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  • 1. Berger, Robert
    et al.
    Bexell, Ulf
    Dalarna University, School of Technology and Business Studies, Material Science.
    Grehk, Mikael
    Dalarna University, School of Technology and Business Studies, Material Science.
    Hörnström, Sven Erik
    A comparative study of the corrosion protective properties of chromium and chromium free passivation methods2007In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 202, no 2, p. 391-397Article in journal (Refereed)
    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.

  • 2.
    Bexell, Ulf
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Grehk, Mikael
    Dalarna University, School of Technology and Business Studies, Material Science.
    A corrosion study of hot-dip galvanized steel sheet pre-treated with gamma-mercaptopropyltrimethoxysilane2007In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 201, no 8, p. 4734-4742Article in journal (Refereed)
    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

  • 3.
    Bexell, Ulf
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Material Science.
    Johansson, M
    Samuelsson, J
    Sundell, P.-E
    A Tribological Study of a Novel Pre-Treatment With Linseed Oil Bonded to Mercaptosilane Treated Aluminium2003In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, no 166, p. 141-152Article in journal (Refereed)
  • 4.
    Carlsson, Per
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Bexell, Ulf
    Dalarna University, School of Technology and Business Studies, Material Science.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Material Science.
    Tribological Behaviour of Thin Organic Permanent Coatings Deposited on Hot-Dip Coated Steel Sheet - a Laboratory Study2000In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 132, no 2-3, p. 169-180Article in journal (Refereed)
    Abstract [en]

    The forming and handling of hot-dip coated steel sheets is frequently associated with problems such as galling, scratching and discoloration. Recently, a new generation of thin organic coatings has been introduced on the market in order to improve the performance of hot-dip coated steel sheets and reduce these kinds of problems. In summary, these coatings have the potential to increase the formability of the steel sheet without additional lubrication, the anti-finger print properties and the corrosion protection of the product. Besides, they should also provide a pre-treatment for painting, i.e. they can be classified as permanent coatings. In the present study, the tribological behaviour of three different thin organic permanent coatings deposited on hot-dip coated (pure zinc and 55% Al–Zn) steel sheets is evaluated by three different laboratory tests; modified scratch testing, pin-on-disc testing and bending under tension testing. The results obtained show that all tests yield consistent and valuable information concerning the friction and wear properties of the materials and can, therefore, be used in order to study the tribology in sheet metal forming and the performance of different types of permanent coatings. Of the permanent coatings investigated, a pure organic coating shows the lowest coefficient of friction (µ close to 0.1) and the highest wear resistance, thus offering excellent anti-galling properties. In contrast, a mixed organic/inorganic coating displays a relatively high coefficient of friction (µ close to 0.3) and a significantly lower wear resistance. Surface analyses of the tested surfaces show that the thickness and coverage of the thin organic coating play an important role in controlling friction and wear. Furthermore, a thin organic coating optimized for improved formability and handling should display: a high adhesion to the underlying substrate material, a low coefficient of friction, a high load carrying capacity and a high intrinsic wear resistance.

  • 5. Carlsson, Per
    et al.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Material Science.
    PVD coatings for sheet metal forming: a tribological evaluation2006In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 200, no 14-15, p. 4654-4663Article in journal (Refereed)
    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.

  • 6.
    Engkvist, Josefin
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Grehk, Mikael
    Dalarna University, School of Technology and Business Studies, Material Science.
    Bexell, Ulf
    Dalarna University, School of Technology and Business Studies, Material Science.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Material Science.
    Early stages of oxidation of uncoated and PVD SiO2 coated FeCrAl foils2009In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 203, no 19, p. 2845-2850Article in journal (Refereed)
    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.

