and gradually disappear with increasing temperature. We conclude that, for a given grain size there is a critical temperature above which the critical twinning stress cannot be reached by normal tensile deformation, and the disappearance of the deformation twinning leads to lower strain hardening rate and decreased ductility.

  • 155.
    Molnar, David
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. KTH.
    Vida, Ádám
    Huang, Shuo
    Chinh, Nguyen Q
    The effect of cooling rate on the microstructure and mechanical properties of NiCoFeCrGa high-entropy alloy2019Inngår i: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 54, nr 6, s. 5074-5082Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The effect of cooling rate on the microstructure and mechanical properties of equimolar NiCoFeCrGa high-entropy alloy (HEA) was studied by scanning electron microscopy, energy-dispersive X-ray spectroscopy and electron backscatter diffraction (EBSD), as well as by microhardness tests. Experimental results show that the cooling rate has a crucial impact on the developing microstructure which has a mixture of two—FCC and BCC—phases, leading to a self-similarity of the solidified structure formed in the sample. Furthermore, the cooling rate influences both the composition of the two phase-components and the ratio of their volume fractions, determining the mechanical properties of the sample. The present results confirm the grouping of Co, Fe and Cr in the FCC phase and that of Ni and Ga in BCC phase in the NiCoFeCrGa high-entropy alloy system. An empirical rule is suggested to predict how the phase-components can be expected in this complex high-entropy alloy.

  • 156.
    Nilsson, Maria
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Tribology in Metal Working2012Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    This thesis focuses on the tribological performance of tool surfaces in two steel working operations, namely wire drawing and hot rolling. In all forming operations dimensions and surface finish of the products are of utmost importance. Forming basically includes three parts – forming conditions excluded – that may be changed; work material, tool and (possibly) lubricant. In the interface between work material and tool, the conditions are very aggressive with – generally or locally – high temperatures and pressures. The surfaces will be worn in various ways and this will change the conditions in the process. Consequently, the surface finish as well as the dimensions of the formed product may change and in the end, the product will not fulfil the requirements of the customer. Therefore, research and development in regard to wear, and consequently tribology, of the forming tools is of great interest.

    The investigations of wire drawing dies focus on coating adhesion/cohesion, surface characteristics and material transfer onto the coated steel both in laboratory scale as well as in the wire drawing process. Results show that it in wire drawing is possible to enhance the tribological performance of drawing dies by using a lubricant together with a steel substrate coated by a polished, dual-layer coating containing both hard and friction-lowering layers.

    The investigations of hot rolling work rolls focus on microstructure and hardness as well as cracking- and surface characteristics in both laboratory scale and in the hot strip mill. Results show that an ideal hot work roll material should be made up of a matrix with high hardness and a large amount of complex, hard carbides evenly distributed in the microstructure. The surface failure mechanisms of work rolls are very complex involving plastic deformation, abrasive wear, adhesive wear, mechanical and thermal induced cracking, material transfer and oxidation.

    This knowledge may be used to develop new tools with higher wear resistance giving better performance, lower costs and lower environmental impact.

  • 157.
    Nilsson, Maria
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    An investigation of worn work roll materials used in the finishing stands of the hot strip mill for steel rolling2012Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The surface failure characteristics of different work roll materials, i.e. High Speed Steel, High Chromium Iron and Indefinite Chill Iron, used in the finishing stands of a hot strip mill have been investigated using stereo microscopy, 3D optical profilometry, scanning electron microscopy and energy dispersive X-ray spectroscopy. The results show that the surface failure mechanisms of work rolls for hot rolling are very complex, involving plastic deformation, abrasive wear, adhesive wear, mechanical and thermal induced cracking, material transfer and oxidation. Despite the differences in chemical composition and microstructure, the tribological response of the different work roll materials was found to be strongly dependent on the material microstructure and especially the presence and distribution of microstructural constituents, such as the different carbide phases and graphite (in the case of Indefinite Chill Iron). Cracking and chipping of the work roll surfaces, both having a negative impact on work roll wear, are strongly influenced by the presence of carbides, carbide networks and graphite in the work roll surface. Consequently, the amount of carbide forming elements as well as the manufacturing process must be controlled in order to obtain an optimised microstructure and a predictable wear rate.

  • 158.
    Nilsson, Maria
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    An investigation of worn work roll materials used in the finishing stands of the hot strip mill for steel rolling2013Inngår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 227, nr 8, s. 837-844Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The surface failure characteristics of different work roll materials, i.e. High Speed Steel, High Chromium Iron and Indefinite Chill Iron, used in the finishing stands of a hot strip mill have been investigated using stereo microscopy, 3D optical profilometry, scanning electron microscopy and energy dispersive X-ray spectroscopy. The results show that the surface failure mechanisms of work rolls for hot rolling are very complex, involving plastic deformation, abrasive wear, adhesive wear, mechanical and thermal induced cracking, material transfer and oxidation. Despite the differences in chemical composition and microstructure, the tribological response of the different work roll materials was found to be strongly dependent on second phase constituents such as the size, morphology and distribution of different carbide phases and graphite (in the case of Indefinite Chill Iron) which was found to promote cracking. Cracking and chipping of the work roll surfaces, both having a negative impact on work roll wear, are strongly influenced by the presence of carbides, carbide networks and graphite in the work roll surface. Consequently, the amount of carbide forming elements as well as the manufacturing process must be controlled in order to obtain an optimised microstructure and a predictable wear rate.

  • 159.
    Nilsson, Maria
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. Tribomaterials group, The Ångström Laboratory, Uppsala University, Sweden.
    Microstructural, mechanical and tribological characterisation of roll materials for the finishing stands of the hot strip mill for steel rolling2013Inngår i: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 307, nr 1-2, s. 209-217Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The microstructure, mechanical and tribologicalproperties for three different materials, High Speed Steel, High Chromium ironand Indefinite Chill iron, used for hot strip mill work rolls have beenevaluated. Microstructural characterisation was performed using light opticalmicroscopy, scanning electron microscopy and energy dispersive X-rayspectroscopy. The mechanical and tribological properties were evaluated usingmicro Vickers indentation and scratch testing in combination with post-testmicroscopy. The microstructures of the investigated materials were found to berather complex with a number of secondary phases andalso materials with similar nominal composition display significant differenceswith respect to distribution, size and morphology of carbides. Scratch testing,including detection of friction coefficient, acoustic emission and penetrationdepth, gives valuable information concerning the mechanical and tribologicalresponse on a microscopic level of the investigated materials. Type,amount, distribution, size and morphology of the secondary phases in thematerials have a strong impact on the surface deformation and wear mechanismsduring scratching. Cracking and chipping are frequently observed in connectionto the ridges surrounding the scratches. However, cross-sectional analyses ofthe scratched microstructures reveal that cracking of the brittle carbidephases may extend to significant depths, >100 µm, reducing the mechanicalstrength of the material. Based on the results, it is believed that a moreisotropic microstructure, e.g. obtained via a powder metallurgy process, withfiner carbides would result in improved properties and performance in a hotrolling application.

