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  • 151.
    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.

  • 152.
    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.

  • 153.
    Saketi, Sara
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology. Uppsala University.
    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 University.
    Wear mechanism of cemented carbide cutting tool in the turning of 316L stainless steel2018Conference paper (Refereed)
  • 154.
    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.
    Östy, 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 1873-2577Article 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.

  • 155.
    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: Wear, ISSN 0043-1648, E-ISSN 1873-2577Article 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 / feeds crater and flank wear were found to be controlled by an attrition wear mechanism while for combinations of medium to high cutting speeds / 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.

  • 156.
    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.

  • 157.
    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. 

  • 158.
    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.

  • 159.
    Saketi, Sara
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    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: Wear, ISSN 0043-1648, E-ISSN 1873-2577Article 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 inserts, metallographic cross-sectioned as-tested worn inserts as well as the back-side of the produced chips. Characterization techniques used include SEM, AES and 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 study the formation of a fine crystalline W layer (carbon depleted WC layer) at the tool / work material interface. The present work also illuminates the potential of AES analysis when it comes to analyzing the degradation of cemented carbide in contact with the work material (in the present study Ti6Al4V) 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.

  • 160.
    Saketi, Sara
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    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.
    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.

  • 161.
    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.

  • 162.
    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.

  • 163. 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.

  • 164.
    Scudino, S.
    et al.
    IFW Dresden, Inst Complex Mat, Solidificat Proc & Complex Struct, Helmholtzstr 20, D-01069 Dresden, Germany..
    Surreddi, Kumar Babu
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Wang, G.
    Shanghai Univ, Lab Microstruct, Shanghai 200444, Peoples R China..
    Liu, G.
    Xi An Jiao Tong Univ, State Key Lab Mech Behav Mat, Xian 710049, Peoples R China.;Xi An Jiao Tong Univ, Sch Mat Sci & Engn, Xian 710049, Peoples R China..
    Effect of stress concentration on plastic deformation of Zr41.2Ti13.8Cu12.5Ni10Be22.5 bulk metallic glass under compressive loading2016In: Materials letters (General ed.), ISSN 0167-577X, E-ISSN 1873-4979, Vol. 179, p. 202-205Article in journal (Refereed)
    Abstract [en]

    The influence of different sources of stress concentration on the plastic deformation of the Zr41.2Ti13.8Cu12.5Ni10Be22.5 metallic glass during room temperature compression tests is evaluated. Stress concentration introduced by sample geometry has a significant effect on the mechanical properties: in contrast to the specimen with square cross-section, which shows negligible plastic deformation, a substantial improvement in the plasticity can be achieved for the sample with round cross-section. Simulations of the stress distribution during the compression tests reveal that the stress concentration at the interface corners is responsible for the early fracture of the sample with square cross-section. Additionally, stress concentration during compression tests in the samples with square cross-section can be significantly reduced, and plastic deformation can be enhanced, by removing the interface corners as well as by reducing the friction arising between loading platens and specimen. 

  • 165.
    Sepehr, Omid
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Optimering av härdrecept – En förstudie2015Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    SKF has installed a relative new heat treatment line for large dimensions in Gothenburg. The line is a quality and capacity increasing investment which primarily will supply the European market. Currently there are three hardening recipes used to meet the range of large dimensions with the right quality according to SKF’s internal standard. Now, SKF wants to improve the recipes further by investigating the possibility of creating more specific hardening recipes based on the composition. To succeed with this, it is necessary to obtain knowledge regarding the composition’s impact on the hardening. One of the quality requirements is that the entire part has a lower bainitic structure. The material property which is crucial to know about is the hardenability. The hardenability is a measure of how thick dimensions that can be fully hardened, which is influenced by both the composition and the austenitizing treatment.

    In this thesis, the composition's contribution to the hardenability and the effect of alloy variations on hardenability has been investigated. The steel supplier’s composition variation for respective material standard is well controlled and do not affect the hardenability for the recommended goods dimensions. The steel supplier can therefore guarantee fully hardening of a certain thickness. The investigation made in this thesis show that this recommended thickness is exceeded and this must somehow be compensated. A low hardenability can effectively be offset by a temperature increase, but this is limited by strength requirements. Whether the correct treatment parameters are selected for compensation must be examined, which has been proposed in this work.

  • 166.
    Skalare, Henrik
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Optimering av patenteringsprocess: En undersökning om blypatentering2014Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    When producing thin spring- and piano wire the method used in the heat treatment process is called “lead patenting”. During the method you want the coarse lamellar structure of pearlite to become fine. The first step in the process is to heat the wire in to the austenite range. After the wire has reached the temperature of ca 900 ˚C in the oven it´s drawn into a bath of liquefied lead. The bath cools down the wire to a temperature of approximately 530 ˚C. The result of the heat treatment process will show fine plates of ferrite and cementite in the microstructure. The degree project will analyze the microstructures after the heat treatment in Springwire AB process. To analyze the microstructure of the material different test methods have been used. If the study finds any flaws in the microstructures of the materials or in the process these will be adjusted during the project. The microstructures that’s been analyzed in this study shows the structure of fine pearlite with small carbides of cementite. After the analysis of the microstructure the conclusion reached that the speeds in the heat treatment process are a bit high compared to the theoretical paces. Different kinds of suggestions has been presented to improve the process.

