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  • 1.
    Azizoğlu, Yağız
    Dalarna University, School of Technology and Business Studies, Materials Technology. Luleå University of Technology.
    Modeling of Cold Pilgering of Tubes2017Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Cold pilgering is a challenging tube forming process in terms of modeling due to the complexity in kinematic of tools, friction condition and material behavior. The process development has mostly been based on simple formulas and costly full-scale tryouts. The aim in this study is to develop validated Finite element models of cold pilgering to increase the understanding of influence of the process parameters on the produced tubes.

    In the course of this thesis, three-dimensional mechanical and thermo-mechanical Finite element models of cold pilgering were developed. The commercial code MSC.Marc was used in the simulations. General 3D models are needed to be able to capture asymmetric deformation in cold pilgering. It was found that tool deflections together with elastic deformation of roll dies have considerable influence on the rolling force. Furthermore, the strain rate and temperature effects on the response of the material and thereby on the rolling force were evaluated.

  • 2.
    Azizoğlu, Yağız
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Gardsback, M.
    Sjoberg, B.
    Lindgren, L. -E
    Finite element modelling of cold pilgering of tubes2015In: Proceedings of the 8th International Conference on Computational Plasticity - Fundamentals and Applications, COMPLAS 2015, 2015, 716-726 p.Conference paper (Refereed)
    Abstract [en]

    Cold pilgering is a cold forming process used during manufacturing of seamless tubes. The tube with a mandrel inside is fed forward and rotated in stepwise increments, while the roll stand moves back and forth. The total plastic deformation of the tube is such that the cross-sectional area of the tube decreases and the length of the tube increases during the process. However, this is performed in many small incremental steps, where the direction of deformation in a material point changes at each stroke. Most published models of cold pilgering use simplified material models. In reality, the flow stress is dependent on temperature, strain rate, strain history and microstructure. In this work, temperature and strain rate distributions are computed, using a 3D thermo-mechanical FE model, and the influence of temperature and strain rate on the rolling force is investigated. The Johnson-Cook model is employed to describe the flow stress using isotropic hardening. The results show that strain rate and temperature have a significant influence on the roll separation force.

  • 3.
    Azizoğlu, Yağız
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology. Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Gärdsback, Mattias
    Sandvik Materials Technology, R&D, Sandviken..
    Sjöberg, Bengt
    Sandvik Materials Technology, R&D, Sandviken..
    Lindgren, Lars-Erik
    Luleå University of Technology.
    Finite Element Analysis of cold pilgering using elastic roll dies2017Conference paper (Refereed)
    Abstract [en]

    A finite element model of cold pilgering with elastic roll dies have been developed and used to investigate the influence of roll die deformation on the material flow, contact region, roll separating force and tube dimensions. Full scale experiments were performed to validate the contact surface and tube dimensions. The results show that the influence of roll die flattening is not significant on the contact length. However, elastic deformation of roll die has strong influence on both the wall thickness reduction and roll separating force. Thus it is recommended to consider elasticity of roll dies when forces and tube dimensions are estimated.

  • 4.
    Azizoğlu, Yağız
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology. Luleå University of Technology.
    Gärdsback, Mattias
    Sjöberg, Bengt
    Lindgren, Lars-Erik
    Finite element modeling of tube deformation during cold pilgering2016In: MATEC Web of Conferences, 2016, Vol. 80, 15004Conference paper (Refereed)
    Abstract [en]

    A three-dimensional finite element model of cold pilgering of stainless steel tubes is developed in this paper. The objective is to use the model to increase the understanding of forces and deformations in the process. The focus is on the influence of vertical displacements of the roll stand and axial displacements of the mandrel and tube. Therefore, the rigid tools and the tube are supported with elastic springs. Additionally, the influences of friction coefficients in the tube/mandrel and tube/roll interfaces are examined. A sensitivity study is performed to investigate the influences of these parameters on the strain path and the roll separation force. The results show the importance of accounting for the displacements of the tube and rigid tools on the roll separation force and the accumulative plastic strain.

  • 5.
    Bengtsson, Sebastian
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Påverkan på mätresultatet av slagprovets läge i slagprovmaskinen2014Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    The project assumes that test whether the height of the smaller pendulum test dimensions (10 mm x 7.5 mm, 10 mm x 5 mm and 10 mm x 2.5 mm) is irrelevant to the outcome and to correct for the internal friction in the pendulum test machine. This is because the firm recently received accreditation for the new testing standard. The different materials tested were both brittle and ductile materials from the company and fought at predetermined temperatures. Under this standard, the smaller specimen the results are affected by the pendulum does not hit them in the center. Therefore made some shims (spacers) to raise up the samples so that the pendulum strikes the sample at the center. A comparison between the shim and without shims are made and how the internal friction off the machine can be checked in the smoothest and most appropriate way. The report shows how the samples are manufactured and prepared before they hit, which machines and the different grades used in this thesis. The results of battles show that there is no significant difference with or without shims for the different materials at those predetermined temperatures. Even a paired t-test is done to know whether there is any significant difference between with and without shims. The results of the paired t-tests revealed that the only one of the tests there was a significant difference between with and without the shims. The values of the internal friction shows that the internal friction does not varies much. How to control the internal friction off the machine in the smoothest and most appropriate way is to acquire a system that allows workers must turn blank firing at the beginning of each shift and then check the results and correct results are automatic. Since the centering pin used by the company today centers along the edge of the sample must test bar to be exactly 55 mm long. To get a better alignment can now acquire a centering pin that centers through the notch instead. This is mostly because the centering should not affect the measured test result. The conclusions that can be drawn from the results is that for certain temperatures it does not matter if the test pieces struck with or without shims even if there was one test that was significantly different. Since it is a tiny difference of tenths of a joule and the company reports only integers the difference does not matter. The internal friction does not vary so much that it affects the result.

