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  • 201.
    Olsson, Mikael
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Heinrichs, Jannica
    Yvell, Karin
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Jacobson, Staffan
    Initial degradation of cemented carbides for rock drilling: model studies of the tribological contact against rock2015In: International journal of refractory metals & hard materials, ISSN 0958-0611, E-ISSN 2213-3917, Vol. 52, p. 104-113Article in journal (Refereed)
    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.

  • 202.
    Olsson, Mikael
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Högman, B
    Uddeholms.
    Influence of tool steel microstructure on the prevailing wear mechanisms in metal powder compaction2012In: 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, p. 409-416Conference paper (Refereed)
  • 203.
    Olsson, Mikael
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Karlsson, P.
    Eriksson, Jenny
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Gåård, A.
    Krakhmalev, P.
    Bergström, J.
    Galling resistance evaluation of tool steels by two different laboratory test methods for sheet metal forming2011In: Proceedings of the 18th International Conference on Wear of Materials, Philadelphia, USA, 2011Conference paper (Other academic)
  • 204.
    Olsson, Mikael
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Sandberg, Odd
    Tribological evaluation of tool materials for powder compaction2010In: Proceedings of the World Powder Metallurgy Congress and Exhibition, World PM 2010, Florence, 2010, Vol. 5Conference paper (Refereed)
    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.

  • 205.
    Olsson, Mikael
    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.
    Scratch testing of cemented carbides - Influence of Co binder phase and WC grain size on surface deformation and degradation mechanisms2018In: Proceedings of The 18th Nordic Symposium on Tribology - Nordtrib 2018 / [ed] Staffan Jacobson, Uppsala: Uppsala University, 2018Conference paper (Refereed)
    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.

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  • 206.
    Olsson, Mikael
    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.
    Thin hard CVD and PVD coatings and their potential in steel wire drawing applications2018In: Proceedings of The 18th Nordic Symposium on Tribology - NORDTRIB 2018 / [ed] Staffan Jacobson, Uppsala: Uppsala University, 2018Conference paper (Refereed)
    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.

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  • 207.
    Olsson, Mikael
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Wadman, B.
    Eriksson, Jenny
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Schedin, E.
    Madsen, E.
    Bay, N.
    Influence of stainless steel surface texture on galling2011In: Proceedings of the 18th International Conference on Wear of Materials, Philadelphia, USA, 2011Conference paper (Other academic)
  • 208.
    Olsson, Mikael
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology. Ångström Tribomaterials Group, Uppsala University.
    Yvell, Karin
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Heinrichs, J.
    Bengtsson, M.
    Jacobson, S.
    Surface degradation mechanisms of cemented carbide drill buttons in iron ore rock drilling2017In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 388-389, p. 81-92Article in journal (Refereed)
    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.

  • 209.
    Olsson, Mikael
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Yvell, Karin
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    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 drilling2016In: Proceedings of the 17th Nordic Symposium on Tribology - Nordtrib 2016, 2016Conference paper (Refereed)
    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).

  • 210.
    Osterman, Jesper
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Skarp, Kent
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Tong, Au Ping
    Zhukov, Andrey
    Chigrinov, Vladimir
    Kwok, Hoi Sing
    Mechanically stabilized bistable FLC cells on plastic substrates2005In: Proceedings of the twenty-fifth international display research conference, Eurodisplay 2005, 2005Conference paper (Refereed)
    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.

  • 211.
    Osterman, Jesper
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Tong, Au Ping
    Skarp, Kent
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Chigrinov, Vladimir
    Kwok, Hoi Sing
    Properties of azo-dye alignment layer on plastic substrates2005In: Journal of the Society for Information Display, ISSN 1071-0922, E-ISSN 1938-3657, Vol. 13, no 12, p. 1003-1009Article in journal (Refereed)
    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.