  • 160.
    Nilsson, Maria
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Tribological Testing of Some Potential PVD and CVD Coatings for Steel Wire Drawing Dies2010Inngår i: Nordtrib 2010, Storforsen, 2010Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Cemented carbide is today the most frequently used drawing die material in steel wire drawing applications. This is mainly due to the possibility to obtain a broad combination of hardness and toughness thus meeting the requirements concerning strength, crack resistance and wear resistance set by the wire drawing process. However, the increasing cost of cemented carbide in combination with the possibility to increase the wear resistance of steel through the deposition of wear resistant CVD and PVD coatings have enhanced the interest to replace cemented carbide drawing dies with CVD and PVD coated steel wire drawing dies. In the present study, the possibility to replace cemented carbide wire drawing dies with CVD and PVD coated steel drawing dies have been investigated by tribological characterisation, i.e. pin-on-disc and scratch testing, in combination with post-test observations of the tribo surfaces using scanning electron microscopy, energy dispersive X-ray spectroscopy and 3D surface profilometry. Based on the results obtained, CVD and PVD coatings aimed to provide improved tribological performance of steel wire drawing dies should display a smooth surface topography, a high wear resistance, a high fracture toughness (i.e. a high cracking and chipping resistance) and intrinsic low friction properties in contact with the wire material. Also, the steel substrate used must display a sufficient load carrying capacity and resistance to thermal softening. Of the CVD and PVD coatings evaluated in the tribological tests, a CVD TiC and a PVD CrC/C coating displayed the most promising results.

  • 161. Olofsson, J.
    et al.
    Bexell, Ulf
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Jacobson, S.
    Tribofilm formation of lightly loaded self mated alumina contacts2012Inngår i: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 289, s. 39-45Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A tribofilm is formed on alumina surfaces that have been slid against alumina surfaces. The tribofilm is formed by alumina wear particles that have been ground, agglomerated and tribosintered to a film. The tribofilm smoothens out the surface topography and fills up cavities. Tribofilms on alumina surfaces have been investigated with respect to surface appearance, hardness and chemical composition. Surface preparation and surrounding humidity have shown to affect the character and lateral distribution of the tribofilm. The tribofilm that was formed in humid air was softer than the tribofilm formed in dry air. XPS analysis revealed the chemical shift of the Al 2p peak did not differ between the tribofilms that was formed in different humidity, nor the unworn reference surface, finding that no hydroxide was found on the alumina surfaces. Also, no tribochemical changes could be detected by ToF-SIMS analysis. (C) 2012 Elsevier B.V. All rights reserved.

  • 162.
    Olovsjö, S
    et al.
    Atlas Copco.
    Johanson, R
    Atlas Copco.
    Bexell, Ulf
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    On the understanding of cemented carbide degradation in rock drilling: the importance of metallographic sample preparation2012Inngår i: Proceedings of Euro PM 2012 Congress & Exhibition Vol. 2, 2012Konferansepaper (Fagfellevurdert)
  • 163.
    Olovsjö, S
    et al.
    Atlas Copco.
    Johanson, R
    Atlas Copco.
    Falsafi, M
    Atlas Copco.
    Bexell, Ulf
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Surface failure and wear of cemented carbide rock drill buttons: the importance of sample preparation and optimized microscopy settings2013Inngår i: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 302, nr 1-2, s. 1546-1554Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The combination of suitable mechanical properties and wear resistance makes cemented carbide one of the most interesting engineering composite materials for tribological applications, such as in rock drilling. Despite the fact that cemented carbide buttons have been used in rock drilling applications for a long time the detailed understanding of the prevailing wear mechanisms is far from complete and wear and breakage of rock drill buttons are still one of the lifetime-limiting factors for rock drill bits. Consequently, further research in this area, including detailed characterization of worn drill button surfaces and sub-surface regions, is needed in order to support the future development of new cemented carbide grades with improved failure and wear resistance. In the present paper, high resolution scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and Auger electron spectroscopy (AES) have been used to characterize the wear and failure mechanisms of worn drill buttons and samples exposed to well controlled impact and scratch tests performed in the laboratory. The most important mechanisms of surface failure and wear were found to be severe plastic deformation, cracking, crushing of individual WC grains and mechanical/tribochemical degradation of the Co binder phase including Co depletion. Fracture cross-sectioning under tensile stress-state was found to be the best method for achieving large and reliable sub-surface cross-sections within a short time and to a low cost. The importance of optimized microscopy and spectroscopy settings for enhanced surface sensitivity for the examination of small-scale tribological phenomena is illuminated and discussed.

  • 164.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    A new test method for measuring the galling resistance between metal powders and die tool materials in powder compaction2011Inngår i: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 273, nr 1, s. 49-54Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The friction characteristics and galling resistance between metal powder and die tool material in metal powder compaction is of outmost importance since they will influence the porosity and surface quality of the green body and consequently the porosity, tolerances and surface quality of the final sintered product. In the present study, a new test method for evaluating the tribological performance of die tool materials aimed for powder compaction is presented. The test method is based on controlled scratch testing using a commercial scratch tester but instead of the commonly used Rockwell C diamond stylus a sample holder with a small green body of compacted powder particles is drawn over the surface in a well controlled multi pass linear reciprocating sliding contact. The capability of the test method was evaluated for different types of tool materials including two PVD coatings in contact with different types of metal powders to determine the friction characteristics and the adhesion and material transfer tendency at the sliding interface. Post-test examination of the tool surfaces using FEG-SEM and EDS were performed in order to evaluate the mechanisms controlling the friction behavior and the material transfer tendency. The results show that the proposed test is a simple and fast method to obtain relevant data regarding the friction and galling characteristics of die tool materials in metal powder compaction. The mechanisms prevailing at the green body/die tool material interface, e.g. cold welding, can easily be monitored by the friction and acoustic emission signals. Of the die tool materials investigated the low friction PVD a-C:Cr coating displayed the lowest friction and highest galling resistance.

  • 165.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    On the use of scratch testing as a model experiment for evaluating the initial wear of cemented carbidein rock drilling2013Konferansepaper (Fagfellevurdert)
  • 166.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Tribological evaluation of some potential tribo materials used in column lift rolling contacts: a case study2011Inngår i: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 270, nr 9-10, s. 720-724Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The friction and wear characteristics of some potential tribological pairs aimed for the wheel/rail rolling contact in column lifts were studied. Tribo tests were performed using a pin-on-disc equipment and the tribological pairs included; stainless steel against ball bearing steel, stainless steel against WC/C-coated ball bearing steel and stainless steel against cast nylon (polyamide 6). The influence of coating surface topography as well as stainless steel surface topography on the friction and wear behaviour of the tribological pairs was investigated. The results show that the WC/C-coating significantly improves the tribological performance of the stainless steel/ball bearing steel sliding couples but that the WC/C-coating show a limited life-time in sliding contact with stainless steel under the prevailing contact conditions. In contrast, the stainless steel/ball bearing steel sliding couples suffer from high friction and wear due to strong adhesion between the mating surfaces followed by metal transfer and severe adhesive wear. The stainless steel/cast nylon sliding couples show a somewhat intermediate behaviour regarding friction and wear where the friction is controlled by the generation of a polymer transfer film and wear of the cast nylon is controlled by the surface topography of the mating stainless steel surface. The results obtained are discussed in relation to the identified friction and wear mechanisms as characterized by SEM and EDX.

