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  • 1.
    Adegoke, Olutayo
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Homogenization of Precipitation Hardening Nickel Based Superalloys2012Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Allvac 718 Plus and Haynes 282 are relatively new precipitation hardening nickel based superalloys with good high temperature mechanical properties. In addition, the weldability of these superalloys enhances easy fabrication. The combination of high temperature capabilities and superior weldability is unmatched by other precipitation hardening superalloys and linked to the amount of the γ’ hardening precipitates in the materials. Hence, it is these properties that make Allvac 718 Plus and Haynes 282 desirable in the manufacture of hot sections of aero engine components.

    Studies show that cast products are less weldable than wrought products. Segregation of elements in the cast results in inhomogeneous composition which consequently diminishes weldability. Segregation during solidification of the cast products results in dendritic microstructure with the segregating elements occupying interdendritic regions. These segregating elements are trapped in secondary phases present alongside γ matrix. Studies show that in Allvac 718Plus, the segregating phase is Laves while in Haynes 282 the segregating phase is not yet fully determined.

    Thus, the present study investigated the effects of homogenization heat treatments in eliminating segregation in cast Allvac 718 Plus and Haynes 282. Paramount to the study was the effect of different homogenization temperatures and dwell time in the removal of the segregating phases. Experimental methods used to both qualify and quantify the segregating phases included SEM, EDX analysis, manual point count and macro Vickers hardness tests.

    Main results show that there is a reduction in the segregating phases in both materials as homogenization proceeds hence a disappearance of the dendritic structure. In Allvac 718 Plus, plate like structures is observed to be closely associated with the Laves phase at low temperatures and dwell times. In addition, Nb is found to be segregating in the interdendritic areas. The expected trend of increase in Laves as a result of the dissolution of the plate like structures at the initial stage of homogenization is only detectable for few cases. In Haynes 282, white and grey phases are clearly distinguished and Mo is observed to be segregating in interdendritic areas.

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  • 2.
    Andersson, Joel Håkan
    et al.
    GKN Aerospace Engine Systems, Trollhätten, SE-46181, Sweden; Department of Engineering Science, University West, Trollhätten, SE-46186, Sweden.
    Raza, Shahzad
    Department of Materials Science and Engineering, Royal Institute of Technology, SE-10044, Stockholm, Sweden.
    Eliasson, Anders
    Department of Materials Science and Engineering, Royal Institute of Technology, SE-10044, Stockholm, Sweden.
    Surreddi, Kumar Babu
    Chalmers University of Technology, Gothenburg.
    Solidification of Alloy 718, ATI 718Plus® and Waspaloy2014Ingår i: 8th International Symposium on Superalloy 718 and Derivatives 2014, 2014, s. 181-192Konferensbidrag (Refereegranskat)
    Abstract [en]

    Alloy 718, ATI 718Plus® and Waspaloy have been investigated in terms of what their respective solidification process reveals. Differential thermal analysis was used to approach the task together with secondary electron and back scattered electron detectors equipped with an energy dispersive X-ray spectroscopy detector. These experimental methods were used to construct pseudo binary phase diagrams that could aid in explaining solidification as well as liquation mechanisms in processes such as welding and casting. Furthermore, it was seen that Waspaloy has the smallest solidification range, followed by Alloy 718, and finally ATI 718Plus® possessing the largest solidification interval in comparison.

  • 3. Arzpeyma, N.
    et al.
    Alam, Moudud
    Högskolan Dalarna, Institutionen för information och teknik, Statistik.
    Gyllenram, R.
    Jönsson, P. G.
    Model development to study uncertainties in electric arc furnace plants to improve their economic and environmental performance2021Ingår i: Metals, ISSN 2075-4701, Vol. 11, nr 6, artikel-id 892Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A statistical model is developed in order to simulate the melt composition in electric arc furnaces (EAFs) with respect to uncertainties in 1) scrap composition, 2) scrap weighing and 3) element distribution factors. The tramp element Cu and alloying element Cr are taken into account. The model enables simulations of a charge program as well as backwards estimations of the element concentrations and their variance in scrap. In the backwards calculation, the maximum likelihood method is solved by considering three cases corresponding to the involved uncertainties. It is shown that the model can estimate standard deviations for elements so that the real values lie within the estimated 95% confidence interval. Moreover, the results of the model application in each target product show that the estimated scrap composition results in a melt composition, which is in good agreement with the measured one. The model can be applied to increase our understanding of scrap chemical composition and lower the charged material cost and carbon footprint of the products. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.

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  • 4.
    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.

  • 5.
    Azizoğlu, Yağız
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. Luleå University of Technology.
    Gärdsback, M.
    Yamanaka, A.
    Kuwabara, T.
    Lindgren, L. -E
    Work hardening during alternating load directions of 316L SS2018Ingår i: Procedia Manufacturing, E-ISSN 2351-9789, Vol. 15, s. 1777-1784Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Understanding and modelling the plastic behavior of a material are essential for simulation and design of metal forming processes. Cold pilgering of tubes is a process with very complex strain history with alternating loading direction. This makes evaluation of the work hardening challenging. Cold deformation applied in a single direction predominantly exhibit work hardening, while changes of the loading direction may even cause softening in other directions. The influence of alternating loading directions on work hardening has been experimentally investigated for 316L stainless steel (SS). Cubic specimens were cut out from the preform of the tube. The specimens are subjected to uniaxial compressions in alternating directions along two perpendicular axes. From the results, a cyclic elastic-plastic constitutive model based on a Chaboche-type approach is calibrated and implemented in the commercial finite element code MSC.Marc.

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  • 6.
    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.