  • 212. Park, J. M.
    et al.
    Jayamani, Jayaraj
    Kim, D. H.
    Mattern, N.
    Wang, G.
    Eckert, J.
    Tailoring of in situ Ti-based bulk glassy matrix composites with high mechanical performance2010In: Intermetallics (Barking), ISSN 0966-9795, E-ISSN 1879-0216, Vol. 18, no 10, p. 1908-1911Article in journal (Refereed)
    Abstract [en]

    In this study, we developed ductile dendrite-reinforced composites in the Ti–Zr–Ni–Cu–Be–(Nb) system. Although in situ composites have been successfully obtained by optimizing alloy composition and cooling rate, plasticity does not always occur. Only when the size, distribution, and elastic constants of the constituent phases are properly controlled, i.e. by creating homogeneously distributed dendrites with lower shear modulus than the glassy matrix, the composites exhibit large plasticity. By controlling the microstructural length scale and by tuning the intrinsic elastic constants of the constituent phases Ti-based bulk glassy matrix composites with good mechanical performance (high yield strength of ∼1.7GPa and large plasticity of ∼25%) have been achieved.

  • 213.
    Persson, Petter
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Finite element analysis of hot rolling in the blooming mill2016Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    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.

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  • 214.
    Persson, Petter
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Mätsystemanalys av mätmetod för kontroll av anoljningsgrad2014Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    At the end of the continuous annealing line at SSAB´s production plant in Borlänge a large portion of the produced sheet metal is oiled. Oiling of sheet metal is performed when a higher corrosion resistance is desirable, for example during transportation in a ship where it is exposed to a corrosive environment. To ensure that the correct amount of oil is applied, a visual inspection is done three times a day and each time the degree of oiling is changed. In addition, controls are done six times a year with a consumption measuring device. 

    The purpose of this thesis is to evaluate the current measurement method and to consider its use in the future. Possible improvements of this method are sought. Also, an oil thickness sensor is evaluated as an alternative.

    Three different measurement methods are used during the work with this thesis and a measurement systems analysis is carried out. This is done by compiling data in the statistical software Minitab 16 and the results were interpreted with regards to accuracy and precision.

    The results show that the consumption measuring device delivers more stable values than the oil thickness sensor when used during production. This is due to the sensors small measurement area and the drop-like way the oiling device applies oil. 

  • 215.
    Pirouznia, Pouyan
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Andersson, N. A. I.
    Tilliander, A.
    Jonsson, P. G.
    A mathematical model of martempering of thin martensitic stainless steel strips2015In: Proceedings of the 6th International Congress on the Science and Technology of Steelmaking, ICS 2015, 2015, p. 1027-1030Conference paper (Refereed)
    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.

  • 216.
    Pirouznia, Pouyan
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology. KTH Royal Institute of Technology; voestalpine Precision Strip AB, Munkfors.
    Andersson, N. ÅI.
    Tilliander, A.
    Jönsson, P. G.
    The impact of the gas inlet position, flow rate, and strip velocity on the temperature distribution of a stainless-steel strips during the hardening process2019In: Metals, E-ISSN 2075-4701, Vol. 9, no 9, article id 928Article in journal (Refereed)
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  • 217.
    Pirouznia, Pouyan
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology. 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 process2019In: Metals, ISSN 2075-4701, Vol. 9, no 6, p. 1-14Article in journal (Refereed)
    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.

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  • 218. Poddar, C.
    et al.
    Ningshen, S.
    Jayamani, Jayaraj
    Corrosion assessment of Ni60 Nb30Ta10 metallic glass and its partially crystallized alloy in concentrated nitric acid environment2020In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 813Article in journal (Refereed)
    Abstract [en]

    The corrosion resistance and passive film properties of Ni60Nb30Ta10 metallic glass and partially crystallized ribbon were investigated in 11.5 M nitric acid. The XRD study confirms the formation of nano-crystalline α-Ni in the amorphous matrix during crystallization at 650 °C under vacuum for 1 h. The electrochemical impedance spectroscopy, potentiodynamic polarization, and Mott-Schottky studies on the metallic glass exhibited higher corrosion resistance compared to the partially crystallized ribbon. XPS confirms the enrichment of Nb2O5 and Ta2O5 in the passive film of the glassy structure, while α-Ni is depleted in a partially crystallized alloy that affected the corrosion resistance.