  • 167.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Tråddragningens tribologi2015Inngår i: Nordisk Trådteknisk Förening: Årsbok 2015 / [ed] Leif Eriksson, NTTF , 2015Kapittel i bok, del av antologi (Annet vitenskapelig)
  • 168.
    Olsson, Mikael
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Bexell, Ulf
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Friction characteristics and material transfer tendency in metal powder compaction2011Inngår i: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 271, nr 9-10, s. 1903-1908Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The friction characteristics and material transfer tendency between metal powder and die tool material in metal powder compaction play an important role in the production of near-net-shape components of high density. A natural step to further increase the green density and simplify the sintering process is to reduce the amount of internal lubricant in the powder since the volume fraction of an organic lubricant will result in a significant contribution to the resulting porosity. However, this will significantly increase the adhesive contact and thus the friction between the die and the powder/green body during the powder compaction process. As a result, the compaction and ejection forces as well as the wear rate of the die and punch surfaces will increase. Consequently, improved knowledge concerning the friction mechanisms prevailing at the metal powder/die tool material interface is needed. The present paper will present data regarding the influence of type of tool and coating material on the friction characteristics and material transfer tendency during simulated powder compaction of a water atomized plain iron powder under no or starved lubrication conditions using two different laboratory tribo tests. Tool materials investigated include ingot cast tool steel, powder metallurgy (PM) tool steel and TiAlN and DLC-type PVD coatings. Post-test characterization using scanning electron microscopy and energy dispersive X-ray spectroscopy was used to analyse the tribo surfaces and especially the tendency to material transfer and tribo film formation. The results show that the material transfer tendency is mainly controlled by strong adhesive metal–metal contacts and that a PVD coating showing intrinsic low-friction properties and a smooth surface topography may significantly reduce the interaction between the mating surfaces promoting a stable friction and a low material transfer tendency.

  • 169.
    Olsson, Mikael
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Heinrichs, Jannica
    Yvell, Karin
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Jacobson, Staffan
    Initial degradation of cemented carbides for rock drilling: model studies of the tribological contact against rock2015Inngår i: International journal of refractory metals & hard materials, ISSN 0958-0611, E-ISSN 2213-3917, Vol. 52, s. 104-113Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Hardness and fracture toughness are often used as the prime material parameters to characterise cemented carbides used in rock drilling. However, the deformation and wear of cemented carbide are too complicated to be described by these parameters alone. The cemented carbide and the wearing rock mineral are both composite materials, containing phases with widely varying hardness. Moreover, the deformation behaviour of the individual phases may be strongly anisotropic, as for the WC grains in the cemented carbide. The wear of the cemented carbide typically occurs on the scale of individual grains or smaller. Contrastingly, the hardness stated for both is typically a macroscopic value, averaged over numerous grains, orientations, etc. The present investigation aims to contribute to the understanding of the relations between microstructure, properties and wear mechanisms of cemented carbide buttons in rock drilling. It is focused on the role of scale of deformation in relation to size of the different phases of the cemented carbide. This is achieved by simplifying the contact situation of the rock drill button to a single stylus sliding contact between a granite stylus and a polished cemented carbide surface. The deformation and wear of this well controlled contact is then evaluated on the sub-micrometer scale; using high resolution FEG-SEM with EBSD, FIB cross-sectioning and AFM. The results show that even an extremely local deformation, such as slip within individual WC grains, affects the tribological contact, and that the nominally much softer granite may cause deformation both within individual WC grains, and on the composite scale. The results are discussed with respect to their significance for wear of cemented carbides in rock drilling. (C) 2015 Elsevier Ltd. All rights reserved.

  • 170.
    Olsson, Mikael
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Högman, B
    Uddeholms.
    Influence of tool steel microstructure on the prevailing wear mechanisms in metal powder compaction2012Inngår i: TOOL 2012 : proceedings of the 9th international tooling conference, developing the world of tooling, Montanuniversität Leoben 11-14 September 2012 / [ed] Herald Leitner, Regina Kranz, Angelika Tremmel, Knittelfeld: Gutenberghaus , 2012, s. 409-416Konferansepaper (Fagfellevurdert)
  • 171.
    Olsson, Mikael
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Karlsson, P.
    Eriksson, Jenny
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Gåård, A.
    Krakhmalev, P.
    Bergström, J.
    Galling resistance evaluation of tool steels by two different laboratory test methods for sheet metal forming2011Inngår i: Proceedings of the 18th International Conference on Wear of Materials, Philadelphia, USA, 2011Konferansepaper (Annet vitenskapelig)
  • 172.
    Olsson, Mikael
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Sandberg, Odd
    Tribological evaluation of tool materials for powder compaction2010Inngår i: Proceedings of the World Powder Metallurgy Congress and Exhibition, World PM 2010, Florence, 2010, Vol. 5Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The friction characteristics and material transfer tendency between metal powder and tool material in metal powder compaction have been evaluated using a new tribo test method. The method is based on controlled scratch testing using a commercial scratch tester but instead of the commonly used Rockwell C diamond stylus a sample holder with a small green body of compacted powder particles is drawn over the surface in a well controlled multi pass linear reciprocating sliding contact. In the present study a number of combinations of metal powder and tool materials have been evaluated with respect to the friction characteristics and the sticking and cladding tendency at the sliding interface. Post test scanning electron microscopy and energy dispersive X-ray spectroscopy in combination with 3D white light interferometry were used to analyse the tool material surfaces and material pick-up tendency. The tribological performance of potential powder compacting tool materials is discussed in relation to the identified friction and wear mechanisms.

  • 173.
    Olsson, Mikael
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Surreddi, Kumar Babu
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Scratch testing of cemented carbides - Influence of Co binder phase and WC grain size on surface deformation and degradation mechanisms2018Inngår i: Proceedings of The 18th Nordic Symposium on Tribology - Nordtrib 2018 / [ed] Staffan Jacobson, Uppsala: Uppsala University, 2018Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In the present study, the microstructural response of some commercial cemented carbide grades during scratchinghas been analyzed and evaluated by a number of post-test characterization techniques. The influence of Co binder phase content and WC grain size on the deformation and degradation on a WC grain size scale and on a composite scaleare evaluated. The results clearly illustrate the complexity of deformation, degradation and wear of cemented carbide and the dynamics of the diamond stylus / cemented carbide contact during the scratching event. For all cementedcarbide grades the microstructure has a strong impact on the observed degradation mechanisms and the resistance to deformation and degradation was found to increase with decreasing Co content and decreasing WC grain size.

  • 174.
    Olsson, Mikael
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Surreddi, Kumar Babu
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Thin hard CVD and PVD coatings and their potential in steel wire drawing applications2018Inngår i: Proceedings of The 18th Nordic Symposium on Tribology - NORDTRIB 2018 / [ed] Staffan Jacobson, Uppsala: Uppsala University, 2018Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In the present work, the potential of using thin hard CVD and PVD coatings in order to improve the performance of cemented carbide steel wire drawing nibs is evaluated. Coating materials include some state-of-the-art CVD and PVD coatings and pre- and post-coating treatments were used to improve the surface topography of the coated functional surfaces. The tribological performance of the coatings has been evaluated by sliding wear tests and wire drawing experiments under well controlled conditions. Post-test characterization of the coated nibs using 3D optical surface profilometry, scanning electron microscopy and energy dispersive X-ray spectroscopy illustrates the pros and cons of the two deposition techniques but also that the coatings have a potential to improve the performance of cemented carbide nibs in steel wire drawing applications.

