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  • 1.
    Azizoğlu, Yağız
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. Luleå University of Technology.
    Modeling of Cold Pilgering of Tubes2017Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    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.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Gardsback, M.
    Sjoberg, B.
    Lindgren, L. -E
    Finite element modelling of cold pilgering of tubes2015Ingår i: Proceedings of the 8th International Conference on Computational Plasticity - Fundamentals and Applications, COMPLAS 2015, 2015, s. 716-726Konferensbidrag (Refereegranskat)
    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.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. 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 dies2017Konferensbidrag (Refereegranskat)
    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.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. Luleå University of Technology.
    Gärdsback, Mattias
    Sjöberg, Bengt
    Lindgren, Lars-Erik
    Finite element modeling of tube deformation during cold pilgering2016Ingår i: MATEC Web of Conferences, 2016, Vol. 80, artikel-id 15004Konferensbidrag (Refereegranskat)
    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
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Påverkan på mätresultatet av slagprovets läge i slagprovmaskinen2014Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Projektet utgår från att testa om höjden av de mindre slagprovsdimensionerna (10 mm x 7.5 mm, 10 mm x 5 mm och 10 mm x 2.5 mm) har någon betydelse av resultatet samt att korrigera för inre friktion i slagprovsmaskinen. Detta på grund av att företaget nyligen fått ackreditering för den nya provningsstandarden. De olika materialen som testades var både spröda och sega material från företaget och slogs i förbestämda temperaturer. Enligt denna standard kan de mindre provstavarnas resultat påverkas genom att pendeln inte träffar dem i centrum. Därför tillverkas några shims (mellanlägg) som skall höja upp provstavarna så att pendeln träffar provet i centrum. En jämförelse mellan shims och utan shims görs samt hur den inre friktionen från slagmaskinen kan kontrolleras på smidigast och lämpligast sätt. I rapporten framgår hur provstavarna tillverkas och förbereds innan de slås, vilka maskiner samt vilka olika stålsorter som används under detta exjobb. Resultaten från slagen visar att det inte är någon större skillnad med eller utan shims för de olika materialen vid dem förbestämda temperaturerna. Även ett parat t-test görs för att veta om det finns någon signifikant skillnad mellan med och utan shims. Av resultaten från de parade t-testerna visade det sig att vid endast en av alla tester fanns det en signifikant skillnad mellan med och utan shims. Värdena från den inre friktionen visar att den inre friktionen inte varierar speciellt mycket. Hur man kontrollerar den inre friktionen från slagmaskinen på smidigast och lämpligast sätt är att skaffa ett system som gör att arbetarna måste slå tomslag i början på varje skift som sedan kontrollera resultaten och korrigerar resultaten automatisk. Eftersom den centreringspinnen som företaget använder idag centrerar längs kanten på provet måste provstaven vara exakt 55 mm lång. För att få en bättre centrering kan företaget införskaffa en centreringspinne som centrerar via notchen istället. Detta mest för att centreringen inte ska påverka det uppmätta provningsresultatet. De slutsatser som kan dras från resultaten är att för de bestämda temperaturerna spelar det ingen roll om provbitarna slås med eller utan shims även om det fanns ett test som visade signifikant skillnad. Eftersom det handlar om tiondelars joule och företaget redovisar endast i heltal blev skillnaden betydelselös. Den inre friktionen varierar inte så pass mycket att det påverkar resultatet.

  • 6.
    Bengtsson, Sebastian
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Validering av ny laserskärande provberedningsteknik inför materialprovning2016Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Projektets syfte är undersöka vad det är som gör att förlängningsgränsen, Rp02, blir högre för laserskurna dragprovstavar jämfört med manuellt klippta provstavar. Detta fenomen beror troligtvis på upphettningen som fås vid laserskärningen. En undersökning av hur valet av skärparametrar inverkar provkupongens temperatur samt hur skärordningen eventuellt kan hålla temperaturen nere gjordes. Brinellhårdheten för laserskurna och manuellt klippta plattor jämfördes mot varandra och om storleken på de laserskurna plattorna eventuellt behöver ändras. Tyngdpunkten för detta projekt ligger på dragprovstavarna och provkupongerna för mätning av Brinellhårdheten.