  • 219. Poddar, Chiranjit
    et al.
    Jayamani, Jayaraj
    Amirthapandian, S.
    Ningshen, S.
    Effect of thermally grown amorphous oxide film on the corrosion resistance properties of Ni50Zr25Nb25 metallic glass in nitric acid medium2019In: Intermetallics (Barking), ISSN 0966-9795, E-ISSN 1879-0216, Vol. 113Article in journal (Refereed)
    Abstract [en]

    In the presents work, the effects of the surface oxidation of the Ni50Zr25Nb25 metallic glass on the corrosion behavior in nitric acid environment were investigated. The oxidation kinetics at 200 and 400 °C in air environment followed two-stage rate law. SEM and XPS investigation revealed the surface of thin (106 nm) amorphous oxide film composed of NiO, Ni2O3, ZrO2, and Nb2O5 when sample was oxidized at 200 °C. However, oxidation at 400 °C resulted in a thicker (721 nm) amorphous oxide film, enriched with only ZrO2 and Nb2O5. Potentiodynamic polarization results of the thermally oxidized metallic glass at 400 °C exhibited the wider passive range and significantly higher corrosion resistance in concentrated nitric acid when compared to the as-prepared and oxidized sample at 200 °C. After polarization at 2.2 V (Vs. Ag/AgCl), thermally oxidized sample at 400 °C exhibits smooth surface while the as-prepared MG undergoes a severe dissolution in 11.5 M nitric acid.

  • 220. Poddar, Chiranjit
    et al.
    Jayamani, Jayaraj
    Mallika, C.
    Kamachi Mudali, U.
    Oxidation behaviour of Ni60Nb30Ta10 metallic glass below its glass transition temperature2017In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 728, p. 1146-1152Article in journal (Refereed)
    Abstract [en]

    The oxidation behaviour of Ni60Nb30Ta10 metallic glass in air was investigated below its glass transition temperature (665 °C). The oxidation kinetics followed two-stage parabolic rate law at 450 and 550 °C. The parabolic rate constant increased with increase in the oxidation temperature. At 450 °C, a thin amorphous oxide film consisting predominantly Nb2O5 and Ta2O5, with traces of NiO and Ni2O3 was observed on the surface. At 550 °C, oxidation induced outward diffusion of Ni2+ and Ni3+ ions resulted in a thick oxide layer, containing extensive cubic NiO and monoclinic Ni2O3 with traces of metallic Ni on the surface. Interestingly, at 550 °C the Nb2O5 and Ta2O5 oxides were completely absent on the surface of the oxidised layer.

  • 221. Poddar, Chiranjit
    et al.
    Jayamani, Jayaraj
    Ningshen, S.
    Passive film characteristics and corrosion behavior of thermally oxidized Ni60Nb30Ta10 metallic glass in nitric acid medium2019In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 783, p. 680-686Article in journal (Refereed)
    Abstract [en]

    X-ray photoelectron spectroscopy (XPS) analyses confirmed the formation of different oxides upon thermal air oxidation (TO) of Ni60Nb30Ta10 metallic glass (MG) below the glass transition temperature. At 450 °C (450 TO-MG), surface of the oxide film was enriched with Nb2O5 (65%) and Ta2O5 (26%). Similarly, at 550 °C (550 TO-MG), the upper oxide layer was composed with NiO (67%), Ni2O3 (28.5%) and small fraction metallic Ni (4.5%). The electrochemical corrosion behavior of the thermally oxidized metallic glass samples was studied in 1, 6 and 11.5 M nitric acid at room temperature. Mott-Schottky analyses in nitric acid solutions confirmed the n-type semiconducting nature of the film for as-spun MG. On the other hand, the films formed on 450 TO-MG, and 550 TO-MG exhibited insulating and p-type, respectively. The donor (n-type) and acceptor (p-type) densities increases as the solution concentration increased. In nitric acid solutions, the current densities values obtained from potentiodynamic polarization studies indicated that 450 TO-MG exhibited higher corrosion resistance than the as-spun and 550 TO-MG samples.

  • 222. Poddar, Chiranjit
    et al.
    Jayamani, Jayaraj
    Ningshen, S.
    Mudali, U. Kamachi
    Effect of thermal oxidation on the oxide characteristic and corrosion behavior of Ni60Nb40 amorphous ribbon in nitric acid2019In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 479, p. 430-439Article in journal (Refereed)
    Abstract [en]

    The air-oxidation is a useful processing treatment to improve the corrosion resistance of Ni60Nb40 amorphous alloy. The oxidation kinetics of Ni60Nb40 amorphous ribbon follow two stage parabolic rate laws at 450 °C and 550 °C. The XPS analysis revealed that the surface of oxidized sample at 450 °C is enriched with Nb2O5, while oxidized sample at 550 °C, comprises of NiO and Ni2O3. The Mott-Schottky analyses confirmed the formation of n-type semiconducting film on the 450 °C oxidized sample in the nitric acid medium, while p-type semiconducting film on the 550 °C oxidized sample. Potentiodynamic polarization and EIS studies show that oxide film on the 450 °C oxidized sample exhibits highly protective barrier to the nitric acid when compared to the oxide film at 550 °C.