  • 6.
    Bengtsson, Sebastian
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Validering av ny laserskärande provberedningsteknik inför materialprovning2016Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The purpose of this project is to investigate why the 0,2 % proof strength are stronger for the tensile specimens that are produced from laser cutting compare to these that are produced by manual cutting. This phenomenon is likely depending on the higher temperature that’s formed from the laser cutting. An investigation on the choice of the cutting parameters affects the temperature of the test coupon and also how the cutting order could keep the temperature low was made. The Brinell toughness for the laser cut and manual cut plates shall been compared against each other and if it’s necessary to change the size of the laser cut plates. The focus in this project is on the tensile specimens and the Brinell plates.

    The results shown that it’s a significant difference between the laser cut and manual cut tensile specimens and also that the laser cut tensile specimens has a temperature of 120 °C under the cutting process. The various settings for the cutting parameters does not results in any major difference except that a lower ultimate tensile strength, Rm, is shown at the new settings and that the tensile specimens are more likely to get stuck in the coupon. The results from the Brinell hardness tests show that there are no bigger differences between the laser and manual cut test pieces. It also shows that there are no differences between the various milling machines.

    Hardness profiles were made on already milled tensile specimens because according to earlier studies it’s shown that the HAZ disappear after milling. This result shows that it isn’t any bigger difference between the various manufacturing methods, however it’s difficult to interpret the result because the hardness value is resulting from putting the lines manually for calculating the diagonals from the impact. The result can vary with approximately ±5 kg/mm2 because the lines are added manually.

    Pictures of the microstructure was taken see if there is any changes in the structure from the cutting process and no changes in the structure can be determined from these pictures. A statistical analysis was made on all the tests to get a correctly statistical conclusion and these analyses were made in the program MINITAB. The conclusions that are made from the results are that the increase on the 0,2 % proof strength depends likely on epsilon carbides and can be minimized either through a lower or higher temperature in the tensile specimens at the cutting process or adding more Si to the material. There are no differences between the various milling machines at the milling on the Brinell plates or between the laser cut and manually cut plates. There might be some remaining HAZ after the milling on the tensile specimens, however it’s only on the upper part of the specimen.

  • 7. Berglund, T.
    et al.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    High velocity compaction of high speed steel powder: possibilities and constraints2007In: Proceedings of the Euro Powder Metallurgy Congress and Exhibition, Euro PM 2007, 2007, Vol. 3, 21-26 p.Conference paper (Refereed)
    Abstract [en]

    It is known that gas atomized powders as well as high alloyed metal powders are difficult to press into green bodies using conventional quasi static pressing techniques. However, the development of the high velocity compaction (HVC) technique has expanded the possibility to compact a larger spectrum of metal powders. Although the HVC technique has many similarities with conventional pressing techniques, the high energy impact makes it an interesting technique not only for the pressing of conventional metal powders to green bodies of high density but also for the pressing of "difficult to press metal powders". Today, high speed steel (HSS) is increasingly being used in different types of components. Consequently, there is an increasing interest in the near net shape manufacturing of HSS components. The aim of the present study is to evaluate the possibility to utilize HVC to press green bodies from different types of HSS powder covering both gas and water atomized HSS powders. The results show that the HSS powders investigated differ with respect to compaction properties, i.e. compressibility and green body quality. While the water atomized powders exhibit very good compaction properties, resulting in green bodies of high density, good surface finish and high strength, the gas atomized powders cannot be pressed in the as-atomized condition using HVC. However, agglomerated as well as milled gas atomized HSS powders show significant improved compaction properties compared to the as-atomized powders, although all showed defects of varying sizes depending on the applied energy during compaction.

  • 8.
    Bexell, Ulf
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Beläggningar till högtemperaturbränsleceller2011In: Stålforskningsdagarna 2011 / [ed] Joakim Storck, Borlänge: Högskolan Dalarna , 2011, 89-99 p.Conference paper (Other academic)
    Abstract [sv]

    Det finns en tro om att framtida högtemperaturbränslecellssystem kommer att ha en arbetstemperatur i intervallet 700-850°C. Vid dessa temperaturer kan man utnyttja metalliska material som bipolära plattor i en bränslecellsstack. Det har utvecklats speciella legeringar i just detta syfte men för ytterligare öka på prestandan måste dessa legeringar beläggas med lämpliga föreningar. Syftet med denna artikel är att visa att man kan förbättra olika egenskaperna av ett ferritiskt rostfritt stål genom att belägga det med lämpliga metalliska skikt.

  • 9.
    Bexell, Ulf
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Engkvist, Josefin
    Chalmers University of Technology, Göteborg, Sweden.
    Malmberg, Per
    Chalmers University of Technology, Göteborg, Sweden.
    Comparing 69Ga+ and C60+ for ToF-SIMS sputter depth profiling in a Cr2O3 formed during oxidation of a Ce coated FeCr steel substrate2012Conference paper (Other academic)
  • 10.
    Bexell, Ulf
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Material Science.
    Time-of-Flight SIMS Characterization of Hydrolysed Organofunctional and Non-Organofunctional Silanes Deposited on Al, Zn and Al-43.4Zn-1.6Si Alloy-Coated Steel2003In: Surface and Interface Analysis, ISSN 0142-2421, E-ISSN 1096-9918, Vol. 35, no 11, 880-887 p.Article in journal (Refereed)
  • 11.
    Bexell, Ulf
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Material Science.
    Jani, Simon
    AB Sandvik Materials Technology, Sandviken, Sweden.
    Lundberg, Mats W.
    AB Sandvik Materials Technology, Sandviken, Sweden.
    Initial oxidation of ferritic interconnect steel, effect due to a thin ceria coating2012In: European Fuel Cell Forum 2012 - Proceedings (memory stick), 2012Conference paper (Other academic)
    Abstract [en]