    Resultaten visar att det är en skillnad i förlängningsgränsen och brottgränsen mellan de laserskurna och manuellt klippta dragprovstavarna samt att de laserskurna dragprovstavarna har en temperatur på ungefär 120 °C under skärningsprocessen. De olika inställningarna för skärparametrarna resulterar i en lägre brottgräns, Rm, vid de nya inställningarna samt att dragprovstavarna har lättare att fastna kvar i kupongen. I övrigt finns det ingen större skillnad på de mekaniska egenskaperna. Resultatet från hårdhetsprovningen visar att det inte är någon större skillnad mellan de laserskurna och manuellt klippta plattorna. Det visar även att det inte är någon skillnad mellan de olika fräsningsmaskinerna.

    Hårdhetsprofiler gjordes på redan frästa dragprover då tidigare studier visar att den värmepåverkade zonen försvinner efter fräsningen. Detta resultat visar att det inte är någon större skillnad mellan de olika tillverkningsmetoderna och är dock svårt att tolka resultatet eftersom hårdhetsvärdet fås genom att manuellt mäta diagonalerna hos intrycket. Det gör att resultatet kan variera med ungefär ± 5 kg/mm2.

    Mikroskopibilder togs för att undersöka om det sker någon form av strukturförändring under laserskärningsprocessen. Från dessa bilder kan ingen direkt skillnad utläsas. En statistisk undersökning gjordes på alla tester i programmet MINITAB (för att komma fram till en statistisk korrekt slutsats). De slutsatser som kan dras är att ökningen av förlängningsgränsen troligtvis beror på epsilonkarbider och kan minimeras antingen genom en lägre eller högre temperatur i dragprovstavarna vid skärningsprocessen eller genom att tillsätta mer kisel i materialet. Det är ingen skillnad mellan de olika fräsningsmaskinerna vid fräsningen av provkupongerna för Brinellhårdheten eller mellan de laserskurna och manuellt klippta provkupongerna. Det finns eventuellt en kvarvarande värmepåverkad zon hos dragprovstavarna efter fräsningen, dock endast vid ovansidan på provet.

  • 7. Berglund, T.
    et al.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    High velocity compaction of high speed steel powder: possibilities and constraints2007Ingår i: Proceedings of the Euro Powder Metallurgy Congress and Exhibition, Euro PM 2007, 2007, Vol. 3, s. 21-26Konferensbidrag (Refereegranskat)
    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
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Beläggningar till högtemperaturbränsleceller2011Ingår i: Stålforskningsdagarna 2011 / [ed] Joakim Storck, Borlänge: Högskolan Dalarna , 2011, s. 89-99Konferensbidrag (Övrigt vetenskapligt)
    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.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    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 substrate2012Konferensbidrag (Övrigt vetenskapligt)
  • 10.
    Bexell, Ulf
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Time-of-Flight SIMS Characterization of Hydrolysed Organofunctional and Non-Organofunctional Silanes Deposited on Al, Zn and Al-43.4Zn-1.6Si Alloy-Coated Steel2003Ingår i: Surface and Interface Analysis, ISSN 0142-2421, E-ISSN 1096-9918, Vol. 35, nr 11, s. 880-887Artikel i tidskrift (Refereegranskat)
  • 11.
    Bexell, Ulf
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    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 coating2012Ingår i: European Fuel Cell Forum 2012 - Proceedings (memory stick), 2012Konferensbidrag (Övrigt vetenskapligt)
    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.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Lundberg, M.
    High temperature oxidation of plastically deformed ferritic interconnect steel2011Ingår i: ECS Transactions, ISSN 1938-5862, E-ISSN 1938-6737, Vol. 35, nr 1, s. 2463-2470Artikel i tidskrift (Refereegranskat)
    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.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Persson, B
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Blomberg, A
    Effects of semi-isostatic densification of wood on the variation in strength properties with density2005Ingår i: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 39, nr 5, s. 339-350Artikel i tidskrift (Refereegranskat)
    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
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Elastic strain at semi-isostatical compression of Scots pine (pinus sylvestris L.)2005Ingår i: Journal of Wood Science, ISSN 1435-0211, E-ISSN 1611-4663, Vol. 51, nr 4, s. 401-404Artikel i tidskrift (Refereegranskat)
    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
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Härdprocessens inverkan på sprickuppkomst och spricktillväxt vid induktionshärdning av Ovako 495B: Seghärdning i induktionsline2014Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Induktionshärdning är en mycket snabb termisk härdningsprocess som ställer höga krav på utrustningen. Ovako Sweden AB i Hällefors induktionshärdar stålsort 495B och har stora problem med att sprickor initieras och propagerar. Syftet med arbetet är att utreda hur induktionshärdningen påverkar sprickuppkomsten och spricktillväxten i materialet och hitta vilka faktorer som påverkar detta. Det är viktigt att kundens krav på hårdhetsprofilen genom hela tvärsnittet uppfylls. Två olika tester har utförts där målet har varit att hitta ett körsätt som minimerar sprickuppkomst och spricktillväxt. Resultatet av test ett visar att härdtemperaturen kan sänkas från 915 ˚C ner till 870 ˚C. Test två visar att sprickuppkomst och spricktillväxt kan minimeras om kylningen sker med en polymertillsats i kylvattnet istället för rent vatten, dessutom erhålls en jämnare hårdhetsprofil. Utifrån de resultat som presenteras i denna rapport kan fler tester genomföras för att verifiera ett nytt körsätt där sprickuppkomsten minimeras. De två mest kritiska stångdiametrarna har granskats och fokus har lagts på härdtemperatur och kylningshastighet.