  • 223.
    Prashanth, Konda Gokuldoss
    et al.
    IFW Dresden, Institut für Komplexe Materialien, Postfach 27 01 16, D-01171 Dresden, Germany.
    Scudino, Sergio
    IFW Dresden, Institut für Komplexe Materialien, Postfach 27 01 16, D-01171 Dresden, Germany.
    Khoshkhoo, Mohsen Samadi
    IFW Dresden, Institut für Komplexe Materialien, Postfach 27 01 16, D-01171 Dresden, Germany.
    Surreddi, Kumar Babu
    IFW Dresden, Institut für Komplexe Materialien, Chalmers University of Technology, Gothenburg.
    Stoica, Mihai
    IFW Dresden, Institut für Komplexe Materialien, Postfach 27 01 16, D-01171 Dresden, Germany.
    Vaughan, Gavin
    European Synchrotron Radiation Facilities (ESRF), BP 220, Grenoble 38043, France.
    Eckert, Jürgen
    Structural and mechanical characterization of Zr58.5Ti8.2Cu14.2Ni11.4Al7.7 bulk metallic glass2012In: Materials, Vol. 5, no 1, p. 1-11Article in journal (Refereed)
  • 224.
    Prashanth, Konda Gokuldoss
    et al.
    IFW Dresden, Institut für Komplexe Materialien, Postfach 27 01 16, D-01171 Dresden, Germany.
    Scudino, Sergio
    IFW Dresden, Institut für Komplexe Materialien, Postfach 27 01 16, D-01171 Dresden, Germany.
    Klauss, Hansjörg J
    IFW Dresden, Institut für Komplexe Materialien, Postfach 27 01 16, D-01171 Dresden, Germany.
    Surreddi, Kumar Babu
    Chalmers University of Technology, Gothenburg.
    Löber, Lukas
    IFW Dresden, Institut für Komplexe Materialien, Postfach 27 01 16, D-01171 Dresden, Germany.
    Wang, Zhi
    IFW Dresden, Institut für Komplexe Materialien, Postfach 27 01 16, D-01171 Dresden, Germany.
    Chaubey, Anil Kumar
    IFW Dresden, Institut für Komplexe Materialien, Postfach 27 01 16, D-01171 Dresden, Germany.
    Kühn, Uta
    IFW Dresden, Institut für Komplexe Materialien, Postfach 27 01 16, D-01171 Dresden, Germany.
    Eckert, Jürgen
    IFW Dresden, Institut für Komplexe Materialien, Postfach 27 01 16, D-01171 Dresden, Germany.
    Microstructure and mechanical properties of Al–12Si produced by selective laser melting: Effect of heat treatment2014In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 590, p. 153-160Article in journal (Refereed)
  • 225.
    Prashanth, Konda Gokuldoss
    et al.
    IFW Dresden, Institut für Komplexe Materialien, Postfach 27 01 16, D-01171 Dresden, Germany.
    Scudino, Sergio
    IFW Dresden, Institut für Komplexe Materialien, Postfach 27 01 16, D-01171 Dresden, Germany.
    Surreddi, Kumar Babu
    IFW Dresden, Institut für Komplexe Materialien.
    Sakaliyska, Mira
    IFW Dresden, Institut für Komplexe Materialien, Postfach 27 01 16, D-01171 Dresden, Germany.
    Murty, B S
    Department of Metallurgical and Materials Engineering, Indian Institute of Technology Madras, Chennai – 600036, India.
    Eckert, Jürgen
    IFW Dresden, Institut für Komplexe Materialien, Postfach 27 01 16, D-01171 Dresden, Germany.
    Crystallization kinetics of Zr65Ag5Cu12.5Ni10Al7.5 glassy powders produced by ball milling of pre-alloyed ingots2009In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 513, p. 279-285Article in journal (Refereed)
  • 226.
    Prashanth, Konda Gokuldoss
    et al.
    IFW Dresden, Institut für Komplexe Materialien, Postfach 27 01 16, D-01171 Dresden, Germany.
    Surreddi, Kumar Babu
    IFW Dresden, Institut für Komplexe Materialien; Chalmers University of Technology, Gothenburg.
    Scudino, Sergio
    IFW Dresden, Institut für Komplexe Materialien, Postfach 27 01 16, D-01171 Dresden, Germany.
    Khoshkhoo, Mohsen Samadi
    IFW Dresden, Institut für Komplexe Materialien, Postfach 27 01 16, D-01171 Dresden, Germany.
    Wang, Zhi
    IFW Dresden, Institut für Komplexe Materialien, Postfach 27 01 16, D-01171 Dresden, Germany.
    Sordelet, D J
    Advanced Materials Technology Group, Caterpillar Inc.Mossville, USA.
    Eckert, Jürgen
    IFW Dresden, Institut für Komplexe Materialien, Postfach 27 01 16, D-01171 Dresden, Germany.
    Powder metallurgy of high-strength Al90.4Y4.4Ni4.3Co0.9 gas-atomized powder2012In: 13th International Conference on Aluminum Alloys (ICAA13), Springer, Cham , 2012, p. 1017-1022Conference paper (Refereed)
    Abstract [en]