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  • 7. Bejjani, Roland
    et al.
    Salame, Charlie
    Olsson, Mikael
    Högskolan Dalarna, Institutionen för information och teknik, Materialteknik.
    An Experimental and Finite Element Approach for a Better Understanding of Ti-6Al-4V Behavior When Machining under Cryogenic Environment2021Ingår i: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 14, nr 11, artikel-id 2796Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Due to increasing demand in manufacturing industries, process optimization has become a major area of focus for researchers. This research optimizes the cryogenic machining of aerospace titanium alloy Ti-6Al-4V for industrial applications by studying the effect of varying the nozzle position using two parameters: the nozzle's separation distance from the tool-chip interface and its inclination angle with respect to the tool rake face. A finite element model (FEM) and computational fluid dynamics (CFD) model are used to simulate the cryogenic impingement of cryogenic carbon dioxide on the tool-workpiece geometry. Experiments are conducted to evaluate cutting forces, tool wear, and surface roughness of the workpiece, and the results are related to the CFD and FEM analyses. The nozzle location is shown to have a significant impact on the cutting temperatures and forces, reducing them by up to 45% and 46%, respectively, while the dominant parameter affecting the results is shown to be the separation distance. Cryogenic machining is shown to decrease adhesion-diffusion wear as well as macroscopic brittle chipping of the cutting insert compared to dry turning, while the workpiece surface roughness is found to decrease by 44% in the case of cryogenic machining.

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  • 8.
    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.

  • 9.
    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.

  • 10. Berger, Robert
    et al.
    Bexell, Ulf
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Grehk, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Hörnström, Sven Erik
    A comparative study of the corrosion protective properties of chromium and chromium free passivation methods2007Ingår i: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 202, nr 2, s. 391-397Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Commercially available passivation methods for white-rust protection of hot-dip galvanized steel have been investigated. The passivations were either based on trivalent chromium or chromium free. A chromate based conversion coating was used for reference. The treated panels were tested with regard to white rust protection and paintability. The surface chemistry of the conversion coatings was monitored with scanning Auger electron spectroscopy and X-ray photoelectron spectroscopy. Coating thicknesses were measured using Auger electron sputter depth profiling. The passivations were applied with a thickness recommended by the supplier and thus showed large variation. The thickness of the chromium free passivation (Cr-free) is approximately 75 nm. The coating contains the active ions; H3O+, Ti4+, Mn2+, Zn2+, PO4 3-. The passivation based on trivalent chromium (Cr-III) is approximately 30 nm thick and contains the active ions; H3O+ Cr3+, PO4 3-, F. The chromate based passivation (Cr- VI) is approximately 5 nm thick and contains the active ions Cr6+/Cr3+, F-. The Cr-free and the Cr-III passivations showed similar white rust protection in the corrosion tests. The corrosion resistance was good although it did not fully reach the level of the Cr-VI passivation. The results from the tests of the painted panels showed that the powder paint worked well on all three passivations. The solvent born paint worked best on the passivation based on trivalent chromium. The water born paint showed poor resistance to blistering in the Cleveland humidity test for all three passivations. In this test the passivation with hexavalent chromium showed slightly better results than the chromate free passivations.

  • 11.
    Berger, Robert
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Bexell, Ulf
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Stavlid, N.
    Grehk, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    The influence of alkali-degreasing on the chemical composition of hot-dip galvanized steel surfaces2006Ingår i: Surface and Interface Analysis, ISSN 0142-2421, E-ISSN 1096-9918, Vol. 38, nr 7, s. 1130-1138Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The influence of dipping temperature and time on the surface chemistry of hot-dipped galvanized steel sheets during the alkaline degreasing process is investigated. The surface chemistry was monitored with scanning Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), and time-of-flight secondary ion mass spectroscopy (ToF-SIMS). The results show high Al concentrations on the untreated surfaces, which are significantly reduced during alkaline degreasing. The same conclusions could be drawn for the carbon compounds that accumulate on the surface during storage. The measurements reveal a gradual reduction in surface Al as the alkali solution temperature and/or degreasing time are increased. When degreasing was conducted at 70 °C for 30 s the surface was practically free from Al, which was present only in small islands. Furthermore, the experiments showed that the thickness of the oxide film covering the surfaces before and after alkaline degreasing is approximately 20 Å. The main constituents of the film varied from ZnAl hydroxide/oxide to Zn hydroxide/oxide, before and after degreasing, respectively. 

  • 12. 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.

  • 13.
    Berglund, Tomas
    et al.
    Sandvik Powder Solutions.
    Hall, Josefine
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Wear of PM HIP Metal Matrix Composites - Influence of Carbide Type2019Ingår i: HOT ISOSTATIC PRESSING, HIP' 17 / [ed] Dayal, P Triani, G, MATERIALS RESEARCH FORUM LLC , 2019, s. 142-148Konferensbidrag (Refereegranskat)
    Abstract [en]

    The type of hard phase in combination with matrix material has a great influence on the wear properties of PM HIP Metal Matrix Composites. The hardness and toughness of the hard phase as well as its reaction with the matrix in combination with wear mechanism can cause significant differences in performance of the material. Three materials with the same matrix alloy but different carbide types have been studied with regards to tribological behavior in low stress and high stress abrasion as well as scratch testing against a quartz stylus. In low stress abrasion testing the materials has only very small differences in the performance between the materials. The materials containing crushed or spherical fused tungsten carbide had a higher initial wear rate compared to the material with macrocrystalline carbide. This can be explained by the higher degree of carbide dissolution in these materials. In the later stages of wear the three materials have similar performance. In the scratch testing a clear difference can be observed between the materials. The material containing the fused tungsten carbide exhibits a higher degree of carbide damage at the exit side of the wear scar sliding over the carbide. This can be attributed to the much higher degree of carbide dissolution in the fused carbide compared to the MC carbide. The results from tribology testing are discussed and compared to wear mechanisms observed in parts that have been in service in a slurry pump and a crusher.