  • 167.
    Ssemakula, Hamzah
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Minimization of stock weight during close-die forging of a spindle2013In: Materials Sciences and Applications, ISSN 2153-117X, E-ISSN 2153-1188, Vol. 4, p. 217-224Article in journal (Refereed)
    Abstract [en]

    In this paper, Finite Element method and full-scale experiments have been used to study a hot forging method for fabri-cation of a spindle using reduced initial stock size. The forging sequence is carried out in two stages. In the first stage, the hot rolled cylindrical billet is pre-formed and pierced in a closed die using a spherical nosed punch to within 20 mm of its base. This process of piercing or impact extrusion leads to high strains within the work piece but requires high press loads. In the second stage, the resulting cylinder is placed in a die with a flange chamber and upset forged to form a flange. The stock mass is optimized for complete die filling. Process parameters such as effective strain distribution, material flow and forging load in different stages of the process are analyzed. It is concluded from the simulations that minor modifications of piercing punch geometry to reduce contact between the punch and emerging vertical walls of the cylinder appreciably reduces the piercing load. In the flange chamber, a die surfaces angle of 52° instead of 45° is pro-posed to ensure effective material flow and exert sufficient tool pressure to achieve complete cavity filling. In order to achieve better compression, it is also proposed to shorten both the length of the inserted punch and the die “tongues” by a few mm.

  • 168.
    Stjärne, Linice
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Materialanalys och jämförelse av badrumsskåp från tre olika tillverkare2015Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    This report is based on a thesis carried out in collaboration with CSI Nordic AB. The work has been done to help a client to get more knowledge and information about one of its own products, a bathroom cabinet, and also two competitors bathroom cabinets.

    The report contains a material analysis of the three bathroom cabinets, which because of an anonymity request are named A, B and C.

    The tests that have been performed is humidity test, tensile test, hardness test and scratch test. Structural analyzes of the steels and chemical analyzes of the materials and surface coatings have also been carried out.

    The results shows that the bathroom cabinets are made of equivalent steel, ie, the steels have very small differences in chemical composition and mechanical properties. Cabinet A shows distinct differences in structure and hardness of samples taken longitudinal or transverse the rolling direction.

    The scratch test shows that cabinet B and cabinet C don’t have as good scratch resistance as cabinet A. The scratch resistance depends on the paints composition, properties and adhesion.

    The chemical analysis of the coatings shows that cabinet A and B have a zinc coating, while cabinet C has a zinc phosphate coating. Cabinet C was also the only cabinet that showed local corrosion after the humidity test.

  • 169.
    Storck, Joakim
    Dalarna University, School of Technology and Business Studies, Material Science. Dalarna University, School of Technology and Business Studies, Materials Technology. Kungliga tekniska högskolan.
    Strategic and operational capabilities in steel production: Product variety and performance2009Doctoral thesis, monograph (Other academic)
    Abstract [en]

    Steel producers that employ niche market strategies are continuously seeking to reduce production cost while maintaining a diverse product mix. The business model is typically based on marketing of high–strength special or stainless steels. However, the desire to avoid direct cost competition is over time gradually leading towards increased product variety and smaller order volumes (tonnes per order) for each product. This thesis analyses how production cost is linked to product variety in steel strip production. Results are based on new models for assessment of opportunities for performance improvement in high product–variety steel production. The need for flexible production processes increases with increasing product variety. Operational capabilities linked to process flexibility determine the extent to which steel producers can eliminate in–process inventory and accomplish close coupling between process steps. Niche market producers that invest in process flexibility improvements can lower production costs both due to reduced work–in–process and lower energy consumption. An additional benefit is reduced environmental impact. The following problems are addressed: • Development of a method to assess the influence of product variety on performance in steel production. • Development of models of continuous casting and hot rolling that account for product variety and cost effects with consideration of varying degrees of process flexibility. • Development of a strategy process model that focus on the strategic value of operational capabilities related to process flexibility. Investments in operational capabilities regarding process flexibility have a strategic impact. An appreciation for the effects of process flexibility should permeate the organisation’s daily work since the accumulated contribution of many, seemingly unimportant, incremental changes significantly influences the strategic opportunities of the company.

  • 170.
    Surreddi, Kumar Babu
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Oikonomou, C.
    Uddeholms AB, SE-68385 Hagfors, Sweden..
    Karlsson, P.
    Orebro Univ, Dept Mech Engn, SE-70182 Orebro, Sweden..
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Pejryd, L.
    Orebro Univ, Dept Mech Engn, SE-70182 Orebro, Sweden..
    In-situ micro-tensile testing of additive manufactured maraging steels in the SEM: Influence of build orientation, thickness and roughness on the resulting mechanical properties2018In: La Metallurgia Italiana, ISSN 0026-0843, no 3, p. 27-33Article in journal (Refereed)
    Abstract [en]

    Selective laser melting (SLM) is frequently used additive manufacturing technique capable of producing various complex parts including thin-wall sections. However the surface roughness is a limiting factor in thin sections produced by SLM process when strength is the main criterion. In this study, the influence of build orientation, thickness and roughness on the resulting mechanical properties of as-built test samples was investigated. Various thin sheets of EN 1.2709 maraging steel built in horizontal and vertical orientations produced by SLM were investigated using in-situ micro-tensile testing in a scanning electron microscope. The mechanical strength and deformation mechanisms were analyzed and explained based on thickness and build orientation. Increased ductility was observed in thicker samples as well as in the horizontal build samples. The results illustrate the potential of the in-situ test technique and aspects important to consider in design guidelines for thin AM structures.