  • 16.
    Cederberg, Emil
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Utredning om alternativ kontrollmetod av härdresultat hos martensitiskt rostfritt stål2017Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Morakniv AB är ett företag som tillverkar knivar och isborrsskär. Kvaliteten på materialet och värmebehandlingsprocessen är en viktig del då produkterna används i miljöer där kravet på prestanda är viktigt. För att kunna verifiera kvaliteten ytterligare, i tillägg till den ordinarie hårdhetsprovningen, ville man undersöka en alternativ provningsmetod.

    I försöken ingick ett material som skulle värmebehandlas på fyra olika sätt för att kunna utvärdera den mekaniska provningen. De härdades från två olika austenitiseringstemperaturer med två olika kylhastigheter. Härdningen skedde i en så kallad bandugn där proven matas in kontinuerligt, värms upp och kyls i luft. Efter kylningen genomfördes en sub-zero-behandling följt av anlöpning. Resultatet utvärderades sedan genom böjprovning, hårdhetsmätning och optisk mikroskopi.

    Resultatet visade att en härdtemperatur vid

    T+10 °C gav en större standardavvikelse och högre duktilitet jämfört med de prov härdade från T-normal, med avseende på den maximala nedböjningen. Sänkt kylhastighet tenderade att minska den maximala nedböjningen och minska standardavvikelsen. Värdena från hårdhetsprovningen varierade inte nämnvärt mellan provserierna och standardavvikelsen mellan dessa ansågs vara försumbar. Bilderna från mikroskopin visade inte någon konkret strukturändring vid jämförelse mellan de olika värmebehandlingsparametrarna.

  • 17.
    Ceron, Ermanno
    et al.
    Technical University of Denmark.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    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 lubricants2014Ingår i: Advanced Materials Research, ISSN 1022-6680, E-ISSN 1662-8985, Vol. 966-967, s. 219-227Artikel i tidskrift (Refereegranskat)
    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
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Ink-Jet Printing of Color Optical Filters for LCD Applications2006Självständigt arbete på grundnivå (kandidatexamen)Studentuppsats (Examensarbete)
    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
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Jämförelse av restaustenit i ett härdat verktygsstål för varmarbetsapplikationer: martensitisk och baintisk mikrostruktur2014Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Detta examensarbete har utförts på Uddeholms AB i Hagfors. Prover och mätningar har gjorts på verktygsstålet Uddeholm Dievar. Dievar är ett varmarbetsstål som är bäst lämpat för stora verktyg