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  • 14. Bergström, Yngve
    et al.
    Granbom, Ylva
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Sterkenburg, Dirk
    A dislocation based theory for the deformation hardening behavior of DP steels: Impact of martensite content and ferrite grain size2010Ingår i: Journal of Metallurgy, ISSN 1687-9465Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A dislocation model, accurately describing the uniaxial plastic stress-strain behavior of dual phase (DP) steels, is proposed and the impact of martensite content and ferrite grain size in four commercially produced DP steels is analyzed. It is assumed that the plastic deformation process is localized to the ferrite. This is taken into account by introducing a non-homogeneity parameter, f(e), that specifies the volume fraction of ferrite taking active part in the plastic deformation process. It is found that the larger the martensite content the smaller the initial volume fraction of active ferrite which yields a higher initial deformation hardening rate. This explains the high energy absorbing capacity of DP steels with high volume fractions of martensite. Further, the effect of ferrite grain size strengthening in DP steels is important. The flow stress grain size sensitivity for DP steels is observed to be 7 times larger than that for single phase ferrite.

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  • 15.
    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.

  • 16.
    Bexell, Ulf
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Berger, Robert
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Grehk, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Sundell, Per-Erik
    Johansson, Mats
    Bonding of vegetable oils to mercapto silane treated metal surfaces: surface engineering on the nano scale2006Ingår i: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 515, nr 2, s. 838-841Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper the bonding of thin vegetable oil films on mercapto silane treated aluminium surfaces has been studied. The silane molecules are attached to the surface by metal–oxygen–silicon bonds. The coupling between the unsaturated bonds of the vegetable oil and the thiol functionalised surface was obtained through a photoinduced thiol-ene reaction. The surfaces were characterised by X-ray photoelectron spectroscopy (XPS). Vegetable oil contains both saturated and unsaturated carbon chains. For the reactions investigated in this study it is the unsaturated carbon chains that can react by a thiol-ene reaction and the results indicate that it is possible to attach a vegetable oil to a metal surface pre-treated with a thiol functionalised silane.

  • 17.
    Bexell, Ulf
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Grehk, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    A corrosion study of hot-dip galvanized steel sheet pre-treated with gamma-mercaptopropyltrimethoxysilane2007Ingår i: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 201, nr 8, s. 4734-4742Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In the present work an organofunctional silane, gamma-mercaptopropyltrimethoxysilane (gamma-MPS), has been deposited on hot-dip galvanized cold rolled steel from different silane solution concentrations. Painted and unpainted silane treated samples were corrosion tested and painted samples were adhesion tested. The surface chemistry of the unpainted silane treated samples was investigated with AES, ToF-SIMS and EDS and the surface morphology was studied with SEM. The results show that the silane film thickness is dependent on the silane concentration in the silane solution and a higher silane concentration gives a thicker film. Moreover, thicker films tend to give films with a pronounced crack pattern and even detachment of film debris. Corrosion tests of unpainted samples show that gamma-MPS can not work as a passivation treatment but gives a very good adhesion to the paint

  • 18.
    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)
  • 19.
    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.

  • 20.
    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.

  • 21.
    Bexell, Ulf
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Stanciu, V.
    Warnicke, P.
    Östh, M.
    Svedlindh, P.
    ToF-SIMS depth profiling of (Ga,Mn)As capped with amorphous arsenic: effects of annealing time2006Ingår i: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 252, nr 19, s. 7252-7254Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The influence of annealing time on an amorphous As cap layer and the depth distribution of Mn atoms have been investigated. The results show that a 1600 Å thick As cap layer is completely desorbed after 3 h of annealing time. The depth distributions of Mn indicate that interstitial Mn atoms have diffused to the outer surface and being passivated. The thickness of the Mn passivation layer was around 90 Å.

  • 22.
    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.

  • 23. Blomberg, Jonas
    et al.
    Persson, Bengt
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Bexell, Ulf
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Effects of semi-isostatic densification on anatomy and cell-shape recovery on soaking2006Ingår i: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 60, nr 3, s. 322-331Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Images obtained by scanning electron microscopy (SEM) helped to clarify the question as to how anatomy influences the deformation on compression and the spring-back of densified wood on water soaking. Transverse sections of Norway spruce (Picea abies), Scots pine (Pinus sylvestris), black alder (Alnus glutinosa), Swedish aspen (Populus tremula), European birch (Betula pubescens), European beech (Fagus sylvatica) and pedunculate oak (Quercus robur) were studied. Wood is reinforced with rays in the radial direction and with dense latewood in the tangential direction. When strained radially, rays buckle or tilt tangentially. Softwoods were mainly compressed radially, owing to low number of rays and since latewood is much denser than earlywood. The diffuse-porous hardwoods with low density variation between latewood and earlywood were mainly deformed tangentially, except birch, which has high density at the annual ring border and is mainly compressed radially. The ring-porous hardwoods were relatively equally deformed in the radial and tangential directions because of the high number of rays and high latewood density. Moisture-induced spring-back (shape recovery) was proportional to the degree of compression. Rays remained deformed, which also influenced the surrounding wood. Longitudinal wood cells almost resumed their original shape. Wood with low density and a low degree of compression showed the highest structural recovery. Shearing deformation was particularly pronounced and permanent in woods with high strength anisotropy. Thin-walled and sheared cells, such as earlywood in softwood, tended to crack on compression. Cracks usually stopped at the middle lamella and had a lesser influence on strength properties than for lumen-to-lumen cracks.