    Today there exist many ferritic stainless steel grades with a chemical composition speciallydesigned to be used as interconnects in solid oxide fuel cell applications in a temperatureinterval of 650-850°C. The steels have good high temperature mechanical properties andcorrosion resistance as well as good electron conductivity in the formed chromium oxidescale.One way to substantially decrease the high temperature degradation of the interconnectsteel i.e. improve properties such as increased surface conductivity and decreasedoxidation and chromium evaporation is to coat the interconnect steel with suitablecoatings. Today it is well known that a thin cobalt coating hinders chromium evaporationand a ceria coating lowers the oxidation rate at high temperature. Thus, by coating theinterconnect steel the properties are improved to an extent that it should be possible to usea cheaper standard steel, e.g. AISI 441, as substrate for the coatings.In this study the ferritic stainless steel alloys Sandvik Sanergy HT and AISI 441 is oxidizedin laboratory air at temperatures at 750°C, 800°C and 850°C. The results show that a welladhered oxide scale of a complex layered structure is formed with significant amounts ofMn, Fe, Cr and Ti in the oxide scale. A Ce coating significantly reduces the growth rate ofthe oxide scale. The lower Cr content in the AISI 441 alloy does not affect the initial hightemperature corrosion properties when coated with Ce. Also, the results demonstrate theusefulness of ToF-SIMS depth profiling for characterisation of the initial stages of oxidationof SOFC materials.

  • 12.
    Bexell, Ulf
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Lundberg, M.
    High temperature oxidation of plastically deformed ferritic interconnect steel2011In: ECS Transactions, ISSN 1938-5862, E-ISSN 1938-6737, Vol. 35, no 1, 2463-2470 p.Article in journal (Refereed)
    Abstract [en]

    In this study, thin sheets of a 22% Cr ferritic steel, Sandvik Sanergy HT has been coated with a thin metallic cobalt film. Samples of the coated steel sheet were exposed to two different forming experiments simulating different aspects of sheet metal forming and post high temperature oxidation. The results show that the metallic cobalt film cracks when the steel sheet is subjected to biaxial straining but that the cracks heal at high temperature. Material subjected to modified scratch testing i.e. simulating the contact between sheet metal and forming tool will oxidize in the same manner as non-scratched material. Also, from high temperature corrosion point of view there is no difference between materials formed under lubricated or dry conditions when oxidized. However, from a tribological point of view a lubricated contact situation is preferred.

  • 13.
    Blomberg, J
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Persson, B
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Blomberg, A
    Effects of semi-isostatic densification of wood on the variation in strength properties with density2005In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 39, no 5, 339-350 p.Article in journal (Refereed)
    Abstract [en]

    The variation in strength properties with density was compared between semi-isostatically densified and non-densified wood. Strength properties were compared with published data from earlier studies using other methods for densification. Small clear specimens of eight species were analysed for compression strength in axial, radial and tangential direction, three-point bending and Brinell hardness. After densification, all tested strength properties increased with density, but especially strength perpendicular to grain became lower than expected from the density of non-densified wood. Strength of densified wood relative to what could be expected for non-densified wood of similar density was denoted as `strength potential index'. For axial compression strength and bending strength, strength potential index of individual wood species varied between 0.7 and 1.0, i.e. densified wood is slightly weaker than what could be expected from its density. Strength potential index was lower for properties much determined by strength perpendicular to grain. In radial direction, densified wood was rubbery with low modulus of elasticity and nearly no proportional limit or modulus of rupture. Generally, wood was apparently weakened in proportion to the degree of compression in respective direction. Strength potential index also increased with increasing original density of the species.

  • 14.
    Blomberg, Jonas
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Elastic strain at semi-isostatical compression of Scots pine (pinus sylvestris L.)2005In: Journal of Wood Science, ISSN 1435-0211, E-ISSN 1611-4663, Vol. 51, no 4, 401-404 p.Article in journal (Refereed)
    Abstract [en]

    Quarter-sawn and plain-sawn specimens of Scots pine were semi-isostatically compressed at 5, 15, 50, and 140MPa in a Quintus press. Elastic strain was measured using a telescope device that was pushed together when wood was compressed and remained in this position at release of pressure. Delayed elastic and plastic strains were assessed through repeated callipering during 5 years after densification. At 140MPa, wood reached an almost compact structure (rho approximate to 1450kg/m(3)) but as a result of elastic springback the density decreased to just below 1000kg/m(3). At 140MPa, the elastic and delayed elastic strains were 14.6% and 1.8%, respectively, in quarter-sawn specimens, and were 13.1% and 0.8%, respectively, in plain-sawn specimens. The higher elastic strains in quarter-sawn specimens can be attributed to elastic springback in the tangentially deformed latewood bands.

  • 15.
    Böe, Hampus
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Härdprocessens inverkan på sprickuppkomst och spricktillväxt vid induktionshärdning av Ovako 495B: Seghärdning i induktionsline2014Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Abstract Induction hardening is a rapid thermal hardening process with high demands on the equipment. Ovako Sweden AB in Hällefors performs induction hardening on steel grade 495B and has major problems with crack initiation and propagation. The purpose of this work is to investigate how induction hardening affects the crack initiation and crack growth in the material and find the factors with major influences. It is very important to meet the customer's demands on hardness profile through the whole cross section. Two different tests have been performed where the goal has been to find an operational process that minimizes crack initiation and crack growth. The results of test one showing that the hardening temperature can be reduced from 915 ˚C down to 870 ˚C. Test two shows that cracks can be minimized if the cooling is done with a polymeric coolant instead of pure water and also achieve a more equal hardness profile. Based on the presented results more tests can be carried out to verify a new way of operational process that leads to a heavily reduced risk for cracks in the material. The two most critical bar diameters have been examined with focus upon the hardening temperature and cooling rate.

  • 16.
    Cederberg, Emil
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Utredning om alternativ kontrollmetod av härdresultat hos martensitiskt rostfritt stål2017Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Morakniv AB is a company that produces knives and ice drill bits. The quality of the material and heat treatment process is an important factor when the products are used in environments where the demand for performance is important. To further verify the quality, in addition to the ordinary hardness testing, they wanted to investigate an alternative test method.