  • 171.
    Surreddi, Kumar Babu
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Oikonomou, Christos
    Karlsson, Patrik
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Pejryd, Lars
    In-situ Micro-tensile Testing of Additive Manufactured Maraging Steels in the SEM: Influence of Build Orientation, Thickness and Roughness on the Resulting Mechanical Properties2017In: Proceedings Euro PM 2017: International Powder Metallurgy Congress and Exhibition2017: Session 30: Mechanical Behaviour of AM Materials, 2017, article id Session 30Conference paper (Refereed)
    Abstract [en]

    Selective laser melting (SLM) is frequently used additive manufacturing technique capable of producing various complex parts including thin-wall sections. However the surface roughness is a limiting factor in thin sections produced by SLM process when strength is the main criterion. In this study, the influence of build orientation, thickness and roughness on the resulting mechanical properties of as-built test samples was investigated. Various thin sheets of EN 1.2709 maraging steel built in horizontal and vertical orientations produced by SLM were investigated using in-situ micro-tensile testing in a scanning electron microscope. The mechanical strength and deformation mechanisms were analyzed and explained based on thickness and build orientation. Increased ductility was observed in thicker samples as well as in the horizontal build samples. The results illustrate the potential of the in-situ test technique and aspects important to consider in design guidelines for thin AM structures.

  • 172.
    Surreddi, Kumar Babu
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Wear of cemented carbide nibs in steel wire drawing2018In: The 18th Nordic Symposium on Tribology – NORDTRIB 2018 / [ed] Prof. Staffan Jacobson, 2018Conference paper (Other academic)
    Abstract [en]

    The tribological interaction between a cemented carbide drawing die and a steel wire under lubricated wire drawing conditions has been characterized using 3D optical surface profilometry, scanning electron microscopy and energy dispersive X-ray spectroscopy. The results show that wear of the cemented carbides mainly is located to three different wear zones, i) at the entrance of the reduction zone, ii) at the exit of the reduction zone/ entrance of the bearing zone and iii) at the exit of the bearing zone. In the first wear zone, wear of the cemented carbide occurs on a WC grain size level and is controlled by plastic deformation, cracking and fragmentation of individual WC grains. In the second wear zone, wear of the cemented carbide is controlled by chipping of small WC/Co composite fragments resulting in craters, ~ 10μm in diameter.

  • 173.
    Surreddi, Kumar Babu
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Yvell, Karin
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Norgren, Susanne
    Sandvik Mining and Rock Technology, Rock Tools division, Sweden; Department of Engineering Sciences, Uppsala University, Sweden.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Characterization of surface degradation and wear damage Of cemented carbide in rock drilling2018In: The 18th Nordic Symposium on Tribology – NORDTRIB 2018 / [ed] Prof. Staffan Jacobson, 2018Conference paper (Other academic)
    Abstract [en]

    In this work, worn top hammer drill bit buttons after underground drifting in Granodiorite are analysed using scanning electron microscopy (SEM), Auger electron spectroscopy (AES) and electron backscatter diffraction (EBSD) to understand the dominant surface failure and wear mechanisms on the flank wear land region, i.e. the outer side of the gauge row cemented carbide buttons. SEM shows that the worn surface of the flank wear land is partly covered with islands of a thin rock material transfer layer and that the exposed cemented carbide show deformed, cracked and fragmented WC grains. AES gives that the transferred rock material is mainly located on the surface but may penetrate into cemented carbide microstructure to a depth of 1-2 WC grain diameters. Finally, EBSD reveals that the deformation of the cemented carbide in the flank wear land region is located to a thin zone, about ~10 μm in depth.

  • 174.
    Sveen, Susanne
    Dalarna University, School of Technology and Business Studies, Materials Technology. Linköpings universitet, Institutionen för fysik, kemi och biologi.
    Wear of coated and uncoated PCBN cutting tool used in turning and milling2014Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    This licentiate thesis has the main focus on evaluation of the wear of coated and uncoated polycrystalline cubic boron nitride cutting tool used in cutting operations against hardened steel. And to exam the surface finish and integrity of the work material used. Harder work material, higher cutting speed and cost reductions result in the development of harder and more wear resistance cutting tools. Although PCBN cutting tools have been used in over 30 years, little work have been done on PVD coated PCBN cutting tools. Therefore hard turning and hard milling experiments with PVD coated and uncoated cutting tools have been performed and evaluated. The coatings used in the present study are TiSiN and TiAlN. The wear scar and surface integrity have been examined with help of several different characterization techniques, for example scanning electron microscopy and Auger electron spectroscopy.