  • 24. Borgström, Henrik
    et al.
    Harlin, Peter
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Paiar, Tomaso
    Wang, Yu
    Nyborg, Lars
    Possibilities and constraints of implementing starch consolidated high speed steel in prototyping2008Ingår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 475, nr 1-2, s. 34-38Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In the starch consolidation (SC) process, a water-based slurry containing powder, starch, dispersant and thickener is used to fabricate near net-shape green bodies that are de-binded and further consolidated by sintering. In this study, gas atomized M3/2 as well as high and low carbon V-rich M4 type high speed steel powder (<150 mu m) are considered, Both material types undergo high volumetric shrinkage during super-solidus liquid phase sintering enabling them to reach near full density. The analyses and the review cover different process aspects like: recipe optimisation, post-gelatinization drying, de-binding and sintering. A SC recipe consisting of 58 vol.% powder, 3 vol.% starch, 1 vol.% dispersant and a thickener solution resulted in a density of >98% than what is theoretically stated after sintering. It is found that the success of the post-gelatinization drying procedure depends on the smoothness of mould material and controlling powder oxidation. The best combination was freeze drying the slurry in a silicon rubber mould. For V-rich alloys a total or partial control of eutectic carbides in the final microstructure could be realized for vacuum and nitrogen sintering atmospheres, respectively.

  • 25. Brandberg, A.
    et al.
    Reyier Österling, Sofia
    Högskolan Dalarna, Verksamhetsstödet.
    Kulachenko, A.
    Hirn, U.
    Characterization and impact of fiber size variability on the mechanical properties of fiber networks with an application to paper materials2022Ingår i: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 239-240, artikel-id 111438Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Cellulose fibers come in a wide range of shapes and sizes. The heterogeneity of the fiber length, width, wall thickness, curl and external fibrillation is detrimental to the mechanical performance of products such as paper and paperboard. Although micro-mechanical models of these materials sometimes incorporate features of this heterogeneity, so far there is no standardized method of fully incorporating this. We examine a large number of industrial mechanical fiber pulps to determine what information such a standardized method would have to have. We find that the method must allow for both non-Gaussian distributions and dependence between the variables. We present a method of characterizing mechanical pulp under these conditions that views the individual fiber as outcome of a sampling process from a multivariate distribution function. The method is generally applicable to any dataset, even a non-Gaussian one with dependencies. Using a micro-mechanical model of a paper sheet the proposed method is compared with previously presented methods to study whether incorporating both a varying fiber size and dependencies is necessary to match the response of a sheet modeled with measured characterization data. The results demonstrate that micro-mechanical models of paper and paperboard should not neglect the influence of the dependence between the characteristic shape features of the fibers if the model is meant to match physical experiments. © 2022 The Authors

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  • 26.
    Brandberg, August
    et al.
    KTH, Farkostteknik och Solidmekanik.
    Reyier Österling, Sofia
    Högskolan Dalarna, Verksamhetsstödet.
    Kulachenko, Artem
    KTH, Farkostteknik och Solidmekanik.
    Hirn, Ulrich
    Graz University of Technology.
    Characterization and impact of fiber size variability on the mechanical properties of fiber networks with an application to paper materials2021Rapport (Övrigt vetenskapligt)
    Abstract [en]

        Cellulose fibers exhibit a wide range of shapes and sizes. This variation influences the mechanical performance of paper and paperboard by affecting the stress distribution inside the network and the degree of fiber-to-fiber bonding which is possible at a given density. However, the methods used to characterize the distribution of fiber sizes in the pulp neglect that the characteristic features of a fiber are generally not independent.

        Here, we resolve this shortcoming by fitting the fiber population to a multivariate distribution without enforcing normality or independence between the properties. The high-dimensional multivariate function is recast as a set of univariate distribution functions and a series of bivariate distributions connected by a canonical vine. 

        Using a micro-mechanical model of a paper sheet the influence of this improved characterization is investigated. Reasonable margins and a description of the dependency is shown to be superior to assuming independence even for perfectly preserved marginal distributions. This result demonstrates that micro-mechanical models of paper and paperboard cannot by assumption neglect the influence of the interdependence between the characteristic features of fibers. 

  • 27.
    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.

  • 28. Canovic, Sead
    et al.
    Engkvist, Josefin
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Liu, Fang
    Götlind, Helena
    Hellström, Kristina
    Svensson, Jan-Erik
    Johansson, Lars-Gunnar
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Halvarsson, Mats
    Microstructural investigation of the initial oxidation of the FeCrAlRE alloy Kanthal AF in dry and wet O2 at 600 and 800°C2010Ingår i: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 157, nr 6, s. C223-C230Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The FeCrAlRE (where RE is reactive element) alloy Kanthal AF was exposed isothermally at 600 and 800°C for 72 h in dry O2 and in O2 with 10 vol % H2O. The mass gains were 3–5 times higher at the higher temperature. The presence of water vapor increased the oxidation rate at 800°C, while no significant effect was observed at 600°C. A thin two-layered oxide formed at 600°C: an outer (Fe,Cr)2O3 corundum-type oxide, containing some Al, and an inner, probably amorphous, Al-rich oxide. At 800°C a two-layered oxide formed in both environments. The inner layer consisted of inward grown a-Al2O3. In dry O2 the originally formed outward grown g-Al2O3 had transformed to a-Al2O3 after 72 h. Water vapor stabilized the outward grown g-Al2O3 and hence no transformation occurred after 72 h in humid environment. RE-rich oxide particles with varying composition (Y, Zr, and Ti) were distributed in the base oxide at both temperatures and in both environments. The RE-rich particles were separated from the alloy substrate by a layer of Al-rich oxide. At 800°C the Y-rich RE particles were surrounded by thick oxide patches in both dry and humid O2.