  • 7.
    Eriksson, Jenny
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Tribological testing of commercial CrN, (Ti,Al)N and CrC/C PVD coatings: evaluation of galling and wear characteristics against different high strength steels2011In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 205, no 16, p. 4045-4051Article in journal (Refereed)
    Abstract [en]

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

  • 8.
    Fallqvist, Mikael
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Ruppi, S
    Abrasive wear of textured-controlled CVD a-Al2O3 coatings2007In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 202, no 4-7, p. 837-843Article in journal (Refereed)
    Abstract [en]

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

  • 9.
    Fallqvist, Mikael
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Ruppi, S
    Seco Tools.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Ottosson, M
    Uppsala Universitet.
    Grehk, Mikael
    Dalarna University, School of Technology and Business Studies, Materials Technology. Sandvik Materials Technology.
    Nucleation and growth of CVD α-Al2O3on TixOy template2012In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 207, p. 254-261Article in journal (Refereed)
    Abstract [en]

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

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

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

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

  • 11.
    Harlin, Peter
    et al.
    Sandvik Materials Technology.
    Bexell, Ulf
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Influence of surface topography of arc-deposited TiN and sputter-deposited WC/C coatings on the initial material transfer tendency and friction characteristics under dry sliding contact conditions2009In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 203, no 13, p. 1748-1755Article in journal (Refereed)
    Abstract [en]

    The influence of surface topography of PVD coatings on the initial material transfer tendency and friction characteristics in dry sliding contact conditions has been investigated. A modified scratch test was used to evaluate the material transfer tendency between ball bearing steel and two different PVD coatings, TiN and WC/C, under dry sliding contact conditions. Post test characterisation of the contact surfaces was performed using SEM/EDS and AES in order to map the initiation points and mechanisms for material transfer. The results show that the resulting topography of the PVD coated surfaces is strongly dependent on both the substrate material topography and the topography induced by the coating deposition process used. In sliding contact with a softer surface the coating topography results in a significant material pick-up tendency of the PVD coated surfaces. The material pick-up is mainly controlled by the abrasive action of hard coating asperities and as a result a polishing post treatment of the as-deposited PVD coatings significantly reduces the material pick-up tendency. For the WC/C coating, showing intrinsic low friction properties, the post treatment inhibits the material pick-up and results in a low and stable friction coefficient (mu similar to 0.1). For the TiN coating, that lacks intrinsic low friction properties, the post treatment reduces the material pick-up tendency but has no significant influence on the friction characteristics. This is mainly due to the presence of metallic Ti originating from the macroparticles on the TiN coating which results in a reactive surface that promotes a strong adhesion between the mating surfaces.

  • 12.
    Harlin, Peter
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Carlsson, Per
    Dalarna University, School of Technology and Business Studies, Material Science.
    Bexell, Ulf
    Dalarna University, School of Technology and Business Studies, Material Science.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Material Science.
    Influence of surface roughness of PVD coatings on tribological performance in sliding contacts2006In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 201, no 7, p. 4253-4259Article in journal (Refereed)
    Abstract [en]

    The influence of surface roughness on the tribological performance, i.e. friction, wear and material pick-up tendency, of two different commercial PVD coatings, TiN and WC/C, in sliding contact with ball bearing steel has been evaluated using two different types of sliding wear laboratory tests. Post-test characterisation using SEM/EDS, AES, ToF-SIMS and XPS was used to evaluate the prevailing friction and wear. The results show that the surface roughness of the coating is of importance in order to control the initial material pick-up tendency and thus the friction characteristics in a sliding contact. Once initiated, the material pick-up tendency will increase, generating a tribofilm at the sliding interface. For steel–TiN sliding couples a FeO-based tribofilm is generated on the two surfaces and FeO/FeO becomes the sliding interface (interfilm sliding) resulting in a high friction coefficient. For steel–WC/C sliding couples the WC/C displays a pronounced running-in behaviour which generates a WO3-based tribofilm on the steel surface while a carbon rich surface layer is formed on the WC/C surface, i.e. WO3/C becomes the sliding interface (interface sliding) resulting in a low friction coefficient.

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