    Restaustenit finns alltid i härdat högt legerat stål. Den sägs sönderfalla till cementit och ferrit under anlöpning. Sönderfallsprodukten påverkar slagsegheten på ett negativt sätt. En försämrad slagseghet ökar risken för sprickbildning. Genom att minimera restaustenithalten med hjälp av korrekt austenitiseringstemperatur gynnas stålets egenskaper. Proverna som använts har olika austenitiseringstemperaturer och skillnader i svalningstid, en snabb kylning samt en långsam kylning. Den långsamma motsvarar kylningen i kärnan för ett stort verktyg. Jämförelse av strukturer har utförts i svepelektronmikroskop (SEM).  För kartläggning av faser har försök gjorts i SEM, med en EBSD-detektor. Slagseghetsvärden har kopplats samman med restaustenithalt för att på så vis se hur slagsegheten ändras med avseende på restaustenithalten.  Arbetet visar hur austenitiseringstemperatur och svalningstid påverkar restaustenithalten samt hur halten påverkar slagsegheten när den sönderfaller vid anlöpning.

    Mikrostrukturen varierar beroende på vilken austenitiseringstemperatur som används. Några slutsatser som kan dras utifrån denna rapport är att restaustenithalten blir högre i det bainitiska provet med lägre autenitiseringstemperatur men lägre i det martensitiska med samma temperatur. Vid sammanställningen av slagseghetsprovningen framgick att det prov med högst restaustenithalt före anlöpning var det prov som hade sämst slagseghet vid Charpy-V provning.

  • 20.
    Engberg, Göran
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Constitutive models, physically based models for plasticity2014Ingår i: Encyclopedia of Thermal Stresses / [ed] Hetnarski RB, Dordrecht, Heidelberg, New York, London: Springer, 2014, s. 649-662Kapitel i bok, del av antologi (Refereegranskat)
    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.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Kero, Ida
    Yvell, Karin
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Modeling microstructure development during hot working of an austenitic stainless steel2013Ingår i: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 753, s. 423-426Artikel i tidskrift (Refereegranskat)
    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.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Canovic, S.
    Liu, F.
    Gotlind, H.
    Svensson, J. -E
    Johansson, L. -G
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Halvarsson, M.
    Oxidation of FeCrAl foils at 500-900 degrees C in dry O2 and O2 with 40% H2O2009Ingår i: Materials at High Temperature, ISSN 0960-3409, E-ISSN 1878-6413, Vol. 26, nr 2, s. 199-210Artikel i tidskrift (Refereegranskat)
    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.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap. Chalmers University of Technology, Göteborg, Sweden.
    Israelsson, Niklas
    Chalmers University of Technology, Göteborg, Sweden.
    Bexell, Ulf
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    The initial effect of KCl deposit on alumina scales characterized by ToF-SIMS and AES2013Ingår i: Surface and Interface Analysis, ISSN 0142-2421, E-ISSN 1096-9918, Vol. 45, nr 1, s. 445-448Artikel i tidskrift (Refereegranskat)
    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
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Kiselhaltens inverkan på slagsegheten hos Charpy-V och oanvisad slagseghetsprovning: Slagseghetsprovning vid rumstemperatur, godstjocklek 150 mm2014Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Examensarbetet bygger på en undersökning av två segjärn med olika kiselhalt. Undersökningen ska ge en djupare förståelse om hur resultaten från slagprovning av de två materialtyperna skiljer sig från varandra, och hur väl de båda provstavstyperna kan spegla den ändring i mikrostrukturen som borde bli resultatet av varierad kiselhalt. Ett gjutgods av trappliknade form har gjutits för de båda segjärnen. Med en kärnborr borrades provstavar ut från två godstjocklekar och bearbetades. Dessa prover blev till hälften vardera Charpy-V och oanvisade provstavar. Provstavarna delades in i åtta provserier. Proverna användes till slagprovning och data sammanställdes.  Strukturundersökningar har gjorts i svepelektronmikroskop, SEM och ljusmikroskop, LOM och hårdhetsprovning genom mikrovikers. Materialen skiljer sig på så sätt att materialet med det med lägre kiselhalt innehåller mer grafitmoduler, har högre slagseghetsvärden och är mjukare än högkiselmaterialet. Detta beror på att perliten har en kraftigare påverkan på slagseghet i EN-GJS-400-18. Dessutom har EN-GJS-400-18 grövre grafitpartiklar. Då både perliten och grafiten riskerar att ha en något ojämn fördelning i grundmassan kommer spridningen vid slagseghetsprovningen att sprida relativt mycket. Vad gäller den lägre slagsegheten hos EN-GJS-500-14 så kan den förmodligen förklaras av den högre hårdheten i grundmassan till följd av kislets lösningshärdande effekt på grundmassan. Den högre hårdheten påverkar slagsegheten negativt.