  • 29.
    Carlsson, Per
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Bexell, Ulf
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Klang, Hans
    A study of the initial stages of atmospheric corrosion of formed hot dip zinc coated steel1997Ingår i: EUROCORR-97, Trondheim, Norway, 1997Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    Hot-dip zinc coated steel sheet is extensively used to improve the corrosion protection of steel constructions. When the sheet is formed cracks in the zinc coating develop in strained areas. The zinc coating gives a galvanic protection of the steel in damaged areas of the coating and at cut edges of the sheet. The degree of protection is, however, dependent on factors such as the geometry and the area of the defects, the coating thickness, the presence of corrosive ions in the electrolyte and the wet time. In this work we have studied the initial atmospheric corrosion of zinc coated steel in defects on bended and scribed material. The samples were exposed to a cyclic indoor corrosion test developed by Volvo (Volvo standard 1027). Scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDS) and Auger electron spectroscopy (AES) were used to monitor the initial stages of corrosion and the growth of corrosion products. The corrosion products were identified as predominantly zinc hydroxycarbonate, zinc hydroxychloride and zinc hydroxide. The amount of corrosion products increases with the size of the damaged area, which suggests that the cathodic reduction of oxygen at the steel substrate controls the corrosion rate.

  • 30. Carlsson, Per
    et al.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    PVD coatings for sheet metal forming: a tribological evaluation2006Ingår i: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 200, nr 14-15, s. 4654-4663Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The use of liquid-based lubricants in sheet metal forming mutually has a negative impact on the environment and on the whole economy, and, consequently, there is an urgent need to find a solution to make the forming processes dry or nearly dry. The deposition of a low-friction PVD coating on the forming tool has during the last years proved to be an interesting choice when it comes to create an “unlubricated” forming process. In the present study, five different PVD coatings (one CrN and four metal-carbide-doped DLC coatings) have been evaluated in sliding contact against hot dip Zn and 55% Al–Zn-coated steel sheet using a ball-on-disc test. From the investigation, it was found that all DLC coatings have potential to prevent material pickup during dry forming of hot dip Zn-coated steel. However, the as-deposited surface morphology, showing surface irregularities such as droplets and dimples, of the coatings will strongly influence the tribological performance, and, consequently, a polishing treatment or a running-in process, resulting in a smooth surface, will significantly reduce the tendency to material pickup. In sliding contact against 55% Al–Zn-coated steel, all PVD coatings display material pickup and high friction values, the only exception being a CrC-doped DLC coating in the as-polished condition. The CrN coating showed poor performance in sliding contact against both steel sheet materials due to a high tendency to material pickup. The study focuses on the tribo-induced changes of the surface condition of the PVD coating and the steel sheet surface during the sliding event. The changes in surface chemistry and topography of the tribo surfaces were characterised using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), Auger electron spectroscopy (AES) and light interference profilometry.

  • 31.
    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.

  • 32. Cinca, N.
    et al.
    Gordon, S.
    Llanes, L. M.
    Olsson, Mikael
    Högskolan Dalarna, Institutionen för information och teknik, Materialteknik.
    Friction, Material Transfer And Wear Phenomena In Sliding Contacts Between Cemented Carbide And Aluminum During Metal Forming2022Ingår i: World PM 2022 Congress Proceedings, European Powder Metallurgy Association (EPMA) , 2022Konferensbidrag (Refereegranskat)
    Abstract [en]

    In many metal forming processes, certain texturization of the tool is necessary to have some friction that can make the operation possible. One example of that is the use of crosshatching methods on cemented carbide punches to manufacture beverage cans. The deep drawing and ironing process of the aluminum foil during can production involves different wear mechanisms being active on the punch surface, i.e. adhesive and abrasive wear. The present work examines the abrasive wear performance and friction characteristics of two cemented carbide grades by means of scratch and linear reciprocating sliding wear testing with Al2O3 counterparts under dry and lubricated conditions, with smooth polished and textured cemented carbide surfaces respectively. Additionally, well-controlled tests in which an aluminum pin is sliding over the cemented carbide surface were performed to evaluate the initial metal transfer. Post-test characterization shows the influence of carbide microstructure on the friction, material transfer and wear mechanisms. © European Powder Metallurgy Association (EPMA)

  • 33. Cinca, Nuria
    et al.
    Olsson, Mikael
    Högskolan Dalarna, Institutionen för information och teknik, Materialteknik.
    Assessment of initial transfer of metal work material on cemented carbide tools - Influence of cemented carbide composition, microstructure and surface topography2022Ingår i: Proceedings of 20th Plansee Seminar 2022, 2022Konferensbidrag (Refereegranskat)
    Abstract [en]

    In many applications such as metal cutting and metal forming, cemented carbide tools work in sliding friction wear mode resulting in transfer of the metal work material to the tool surface. In these applications, a surface showing good anti-galling properties needs to be balanced with other desired tool material properties. In the present study, the metal transfer and friction characteristics of aluminum in sliding contact with cemented carbide were evaluated by performing tests under dry and lubricated conditions, where an Al tip is put into sliding contact with the polished surface of the cemented carbide under well-defined contact conditions. Cemented carbide grades include a straight WC-Co grade and two grades containing cubic carbides (i.e. TiC, TaC and NbC), to gain fundamental knowledge into the relation between microstructure and composition and anti-galling properties. Post-test characterization using high resolution FEG-SEM and EDS has been used to show the influence of carbide composition (chemical affinity effects) and topography on the tendency to initial material transfer.

  • 34.
    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.