     

    The results showed that the PCBN cutting tools used displayed crater wear, flank wear and edge micro chipping. While the influence of the coating on the crater and flank wear was very small and the coating showed a high tendency to spalling. Scratch testing of coated PCBN showed that, the TiAlN coating resulted in major adhesive fractures. This displays the importance of understanding the effect of different types of lapping/grinding processes in the pre-treatment of hard and super hard substrate materials and the amount and type of damage that they can create. For the cutting tools used in turning, patches of a adhered layer, mainly consisting of FexOy were shown at both the crater and flank. And for the cutting tools used in milling a tribofilm consisting of SixOy covered the crater. A combination of tribochemical reactions, adhesive wear and mild abrasive wear is believed to control the flank and crater wear of the PCBN cutting tools. On a microscopic scale the difference phases of the PCBN cutting tool used in turning showed different wear characteristics. The machined surface of the work material showed a smooth surface with a Ra-value in the range of 100-200 nm for the turned surface and 100-150 nm for the milled surface. With increasing crater and flank wear in combination with edge chipping the machined surface becomes rougher and showed a higher Ra-value. For the cutting tools used in milling the tendency to micro edge chipping was significant higher when milling the tools steels showing a higher hard phase content and a lower heat conductivity resulting in higher mechanical and thermal stresses at the cutting edge.

  • 175.
    Sveen, Susanne
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology. Linköping University, SE-581 83 Linköping, Sweden.
    Andersson, J
    Seco Tools.
    M’Sauobi, R
    Seco Tools.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Scratch adhesion characteristics of PVD TiAlN deposited on high speed steel, cemented carbide and PCBN substrates2013In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 308, no 1-2, p. 133-141Article in journal (Refereed)
    Abstract [en]

    Modern tool materials, ranging from powder metallurgical high speed steel to super hard materials such as polycrystalline cubic boron nitride and diamond, are used as cutting tools in the metal cutting industry. In order to further improve the cutting performance, these tools are frequently coated by thin, hard PVD coatings such as TiN, TiAlN, AlCrO3, etc. In order to develop and design new PVD coatings it is important to characterize the mechanical properties of the coatings and understand the coating/substrate deformation mechanisms in a tribological contact, e.g. metal cutting. For example, it is important to be aware that the mechanical properties of the substrate (tool material) have a significant impact on the practical coating adhesion and the coating failure mechanisms.

    In the present study scratch testing has been used in order to evaluate to increase the understanding of the mechanical response and potential coating failure modes of cathodic arc evaporated TiAlN deposited on high speed steel, cemented carbide and polycrystalline cubic boron nitride. Post-test characterization of the scratched samples using optical profilometry, scanning electron microscopy and energy dispersive X-ray spectroscopy were performed and the cohesive and adhesive surface failure mechanisms are described and related to the substrate material properties. The results clearly show that, although all substrate materials can be regarded as hard, they result in completely different coating failure mechanisms at the normal load corresponding to substrate exposure. Also, coating failure resulting in substrate exposure does not necessarily correspond to interfacial cracking resulting in adhesive fracture along the coating-substrate interface.

  • 176.
    Sveen, Susanne
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology. Linköpings Universitet.
    M’Sauobi, R
    Seco Tools.
    Bexell, Ulf
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    PCBN hard turning of ball bearing steel: Influence of PVD coating deposition on tool wear and surface finish/surface integrity of machined surfaceManuscript (preprint) (Other academic)
  • 177.
    Svensson, Jennie
    Dalarna University, School of Technology and Business Studies, Materials Technology. KTH, Tillämpad processmetallurgi.
    An Experimental Study to Improve the Casting Performance of Steel Grades Sensitive for Clogging2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In this study, the goal is to optimize the process and to reduce the clogging tendency during the continuous casting process. The focus is on clogging when the refractory base material (RBM) in the SEN is in contact with the liquid steel. It is difficult or impossible to avoid non-metallic inclusions in the liquid steel, but by a selection of a good RBM in the SEN clogging can be reduced.

     

    Different process steps were evaluated during the casting process in order to reduce the clogging tendency. First, the preheating of the SEN was studied. The results showed that the SEN can be decarburized during the preheating process. In addition, decarburization of SEN causes a larger risk for clogging. Two types of plasma coatings were implemented to protect the RBM, to prevent reactions with the RBM, and to reduce the clogging tendency. Calcium titanate (CaTiO3) mixed with yttria stabilized zirconia (YSZ) plasma coatings were tested in laboratory and pilot plant trials, for casting of aluminium-killed low-carbon steels. For casting of cerium alloyed stainless steels, YSZ plasma coatings were tested in laboratory, pilot plant and industrial trials. The results showed that the clogging tendency was reduced when implementing both coating materials.

     

    It is also of importance to produce clean steel in order to reduce clogging. Therefore, the steel cleanliness in the tundish was studied experimentally. The result showed that inclusions originated from the slag, deoxidation products and tundish refractory and that they were present in the tundish as well as in the final steel product.