    The tests included one type of material that would be heat treated in four different ways in order to evaluate the mechanical tests. The hardening process was carried out by two different austenitizing temperatures and by two different cooling rates. The hardening process took place in a belt furnace where the samples were continuously fed, heated and cooled in air. After cooling there was a sub-zero treatment followed by tempering. The results were then evaluated by bending test, hardness test and optical microscopy.

    The result showed that a hardening temperature of

    T+10 °C gave a larger standard deviation and higher ductility than at T-normal with respect to the maximum deflection. A lower cooling rate tended to decrease the maximum deflection and reduce the standard deviation. The hardness values did not vary significantly and the standard deviation were considered as negligible. The microscopy images did not show any specific structure changes when comparing the samples from the different heat treatment settings.

  • 17.
    Ceron, Ermanno
    et al.
    Technical University of Denmark.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Bay, Niels
    Technical University of Denmark.
    Lubricant film breakdown and material pick-up in sheet forming of advanced high strength steels and stainless steels when using environmental friendly lubricants2014In: Advanced Materials Research, ISSN 1022-6680, E-ISSN 1662-8985, Vol. 966-967, 219-227 p.Article in journal (Refereed)
    Abstract [en]

    Increasing focus on environmental issues in industrial production has urged sheet metal stamping companies to look for new tribo-systems in order to substitute hazardous lubricants such as chlorinated paraffin oils. The efficiency of chlorinated paraffin is due to the fact that the lubricant reacts chemically with the tool and workpiece material forming thin films, which adhere strongly to the surfaces and reduce the tendency to metal-metal contact and material pick-up. Production tests of new, environmentally benign tribo-systems are, however, costly and laboratory tests are preferred as a preliminary simulative method to investigate alternative tribo-systems. The present paper presents a case study where an industrial process, consisting of deep drawing with two subsequent re-drawings, was selected and four potential new tribo-systems were tested including different workpiece materials, i.e. AHSSs and stainless steels. The performance of the tribo-systems was analyzed in the laboratory by means of a newly developed simulative test as well as in an industrial production process. The results obtained show a good agreement between the laboratory test and the industrial production process regarding the tribological performance, i.e. tendency to material pick-up and galling, of the evaluated tribo-systems. Moreover the SEM analysis shows that different workpiece materials result in different types of material pick-up.

  • 18.
    Compagnon, Maxime
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Ink-Jet Printing of Color Optical Filters for LCD Applications2006Independent thesis Basic level (degree of Bachelor)Student thesis
    Abstract [en]

    At the age of multi-media, portable electronic devices such as mobile phones, personal digital assistant and handheld gaming systems have increased the demand for high performance displays with low cost production. Inkjet printing color optical filters (COF) for LCD applications seem to be an interesting alternative to decrease the production costs. The advantage of inkjet printing technology is to be fast, accurate, easy to run and cheaper than other technologies. In this master thesis work, we used various disciplines such as optical microscopy, rheology, inkjet printing, profilometering and colorimetry. The specific aim of the thesis was to investigate the feasibility of using company-A pigment formulation in inkjet production of COF for active matrix LCD applications. Ideal viscosity parameters were determined from 10 to 20mPa·s for easy inkjet printing at room temperature. The red pigments used are fully dispersed into the solvent and present an excellent homogenous repartition after printing. Thickness investigations revealed that the printed COF were equal or slightly thicker than typically manufactured ones. The colorimetry investigations demonstrated color coordinates very close to the NTSC red standard. LED backlighting seems to be a valuable solution to combine with the printed COF regarding to the spectrum and color analysis. The results on this thesis will increase the understanding of inkjet printing company-A pigments to produce COF for LCD applications.

  • 19.
    Dalin Nilsson, Anette
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Jämförelse av restaustenit i ett härdat verktygsstål för varmarbetsapplikationer: martensitisk och baintisk mikrostruktur2014Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    This thesis has been conducted at Uddeholms AB in Hagfors. Samples and measurements have been made on a tool steel; Uddeholm Dievar. Dievar is a hot work tool steel which is best suited for large tools.

    Retained austenite is always found in hardened high alloyed steel. It is said to decompose into cementite and ferrite during tempering. The decomposition product affects the impact toughness in a negative way. An impaired impact toughness increases the risk for cracking. Using the correct temperature during austenitizing improves the steel properties.

    The sample that have been used varies in austenitizing and in cooling rate. There is a fast cooling and one slow cooling rate which corresponds to cooling of the core in a large tool. A comparison have been made on the microstructure of the different samples, this has been conducted in a SEM. The mapping of phases has also been made with the use of a SEM (Scanning Electron Microscope) and with an ESBD-detector (Electron Backscatter Diffraction). The values on impact toughness have been relative to the content of retained austenite. This report shows how the austenitizing and cooling rate affect the contents of retained austenite and how the content influences the impact toughness.

    The microstructure of the samples varies depending on austenitizing temperature. Some conclusions that can be made from this thesis are that the content of retained austenite increase with the lowering of the temperature during austenitizing when it comes to bainitic micro structure. In the martensitic sample the retained austenite decreases with the austenitizing temperature. During the assembly of the impact toughness values it showed that the samples with the highest content of retained austenite prior tempering were the ones with the lowest value when the test was conducted.

  • 20.
    Engberg, Göran
    Dalarna University, School of Technology and Business Studies, Materials Technology. Dalarna University, School of Technology and Business Studies, Material Science.
    Constitutive models, physically based models for plasticity2014In: Encyclopedia of Thermal Stresses / [ed] Hetnarski RB, Dordrecht, Heidelberg, New York, London: Springer, 2014, 649-662 p.Chapter in book (Refereed)
    Abstract [en]

    Physically based models for the plastic behavior of crystalline, metallic materials are discussed. However, deformation by twinning and phase transformations as well as the evolution of texture are omitted. 