  • 25.
    Eriksson, Jenny
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Tribological testing of commercial CrN, (Ti,Al)N and CrC/C PVD coatings: evaluation of galling and wear characteristics against different high strength steels2011Ingår i: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 205, nr 16, s. 4045-4051Artikel i tidskrift (Refereegranskat)
    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
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    HÄRDBARHET HOS BORSTÅL – INVERKAN AVBORFÖRSPRÖDNING2017Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    En komponent av härdat och anlöpt borstål som uppvisat

    interkristallint restbrott och oönskat låg utmattningshållfasthet har studerats.

    Misstankar fanns att komponenten försprödats genom utskiljning av borpartiklar i

    materialets korngränser. Denna misstanke är grunden till arbetet. Som referens har

    en likadan komponent studerats med skillnaden att denna visat god

    utmattningshållfasthet och problemfri användning. För att förstå orsaken bakom de

    skiftande egenskaperna har de båda komponenterna undersökts i detalj.

    Provstavar har slagits av

    in-situ i vakuum i ett Augerelektronmikroskop (AES) för

    att undersöka brottytan med minimerade möjligheter för denna att oxidera. Vid

    AES-analysen fann man bornitrider i korngränserna samt kalcium- och

    manganpartiklar från stålframställningen i båda proverna. Brottytorna bestod i

    båda fallen av duktila och spröda områden där fosfor och kol förekom på alla

    interkristallina brottytor som undersöktes.

    Brottytorna samt polerade och etsade tvärsnitt av proverna har studerats i ett

    svepelektronmikroskop (SEM), det senare för att bestämma mikrostrukturen.

    Studien av tvärsnitten kombinerat med mikrohårdhetsmätning visade att provet

    med sämst utmattningsegenskaper innehåller en större mängd av en mjukare fas.

    Då både proverna innehåller stora mängder defekter var problemet inte kopplat till

    borförsprödning i sig även om en minimering av dessa och andra partiklar höjer

    komponentens kvalitet. Orsaken finns istället i den större andelen mjukare fas som

    det sämre provet innehåller. Fasen tros vara restaustenit eller ferrit. De båda

    faserna kan uppkomma genom felaktig värmebehandling men vid olika avvikande

    processparametrar. Ett jominytest visade att komponenternas härdbarhet är lika,

    detta tyder på att värmebehandlingen för dem varit annorlunda i tillverkningen.

  • 27.
    Fallqvist, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Microstructural, Mechanical and Tribological Characterisation of CVD and PVD Coatings for Metal Cutting Applications2012Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    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.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    M’Sauobi, R
    Seco Tools.
    Andersson, J
    Seco Tools.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Mechanical and tribological properties of PVD-coated cemented carbide as evaluated by a new multi-pass scratch testing method2012Ingår i: Advances in Tribology, ISSN 1687-5915, E-ISSN 1687-5923, nr 305209Artikel i tidskrift (Refereegranskat)
    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.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    The influence of surface defects on the mechanical and tribological properties of VN-based arc-evaporated coatings2013Ingår i: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 297, nr 1-2, s. 1111-1119Artikel i tidskrift (Refereegranskat)
    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.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    The role of surface defects on the surface fatigue and tribological characteristics of VxN-PVD coatings in sliding contacts2010Ingår i: 14th Nordtrib Conference, Storforsen, 2010Konferensbidrag (Övrigt vetenskapligt)
    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.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Ruppi, S
    Abrasive wear of textured-controlled CVD a-Al2O3 coatings2007Ingår i: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 202, nr 4-7, s. 837-843Artikel i tidskrift (Refereegranskat)
    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.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Ruppi, Sakari
    Abrasive wear of multilayer kappa-Al2O3-Ti(C,N) CVD coatings on cemented carbide2007Ingår i: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 263, nr 1-6, s. 74-80Artikel i tidskrift (Refereegranskat)
    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.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Ruppi, S
    Seco Tools.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Ottosson, M
    Uppsala Universitet.
    Grehk, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. Sandvik Materials Technology.
    Nucleation and growth of CVD α-Al2O3on TixOy template2012Ingår i: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 207, s. 254-261Artikel i tidskrift (Refereegranskat)
    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.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Schultheiss, F
    Lunds Universitet.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    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 I2013Ingår i: Wear, ISSN 0043-1648, E-ISSN 1873-2577, s. 87-98Artikel i tidskrift (Refereegranskat)
    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. Fazakas, E.
    et al.
    Heczel, A.
    Molnar, David
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Varga, B.
    Zadorozhnyy, V.
    Vida, A.
    Comparative microstructural and corrosion development of VCrNiCoFeCu equiatomic multicomponent alloy produced by induction melting and spark plasma sintering2018Ingår i: IOP Conference Series: Materials Science and Engineering, 2018, Vol. 329, nr 1, artikel-id 012016Konferensbidrag (Refereegranskat)
    Abstract [en]