    Al90.4Y4.4Ni4.3Co0.9 gas-atomized powder was hot pressed (HP) to produce highly dense bulk samples through combined devitrification and consolidation. The microstructure of the as-atomized powder is a mixture of amorphous phase with nanocrystalline fcc Al, whereas the consolidated samples consists of fcc Al and a series of intermetallic phases with or without residual amorphous phase depending on the hot pressing temperature (673 or 723 K). The HP samples exhibit a remarkable high strength of ~ 925 MPa (HP at 673 K) and ~ 820 MPa (HP at 723 K) combined with a plastic strain ranging between 14 and 30%. The reduction in strength for the sample HP at 723 K is linked to the complete crystallization of the powder with no residual amorphous phase.

  • 227. Prosek, T
    et al.
    Nazarov, A
    Bexell, Ulf
    Dalarna University, School of Technology and Business Studies, Material Science.
    Thierry, D
    Serak, J
    Corrosion mechanism of model zinc–magnesium alloys in atmospheric conditions2008In: Corrosion Science, ISSN 0010-938X, E-ISSN 1879-0496, Vol. 50, no 8, p. 2216-2231Article in journal (Refereed)
    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.

  • 228. Prosek, T.
    et al.
    Thierry, D.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Material Science.
    Bexell, Ulf
    Dalarna University, School of Technology and Business Studies, Material Science.
    Effects of chloride-to-chromate ratio on the protective action of zinc surface films under atmospheric weathering conditions2007In: Corrosion, ISSN 0010-9312, E-ISSN 1938-159X, Vol. 63, no 3, p. 258-267Article in journal (Refereed)
    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.

  • 229.
    Prosek, Tomas
    et al.
    Institut de la Corrosion / French Corrosion Institute.
    Nazarov, Andrej
    Institut de la Corrosion / French Corrosion Institute.
    Bexell, Ulf
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    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 alloys2007In: GALVATECH 2007, 2007Conference paper (Other academic)
    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.

  • 230. Rehnlund, D.
    et al.
    Lindgren, F.
    Böhme, S.
    Nordh, T.
    Zou, Y.
    Pettersson, J.
    Bexell, Ulf
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Boman, M.
    Edström, K.
    Nyholm, L.
    Lithium trapping in alloy forming electrodes and current collectors for lithium based batteries2017In: Energy & Environmental Science, ISSN 1754-5692, E-ISSN 1754-5706, Vol. 10, no 6, p. 1350-1357Article in journal (Refereed)
    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.

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  • 231. Rendon, José
    et al.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Material Science.
    Abrasive wear resistance of some commercial abrasion resistant steels evaluated by laboratory test methods2009In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 267, no 11, p. 2055-2061Article in journal (Refereed)
    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.

  • 232. Roizard, X.
    et al.
    Heinrichs, J.
    Et Taouil, A.
    Jacobson, S.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Melot, J. M.
    Lallemand, F.
    Insights into sliding wear and friction behavior of copper in ethanol containing alkylphosphonic acid molecules2016In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 96, p. 141-148Article in journal (Refereed)
    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. 