  • 21.
    Engberg, Göran
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Kero, Ida
    Yvell, Karin
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Modeling microstructure development during hot working of an austenitic stainless steel2013In: Materials Science Forum, ISSN 0255-5476, Vol. 753, 423-426 p.Article in journal (Refereed)
    Abstract [en]

    A number of physically based models are combined in order to predict microstructure development during hot deformation. The models treat average values for the generation and recovery of vacancies and dislocations, recrystallization and grain growth and the dissolution and precipitation of second phase particles. The models are applied to a number of laboratory experiments made on 304 austenitic stainless steel and the model parameters are adjusted from those used for low alloyed steel mainly in order to obtain the right kinetics for the influence of solute drag on climb of dislocations and on grain growth. The thermodynamic data are obtained using Thermo-Calc© to create solubility products for the possible secondary phases. One case of wire rolling has been analyzed mainly concerning the evolution of recrystallization and grain size. The time, temperature and strain history has been derived using process information. The models are shown to give a fair description of the microstructure development during hot working of the studied austenitic stainless steel. © (2013) Trans Tech Publications, Switzerland.

  • 22.
    Engkvist, Josefin
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Canovic, S.
    Liu, F.
    Gotlind, H.
    Svensson, J. -E
    Johansson, L. -G
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Halvarsson, M.
    Oxidation of FeCrAl foils at 500-900 degrees C in dry O2 and O2 with 40% H2O2009In: Materials at High Temperature, ISSN 0960-3409, Vol. 26, no 2, 199-210 p.Article in journal (Refereed)
    Abstract [en]

    High temperature resistant FeCrAl alloys are frequently used in high temperature applications Such as heating elements and metal based catalytic converter bodies. When exposed to high temperatures an adherent, slowly growing, dense aluminium oxide layer forms on the surface, which protects the underlying alloy from severe degradation. The composition, structure and properties of the formed oxide layer are strongly dependent on the alloy composition, temperature and oxidation environment. In this study, the Sandvik 0C404 FeCrAl alloy, in the form of 50 mu m thick foils, was exposed isothermally in the temperature range 500-900 degrees C for 168 hours in dry O-2 and in O-2 with 40 vol.% H2O. The surface morphology, composition and microstructure of the grown oxide scales were characterized by using scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), grazing incidence X-ray diffraction (GI-XRD), Auger electron spectroscopy (AES), and time of flight secondary ion mass spectrometry (TOF-SIMS). The oxidation process was faster at 900 degrees C than at 500 and 700 degrees C. At 500 degrees C a thin (10-20 nm) mixed oxide of Fe, Cr and Al was formed. Exposure at 700 degrees C resulted ill a similar (40-50 nm) duplex oxide, in both dry O-2 and in O-2 With 40 vol.% H2O. These oxide scales consisted of all inner and an outer relatively pure alumina separated by a Cr-rich band. This type of duplex oxide scale also formed at 900 degrees C with a thin inward growing alpha-Al2O3 at the oxide/metal interface and an outward growing layer outside a Cr-rich band. However, at 900 degrees C the Outward growing layer showed two types of oxide morphologies; a thin smooth base oxide and a much thicker nodular oxide grown on top of substrate ridges. In dry O-2 atmosphere, the main part of this outward growing layer had transformed to alpha-Al2O3. Only in the outer part of the thick oxide nodules, metastable alumina was found. When exposed in the presence of water vapour the main pall of the metastable alumina remained untransformed.

  • 23.
    Engkvist, Josefin
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science. Chalmers University of Technology, Göteborg, Sweden.
    Israelsson, Niklas
    Chalmers University of Technology, Göteborg, Sweden.
    Bexell, Ulf
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    The initial effect of KCl deposit on alumina scales characterized by ToF-SIMS and AES2013In: Surface and Interface Analysis, ISSN 0142-2421, E-ISSN 1096-9918, Vol. 45, no 1, 445-448 p.Article in journal (Refereed)
    Abstract [en]

    A FeCrAl alloy was preoxidized to form a protective alumina scale, and the effect of KCl deposits on the alumina scale was investigated while exposed during 1 and 24 h at 600 °C. However, impurity concentrations in the alumina scale change the ion conductivity and hence affect its protective properties. Therefore, Auger electron spectroscopy and time-of-flight secondary ion mass spectrometry were used to characterize the alumina scales and detect traces of K and Cl. The results showed that K and Cl existed as large sharp-edged crystals surrounded by a dendritic network after 1 h. However, after 24 h, those were dissolved, and K together with Cl was detected only in the outer layer of the duplex alumina scale, which was formed during preoxidation.

  • 24.
    Eriksson, Alexandra
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Kiselhaltens inverkan på slagsegheten hos Charpy-V och oanvisad slagseghetsprovning: Slagseghetsprovning vid rumstemperatur, godstjocklek 150 mm2014Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    The thesis is based on a survey of two ductile iron with different silicon content. The study will provide a deeper understanding of how the results of the impact test of the two material types differ from each other, and how well the two specimen types may reflect the change in the microstructure that should be the result of varied silicon content.  A cast of stair similar form has been cast for the two ductile irons. With a core drilling were drilled to test pieces from two thicknesses and processed. These samples were half each Charpy-V and un-notched test bars. The specimens were divided into eight test series. The samples were used for impact testing and data was compiled. Structural studies have been done in a scanning electron microscope, SEM and light microscopy, LOM and hardness testing by mikrovikers. The materials differ in that the material with the lower silicon content of more graphite modules, has higher impact strength values and are softer than the material with higher silicon content. This is because the perlite has a stronger influence on the impact strength of EN-GJS-400-18. In addition, EN-GJS-400-18 has larger graphite particles. As both pearlite and graphite is likely to have a slightly uneven distribution in the matrix, this will result in a greater spread on the impact strength test values. As for the lower impact strength of EN-GJS-500-14, it can probably be explained by the higher hardness in the matrix due to the silicon solution hardening effect on the matrix. The higher hardness affects the impact strength negatively.