  • 175.
    Olsson, Mikael
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Wadman, B.
    Eriksson, Jenny
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Schedin, E.
    Madsen, E.
    Bay, N.
    Influence of stainless steel surface texture on galling2011Inngår i: Proceedings of the 18th International Conference on Wear of Materials, Philadelphia, USA, 2011Konferansepaper (Annet vitenskapelig)
  • 176.
    Olsson, Mikael
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. Ångström Tribomaterials Group, Uppsala University.
    Yvell, Karin
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Heinrichs, J.
    Bengtsson, M.
    Jacobson, S.
    Surface degradation mechanisms of cemented carbide drill buttons in iron ore rock drilling2017Inngår i: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 388-389, s. 81-92Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The wear behavior of cemented carbide rock drill buttons is influenced by many factors, which include the composition and microstructure of the cemented carbide material, the nature of the rock material, and the conditions of the rock drilling operation. Depending on the type of rock and on the drilling procedure used, the cemented carbide is exposed to substantially differing mechanical and thermal conditions. In the present study, the surface degradation and wear mechanisms of cemented carbide drill buttons exposed to iron ore rock drilling have been characterized based on a combination of high resolution scanning electron microscopy (SEM), focused ion beam cross-sectioning (FIB), energy-dispersive X-ray spectroscopy (EDS) and electron back scatter diffraction (EBSD).The results show a significant difference in surface degradation and wear between the front and peripheral buttons of the drill bits. While the front buttons display a relatively smooth worn surface with shallow surface craters the peripheral buttons display a reptile skin pattern, i.e. plateaus, 200-300. μm in diameter, separated by valleys, typically 40-50. μm wide and 15-30. μm deep, The reptile skin pattern is obtained in regions where the peripheral buttons are in sliding contact against the drill hole walls and exposed to high surface temperatures caused by the frictional heating. The results indicate that the reptile skin pattern is related to friction induced thermal stresses rather than mechanical contact stresses, i.e. the reptile skin pattern is formed due to thermal fatigue, rather than mechanical fatigue, caused by the cyclic frictional heating generated at the cemented carbide button/iron ore interface.

  • 177.
    Olsson, Mikael
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Yvell, Karin
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Heinrichs, Jannica
    Uppsala University.
    Bengtsson, Maria
    LKAB Wassara AB.
    Jacobson, Staffan
    Uppsala University.
    Surface degradation mechanisms of cemented carbide drill buttons exposed to iron ore rock drilling2016Inngår i: Proceedings of the 17th Nordic Symposium on Tribology - Nordtrib 2016, 2016Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The wear behavior of cemented carbide rock drill buttons is influenced by many factors, which include the composition and microstructure of the cemented carbide material, plus the conditions of the rock drilling operation, such as drilling parameters, drill button geometry and the nature of the rock material. Depending on the type of rock and on the drilling procedure used, the cemented carbide is exposed to substantially differing mechanical and thermal conditions. Under conditions of high mechanical stress and high temperatures, typical for drilling in highly abrasive rocks such as granite, the worn cemented carbide buttons are usually very smooth, with the roughness limited to within the size of individual WC grains. When drilling under conditions of moderate mechanical stress and high temperatures, typical for drilling in low-abrasive rock, such as ores with e.g. magnetite, the surface damage of the buttons usually includes a macroscopic surface wear pattern, commonly referred to as “reptile skin”, in an otherwise smooth surface. The crack growth associated to the valleys of the reptile skin pattern eventually leads to catastrophic fracture of the button, unless the cracked surface layer is repeatedly ground off before the cracks grow too deep. So despite the low general wear rate, the wear life of drill buttons becomes severely restricted by the surface cracks. The present study focuses on revealing the degradation mechanisms behind the formation of the reptile skin. This is done by analyzing drill buttons exposed to different stages of degradation and wear from drilling in iron ore. The work is based on a combination of high resolution scanning electron microscopy (SEM), focused ion beam microscopy (FIB), energy-dispersive X-ray spectroscopy (EDS) and electron back scatter diffraction (EBSD).

  • 178.
    Osterman, Jesper
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Skarp, Kent
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Tong, Au Ping
    Zhukov, Andrey
    Chigrinov, Vladimir
    Kwok, Hoi Sing
    Mechanically stabilized bistable FLC cells on plastic substrates2005Inngår i: Proceedings of the twenty-fifth international display research conference, Eurodisplay 2005, 2005Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The electro-optical properties of a full v flexible photo-aligned FLC cell are investigated. Two different methods, sticky spacers together with a photo-sensitive monomer and polymer spacers in a regular pattern formed by photo-lithography, are proposed to stabilize the structure in order to increase the bending tolerance of the FLC material during deformation of the cell.

  • 179.
    Osterman, Jesper
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Tong, Au Ping
    Skarp, Kent
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Chigrinov, Vladimir
    Kwok, Hoi Sing
    Properties of azo-dye alignment layer on plastic substrates2005Inngår i: Journal of the Society for Information Display, ISSN 1071-0922, E-ISSN 1938-3657, Vol. 13, nr 12, s. 1003-1009Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The alignment properties of the azo dye photo-alignment material SD-1/SDA-2 on plastic substrates are investigated. Excellent alignment with high anchoring energy can be achieved with a polarized UV dose less than 1.0 J/cm2. A reflective 6-digit flexible passive matrix driven TN-LCD for smart card applications showing excellent electro-optical properties is demonstrated.

  • 180.
    Persson, Petter
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Finite element analysis of hot rolling in the blooming mill2016Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    During this thesis work a coupled thermo-mechanical finite element model (FEM) was builtto simulate hot rolling in the blooming mill at Sandvik Materials Technology (SMT) inSandviken. The blooming mill is the first in a long line of processes that continuously or ingotcast ingots are subjected to before becoming finished products.

    The aim of this thesis work was twofold. The first was to create a parameterized finiteelement (FE) model of the blooming mill. The commercial FE software package MSCMarc/Mentat was used to create this model and the programing language Python was used toparameterize it. Second, two different pass schedules (A and B) were studied and comparedusing the model. The two pass series were evaluated with focus on their ability to healcentreline porosity, i.e. to close voids in the centre of the ingot.

    This evaluation was made by studying the hydrostatic stress (σm), the von Mises stress (σeq)and the plastic strain (εp) in the centre of the ingot. From these parameters the stress triaxiality(Tx) and the hydrostatic integration parameter (Gm) were calculated for each pass in bothseries using two different transportation times (30 and 150 s) from the furnace. The relationbetween Gm and an analytical parameter (Δ) was also studied. This parameter is the ratiobetween the mean height of the ingot and the contact length between the rolls and the ingot,which is useful as a rule of thumb to determine the homogeneity or penetration of strain for aspecific pass.