  • 35.
    Donnadieu, Patricia
    et al.
    Laboratoire SIMaP, CNRS—Université de Grenoble, F-38402 Saint Martin d’Hères, France.
    Pohlmann, Carsten
    IFW Dresden, Institut für Komplexe Materialien, Postfach 27 01 16, D-01171 Dresden, Germany; .
    Scudino, Sergio
    IFW Dresden, Institut für Komplexe Materialien, Postfach 27 01 16, D-01171 Dresden, Germany.
    Blandin, Jean-Jacques
    Laboratoire SIMaP, CNRS—Université de Grenoble, F-38402 Saint Martin d’Hères, France.
    Surreddi, Kumar Babu
    IFW Dresden, Institut für Komplexe Materialien; Chalmers University of Technology, Gothenburg.
    Eckert, Jürgen
    IFW Dresden, Institut für Komplexe Materialien, Postfach 27 01 16, D-01171 Dresden, Germany.
    Deformation at ambient and high temperature of in situ Laves phases-ferrite composites2014Ingår i: Science and Technology of Advanced Materials, ISSN 1468-6996, E-ISSN 1878-5514, Vol. 15, nr 3Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The mechanical behavior of a Fe80Zr10Cr10 alloy has been studied at ambient and high temperature. This Fe80Zr10Cr10 alloy, whoose microstructure is formed by alternate lamellae of Laves phase and ferrite, constitutes a very simple example of an in situ CMA phase composite. The role of the Laves phase type was investigated in a previous study while the present work focuses on the influence of the microstructure length scale owing to a series of alloys cast at different cooling rates that display microstructures with Laves phase lamellae width ranging from ∼50 nm to ∼150 nm. Room temperature compression tests have revealed a very high strength (up to 2 GPa) combined with a very high ductility (up to 35%). Both strength and ductility increase with reduction of the lamella width. High temperature compression tests have shown that a high strength (900 MPa) is maintained up to 873 K. Microstructural study of the deformed samples suggests that the confinement of dislocations in the ferrite lamellae is responsible for strengthening at both ambient and high temperature. The microstructure scale in addition to CMA phase structural features stands then as a key parameter for optimization of mechanical properties of CMA in situ composites.

  • 36. Eklund, Sara
    Icke-metalliska inneslutningars inverkan på tre mekaniska provningsmetoder2014Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    I denna rapport gjordes en undersökning om hur en representativ andel icke-metalliskainneslutningar i verktygsstålet Uddeholm Dievar, påverkar de olika mekaniskaprovningsmetoderna Charpy-V, oanvisad slagprovning och dragprovning. Målet meddenna rapport är att ta reda på vilken av de tre provningsmetoderna som minst påverkasav spridningen av icke-metalliska inneslutningar och att se om oanvisad slagprovning gerett jämnare resutat än vid Charpy-V.

    Tre charger valdes ut för provning av materialets seghet, draghållfasthet och duktilitet.Innan provningen gjordes en analys av inneslutningesmängden i programmet INCAfeature.Detta för att se om mängden inneslutningar kunde anses vara representativ för allatre chargerna. Resultatet från Charpy-V-provningen och den oanvisade slagprovningenutvärderades i testXpert II och sammanställdes därefter i Microsoft Excel. Medanresultatet från dragprovningen plottades upp i tre spännings- töjningsdiagram som sedanjämfördes . Bilder i SEM togs på brottytan hos det prov vars resultat avvek från de övrigai Charpy-V provningen.

    Då materialet Uddeholm Dievar var för duktilt för utrustningen vid den oanvisadeslagprovningen kunde tyvärr inte resultaten från denna provning användas. De slutsatsersom kunde dras av denna undersökning var att dragprovnig var den metod som gav minstspridning av resultatet. Oanvisad slagprovning tros ha gett en mindre spridning änCharpy-V. Företag kommer att fortsätta använda sig av Charpy-V trots att dragprovninggav ett mer korrekt resultat. Detta beror på att Charpy-V är en mer kostnadseffektiv metodoch provstavarna är mindre tidskrävande att producera.

  • 37.
    Emanuelsson, Simon
    Högskolan Dalarna, Institutionen för information och teknik.
    Influence of roll leveler settings on the microstructure and mechanical properties of high strength structural steel2021Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Detta arbete undersöker utvecklingen i mikrostruktur och mekaniska egenskaper hos rullriktat martensitiskt höghållfast konstruktionsstål genom undersökning av rullriktat bandprov och genom rullriktningsimulering. Syftet med arbetet är att generera input till materialmodeller för finita element-simuleringar och utförs vid formatsträcka 4 hos SSAB i Borlänge. I detta arbete undersöks oriktat, förriktat och riktat band. Ett rullriktat prov extraheras från ett stoppat riktverk med 13 valsar. Mekaniska egenskaper på makronivå undersöks genom dragprovning och på mikronivå med nano-hårdhetsprovning. Mikrostrukturen undersöks med EBSD och rullriktningsimulering utförs med mikrobockningsmaskin. Dragprovning indikerar en märkbar minskning i sträckgräns på förriktade band och försumbar minskning i sträckgränsen på riktade band. Nano-hårdhetsprovning i tvärsnittet visar minskande hårdhet i mikroskopisk skala mellan oriktade, förriktade och riktade band. Mikrostrukturundersökningar avslöjar en varmvalsningseffekt som förblir opåverkad av rullriktningsprocessen och inkluderar en konstant kornstorlek i topp- och bottenlager men större kornstorlek i mellanskiktet samt förskjutning ikristallografisk orientering i bandens tvärsnitt. Rullriktningsimulering med bockningsmaskin på oriktade och förriktade böjprover visar Bauschinger-effekt som ett resultat av alternerande böjning. Euler-vinkelkartor på dessa böjprover avslöjar att en stor andel korn roterar en viss vinkel samt att korn återfår sin ursprungliga vinkel under efterföljande böjningar. Det råder ett nära 1: 1-förhållande i Euler-vinklar för drag- och kompression under bockning medan mängden felorienteringar visar sig skilja sig mellan drag- och kompressionsdeformationslägen. Generering av dislokationer under rullriktningssimulering visar sig skilja mellan drag och kompressionsdeformationslägen. Hårdhet på simuleringsprover ses minska som ett resultat av kontinuerlig bockningsprocess och föreslås uppstå som följd av en avslappningseffekt i korn. Flera framtida studier är möjliga från dessa fynd vilket diskuteras och föreslås som ytterligare arbete.