  • 25.
    Eriksson, Jenny
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Tribological testing of commercial CrN, (Ti,Al)N and CrC/C PVD coatings: evaluation of galling and wear characteristics against different high strength steels2011In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 205, no 16, 4045-4051 p.Article in journal (Refereed)
    Abstract [en]

    The increasing use of high strength steels in a variety of mechanical engineering applications has illuminated problems associated with galling in sheet metal forming operations. Galling is a tribological phenomenon associated with transfer of material from the steel sheet to the tool surface during forming resulting in seizure of the tool/steel sheet contact and extensive scratching of the steel sheet surface. As a result, a number of concepts have been developed in order to reduce the tendency of galling in sheet metal forming, including the development of new dry lubricants, new forming tool steel grades and improved surface engineering treatments such as the deposition of low friction CVD- and PVD-coatings. In the present study the potential performance of three commercial PVD coatings, including CrN, (Ti,Al)N and a CrC/C DLC-based coating, in the forming of hot and cold rolled high strength steel as well as electro and hot-dip galvanized high strength steel has been evaluated using pin-on-disc testing under lubricated contact conditions. Post-test examination of the tribosurfaces using FEG-SEM and EDS analyses was performed in order to evaluate the mechanisms controlling the tendency to material transfer and wear. The results show that in contact with the hot and cold rolled steel the material pick-up tendency of the PVD coatings tend to increase in the order CrC/C–CrN–(Ti,Al)N while in contact with the two galvanized steel sheets, the CrC/C and the (Ti,Al)N coating show a significantly lower material pick-up tendency as compared with the CrN coating. Further, the substrate hardness has a strong influence on the wear of the PVD coatings and consequently on the friction characteristics and galling tendency of the coating/substrate composite. Low substrate hardness, resulting in a low load bearing capacity, increases the tendency to cracking and subsequently chipping of the brittle coating.

  • 26.
    Ersbjörs, Andreas
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    HÄRDBARHET HOS BORSTÅL – INVERKAN AVBORFÖRSPRÖDNING2017Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    A hardened and tempered component of boron steel, which revealed

    an intergranular fracture after fatigue testing, have been studied. It was suspected

    that the component was embrittled by boron precipitation in the grain boundaries.

    This hypothesis is the motivation for this work. A reference component which

    exhibits good fatigue properties was used. In order to understand the different

    mechanical properties, both samples was studied in detail.

    A small notched specimen from each component were fractured

    in-situ in an auger

    electron microscope (AES) to study the fracture surfaces with minimum oxygen

    contamination. During the AES-analysis, boron nitride in grain boundaries and

    particles containing Ca and Mn was found in both specimen. The fracture was of

    both brittle and ductile mode for both specimen. P and C were found on every

    intergranular surface studied.

    Fracture surfaces, polished and etched cross sections were studied using scanning

    electron microscope (SEM). Micro hardness measurement reveal that the

    microstructure in the material with low fatigue resistance consists of large fraction

    of a softer phase.

    Since both specimen show a lot of defects, boron embrittlement is not the

    contributing factor for low fatigue resistance. The quality of the product would

    probably increase by reducing the amount of defects. The challenging issue is

    quantification of the amount of the softer phase. It is believed that the softer phase

    can be retained austenite or ferrite. Both can occur as a consequence of faulty heat

    treatment, but with different process parameters. A Jominy test showed equal

    hardenability for both components, this indicates heat treatment differences.

  • 27.
    Fallqvist, Mikael
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Microstructural, Mechanical and Tribological Characterisation of CVD and PVD Coatings for Metal Cutting Applications2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The present thesis focuses on characterisation of microstructure and the resulting mechanical and tribological properties of CVD and PVD coatings used in metal cutting applications. These thin and hard coatings are designed to improve the tribological performance of cutting tools which in metal cutting operations may result in improved cutting performance, lower energy consumption, lower production costs and lower impact on the environment.  In order to increase the understanding of the tribological behaviour of the coating systems a number of friction and wear tests have been performed and evaluated by post-test microscopy and surface analysis. Much of the work has focused on coating cohesive and adhesive strength, surface fatigue resistance, abrasive wear resistance and friction and wear behaviour under sliding contact and metal cutting conditions.

    The results show that the CVD deposition of accurate crystallographic phases, e.g. α-Al2O3 rather than κ-Al2O3, textures and multilayer structures can increase the wear resistance of Al2O3. However, the characteristics of the interfaces, e.g. topography as well as interfacial porosity, have a strong impact on coating adhesion and consequently on the resulting properties.  Through the deposition of well designed bonding and template layer structures the above problems may be eliminated.

    Also, the presence of macro-particles in PVD coatings may have a significant impact on the interfacial adhesive strength, increasing the tendency to coating spalling and lowering the surface fatigue resistance, as well as increasing the friction in sliding contacts.

    Finally, the CVD-Al2Ocoating topography influences the contact conditions in sliding as well as in metal cutting.

    In summary, the work illuminates the importance of understanding the relationships between deposition process parameters, composition and microstructure, resulting properties and tribological performance of CVD and PVD coatings and how this knowledge can be used to develop the coating materials of tomorrow.

  • 28.
    Fallqvist, Mikael
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    M’Sauobi, R
    Seco Tools.
    Andersson, J
    Seco Tools.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Mechanical and tribological properties of PVD-coated cemented carbide as evaluated by a new multi-pass scratch testing method2012In: Advances in Tribology, ISSN 1687-5915, E-ISSN 1687-5923, no 305209Article in journal (Refereed)
    Abstract [en]

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

  • 29.
    Fallqvist, Mikael
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    The influence of surface defects on the mechanical and tribological properties of VN-based arc-evaporated coatings2013In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 297, no 1-2, 1111-1119 p.Article in journal (Refereed)
    Abstract [en]

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

  • 30.
    Fallqvist, Mikael
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Material Science.
    The role of surface defects on the surface fatigue and tribological characteristics of VxN-PVD coatings in sliding contacts2010In: 14th Nordtrib Conference, Storforsen, 2010Conference paper (Other academic)
    Abstract [en]

    The influence of surface defects in arc-evaporated VxN PVD coatings on the adhesion, surface fatigue resistance, friction and wear characteristics has been investigated in a scratching contact using a diamond stylus and a sliding contact using a stainless steel pin. Post-test characterisation using scanning electron microscopy and 3D optical interferometric surface profilometry was performed in order to investigate the mechanical and tribological response of the coatings. The results show that surface defects such as droplets and craters show a strong influence on the tribological behaviour of the coatings causing abrasive wear of the counter surface and material pick-up on the coating surface. In contrast, the influence on the mechanical properties of the coatings, i.e. cracking behaviour, fatigue resistance, etc, was found to be relatively small and cracking seems to be restricted to larger droplets showing a low interfacial bonding to the adjacent coating matrix.