    The pass series designed with fewer passes (B), many with greater reduction, was shown toachieve better void closure theoretically. It was also shown that a temperature gradient, whichis the result of a longer holding time between the furnace and the blooming mill leads toimproved void closure.

  • 181.
    Persson, Petter
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Mätsystemanalys av mätmetod för kontroll av anoljningsgrad2014Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave
    Abstract [sv]

    Sammanfattning:I slutet av den kontinuerliga glödgningslinjen på SSAB:s produktionsanläggning i Borlänge anoljas en stor del av den producerade plåten. Anoljning av plåt görs för att minska risken för korrosion. För att säkerställa att rätt mängd olja appliceras görs en visuell bedömning tre gånger varje dygn samt vid byte av anoljningskod. Utöver detta görs kontroller med en förbrukningsmätare sex gånger om året.

    Syftet med examensarbetet är att utvärdera den nuvarande mätmetoden med förbrukningsmätare och ta ställning till dess framtida användning. Möjliga förbättringar av denna mätmetod söks. Även en oljefilmsensor utvärderas som ett alternativ till förbrukningsmätaren.

    Tre olika mätmetoder användes under olika stadier av arbetets gång. Oljemängdsmätning med hjälp av vägning utfördes i laboratoriemiljö. För mätningarna i produktionen användes en oljefilmsensor och en förbrukningsmätare. En mätsystemanalys gjordes genom att sammanställa mätdata i statistikprogrammet Minitab 16 och resultaten tolkades med avseende på riktighet och precision. 

    Resultaten visar att mätmetoden med förbrukningsmätare levererar stabilare värden än oljefilmsensorn vid mätningar i produktion. Detta eftersom sensorns mätyta är liten och anoljningsmaskinen applicerar olja droppvis på plåten. 

  • 182.
    Pirouznia, Pouyan
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Andersson, N. A. I.
    Tilliander, A.
    Jonsson, P. G.
    A mathematical model of martempering of thin martensitic stainless steel strips2015Inngår i: Proceedings of the 6th International Congress on the Science and Technology of Steelmaking, ICS 2015, 2015, s. 1027-1030Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The martempering process produces thin martensitic stainless steel strips and is widely used for production of valve- and spring steel. Industrial trials were conducted in collaboration with Böhler Uddeholm Precision Strip, Munkfors, Sweden. These trials suggested that the quenching step is critical to control, in order to reduce uneven temperature gradients which will lead to distortions or unevenness. To investigate this, computational modelling of the temperature was performed to estimate the current situation for the conventional martempering process based on physical theories together with Comsol Multiphysics and using a steady state modeling approach. The model boundary conditions were based upon temperature measurements in the real process. Furthermore, the strip was modelled as it comes out of the heating furnace, which is filled with hydrogen gas and continues into a molten lead-bismuth bath for quenching. Thus, the temperature profile was obtained for the strip as well as its surroundings; The results show that a better insight of the martempering line could be achieved. The model results can be used to investigate disturbances in the normal operation. Furthermore, the temperature profiles can be used to optimize the process and possibly to reduce the energy consumption.

  • 183.
    Pirouznia, Pouyan
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. KTH; Voestalpine Precis Strip AB, .
    Andersson, Nils Å. I
    KTH Royal Inst Technol, Dept Mat Sci & Engn, Div Proc, SE-10044 Stockholm, Sweden..
    Tilliander, Anders
    KTH Royal Inst Technol, Dept Mat Sci & Engn, Div Proc, SE-10044 Stockholm, Sweden..
    Jonsson, Par G.
    KTH Royal Inst Technol, Dept Mat Sci & Engn, Div Proc, SE-10044 Stockholm, Sweden..
    An investigation of the temperature distribution of a thin steel strip during the quenching step of a hardening process2019Inngår i: Metals, ISSN 2075-4701, Vol. 9, nr 6, s. 1-14Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The dimension quality of the strip within the hardening process is an essential parameter, which great attention needs to be paid. The flatness of the final product is influenced by the temperature distribution of the strip, specifically across the width direction. Therefore, based on physical theories, a numerical model was established. The temperature of the strip for the section before the martensitic transformation was objected in the predicted model by using a steady state approach. In addition an infrared thermal imaging camera was applied in the real process in order to validate the results and to improve the boundary conditions of the numerical model. The results revealed that the temperature of strip decreased up to 250 degrees C within the area between the furnace and the quenching bath. This, in turn, resulted in significant temperature difference across the width of the strip. This difference can be up to 69 degrees C and 41 degrees C according to the numerical results and thermal imaging data, respectively. Overall, this study gave a better insight into the cooling step in the hardening process. In addition, this investigation can be used to improve the hardening process as well as an input for future thermal stress investigations.

  • 184. Prosek, T
    et al.
    Nazarov, A
    Bexell, Ulf
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Thierry, D
    Serak, J
    Corrosion mechanism of model zinc–magnesium alloys in atmospheric conditions2008Inngår i: Corrosion Science, ISSN 0010-938X, E-ISSN 1879-0496, Vol. 50, nr 8, s. 2216-2231Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Recently, superior corrosion properties of zinc coatings alloyed with magnesium have been reported. Corrosion behaviour of model zinc–magnesium alloys was studied to understand better the protective mechanism of magnesium in zinc. Alloys containing from 1 to 32 wt.% magnesium, pure zinc, and pure magnesium were contaminated with sodium chloride and exposed to humid air for 28 days. Composition of corrosion products was analyzed using infrared spectroscopy (FTIR), ion chromatography (IC), and Auger electron spectroscopy (AES). The exposure tests were completed with scanning Kelvin probe (SKP) and electrochemical measurements. Weight loss of ZnMg alloys with 1–16 wt.% magnesium was lower than that of pure zinc. Up to 10-fold drop in weight loss was found for materials with 4–8 wt.% Mg in the structure. The improved corrosion stability of ZnMg alloys was connected to the presence of an Mg-based film adjacent to the metal surface. It ensured stable passivity in chloride environment and limited the efficiency of oxygen reduction.

  • 185. Prosek, T.
    et al.
    Thierry, D.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Bexell, Ulf
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Effects of chloride-to-chromate ratio on the protective action of zinc surface films under atmospheric weathering conditions2007Inngår i: Corrosion, ISSN 0010-9312, E-ISSN 1938-159X, Vol. 63, nr 3, s. 258-267Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The formation and the corrosion protection of newly formed chromium-rich layers on bare zinc surfaces were studied to model the conditions in defected areas of both organic and conversion chromate coatings that are in contact with water environments contaminated with different amounts of chloride ions. Composition of the layers was idenified with Fourier transformed infrared spectroscopy (FTIR), x-ray absorption near-edge structure (XANES), and secondary ion mass spectroscopy (SIMS). The presence of chloride in the range from 0.06 mM to 1, 000 mM in the chromate treating solution had almost no effect on the amount of chromate adsorbed on zinc. Three independent techniques showed that a more than 4-order increase in chloride concentration results in the drop of the chromate content in the surface film only by 20% to 25%. Cr(VI)-to-total Cr surface ratio was close to 0.3 and constant under present experimental conditions. More chromium was detected in the outer region of the film, whereas chloride accumulated in the inner region. As a result of the linear increase of the surface chloride concentration with the chloride concentration in the chromate treating solution, the chloride-to-chromate surface molar ratio increased sharply. The rate of reduction of Cr(VI) to Cr(III) and the corrosion rate of zinc exposed to atmospheric weathering conditions increased significantly with the chloride-to-chromate ratio. The chromate coatings showed good stability and a high level of corrosion protection, up to the ratio of approximately 2. It represented a threshold value below which relatively low rates of the chromate reduction and zinc corrosion were observed, since the significant part of the chloride ions was inactivated in the first hours of exposure by the formation of insoluble corrosion products. A negative effect of the increasing chloride-to-chromate surface molar ratio on corrosion can be seen in the increasing ability to reduce oxygen on the zinc surface measured by the scanning Kelvin probe (SKP) technique. Inhibition of the cathodic reaction by chromate was less effective at higher ratios.