  • 38.
    Engberg, Göran
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Grehk, Mikael
    Sandvik Materials Technology.
    Yvell, Karin
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Analysis of the plastic deformation behavior for two austenitic NiCr-steels with different stacking fault energies2018Ingår i: International Journal of Computational Physics Series, ISSN 2631-8350, Vol. 1, nr 1, s. 137-141Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Two austenitic stainless steels, with low and medium stacking fault energies (SFE), 20 mJ/m2 and 30 mJ/m2 respectively, have been studied by conventional tensile tests and in situ tensile tests in a FEG-SEM equipped for EBSD. High angle boundaries (HAB) and low angle boundaries (LAB) with misorientations >= 10o and >= 2o respectively have been determined, and size distributions for the LABs have been derived by linear intercepts. It was found that the size distributions could be described by bimodal lognormal functions. For the steel with highest SFE plastic deformation took place by dislocation slip only while the steel with low SFE deformed by slip and twinning. Using a model for slip based on the evolution of the dislocation density with the generation of dislocations inversely proportional to the mean free distance of slip and recovery of dislocations proportional to the dislocation density the stress strain-curves were analyzed and the results compared with the measured quantities. The mean free distance of slip as evaluated from the stress-strain curve for the steel with the highest SFE correlates very well with the mean size of the LABs intercept. The rate of recovery also gave an expected stress dependence. The stress needed to start deformation twinning was based on the assumption that Shockley partials become completely separated in the slip plane. The thus calculated values for the twinning stress showed an excellent agreement with the observed start of twinning as given by EBSD evaluation of twin boundaries (TB). For the alloy with low SFE both surface grains (in situ test) and bulk grains (from interrupted conventional tests) were studied. The stress needed for slip and twinning of surface grains was, as expected, in the order of 0.5-0.6 times the applied stress.

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  • 39.
    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.

  • 40. Engkvist, Josefin
    Characterization of oxide scales formed on FeCrAl alloys at high temperatures2009Doktorsavhandling, monografi (Övrigt vetenskapligt)
    Abstract [un]

    This thesis focuses on the characterization of oxide scales formed on FeCrAl alloys at high temperatures. The effect of water vapour on commercial FeCrAl alloys oxidized in both dry and humid O2 has been investigated. Also, the effect of varying Al concentrations in model FeCrAl alloys was studied as well as the effect of using surface coatings in order to increase the oxidation resistance of FeCrAl alloys. The formed oxide scales were characterized using analysis techniques such as SEM, EDX, TEM, XRD, XPS, AES and SIMS. The main part of the work concerns the SEM, EDX, AES and SIMS techniques. The commercial FeCrAl alloys investigated follow the same trend in oxide formation independent of whether the alloy was conventionally cast or manufactured by powder metallurgy. In the as-received cold rolled condition the surface of the FeCrAl material shows a few nm thin native oxide. This native oxide is a mixture of oxides from Fe, Cr and Al, with a relatively high concentration of Cr. The oxide formation at elevated temperatures can be separated in a low temperature and a high temperature mode. At relatively low temperatures (500-600°C) a mixed oxide similar to the pre-existing native oxide forms, while at higher temperatures a thicker two-layered alumina scale forms. The outer and inner alumina layers are separated by a Cr-rich zone which is believed to be a remnant of the pre-existing native oxide and hence represents the original alloy surface. Accordingly the inner alumina layer is formed by oxygen inward diffusion while the outer alumina layer grows by cation outward diffusion. The inner alumina is composed of a-Al2O3, while the outer layer, during early stages, is composed of rapidly growing metastable polymorphs of alumina which with time transform to a-Al2O3. This phase transformation starts at the Cr-rich zone and progress outward. In presence of water vapour this transformation is inhibited due to hydroxylation of the surface of the metastable phases. Hence, a higher oxidation rate was observed in presence of water vapour. Model FeCrAl alloys having Al concentrations in the range 1.2-5 wt.% were investigated. At 900°C a minimum of 3.2% Al is needed in order to form a continuous alumina scale. Higher Al concentrations (= 4.4%) result in a relatively pure alumina scale and a slower oxidation rate. In order to evaluate the possibility to improve the oxidation resistance of FeCrAl a PVD SiO2 coating was applied on a commercial FeCrAl foil prior to oxidation. Parallel exposures of coated and uncoated samples were made at 1000°C and revealed that the SiO2 coating significantly reduced the initial oxidation rate of the FeCrAl foil. Further, metal organic CVD of a ZrO2 film in situ on an RE free FeCrAl alloy at 400 and 800°C showed that at the lower temperature mainly ZrO2 was formed while at 800°C an oxide scale composed of both ZrO2 and Al2O3 was formed. The results obtained illuminate the importance of advanced electron microscopy and surface analysis techniques in order to increase the understanding of high temperature oxidation of FeCrAl alloys and the oxidation mechanisms of this group of materials.