  • 31.
    Fallqvist, Mikael
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Ruppi, S
    Abrasive wear of textured-controlled CVD a-Al2O3 coatings2007In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 202, no 4-7, 837-843 p.Article in journal (Refereed)
    Abstract [en]

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

  • 32.
    Fallqvist, Mikael
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Material Science.
    Ruppi, Sakari
    Abrasive wear of multilayer kappa-Al2O3-Ti(C,N) CVD coatings on cemented carbide2007In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 263, no 1-6, 74-80 p.Article in journal (Refereed)
    Abstract [en]

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

  • 33.
    Fallqvist, Mikael
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Ruppi, S
    Seco Tools.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Ottosson, M
    Uppsala Universitet.
    Grehk, Mikael
    Dalarna University, School of Technology and Business Studies, Materials Technology. Sandvik Materials Technology.
    Nucleation and growth of CVD α-Al2O3on TixOy template2012In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 207, 254-261 p.Article in journal (Refereed)
    Abstract [en]

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

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

  • 34.
    Fallqvist, Mikael
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Schultheiss, F
    Lunds Universitet.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    M’Sauobi, R
    Seco Tools.
    Ståhl, J E
    Lunds Universitet.
    Influence of CVD Al2O3 coated tool surface micro topography on the tribological characteristics in metal cutting: part I2013In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, 87-98 p.Article in journal (Refereed)
    Abstract [en]

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

  • 35.
    Finnkvist Penttinen, Anna
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Nötningsbeständighet av bestrykningsschaber2015Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

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

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

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

    comparable to the pin‐on‐disc application.

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

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

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

    give a better customer service.

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

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

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

    steel ||| in this rapport.

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

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

    the edge of the coating blade.

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

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

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

  • 36.
    Grehk, Mikael
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Engkvist, Josefin
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Bexell, Ulf
    Dalarna University, School of Technology and Business Studies, Material Science.
    Richter, Jan H
    Karlsson, Patrik G
    Sandell, Anders
    Initial stages of metal-organic chemical-vapor deposition of ZrO2 on a FeCrAl alloy2007In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 516, no 6, 875-879 p.Article in journal (Refereed)
    Abstract [en]

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

  • 37.
    Gustafsson, Emil
    Dalarna University, School of Technology and Business Studies, Materials Technology. Luleå tekniska universitet.
    Design and application of experimental methods for steel sheet shearing2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Shearing is the process where sheet metal is mechanically cut between two tools. Various shearing technologies are commonly used in the sheet metal industry, for example, in cut to length lines, slitting lines, end cropping etc. Shearing has speed and cost advantages over competing cutting methods like laser and plasma cutting, but involves large forces on the equipment and large strains in the sheet material. The constant development of sheet metals toward higher strength and formability leads to increased forces on the shearing equipment and tools.

    Shearing of new sheet materials imply new suitable shearing parameters. Investigations of the shearing parameters through live tests in the production are expensive and separate experiments are time consuming and requires specialized equipment. Studies involving a large number of parameters and coupled effects are therefore preferably performed by finite element based simulations. Accurate experimental data is still a prerequisite to validate such simulations. There is, however, a shortage of accurate experimental data to validate such simulations.

    In industrial shearing processes, measured forces are always larger than the actual forces acting on the sheet, due to friction losses. Shearing also generates a force that attempts to separate the two tools with changed shearing conditions through increased clearance between the tools as result. Tool clearance is also the most common shearing parameter to adjust, depending on material grade and sheet thickness, to moderate the required force and to control the final sheared edge geometry.

    In this work, an experimental procedure that provides a stable tool clearance together with accurate measurements of tool forces and tool displacements, was designed, built and evaluated. Important shearing parameters and demands on the experimental set-up were identified in a sensitivity analysis performed with finite element simulations under the assumption of plane strain. With respect to large tool clearance stability and accurate force measurements, a symmetric experiment with two simultaneous shears and internal balancing of forces attempting to separate the tools was constructed.

    Steel sheets of different strength levels were sheared using the above mentioned experimental set-up, with various tool clearances, sheet clamping and rake angles. Results showed that tool penetration before fracture decreased with increased material strength. When one side of the sheet was left unclamped and free to move, the required shearing force decreased but instead the force attempting to separate the two tools increased. Further, the maximum shearing force decreased and the rollover increased with increased tool clearance.

    Digital image correlation was applied to measure strains on the sheet surface. The obtained strain fields, together with a material model, were used to compute the stress state in the sheet. A comparison, up to crack initiation, of these experimental results with corresponding results from finite element simulations in three dimensions and at a plane strain approximation showed that effective strains on the surface are representative also for the bulk material.

    A simple model was successfully applied to calculate the tool forces in shearing with angled tools from forces measured with parallel tools. These results suggest that, with respect to tool forces, a plane strain approximation is valid also at angled tools, at least for small rake angles.

    In general terms, this study provide a stable symmetric experimental set-up with internal balancing of lateral forces, for accurate measurements of tool forces, tool displacements, and sheet deformations, to study the effects of important shearing parameters. The results give further insight to the strain and stress conditions at crack initiation during shearing, and can also be used to validate models of the shearing process.