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

  • 36.
    Finnkvist Penttinen, Anna
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Nötningsbeständighet av bestrykningsschaber2015Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    En studie om vad för slags nötningar Böhler‐Uddeholms stålschabrar utsätts för vid

    slutanvändning. Företagets egen testapplikation för nötning skulle kunna bestämma

    nötningsbeständigheten hos stålet och jämföras mot pinne/skiva applikationen.

    Detta för att möjligen kunna få ett standardiserat sätt att mäta slitaget hos de olika

    schaberstålen med den idag tillgängliga apparaturen.

    Om man skulle lyckas finna ett sätt kommer detta leda till att man kan ge kunder

    med mer information kring bladen och få en bättre kundservice.

    Två slutanvända schabrar användes för att fastställa den nötning som skett.

    För undersökningen mellan Böhler‐Uddeholms testmetod och pinne/skiva används

    tre olika stålsorter: Stål |, Stål || och Stål |||.

    Den slutgiltiga nötningen som skett var trekroppars abrasion och korrosiv nötning.

    Det hade även, på grund av den basiska bestrykningsmassan, uppkommit en

    vidhäftande kant längst med eggen på schabret.

    Apparaturen på företaget är i dagsläget inte helt optimal för att kunna efterlikna den

    verkliga nötning som sker, och pinne/skiva ger en för hård abrasiv nötning än vad

    som egentligen sker på schabrena i deras användningsområden.

  • 37.
    Grehk, Mikael
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Engkvist, Josefin
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Bexell, Ulf
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Richter, Jan H
    Karlsson, Patrik G
    Sandell, Anders
    Initial stages of metal-organic chemical-vapor deposition of ZrO2 on a FeCrAl alloy2007Ingår i: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 516, nr 6, s. 875-879Artikel i tidskrift (Refereegranskat)
    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.

  • 38.
    Gustafsson, Emil
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. Luleå tekniska universitet.
    Design and application of experimental methods for steel sheet shearing2016Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    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.

  • 39.
    Gustafsson, Emil
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. Luleå tekniska universitet.
    Experiments on Sheet Metal Shearing2013Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
  • 40.
    Gustafsson, Emil
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Karlsson, Lars
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Experimental study of forces and energies during shearing of steel sheet with angled tools2016Ingår i: International Journal of Mechanical and Materials Engineering, ISSN 2198-2791, Vol. 11, artikel-id 10Artikel i tidskrift (Refereegranskat)
    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.

  • 41.
    Gustafsson, Emil
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Karlsson, Lars
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Oldenburg, Mats
    Luleå University of Technology.
    Experimental study of strain fields during shearing of medium and high-strength steel sheet2016Ingår i: International Journal of Mechanical and Materials Engineering, ISSN 2198-2791, Vol. 11, nr 1, artikel-id 14Artikel i tidskrift (Refereegranskat)
    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.

  • 42.
    Gustafsson, Emil
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Marth, Stefan
    Luleå University of Technology.
    Karlsson, Lars
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Oldenburg, Mats
    Luleå University of Technology.
    Strain and stress conditions at crack initiation during shearing of medium- and high-strength steel sheet2017Ingår i: International Journal of Mechanical and Materials Engineering, ISSN 2198-2791, Vol. 12, nr 1, s. 10-Artikel i tidskrift (Refereegranskat)
    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.