  • 41.
    Engkvist, Josefin
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Bexell, Ulf
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Grehk, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    High temperature oxidation of FeCrAl-alloys: influence of Al-concentration on oxide layer characteristics2009Ingår i: Materials and corrosion - Werkstoffe und Korrosion, ISSN 0947-5117, E-ISSN 1521-4176, Vol. 60, nr 11, s. 876-881Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The superior high temperature oxidation resistance of FeCrAl alloys relies on the formation of a dense and continuous protective aluminium oxide layer on the alloy surface when exposed to high temperatures. Consequently, the aluminium content, i.e. the aluminium concentration at the alloy–oxide layer interface, must exceed a critical level in order to form a protective alumina layer. In the present study the oxidation behaviour of six different FeCrAl alloys with Al concentrations in the range of 1.2–5.0wt% have been characterised after oxidation at 900 8C for 72 h with respect to oxide layer surface morphology, thickness and composition using scanning electron microscopy, energy dispersive X-ray spectroscopy and Auger electron spectroscopy.The results show that a minimum of 3.2wt% Al in the FeCrAl alloy is necessary for the formation of a continuous alumina layer. For Al concentrations in the range of 2.0–3.0wt% a three-layered oxide layer is formed, i.e. an oxide layer consisting of an inner alumina-based layer, an intermediate chromia-based layer and an outer iron oxide-based layer. In contrast, the 1.2wt% Al FeCrAl alloy is not able to form a protective oxide layer inhibiting extensive oxidation.

  • 42.
    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.

  • 43.
    Engkvist, Josefin
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Canovic, Sead
    Hellström, Kristina
    Järdnäs, Anders
    Svensson, Jan-Erik
    Johansson, Lars-Gunnar
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Halvarsson, Mats
    Alumina scale formation on a powder metallurgical FeCrAl alloy (Kanthal APMT) at 900-1100 °C in dry O2 and in O2 + H2O2010Ingår i: Oxidation of Metals, ISSN 0030-770X, E-ISSN 1573-4889, Vol. 73, nr 1-2, s. 233-253Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A Rapidly Solidified Powder (RSP) metallurgical FeCrAl alloy, Kanthal APMT, was exposed in dry and humid O2 for 72 h at 900–1,100 °C. The formed oxide scales were characterized using gravimetry in combination with advanced analysis techniques (SEM, EDX, TEM, XRD, AES andSIMS). The oxide scales were at all exposures composed of two-layered α-Al2O3 scales exhibiting a top layer of equiaxed grains and a bottom layer containing elongated grains. A Cr-rich zone, originating in the native oxide present before exposure, separated these two layers. The top α-Al2O3layer is suggested to have formed by transformation of outwardly grown metastable alumina, while the inward-grown bottom α-Al2O3 layer had incorporated small Zr-, Hf- and Ti-rich oxide particles present in the alloy matrix. The scale also contained larger Y-rich oxide particles. Furthermore, in the temperature range studied, the presence of water vapour accelerated alloy oxidation somewhat and affected scale morphology.

  • 44.
    Engkvist, Josefin
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Canovic, Sead
    Liu, Fang
    Götlind, Helena
    Svensson, Jan-Erik
    Johansson, Lars-Gunnar
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Halvarsson, Mats
    Oxidation of FeCrAl foils at 500-900 C in dry O2 and O2 with 40% H2O2009Ingår i: 7th Int. Conf. on the Microscopy of Oxidation, Chester, UK, 2009Konferensbidrag (Övrigt vetenskapligt)
  • 45.
    Engkvist, Josefin
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Grehk, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Bexell, Ulf
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Early stages of oxidation of uncoated and PVD SiO2 coated FeCrAl foils2009Ingår i: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 203, nr 19, s. 2845-2850Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The high temperature oxidation characteristics of uncoated and SiO2 PVD-coated FeCrAl foils have been investigated when exposed to laboratory air at 1000 °C during 1, 2, 4, 8, 16, 32 and 60 min. The oxidized samples were characterized using SEM, EDS, AES and SIMS. The results show that the presence of a 100 nm thin SiO2 PVD coating significantly reduces the oxidation rate of the FeCrAl foil during early stages of oxidation. The decreased oxidation rate displayed by the SiO2 coated FeCrAl foil is the result of the SiO2 coating acting as an initial diffusion barrier promoting the formation of a predominantly inward growing Al2O3 layer during oxidation. Additionally, by using EDS analysis together with AES and SIMS depth profiling it was shown that the total concentration of Si in the grown oxide scale decreased during oxidation.

  • 46.
    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.

  • 47. Eriksson, C.
    et al.
    Börner, K.
    Nygren, H.
    Ohlson, K.
    Bexell, Ulf
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Billerdahl, N.
    Johansson, M.
    Studies by imaging ToF-SIMS of bone mineralization on porous titanium implants after 1 week in bone2006Ingår i: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 252, nr 19, s. 6757-6760Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Anodic oxidation was used to grow porous layers on titanium discs. Six different oxidation procedures were used producing six different surfaces. The implants were inserted in rat bone (tibia) for 7 days. After implant retrieval, mineralization (hydroxyapatite formation) on the implant surfaces was investigated using time-of-flight secondary ion mass spectrometry (TOF-SIMS). Bone tissue around the implants was sectioned and stained. The amount of bone in close apposition to the implant was calculated. The porosity showed great variation between the surfaces. Hydroxyapatite was detected on all surfaces. A slight positive correlation between porosity and mineralization was found, although the most porous surface was not the best mineralized one. Bone had formed around all implants after 7 days. The bone-to-metal contact for the porous implants did not differ significantly from the non-porous control. Porosity is known to influence cellular events. The results indicate that porosity could have an initial, positive influence on bone integration of implants, by stimulating the mineralization process. The methods used were found to be suitable tools for investigation of initial healing around implants in bone.

  • 48.
    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.

  • 49.
    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.

  • 50.
    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.

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