  • 233. Rybalochka, A.
    et al.
    Sorokin, V.
    Valyukh, Sergiy
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Skarp, Kent
    Dalarna University, School of Technology and Business Studies, Material Science.
    Palmer, S.
    Selection of cholesteric liquid crystals for liquid crystal display with high multiplexing level1999In: Advanced display technologies, 1999Conference paper (Refereed)
  • 234.
    Safara Nosar, Nima
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology. KTH Royal Institute of Technology.
    Engberg, Göran
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Ågren, John
    KTH Royal Institute of Technology.
    Modeling microstructure evolution in a martensitic stainless steel subjected to hot working using a physically based model2019In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 50, no 3, p. 1480-1488Article in journal (Refereed)
    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.

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  • 235.
    Safara Nosar, Nima
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology. KTH Royal Institute of Technology.
    Golpayegani, Ardeshir
    Sandvik Materials Technology.
    Engberg, Göran
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Ågren, John
    KTH Royal Institute of Technology.
    Study of the mean size and fraction of the second-phase particles in a 13% chromium steel at high temperature2019In: Philosophical Magazine, ISSN 1478-6435, E-ISSN 1478-6443, p. 1-17Article in journal (Refereed)
    Abstract [en]

    The mean size and fraction of the second-phase particles in a 13% chromium steel are investigated, while no plastic deformation was applied. The results of the measurement are compared with the modelling results from a physicallybased model. The heating sequence is performed on samples using a Gleeble thermo-mechanical simulator over the temperature range of 850?1200°C. Using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS), the size distribution and composition of the carbides were evaluated, respectively. For obtaining particle size distribution (PSD), an image-processing software was employed to analyse the SEM images. Additionally, the relation between the 2D shape factor and size of the particles is also studied at different temperatures and most of the particles turned out to have a shape factor close to two. In order to measure the carbide weight fraction, electrochemical phase isolation was employed. The Ms and fraction of the martensite phase after quenching of samples are calculated and the results were comparable with the measured hardness values at corresponding temperatures. The measured hardness of the samples is found to comply very well with the measured mean size of the precipitates. The calculated mean size of the particles from the model shows very good agreement with both hardness value and experimentally measured mean size, while the calculated volume fraction from simulation follows a slightly different trend.

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  • 236.
    Safara Nosar, Nima
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Influence of tool steel surface topography on adhesion and material transfer in stainless steel/tool steel sliding contact2013In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 303, no 1-2, p. 30-39Article in journal (Refereed)
    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.

  • 237.
    Safara Nosar, Nima
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Sandberg, Fredrik
    Sandvik Materials Technology.
    Engberg, Göran
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Characterization of hot deformation behavior in a 13% chromium steel2018In: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 941, p. 458-467Article in journal (Refereed)
    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.

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  • 238.
    Saketi, Sara
    Dalarna University, School of Technology and Business Studies, Materials Technology. Uppsala universitet.
    Investigation of topography, adhesion and diffusion in sliding contacts during steel and titanium alloy machining2019Doctoral thesis, comprehensive summary (Other academic)
    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.

  • 239.
    Saketi, Sara
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Bexell, Ulf
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Östby, Jonas
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    On the diffusion wear of cemented carbide in the turning of 316L austenitic stainless steel2019In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 430-431, p. 202-213Article in journal (Refereed)
    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.

  • 240.
    Saketi, Sara
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology. Ångström Tribomaterials Group, Uppsala University.
    Odelros, S.
    Östby, J.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Materials Technology. Ångström Tribomaterials Group, Uppsala University.
    Experimental study of wear mechanisms of cemented carbide in the turning of Ti6Al4V2019In: Materials, ISSN 1996-1944, Vol. 12, no 7, article id 2822Article in journal (Refereed)
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  • 241.
    Saketi, Sara
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Odelros, Stina
    Östby, Jonas
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Wear and wear mechanisms of cemented carbide in the turning of Ti6Al4V2019In: Materials, ISSN 1996-1944, E-ISSN 1996-1944Article in journal (Refereed)
    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.

  • 242.
    Saketi, Sara
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology. Ångström Tribomaterials group, Uppsala University.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Materials Technology. 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 study2017In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 388-389, p. 29-38Article in journal (Refereed)
    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.