  • 178.
    Svensson, Jennie
    Dalarna University, School of Technology and Business Studies, Materials Technology. KTH, Tillämpad processmetallurgi.
    The submerged entry nozzle: a study of how to reduce decarburization and clogging2014Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    During continuous casting the submerged entry nozzle (SEN) is one of the critical points. This since sequence casting is favourable, clogging of the SEN results in fever sequences or aborted castings. In this study the preheating of SEN has been evaluated at different steel plants. This since it earlier  has been found, preheating resulted in decarburisation of  the refractory base material (RBM)  which in turn resulted in clogging of the SEN. During the industrial preheating trials it was found that decarburisation of  the SEN is possible.The decarburisation results in a higher oxygen potential near the SEN wall. This in turn makes it possible for aluminum in the molten steel to form alumina particles. For low carbon aluminum killed steel grades, accretion of alumina clusters on the SEN internal wall result in clogging which hinder or reduces the steel flow through the SEN. For this reason, laboratory trials were performed to establish the formation of a liquid phase. Thus simulating the formation of liquid inclusions when alumina clusters attaches to the SEN wall, and which can be washed away by the steel flow. Formation of a liquid phase was indicated at the temperatures 1550-1600°C, and plasma coated nozzles were tried in pilot plant trials. The coating contained of 5-9 pct, 99.9 pct pure, calcium titanate (CaTiO3) mixed with yttria stabilized zirconia (YSZ).

  • 179.
    Svensson, Jennie
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Larsson, F.
    Memarpour, A.
    Ekerot, S.
    Brabie, Voicu
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Jönsson, P.G.
    Implementation of an YSZ coating material to prevent clogging of the submerged entry nozzle (SEN) during continuous casting of Ce-treated steels2018In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 45, no 2, p. 105-113Article in journal (Other academic)
    Abstract [en]

    The possibility to reduce clogging in the submerged entry nozzle (SEN) during continuous casting of Ce alloyed stainless steels has been studied. This was done by implementing a new plasma coating material, consisting of yttria stabilized zirconia (YSZ). The coating was first tested in pilot-plant trials; where the amount of steel teemed through the plasma coated nozzles was monitored. Thereafter, samples of the coatings from the nozzles were studied using a FEG-SEM equipped with EDS. In addition, the coating material was tested in industrial trials where the performance was judged with respect to the clogging tendency detected as the movement of the stopper rod. The results from both the pilot-plant trials and industrial trials showed that the use of an YSZ coating led to a decreased clogging tendency during the casting in comparison to when using an uncoated SEN. Specifically, the pilot-plant trials showed that the clogging factor was lowered when implementing the YSZ coatings. Furthermore, the industrial trials showed that the clogging tendency, measured by the stopper rod movements, were lower when implementing the YSZ coating.

  • 180.
    Svensson, Jennie
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Larsson, Fredrik
    Outokumpu, Avesta SE-774 22, Sweden.
    Memarpour, Arashk
    Dalarna University, School of Technology and Business Studies, Materials Technology. Sandvik Materials Technology, Sandviken SE-811 81, Sweden.
    Brabie, Voicu
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Jönsson, Pär
    Royal Institute of Technology, Brinellvägen 23, Stockholm SE-100 44, Sweden.
    Post-mortem Studies of Submerged Entry Nozzles (SEN) Coated with Yttria Stabilized Zirconia (YSZ)2015In: The 6th International Congress on the Science and Technology of Steelmaking (ICS2015), China, May 12-14, 2015 in Beijing / [ed] Organized by The Chinese Society for Metals (CSM), 2015Conference paper (Refereed)
    Abstract [en]

    During continuous casting of Ce-treated stainless steel grades an accumulation of inclusions at the submerged entry nozzle’s (SEN) internal wall can cause disturbances or even prevent the molten steel flow. Plasma sprayed yttria stabilized zirconia (YSZ) coating of the SEN’s inlet and stopper rod have been implemented in order to decrease the clogging effect. The coating thickness was 210 µm and the plant trials were conducted during continuous casting of slabs. The clogging tendency was measured by the stopper rod position during the casting process. The results of the measured positions were then compared to experimentally determined information from samples cut out from the SEN’s inlet after casting. Specifically, the samples were analysed using a field emission gun scanning electron microscope (FEG-SEM) equipped with an energy dispersive X-ray spectrometry (EDS). Sample with the dimensions of ̴15x10x5 mm were electrolytic extracted before analysis. The chemical composition at the interface between the solidified steel and refractory base materials were analysed, and traces of the YSZ coating were determined.

    The movement of the stopper position indicated that the clogging tendency was reduced for the coated SEN. However, the FEG-SEM analyses showed that clogging of the SEN had occurred during the casting.

  • 181.
    Svensson, Jennie
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology. KTH.
    Memarpour, Arashk
    Brabie, Voicu
    Dalarna University, School of Technology and Business Studies, Materials Technology. KTH.
    Jönsson, Pär
    KTH.
    Studies of the decarburisation phenomena during preheating of submerged entry nozzles (SEN) in continuous casting processes2017In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 44, no 2, p. 108-116Article in journal (Refereed)
    Abstract [en]

    Decarburisation of the submerged entry nozzles (SEN) during the preheating process wasinvestigated based on plant trials and thermodynamic modelling at three different steel plants.During the trials the preheating processes were mapped, the temperature profiles wereregistered and post-mortem studies of the SENs with scanning electron microscopy wereperformed. Typically, the glass/silicon powder will form a dense and protective layer inside theSEN when heated over 1100°C. However, this study found that the temperature distributioninside the SEN did not always reach this critical temperature. Thus, decarburisation of the SENwas found at all steel plants. The overall results illustrate that the control of the preheatingprocess needs to be improved at all steel plants. It is suggested that future research should befocused on the development of new coating materials to prevent decarburisation of therefractory base material, which would decrease the chances of clogging during casting.