  • 186.
    Prosek, Tomas
    et al.
    Institut de la Corrosion / French Corrosion Institute.
    Nazarov, Andrej
    Institut de la Corrosion / French Corrosion Institute.
    Bexell, Ulf
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Thierry, Dominique
    Institut de la Corrosion / French Corrosion Institute.
    Serak, Jan
    Dept. of Metals and Corrosion Engineering, Institute of Chemical Technology, Praha, Czech Republic.
    Corrosion properties of model zinc-magnesium alloys2007Inngår i: GALVATECH 2007, 2007Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    Recently, superior corrosion properties of novel zinc coatings alloyed with magnesium have been reported.The protection mechanism of magnesium in the coatings was studied on model zinc-magnesium alloys containing from1 to 32 wt. % Mg prepared by casting. Their chemical and phase composition was determined. The samples werecontaminated with NaCl and exposed to wet air. Weight loss was evaluated after 28 days of exposure. The compositionof corrosion products was analyzed using different techniques. The exposure tests were completed with scanning Kelvinprobe measurements. Alloying of zinc with small quantities of magnesium significantly decreased the weight lossof zinc-magnesium alloys. The effect was strongest at 4–8 wt. % Mg in the structure. Weight loss of these alloys was upto 10 times lower than that of zinc. This was found to be connected dominantly to the efficiency of the oxygenreduction, which was significantly limited on the surface of ZnMg phases covered with magnesium-based oxide layers.

  • 187. Rehnlund, D.
    et al.
    Lindgren, F.
    Böhme, S.
    Nordh, T.
    Zou, Y.
    Pettersson, J.
    Bexell, Ulf
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Boman, M.
    Edström, K.
    Nyholm, L.
    Lithium trapping in alloy forming electrodes and current collectors for lithium based batteries2017Inngår i: Energy & Environmental Science, ISSN 1754-5692, E-ISSN 1754-5706, Vol. 10, nr 6, s. 1350-1357Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Significant capacity losses are generally seen for batteries containing high-capacity lithium alloy forming anode materials such as silicon, tin and aluminium. These losses are generally ascribed to a combination of volume expansion effects and irreversible electrolyte reduction reactions. Here, it is shown, based on e.g. elemental analyses of cycled electrodes, that the capacity losses for tin nanorod and silicon composite electrodes in fact involve diffusion controlled trapping of lithium in the electrodes. While an analogous effect is also demonstrated for copper, nickel and titanium current collectors, boron-doped diamond is shown to function as an effective lithium diffusion barrier. The present findings indicate that the durability of lithium based batteries can be improved significantly via proper electrode design or regeneration of the used electrodes. © The Royal Society of Chemistry 2017.

  • 188. Rendon, José
    et al.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Abrasive wear resistance of some commercial abrasion resistant steels evaluated by laboratory test methods2009Inngår i: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 267, nr 11, s. 2055-2061Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The aim of the present study is to evaluate the abrasive wear resistance of some potential abrasion resistant steels exposed to different types of abrasive wear contact conditions typical of mining and transportation applications. The steels investigated, include a ferritic stainless steel, a medium alloyed ferritic carbon steel and a medium alloyed martensitic carbon steel. The abrasive wear resistance of the steels was evaluated using two different laboratory test methods, i.e. pin-on-disc testing and paddle wear testing that expose the materials to sliding abrasion and impact abrasion, respectively. All tests were performed under dry conditions in air at room temperature. In order to evaluate the tribological response of the different steels post-test characterization of the worn surfaces were performed using optical surface profilometry, scanning electron microscopy and energy dispersive X-ray spectroscopy. Besides, characterization of the wear induced sub-surface microstructure was performed using optical microscopy. The results show that depending on the abrasive conditions a combination of high hardness and toughness (fracture strain) is of importance in order to obtain a high wear resistance. In the pin-on-disc test (i.e. in sliding abrasion) these properties seem to be controlled by the as-rolled microstructure of the steels although a thin triboinduced sub-surface layer (5-10 mu m in thickness) may influence the results. In contrast, in the paddle wear test (i.e. in impact abrasion), resulting in higher forces acting perpendicular to the surface by impacting stones, these properties are definitely controlled by the properties of the active sub-surface layer which also contains small imbedded stone fragments.

  • 189. Roizard, X.
    et al.
    Heinrichs, J.
    Et Taouil, A.
    Jacobson, S.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Melot, J. M.
    Lallemand, F.
    Insights into sliding wear and friction behavior of copper in ethanol containing alkylphosphonic acid molecules2016Inngår i: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 96, s. 141-148Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this work, the friction and wear behavior of bare copper was investigated for the first time under lubricated sliding conditions in diluted ethanol solutions of butylhosphonic (C4P), octylphosphonic (C8P), dodecylphosphonic (C12P), and hexadecylphosphonic (C16P) acids. The technique aims towards a more environmentally friendly lubrication to be used in shaping of copper sheets. Bare copper samples were subjected to unidirectional sliding using a tribometer with ball-on-disk contact geometry. Copper substrates (20 mm2×1 mm) were run against 100Cr6 ∅10 mm ball bearing counterbodies. All tests were conducted using the same sliding conditions with a normal load of 10 N, tangential velocity of 0.01 m/s, at room temperature of 20 °C. Worn surfaces were analyzed by Scanning Electron Microscopy, Optical Microscopy and White Light Interference Profilometry. When comparing to sliding tests in the pure ethanol solvent, significant decreases in terms of wear track dimensions, transferred material on the ball and friction coefficients are observed when active molecules are present in the solution. These form protective tribofilms exhibiting lubricating and anti-wear properties. Deeper studies on the tribological behavior of copper in C4P solution show that both low friction and low transfer of work material to the ball prevail in a specific range of low molecule concentration (5×10-4 M; 25×10-4 M). Even if the molecules are introduced during the test, after a few cycles, the tribological behavior improves, regardless of both friction level and copper surface degradation. Finally, specific friction tests were performed to further investigate the mechanisms. It was found that two mechanisms are involved; firstly molecules grafting onto the surface directly reduces friction, and secondly transformation of these grafted molecules into a tribofilm during the first mechanical contact cycles reduces it even further. 