  • 243.
    Saketi, Sara
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology. Uppsala Universitet.
    Sveen, Susanne
    Dalarna University, School of Technology and Business Studies, Materials Technology. Linköpings Universitet.
    Gunnarsson, S
    Uddeholm Tooling.
    M’Sauobi, R
    Seco Tools.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Wear of a high cBN content PCBN cutting tool during hard milling of powder metallurgy cold work tool steels2015In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 332, p. 752-761Article in journal (Other academic)
    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. 

  • 244.
    Saketi, Sara
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology. Ångström Tribomaterials Group, Uppsala University.
    Östby, J.
    AB Sandvik Coromant, Sandviken.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Materials Technology. Ångström Tribomaterials Group, Uppsala University.
    Influence of tool surface topography on the material transfer tendency and tool wear in the turning of 316L stainless steel2016In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 368–369, p. 239-252Article in journal (Refereed)
    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.

  • 245.
    Saketi, Sara
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology. Uppsala universitet.
    Östby, Jonas
    Bexell, Ulf
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    A methodology to systematically investigate the diffusion degradation of cemented carbide during machining2019In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 12, no 14, article id 2271Article in journal (Refereed)
    Abstract [en]

    Using Ti6Al4V as a work material, a methodology to systematically investigate the diffusion degradation of cemented carbide during machining is proposed. The methodology includes surface characterization of as-tested worn inserts, wet etched worn inserts, metallographic cross-sectioned worn inserts as well as the back-side of the produced chips. Characterization techniques used include scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), Auger electron spectroscopy (AES) and time of flight secondary ion mass spectroscopy (ToF-SIMS).

    The results show that the characterization of wet etched worn inserts give quick and useful information regarding the diffusion degradation of cemented carbide, in the present work the formation of a fine crystalline W layer (carbon depleted WC layer) at the tool / work material interface. The present study also illuminates the potential of AES analysis when it comes to analyzing the degradation of cemented carbide in contact with the work material during machining. The high surface sensitivity in combination with high lateral resolution makes it possible to analyze the worn cemented carbide surface on a sub-µm level. Especially AES sputter depth profiling, resulting in detailed information of variations in chemical composition across interfaces, is a powerful tool when it comes to understanding diffusion wear. Finally, the present work illustrates the importance of analyzing not only the worn tool but also the produced chips. An accurate characterization of the back-side of the chips will give important information regarding the wear mechanisms taking place at the tool rake face / chip interface. Surface analysis techniques such as AES and ToF-SIMS are well suited for this type of surface characterization.

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  • 246.
    Saketi, Sara
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology. Uppsala universitet.
    Östby, Jonas
    Bexell, Ulf
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Materials Technology. Uppsala universitet.
    Wear behaviour of two different cemented carbide grades in turning 316 L stainless steel2018In: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 941, p. 2367-2372Article in journal (Refereed)
    Abstract [en]

    Cemented carbides are the most common cutting tools for machining various grades of steels. In this study, wear behavior of two different cemented carbide grades with roughly the same fraction of binder phase and carbide phase but different grain size, in turning austenitic stainless steel is investigated. Wear tests were carried out against 316L stainless steel at 180 and 250 m/mincutting speeds. The worn surface of cutting tool is characterized using high resolution scanning electron microscopy (SEM), Energy dispersive X-ray spectroscopy (EDX), Auger electron spectroscopy (AES) and 3D optical profiler.The wear of cemented carbide in turning stainless steel is controlled by both chemical and mechanical wear. Plastic deformation, grain fracture and chemical wear is observed on flank and rake face of the cutting insert. In the case of fine-grained, the WC grains has higher surface contact with the adhered material which promotes higher chemical reaction and degradation of WC grains, so chemical wear resistance of the composites is larger when WC grains are larger. The hardness of cemented carbide increase linearly by decreasing grain size, therefore mechanical wear resistance of the composites is larger when WC grains are smaller.

  • 247.
    Sandberg, Andreas
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Kvalitativ jämförelse av mätt planhet efter sista valsparet i varmvalsverket jämfört med riktverksinställning på formatsträcka2015Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    The customers in the steel industry are demanding that the metal sheet should be

    able to be bought tension-free and flat. SSAB is constantly working to produce

    sheet with good flatness. To improve the flatness on the sheet, the sheet has to be

    leveled in the leveler at the line of cut-to-length. The flatness gauge has been

    improved after the rebuilding in the hot rolling mill, which improved the studies of

    the strips flatness.