  • 182.
    Svensson, Jennie
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology. KTH, Tillämpad processmetallurgi.
    Memarpour, Arashk
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Brabie, Voicu
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Jönsson, Pär
    KTH, Tillämpad processmetallurgi.
    Studies of the decarburization phenomena during heating of submerged entry nozzles (SEN) in continuous casting processesManuscript (preprint) (Other academic)
  • 183.
    Svensson, Jennie
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Memarpour, Arashk
    Ekerot, Sven
    Brabie, Voicu
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Jönsson, Pär
    Tillämpad processmetallurgi, KTH.
    Studies of new coating materials to prevent clogging of the submerged entry nozzle (SEN) during continuous casting of Al killed low carbon steels2017In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 44, no 2, p. 117-127Article in journal (Refereed)
    Abstract [en]

    The possibility to reduce clogging in the submerged entry nozzle (SEN) when casting Al killed low carbon steel has been evaluated. The coating materials have been tested in laboratory trials and pilot plant trials. Totally, 2 mixes of the coating material has been tested; containing 4.8 and 9.1 % CaTiO3 mixed with yttria stabilised zirconia (YSZ) powder. The chemical composition was analysed by using an FEG-SEM equipped with EDS.The major result showed that alumina reacted with CaTiO3 in the temperature interval from 1550-1600°C. In addition, the clogging ratio showed a decreased clogging tendency for coated nozzles compared to standard nozzles. Also, the results showed that an approximately three times higher steel mass could be teemed through the coated nozzles before clogging occurred compared to trials with uncoated standard nozzles. Overall, it is concluded that plasma sprayed CaTiO3 coatings can reduce the clogging tendency during the continuous casting process.

  • 184.
    Sätherblom, Hans-Erik
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Development of a Computer Program for Off-State Optimization of LC-cell Optical Properties2006Independent thesis Basic level (degree of Bachelor)Student thesis
    Abstract [en]

    This thesis project addresses certain off-state optical properties of a liquid crystal cell, namely the problem caused by differences in light transmission and reflection between the figure patterned and the empty parts of the cell. To address the task of optimizing off-state optical properties of liquid crystal cells by making the ITO pixel pattern invisible, a computer code was developed For the present thesis work, calculations were limited to the case of normal incident light. A model based on single reflections, due to the Fresnel formulae, and the extinction according to the absorption coefficient, was used. With values of the refractive and absorption incidences and layer geometry taken from an earlier experimental investigation, numerical results in good agreement with experimental results were found. Furthermore, it was found not possible to match the luminance values from ITO portions with non-ITO portions by varying the polyimide thickness an equal amount on both the ITO and the non-ITO portions, also in agreement with the experimental results. The code was used to match the luminous transmittance of the ITO and non-ITO parts by varying the polyimide thickness at the non-ITO part of the cell independently from the polyimide thickness of the ITO-part. It was found that an additional thickness of polyimide on the non-ITO-part of the cell of the order of 4-5 times the ITO-thickness was needed in order to obtain this matching. Furthermore, it was seen that the matching of the luminous transmittance makes the luminous reflectance matching characteristics worse.

  • 185.
    Tunell, Helena
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Osterman, Jesper
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Selo, Muhammed
    POLY 701-Photoinduced reorientation and LC alignment of novel azobenzene containing polymers2006In: Abstract of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 232Article in journal (Other academic)
  • 186.
    Tunell, Helena
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Selo, Muhammed
    Skarp, Kent
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Hilborn, Johns
    Synthesis and characterization of main chain polyimides containing chalcone derivatives for LC alignment2006In: Polymer journal, ISSN 0032-3896, E-ISSN 1349-0540, Vol. 38, no 7, p. 716-723Article in journal (Refereed)
    Abstract [en]

    Two soluble polyimides containing chalcone derivatives in the main chains were successfully prepared using the Mitsunobu reaction at room temperature, reacting diols with diimides. With this reaction procedure the high temperature imidization step normally needed for the synthesis of polyimides is avoided and the polymers can be used for temperature sensitive applications. The main chain polyimides were characterized with FT-IR, NMR and DSC and the extent of the photoreaction was measured with FT-IR and UV-vis spectroscopy. Isobestic points were observed in the absorption spectral changes at the early stage of UV irradiation as a result of a single photochemical process. Further photoirradiation is accompanied by deviation from the isobestic points, implying that another photochemical process has started. With FT-IR investigations it was concluded that photodimerization is the process occurring at low UV exposure doses and that trans-cis isomerization is starting simultaneously at higher doses. The optical anisotropic properties were investigated upon exposure of the polymers as thin films to linearly polarized UV (LPUV) light of different doses. Selected crosslinking in the parallel direction relative to the direction of the LPUV light and subsequent optical anisotropy in the film were achieved.

  • 187.
    Valyukh, Iryna
    Dalarna University, School of Technology and Business Studies, Materials Technology. Uppsala universitet, Institutionen för teknikvetenskaper.
    Optical Characterization and Optimization of Display Components: Some Applications to Liquid-Crystal-Based and Electrochromics-Based Devices2009Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This dissertation is focused on theoretical and experimental studies of optical properties of materials and multilayer structures composing liquid crystal displays (LCDs) and electrochromic (EC) devices.