  • 43.
    Gustafsson, Emil
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Oldenburg, Mats
    Jansson, Anders
    Design and validation of a sheet metal shearing experimental procedure2014Ingår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 214, nr 11, s. 2468-2477Artikel i tidskrift (Refereegranskat)
    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%.

  • 44.
    Gustafsson, Emil
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Oldenburg, Mats
    Jansson, Anders
    Experimental study on the effects of clearance and clamping in steel sheet metal shearing2016Ingår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 229, s. 172-180Artikel i tidskrift (Refereegranskat)
    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.

  • 45. Gustavsson, Fredrik
    et al.
    Svahn, Fredrik
    Bexell, Ulf
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Jacobson, Staffan
    Nanoparticle based and sputtered WS2 low-friction coatings: differences and similarities with respect to friction mechanisms and tribofilm formation2013Ingår i: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 232, s. 616-626Artikel i tidskrift (Refereegranskat)
    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.

  • 46.
    Gyhlesten Back, Jessica
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. Luleå tekniska universitet, Material- och solidmekanik.
    Modelling and Characterisation of the Martensite Formation in Low Alloyed Carbon Steels2017Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    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.

  • 47.
    Gyhlesten Back, Jessica
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. Luleå tekniska universitet.
    Simplified Implementation of the Koistinen-Marburger Model for Use in Finite Element Simulations2016Ingår i: Proceedings of the 11th international congress on thermal stresses, Severino: Edizioni Paguro , 2016, s. 107-110Konferensbidrag (Övrigt vetenskapligt)
  • 48.
    Gyhlesten Back, Jessica
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. Research and Development, SSAB Europe, Borlänge.
    Engberg, Göran
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Investigation of parent austenite grains from martensite structure using EBSD in a wear resistant steel2017Ingår i: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 10, nr 5, artikel-id 453Artikel i tidskrift (Refereegranskat)
    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.

  • 49.
    Gyhlesten Back, Jessica
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Lindgren, Lars-Erik
    Luleås tekniska universitet.
    Modelling of the Influence of Prior Deformation of Austenite on the Martensite Formation in a Low-Alloyed Carbon Steel2018Ingår i: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 941, s. 95-99Artikel i tidskrift (Refereegranskat)
  • 50. Habainy, J.
    et al.
    Iyengar, S.
    Surreddi, Kumar Babu
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Lee, Y.
    Dai, Y.
    Formation of oxide layers on tungsten at low oxygen partial pressures2018Ingår i: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 506, nr SI, s. 26-34Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This work focuses on the oxidation of tungsten in inert gas atmospheres containing oxygen and moisture. It is particularly relevant for the European Spallation Source where the tungsten target is cooled by purified helium gas and the 5 MW proton beam can raise the maximum target temperature beyond the threshold for oxidation. Tungsten discs were oxidized isothermally at 400° to 900 °C for 2 h in pure helium and helium mixed with oxygen and water vapor, with varying partial pressures up to 500 Pa. Tungsten was oxidized even with a small amount of oxygen (≤5 ppm) present in industrially pure helium. Non-isothermal oxidation of tungsten foils was carried out in water vapor (∼100 Pa), in situ in an environmental scanning electron microscope. On specimens oxidized in inert gas containing water vapor (2 h, pH2O" role="presentation" style="box-sizing: border-box; margin: 0px; padding: 0px; display: inline-block; line-height: normal; font-size: 14.4px; word-spacing: normal; word-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; position: relative;">pH2O ∼790 Pa), Auger electron spectroscopy studies confirmed the presence of a thin oxide layer (40 nm) at 400 °C. At 500 °C the oxide layer was 10 times thicker. A dark, thin and adherent oxide layer was observed below 600 °C. Above this temperature, the growth rate increased substantially and the oxide layer was greenish, thick and porous. Oxide layers with varying stoichiometry were observed, ranging from WO3 at the surface to WO2 at the metal-oxide interface. For comparison, oxidation of tungsten alloysin He-5%O2 was studied. The implications of this work on the design and operation of the helium loop for cooling the target are discussed.

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