    The purpose of this thesis is to calibrate the flatness gauge in the hot rolling mill to

    “true” flatness and examine if there is any connection between the leveler settings

    and the flatness of the sheet.

    Two different production trials were performed during the work of this thesis and

    both were fulfilled at SSAB´s production plant in Borlänge. All data from the hot

    rolling mill and the 4th line of cut-to-length were compiled in the statistics

    program Minitab and the results were interpreted with consideration to leveler

    settings and flatness.

    The result showed that strips which have a longer edge on the free side from the

    hot rolling mill, have better flatness after the leveler compared to strips which have

    been leveled and are longer in the middle or have longer edge on the drive side.

    The strips from the hot rolling mill, which have longer edge on the free side, are

    easier to level in the 4th cut-to-length line. It is because it has been possible to set

    the leveler settings to the same values as the set point values. To level the strips as

    good as possible the leveler settings need to be the same as the set point values.

  • 248. Sandell, A.
    et al.
    Karlsson, P. G.
    Richter, J. H.
    Blomquist, J.
    Uvdal, P.
    Grehk, Mikael
    Dalarna University, School of Technology and Business Studies, Material Science.
    Growth of ultrathin ZrO2 films on Si(100): film-thickness-dependent band alignment2007In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 88, no 13, article id 132905Article in journal (Refereed)
    Abstract [en]

    The band alignment of ultrathin ZrO2 films of different thickness formed on Si(100) have been monitored with synchrotron radiation photoelectron spectroscopy and x-ray absorption spectroscopy. The films were deposited sequentially by way of metal-organic chemical-vapor deposition in ultrahigh vacuum. A significant decrease in the conduction band offset is found for increasing film thickness. It is accompanied by a corresponding increase of the valence band offset. The variations originate in the formation of an interfacial layer characterized by a lower degree of Zr-O interaction than in bulk ZrO2 but with no clear evidence for partially occupied Zr 4d dangling bonds.

  • 249.
    Schultheiss, F
    et al.
    Lunds Universitet.
    Fallqvist, Mikael
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    M’Sauobi, R
    Seco Tools.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Ståhl, J E
    Lunds Universitet.
    Influence of CVD Al2O3 coated tool surface micro topography on the tribological characteristics in metal cutting: part II2013In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 298, p. 23-31Article in journal (Refereed)
    Abstract [en]

    The tribological conditions at the contact between the cutting tool and the chip are of great importance when analyzing the machining process. By knowing the contact conditions on the rake face of the cutting tool the wear on the clearance and rake face may be predicted in terms of size and type of wear. A certain value of the surface stresses is often thought of as leading to a higher wear rate of the cutting tool and thus a shorter tool life. In this article two different methods for experimentally measuring the contact condition on the clearance and rake face of the cutting tool are presented and illustrated with results obtained while turning AISI 4140. Results are also obtained in terms of how the surface roughness value of the cutting tool influences the contact condition. It was found that the tool surface topography may have a significant impact on the tribological performance during machining.

  • 250. Scudino, S.
    et al.
    Surreddi, Kumar Babu
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Shear band morphology and fracture behavior of cold-rolled Zr52.5Ti5Cu18Ni14.5Al10 bulk metallic glass under tensile loading2017In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 708, p. 722-727Article in journal (Refereed)
    Abstract [en]

    The effect of the shear bands generated by cold rolling on the tensile ductility and fracture behavior of the Zr52.5Ti5Cu18Ni14.5Al10 bulk metallic glass (BMG) is analyzed. The results reveal significant changes in the fracture behavior of the cold-rolled material with respect to the as-cast BMG. Fracture in the cold-rolled glass occurs along the pre-existing shear bands forming an angle of 45° with the loading direction. In addition, the fracture morphology shows a regular vein pattern oriented along the shear direction, which indicates that a considerable shear stress is active on the fracture plane. This is in contrast to the fracture behavior of the as-cast glass, where the normal stress plays a significant role. Here, the fracture angle is 55° and the fracture surface is characterized by the conventional irregular pattern of radiating ridges. Finally, work-hardening was observed in the cold-rolled BMG even in the absence of visible shear band intersection. Possible alternative mechanisms for determining this behavior are discussed. © 2017 Elsevier B.V.

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