  • 190. Rybalochka, A.
    et al.
    Sorokin, V.
    Valyukh, Sergiy
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Skarp, Kent
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Palmer, S.
    Selection of cholesteric liquid crystals for liquid crystal display with high multiplexing level1999Inngår i: Advanced display technologies, 1999Konferansepaper (Fagfellevurdert)
  • 191.
    Safara Nosar, Nima
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. KTH Royal Institute of Technology.
    Engberg, Göran
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Ågren, John
    KTH Royal Institute of Technology.
    Modeling microstructure evolution in a martensitic stainless steel subjected to hot working using a physically based model2019Inngår i: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 50, nr 3, s. 1480-1488Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The microstructure evolution of a martensitic Stainless steel subjected to hot compression is simulated with a physically based model. The model is based on coupled sets of evolution equations for dislocations, vacancies, recrystallization and grain growth. The advantage of this model is that with only a few experiments, the material dependent parameters of the model can be calibrated and used for a new alloy in any deformation condition. The experimental data of this work is obtained from a series of hot compression, and subsequent stress relaxation tests performed in a Gleeble thermo-mechanical simulator. These tests are carried out at various temperatures ranging from 900 to 1200⁰C, strains up to 0.7 and strain rates of 0.01, 1 and 10 s-1. The grain growth, flow stress, and stress relaxations are simulated by finding reasonable values for model parameters. The flow stress data obtained at the strain rate of 10 s-1 were used to calibrate the model parameters and the predictions of the model for the lower strain rates were quite satisfactory. An assumption in the model is that the structure of second phase particles does not change during the short time of deformation. The results show a satisfactory agreement between the experimental data and simulated flow stress, as well as less than 5% difference for grain growth simulations and predicting the dominant softening mechanisms during stress relaxation according to the strain rates and temperatures under deformation.

  • 192.
    Safara Nosar, Nima
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Influence of tool steel surface topography on adhesion and material transfer in stainless steel/tool steel sliding contact2013Inngår i: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 303, nr 1-2, s. 30-39Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Transfer of work material to the tool surface is a common problem in many metal forming and metal working operations, especially in the case of work materials with a high adhesion tendency e.g. stainless steel, aluminum and titanium. In many operations, material transfer occurs already during the initial contact and with time it may result in degradation and roughening of the tool surface which will affect the surface quality of the formed or machined work material surface, e.g. problems related to galling in sheet metal forming. In the present study, the mechanisms behind the initial stages of material transfer between stainless steel and tool steel have been investigated under well controlled laboratory conditions and analyzed using optical surface profilometry and scanning electron microscopy.The results show that, independent of tool surface topography, transfer of stainless steel occurs already after a very short sliding distance. Depending on the tool steel surface topography, initial transfer occurs on two different scales. For a fine polished tool steel surface, fine scale transfer occurs in connection to protruding hard phase particles (carbides and carbonitrides) while for a ground rough surface large scale transfer occurs in connection to grinding scratches, where these act to mechanically scrape off material resulting in lumps off stainless steel on the tool steel surface. Also, sliding perpendicular to the grinding scratches results in more severe material transfer as compared with sliding parallel to the grinding scratches. Finally, the present paper illuminates the usefulness of combining optical surface profilometry and scanning electron microscopy as a powerful analytical tool when it comes to understanding the mechanisms controlling material transfer in a sliding contact on a Όm-scale level. © 2013 Elsevier B.V.

  • 193.
    Safara Nosar, Nima
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Sandberg, Fredrik
    Sandvik Materials Technology.
    Engberg, Göran
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Characterization of hot deformation behavior in a 13% chromium steel2018Inngår i: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 941, s. 458-467Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The behavior of a 13% chromium steel subjected to hot deformation has been studied by performing hot compression tests in the temperature range of 850 to 1200 ⁰C and strain rates from 0.01 to 10 s-1. The uniaxial isothermal compression tests were performed on a Gleeble thermo-mechanical simulator. The best function that fits the peak stress for the material and its relation to the Zener-Hollomon parameter (Z) is illustrated. The average activation energy of this alloy for the entire test domain was reviled to be about 557 [kJ mol-1] from the calculations and the dynamic recrystallization (DRX) kinetic were studied to find the fraction DRX in the course of deformation.

  • 194.
    Saketi, Sara
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. Uppsala universitet.
    Investigation of topography, adhesion and diffusion in sliding contacts during steel and titanium alloy machining2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The aim of the present thesis work is to increase the fundamental knowledge of the tribological contact between the cutting tool and the work material in three different cutting operations, i.e. hard milling of cold work tool steels, turning in 316L stainless steel and turning in Ti6Al4V alloy, respectively. The influence of cutting parameters and tool surface topography on the initial material transfer tendency and resulting wear and wear mechanisms were investigated under well controlled cutting conditions. High resolution scanning electron microscopy (SEM) and surface analysis, including energy dispersive X-ray spectroscopy (EDS), Auger electron spectroscopy (AES) and time-of-flight secondary ion mass spectrometry (ToF-SIMS), were used in order to characterize the worn cutting tools on a sub-µm scale and deepen the understanding of the wear mechanisms prevailing at the tool / work material interface. The characterization work includes the analysis of worn tool surfaces as well as cross-sections of these. Also, the back side of collected chips were analysed to further understand the contact mechanisms between the tool rake face and chip.

    The results show that the transfer tendency of work material is strongly affected by the surface topography of the rake face and that an appropriate pre- and post-coating treatment can be used in order to reduce the transfer tendency and the mechanical interaction between the mating surfaces. The continuous wear mechanisms of the cutting tools were found to be dependent on the work materials and the cutting parameters used. In hard milling of cold work tool steels, polycrystalline cubic boron nitride shows a combination of tribochemical wear, adhesive wear and mild abrasive wear. In the turning of 316L stainless steel and Ti6Al4V alloy, using medium to high cutting speeds/feeds, the wear of cemented carbide is mainly controlled by diffusion wear of the WC phase. Interestingly, the diffusion wear processes differ between the two work materials. In contact with 316L stainless steel crater wear is controlled by atomic diffusion of W and C into the passing chip. In contact with Ti6Al4V crater wear is controlled by the diffusion of C into a transfer work material layer generating a W-rich and TiC interfacial layer which repeatedly is removed by the passing chip. The experimental work and results obtained illustrates the importance of in-depth characterization of the worn surfaces in order to increase the understanding of the degradation and wear of tool materials and coatings in metal cutting operations.

  • 195.
    Saketi, Sara
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Bexell, Ulf
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Östby, Jonas
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    On the diffusion wear of cemented carbide in the turning of 316L austenitic stainless steel2019Inngår i: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 430-431, s. 202-213Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The present study focuses on the wear and wear mechanisms of three different cemented carbide grades during orthogonal turning of 316L austenitic stainless steel at different cutting speeds. The influence of WC grain size and cutting speed on the resulting crater and flank wear was evaluated by optical surface profilometry and scanning electron microscopy (SEM). The mechanisms behind the crater and flank wear were characterized on the sub-micrometer scale using high resolution SEM, energy dispersive X-ray spectroscopy (EDS), Auger electron spectroscopy (AES) and time of flight secondary ion mass spectrometry (ToF-SIMS) of the worn cutting inserts and the produced chips.