  • 38.
    Gustafsson, Emil
    Dalarna University, School of Technology and Business Studies, Materials Technology. Luleå tekniska universitet.
    Experiments on Sheet Metal Shearing2013Licentiate thesis, comprehensive summary (Other academic)
  • 39.
    Gustafsson, Emil
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Karlsson, Lars
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Experimental study of forces and energies during shearing of steel sheet with angled tools2016In: International Journal of Mechanical and Materials Engineering, ISSN 2198-2791, Vol. 11, 10Article in journal (Refereed)
    Abstract [en]

    Shearing is a fast and inexpensive method to cut sheet metal that has been used since the beginning of the industrialism. Consequently, published experimental studies of shearing can be found from over a century back in time. Recent studies, however, are due to the availability of low cost digital computation power, mostly based on finite element simulations that guarantees quick results. Still, for validation of models and simulations, accurate experimental data is a requisite. When applicable, 2D models are in general desirable over 3D models because of advantages like low computation time and easy model formulation. Shearing of sheet metal with parallel tools is successfully modelled in 2D with a plane strain approximation, but with angled tools the approximation is less obvious. Therefore, plane strain approximations for shearing with angled tools were evaluated by shear experiments of high accuracy. Tool angle, tool clearance, and clamping of the sheet were varied in the experiments. The results showed that the measured forces in shearing with angled tools can be approximately calculated using force measurements from shearing with parallel tools. Shearing energy was introduced as a quantifiable measure of suitable tool clearance range. The effects of the shearing parameters on forces were in agreement with previous studies. Based on the agreement between calculations and experiments, analysis based on a plane strain assumption is considered applicable for angled tools with a small (up to 2 degrees) rake angle.

  • 40.
    Gustafsson, Emil
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Karlsson, Lars
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Oldenburg, Mats
    Luleå University of Technology.
    Experimental study of strain fields during shearing of medium and high-strength steel sheet2016In: International Journal of Mechanical and Materials Engineering, ISSN 2198-2791, Vol. 11, no 1, 14Article in journal (Refereed)
    Abstract [en]

    There is a shortage of experimentally determined strains during sheet metal shearing. These kinds of data are a requisite to validate shearing models and to simulate the shearing process. In this work, strain fields were continuously measured during shearing of a medium and a high strength steel sheet, using digital image correlation. Preliminary studies based on finite element simulations, suggested that the effective surface strains are a good approximation of the bulk strains below the surface. The experiments were performed in a symmetric set-up with large stiffness and stable tool clearances, using various combinations of tool clearance and clamping configuration. Due to large deformations, strains were measured from images captured in a series of steps from shearing start to final fracture. Both the Cauchy and Hencky strain measures were considered, but the difference between these were found negligible with the number of increments used (about 20 to 50). Force-displacement curves were also determined for the various experimental conditions. The measured strain fields displayed a thin band of large strain between the tool edges. Shearing with two clamps resulted in a symmetric strain band whereas there was an extended area with large strains around the tool at the unclamped side when shearing with one clamp. Furthermore, one or two cracks were visible on most of the samples close to the tool edges well before final fracture. The fracture strain was larger for the medium strength material compared with the high-strength material and increased with increasing clearance.

  • 41.
    Gustafsson, Emil
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Marth, Stefan
    Luleå University of Technology.
    Karlsson, Lars
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Oldenburg, Mats
    Luleå University of Technology.
    Strain and stress conditions at crack initiation during shearing of medium- and high-strength steel sheet2017In: International Journal of Mechanical and Materials Engineering, ISSN 2198-2791, Vol. 12, no 1, 10- p.Article in journal (Refereed)
    Abstract [en]

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

  • 42.
    Gustafsson, Emil
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Oldenburg, Mats
    Jansson, Anders
    Design and validation of a sheet metal shearing experimental procedure2014In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 214, no 11, 2468-2477 p.Article in journal (Refereed)
    Abstract [en]

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

  • 43.
    Gustafsson, Emil
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Oldenburg, Mats
    Jansson, Anders
    Experimental study on the effects of clearance and clamping in steel sheet metal shearing2016In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 229, 172-180 p.Article in journal (Refereed)
    Abstract [en]

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

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

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

  • 45.
    Gyhlesten Back, Jessica
    Dalarna University, School of Technology and Business Studies, Materials Technology. Luleå tekniska universitet, Material- och solidmekanik.
    Modelling and Characterisation of the Martensite Formation in Low Alloyed Carbon Steels2017Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

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

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

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

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

  • 46.
    Gyhlesten Back, Jessica
    Dalarna University, School of Technology and Business Studies, Materials Technology. Luleå tekniska universitet.
    Simplified Implementation of the Koistinen-Marburger Model for Use in Finite Element Simulations2016In: Proceedings of the 11th international congress on thermal stresses, Severino: Edizioni Paguro , 2016, 107-110 p.Conference paper (Other academic)
  • 47.
    Gyhlesten Back, Jessica
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology. Research and Development, SSAB Europe, Borlänge.
    Engberg, Göran
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Investigation of parent austenite grains from martensite structure using EBSD in a wear resistant steel2017In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 10, no 5, 453Article in journal (Refereed)
    Abstract [en]

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

  • 48.
    Gyhlesten Back, Jessica
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology. Luleå tekniska universitet.
    Lindgren, Lars-Erik
    Luleå tekniska universitet, Material- och solidmekanik.
    Influence of prior deformation in austenite on the martensite formation in a low-alloyed carbon steelArticle in journal (Refereed)
  • 49.
    Hall, Josefin
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Beglund, Tomas
    Bexell, Ulf
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Influence of microstructure and hard phase content on the mechanisms of deformation and wear of HIP:ed Stellite® 190 composites2015Conference paper (Refereed)
  • 50.
    Hall, Josefin
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Bexell, Ulf
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Fletcher, J. S.
    Canovic, S.
    Malmberg, Per
    Comparing depth profiling of oxide scale on SOFC interconnect-materials using ToF-SIMS with 69Ga+, Bi3+/Cs+ and C60+/C602+ as primary and sputter ions2015In: Materials at High Temperatures, ISSN 0960-3409, Vol. 32, no 1-2, 133-141 p.Article in journal (Refereed)
    Abstract [en]

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

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