    By applying spectroscopic ellipsometry, we have determined the optical constants of thin films of electrochromic tungsten oxide (WOx) and nickel oxide (NiOy), the films’ thickness and roughness. These films, which were obtained at spattering conditions possess high transmittance that is important for achieving good visibility and high contrast in an EC device.

    Another application of the general spectroscopic ellipsometry relates to the study of a photo-alignment layer of a mixture of azo-dyes SD-1 and SDA-2. We have found the optical constants of this mixture before and after illuminating it by polarized UV light. The results obtained confirm the diffusion model to explain the formation of the photo-induced order in azo-dye films.

    We have developed new techniques for fast characterization of twisted nematic LC cells in transmissive and reflective modes. Our techniques are based on the characteristics functions that we have introduced for determination of parameters of non-uniform birefringent media. These characteristic functions are found by simple procedures and can be utilised for simultaneous determination of retardation, its wavelength dispersion, and twist angle, as well as for solving associated optimization problems.

    Cholesteric LCD that possesses some unique properties, such as bistability and good selective scattering, however, has a disadvantage – relatively high driving voltage (tens of volts). The way we propose to reduce the driving voltage consists of applying a stack of thin (~1µm) LC layers.

    We have studied the ability of a layer of a surface stabilized ferroelectric liquid crystal coupled with several retardation plates for birefringent color generation. We have demonstrated that in order to accomplish good color characteristics and high brightness of the display, one or two retardation plates are sufficient.

  • 188.
    Valyukh, Iryna
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Arwin, Hans
    Chigrinov, Vladimir
    Valyukh, Sergiy
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Characterization of the photo-alignment material SD-1/SDA-2 with spectroscopic ellipsometry2007In: IDW '07: Proceedings of the 14th International Display Workshops, vols 1-3, 2007, Vol. 1-3, p. 391-394Conference paper (Refereed)
    Abstract [en]

    Variable angle spectroscopic ellipsometry (VASE) is applied for investigation of the azo-dye SD-1/SDA-2 which are used for photoalignment of liquid crystals. The azo-dye was spin coated on silicon substrates. Samples as prepared as well as samples illuminated with polarized UV light were studied. The measured optical constants were modelled with an ensemble of the Lorentz oscillators. The results confirm the reorientation mechanism of the photo-induced order formation in the azo-dye films under the action of polarized light, and also show that there exist some photochemical processes.

  • 189.
    Valyukh, Iryna
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Arwin, Hans
    Chigrinov, Vladimir
    Valyukh, Sergiy
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    UV-induced in-plane anisotropy in layers of mixture of the azo-dyes SD-1/SDA-2 characterized by spectroscopic ellipsometry2008In: Physica Status Solidi C - Current topics in solid state physics, vol.5, no.5, 2008, Vol. 5, no 5, p. 1274-1277Conference paper (Refereed)
    Abstract [en]

    The optical properties of the azo-dyes SD-1/SDA-2, which are used for photoaligning of liquid crystals (LCs), are investigated with Variable Angle Spectroscopic Ellipsometry (VASE). Films of mixture of SD-1/SDA-2 are deposited by spin coating on silicon wafers. The estimated thickness is approximately 10 nm. To achieve photo-induced anisotropy, one of the samples is illuminated during 15 minutes with linearly polarized UV light followed by thermal stabilization during 1 hour at 150 degrees C. VASE measurements are performed in the wavelength range 200-1350 rim at several angles of incidence and at different sample orientations. Dielectric functions of azo-dye films without/with polarized UV light illumination were modelled using an ensemble of Lorentz oscillators. The results confirm the diffusion model proposed recently for explanation of the formation of the photo-induced order in azo-dye films under the action of polarized light. Refractive indices, their wavelength dispersion and thicknesses of films of SD-1/SDA-2 are reported here.

  • 190.
    Valyukh, Iryna
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Green, S.
    Arwin, H.
    Niklasson, G. A.
    Wäckelgård, Ewa
    Dalarna University, School of Technology and Business Studies, Energy and Environmental Technology.
    Granqvist, C. G.
    Spectroscopic ellipsometry characterization of electrochromic tungsten oxide and nickel oxide thin films made by sputter deposition2010In: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 94, no 5, p. 724-732Article in journal (Refereed)
    Abstract [en]

    Electrochromic films of tungsten oxide and nickel oxide were made by reactive dc magnetron sputtering and were characterized by X-ray diffraction, Rutherford backscattering spectrometry, scanning electron microscopy, and atomic force microscopy. The optical properties were investigated in detail by spectroscopic ellipsometry and spectrophotometry, using a multiple-sample approach. The W-oxide film was modeled as a homogeneous isotropic layer, whereas the Ni-oxide film was modeled as an anisotropic layer with the optical axis perpendicular to the surface. Parametric models of the two layers were then used to derive complex refractive index in the 300-1700 nm range, film thickness, and surface roughness. A band gap of 3.15 eV was found for the W-oxide film, using a Tauc-Lorentz parameterization. For the Ni-oxide film, taken to have direct optical transitions, band gaps along the optical axis, perpendicular to it, and in an isotropic intermediate layer at the bottom of the film were found to be 3.95, 3.97, and 3.63 eV, respectively. Parameterization for the Ni oxide was made by use of the Lorentz model. (C) 2009 Elsevier B.V. All rights reserved.