    The results show that the wear rate of cemented carbide drastically increases with increasing cutting speed and that the wear is dependent on the WC grain size; i.e. the crater wear decreases with increasing WC grain size while the flank wear increases with increasing WC grain size. High resolution SEM, AES and ToF-SIMS analysis of the worn cemented carbide within the crater and flank wear regions reveal that the degradation of cemented carbide at higher cutting speeds is mainly controlled by diffusion wear of the WC-phase. This is confirmed by ToF-SIMS analysis of the back-side of stainless steel chips which reveals the presence of a 10 nm thin W-containing oxide film. The results are discussed and interpreted in the light of the conditions prevailing at the tool-chip interface.

  • 196.
    Saketi, Sara
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. Ångström Tribomaterials Group, Uppsala University.
    Odelros, S.
    Östby, J.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. Ångström Tribomaterials Group, Uppsala University.
    Experimental study of wear mechanisms of cemented carbide in the turning of Ti6Al4V2019Inngår i: Materials, ISSN 1996-1944, Vol. 12, nr 7, artikkel-id 2822Artikkel i tidsskrift (Fagfellevurdert)
  • 197.
    Saketi, Sara
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Odelros, Stina
    Östby, Jonas
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Wear and wear mechanisms of cemented carbide in the turning of Ti6Al4V2019Inngår i: Materials, ISSN 1996-1944, E-ISSN 1996-1944Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Titanium and titanium alloys such as Ti-6Al-4V are generally considered as difficult-to-machine materials. This is mainly due to their high chemical reactivity, poor thermal conductivity and high strength, which is maintained at elevated temperatures. As a result, the cutting tool is exposed to rather extreme contact conditions resulting in plastic deformation and wear. In the present work, the mechanisms behind the crater and flank wear of uncoated cemented carbide inserts in the turning of Ti6Al4V are characterized using high resolution scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and high resolution Auger electron spectroscopy (AES).

    The results show that for combinations of low cutting speeds and feeds crater and flank wear were found to be controlled by an attrition wear mechanism while for combinations of medium to high cutting speeds and feeds a diffusion wear mechanism was found to control the wear. For the latter combinations, high resolution SEM and AES analysis reveal the formation of an approximately 100 nm thick carbon depleted WC-layer at the cemented carbide/Ti6Al4V interface due to the diffusion of carbon into the adhered build-up layers of work material on the rake and flank surfaces.

  • 198.
    Saketi, Sara
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. Ångström Tribomaterials group, Uppsala University.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. Ångström Tribomaterials group, Uppsala University.
    Influence of CVD and PVD coating micro topography on the initial material transfer of 316L stainless steel in sliding contacts: A laboratory study2017Inngår i: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 388-389, s. 29-38Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Austenitic stainless steels generally display poor tribological properties in sliding contacts partly due to their strong adhesion and transfer tendency to the counter surface. As a result machining of austenitic stainless steels is frequently associated with significant problems such as high stresses and high temperatures resulting in rapid tool wear. In the present study, the influence of coating micro topography on the initial material transfer of 316L stainless steel in sliding contacts has been evaluated using a scratch testing equipment. Coating materials include modern CVD Ti(C,N)-Al2O3-TiN and PVD (Ti,Al)N-(Al,Cr2)O3 coatings deposited on cemented carbide and pre- and post-coating grinding and polishing treatments were used to obtain different micro topographies of the coating surface. Pre- and post-test characterization of the surfaces was performed using high resolution scanning electron microscopy, energy dispersive X-ray spectroscopy and optical surface profilometry.

    The results show that the intrinsic topography of the as-deposited CVD and PVD coatings promotes material transfer. For the as-deposited CVD coating the nanoscale topography of the crystals controls the transfer while for the PVD coating the µm-scale droplets and craters control the transfer. Post-polishing of the coating, especially in combination with pre-polishing of the substrate, significantly improves the tribological performance of the surface reducing the friction coefficient and the material transfer tendency. However, the presence of µm sized droplets and craters in the PVD coating limit the possibility to obtain a smooth post-polished surface and its resistance to material pick-up. In contrast, post-polishing of the CVD coating does not suffer from intrinsic coating defects which results in low friction and a very high resistance to material pick-up.

  • 199.
    Saketi, Sara
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. Uppsala Universitet.
    Sveen, Susanne
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. Linköpings Universitet.
    Gunnarsson, S
    Uddeholm Tooling.
    M’Sauobi, R
    Seco Tools.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Wear of a high cBN content PCBN cutting tool during hard milling of powder metallurgy cold work tool steels2015Inngår i: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 332, s. 752-761Artikkel i tidsskrift (Annet vitenskapelig)
    Abstract [en]

    The wear characteristics of a high cBN content PCBN cutting tool during hard milling of two different hardened cold work tool steels have been evaluated. Post-cutting examination of the worn cutting inserts was performed using high resolution field emission gun scanning electron microscopy, energy dispersive X-ray spectroscopy, Auger electron spectroscopy and optical surface profilometry. Also, the machined work material surfaces and collected chips were characterized in order to evaluate the prevailing wear mechanisms. The results show that both flank and crater wear are controlled by continuous wear due to tribochemical reactions, adhesive wear and mild abrasive wear. Besides, the cutting inserts show a tendency to micro-chipping along the cutting edge especially at higher cutting speed. The latter mechanism was also found to be dependent on type of work material. High lateral resolution Auger electron spectroscopy of the crater region shows that the worn surface is covered by a thin SixOy rich tribofilm with a thickness of 50-500 nm, the tribofilm being thicker on the binder phase regions. Also, the Co-rich regions of the binder phase seem to be more tribochemically affected by the prevailing contact conditions as compared with the W-rich regions of the binder phase and the cBN phase. 

  • 200.
    Saketi, Sara
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. Ångström Tribomaterials Group, Uppsala University.
    Östby, J.
    AB Sandvik Coromant, Sandviken.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. Ångström Tribomaterials Group, Uppsala University.
    Influence of tool surface topography on the material transfer tendency and tool wear in the turning of 316L stainless steel2016Inngår i: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 368–369, s. 239-252Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Abstract The influence of tool surface topography on the initiation and build-up of transfer layers in the orthogonal turning of 316L austenitic stainless steel have been studied under well controlled conditions. Tool materials include CVD Ti(C,N)-Al2O3-TiN and PVD (Ti, Al)N-(Al,Cr)2O3 coated cemented carbide inserts prepared using different grinding and polishing treatments. Post-test characterization of the inserts was performed using high resolution scanning electron microscopy and energy dispersive X-ray spectroscopy. The results show that the transfer tendency of work material is strongly affected by the surface topography of the rake face. For both types of inserts, the initial transfer and the build-up of transfer layers are localised to microscopic surface irregularities on the rake face. Consequently, an appropriate surface treatment of the cemented carbide substrate before coating deposition and the as-deposited CVD and PVD coating can be used in order to reduce the transfer tendency and the mechanical interaction between the mating surfaces. Also, an improved surface finish was found to reduce coating wear and consequently the crater wear rate of the inserts investigated. This can most likely be explained by the reduced tendency to discrete chipping of coating fragments in the contact zone and the formation of a thin transfer layer composed of Al, Si, Ca, O with beneficial friction properties which are promoted by a smooth coating surface.

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