  • 191.
    Valyukh, Iryna
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Slobodyanyuk, A
    Valyukh, S
    Osterman, Jesper
    Dalarna University, School of Technology and Business Studies, Material Science.
    Skarp, Kent
    Dalarna University, School of Technology and Business Studies, Material Science.
    Using the Jones matrix for simulation of light propagation in anisotropic media2003In: Journal of optical technology (Print), ISSN 1070-9762, E-ISSN 1091-0786, Vol. 70, no 7, p. 470-473Article in journal (Refereed)
  • 192.
    Valyukh, Iryna
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Slobodyanyuk, A.
    Valyukh, S.
    Sorokin, V.
    Osterman, Jesper
    Dalarna University, School of Technology and Business Studies, Material Science.
    Skarp, Kent
    Dalarna University, School of Technology and Business Studies, Material Science.
    On accuracy of the Jones matrix method for simulation of light propagation in twisted nematic liquid crystals2002In: Proc. of the 11th Int. Symp. Advanced Display Technologies, UkraineArticle in journal (Refereed)
  • 193.
    Valyukh, Iryna
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Slobodyanyuk, A.
    Valyukh, S.
    Sorokin, V.
    Osterman, Jesper
    Dalarna University, School of Technology and Business Studies, Material Science.
    Skarp, Kent
    Dalarna University, School of Technology and Business Studies, Material Science.
    Simulation of light scattered by reflective polarizer with a rough metallic surface2002In: Eurodisplay 2002, Nice, France, 2002Conference paper (Refereed)
  • 194.
    Valyukh, Iryna
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Valyukh, S.
    Skarp, Kent
    Dalarna University, School of Technology and Business Studies, Material Science.
    Theoretical study of the optical properties of low voltage stacked cholesteric liquid-crystal displays2004In: Asia display, 2004Conference paper (Refereed)
  • 195.
    Valyukh, Iryna
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Valyukh, Sergiy
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Arwin, H.
    Chigrinov, V.
    Characteristic functions for uniformly twisted birefringent media2007In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 102, no 6, article id 063110Article in journal (Refereed)
    Abstract [en]

    We present two functions for characterization of birefringent media with application to twisted nematic liquid crystal (LC) cells in the field off state. The first function is for reflective LC cells and the second is for transmissive LC cells. Based on the Stockes formalism, it is shown that these functions describe the ability of a layer of the twisted birefringent medium to change polarization of the output light and are invariant to the layer orientation. The characteristic functions are found in simple procedures and can be used for simultaneous determination of retardation, its wavelength dispersion, and twist angle, as well as for solving optimization problems. © 2007 American Institute of Physics.

  • 196.
    Valyukh, Iryna
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Valyukh, Sergiy
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Skarp, Kent
    Chigrinov, V.
    Monochromatic bistable reflective and transfiective ferroelectric LCDs2005In: Proceedings of the 25th International Display Research Conference, Eurodisplay 2005, 2005, p. 305-308Conference paper (Refereed)
    Abstract [en]

    We study single and double polarizer monochromatic bistable reflective and transfective direct view ferroelectric liquid crystal displays (FLCDs). Three types of monochromatic displays are considered Black & White, Black & Yellow, Black & Green. Theoretical approach for finding optimal parameters of an FLCD is presented.

  • 197.
    Valyukh, Sergiy
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Adas, C.
    Franklin, G.
    Skarp, K.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Measuring parameters of liquid crystal cells with MePaLC system2005In: IDMC 2005: Proceedings of the International Display Manufacturing Conference, 2005, p. 795-798Conference paper (Refereed)
    Abstract [en]

    We present a sytem MePaLC for measuring retardation, its wavelength dispersion, twist angle, cell gap, and orientation of the input director. MePaLC enables us to measure practically all types of nematic liquid crystal cells: reflective and transmissive ones, with small and large cell gap.

  • 198.
    Valyukh, Sergiy
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Osterman, Jesper
    Dalarna University, School of Technology and Business Studies, Material Science.
    Adås, C.
    Skarp, Kent
    Dalarna University, School of Technology and Business Studies, Material Science.
    Cell gap measurements of flexible reflective TN- and STN-LC cells2004In: SID international symposium, 2004Conference paper (Refereed)
  • 199.
    Valyukh, Sergiy
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Osterman, Jesper
    Dalarna University, School of Technology and Business Studies, Material Science.
    Skarp, Kent
    Dalarna University, School of Technology and Business Studies, Material Science.
    Simple Spectroscopic Method to Measure Cell Gap and Twist Angle of TN-LCD2003In: International display research conference, 2003Conference paper (Refereed)
  • 200.
    Valyukh, Sergiy
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Osterman, Jesper
    Dalarna University, School of Technology and Business Studies, Material Science.
    Skarp, Kent
    Dalarna University, School of Technology and Business Studies, Material Science.
    Chigrinov, V.
    Optical performance of bistable reflective and transflective ferroelectric LCDs2005In: SID international symposium, Boston, 2005Conference paper (Refereed)
12345 151 - 200 of 231
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