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31.
  • Nilsson, Malin, et al. (författare)
  • Microstructural, mechanical and tribological characterisation of roll materials for the finishing stands of the hot strip mill for steel rolling
  • 2013
  • Ingår i: Wear. - : Elsevier BV. - 0043-1648 .- 1873-2577. ; 307:1-2, s. 209-217
  • Tidskriftsartikel (refereegranskat)abstract
    • The microstructure, mechanical and tribological properties for three different materials, high speed steel, high chromium iron and indefinite chill iron, used for hot strip mill work rolls have been evaluated. Microstructural characterisation was performed using light optical microscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy. The mechanical and tribological properties were evaluated using micro-Vickers indentation and scratch testing in combination with post-test microscopy. The microstructures of the investigated materials were found to be rather complex with a number of secondary phases and also materials with similar nominal composition display significant differences with respect to distribution, size and morphology of carbides. Scratch testing, including detection of friction coefficient, acoustic emission and penetration depth, gives valuable information concerning the mechanical and tribological response on a microscopic level of the investigated materials. Type, amount, distribution, size and morphology of the secondary phases in the materials have a strong impact on the surface deformation and wear mechanisms during scratching. Cracking and chipping are frequently observed in connection to the ridges surrounding the scratches. However, cross-sectional analyses of the scratched microstructures reveal that cracking of the brittle carbide phases may extend to significant depths > 100 gm, reducing the mechanical strength of the material. Based on the results, it is believed that a more isotropic microstructure, e.g., obtained via a powder metallurgy process, with finer carbides would result in improved properties and performance in a hot rolling application.
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32.
  • Nilsson, Maria, et al. (författare)
  • Tribological testing of some potential PVD and CVD coatings for steel wire drawing dies
  • 2011
  • Ingår i: Wear. - Amsterdam : Elsevier BV. - 0043-1648 .- 1873-2577. ; 273:1, s. 55-59
  • Tidskriftsartikel (refereegranskat)abstract
    • The aim of this study was to investigate the possibility to replace cemented carbide wire drawing dies with CVD or PVD coated steel dies. Material pick-up tendency, friction and wear characteristics of four different commercial coatings - CVD TiC and PVD (Ti,Al)N, CrN and CrC/C - in sliding contact with ASTM 52100 bearing steel were evaluated using pin-on-disc testing. The load bearing capacity of the coating/substrate composites was evaluated using scratch testing. The results show that the friction characteristics and material pick-up tendency of the coatings to a large extent is controlled by the surface topography of the as-deposited coatings which should be improved by a polishing post-treatment in order to obtain a smooth surface. Based on the results obtained in this study, three different coatings - CrC/C, TiC and dual-layer TiC/CrC/C - are recommended to be evaluated in wire drawing field tests. CrC/C and TiC are recommended due to their intrinsic low friction properties and material pick-up tendency in sliding contact with steel. The dual-layer is recommended in order to combine the good properties of the two coatings CrC/C (low shear strength) and TiC (high hardness). 
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33.
  • Olsson, Mikael, et al. (författare)
  • Initial degradation of cemented carbides for rock drilling : model studies of the tribological contact against rock
  • 2015
  • Ingår i: International journal of refractory metals & hard materials. - : Elsevier BV. - 0263-4368. ; 52, s. 104-113
  • Tidskriftsartikel (refereegranskat)abstract
    • Hardness and fracture toughness are often used as the prime material parameters to characterise cemented carbides used in rock drilling. However, the deformation and wear of cemented carbide are too complicated to be described by these parameters alone. The cemented carbide and the wearing rock mineral are both composite materials, containing phases with widely varying hardness. Moreover, the deformation behaviour of the individual phases may be strongly anisotropic, as for the WC grains in the cemented carbide. The wear of the cemented carbide typically occurs on the scale of individual grains or smaller. Contrastingly, the hardness stated for both is typically a macroscopic value, averaged over numerous grains, orientations, etc. The present investigation aims to contribute to the understanding of the relations between microstructure, properties and wear mechanisms of cemented carbide buttons in rock drilling. It is focused on the role of scale of deformation in relation to size of the different phases of the cemented carbide. This is achieved by simplifying the contact situation of the rock drill button to a single stylus sliding contact between a granite stylus and a polished cemented carbide surface. The deformation and wear of this well controlled contact is then evaluated on the sub-micrometer scale; using high resolution FEG-SEM with EBSD, FIB cross-sectioning and AFM. The results show that even an extremely local deformation, such as slip within individual WC grains, affects the tribological contact, and that the nominally much softer granite may cause deformation both within individual WC grains, and on the composite scale. The results are discussed with respect to their significance for wear of cemented carbides in rock drilling. (C) 2015 Elsevier Ltd. All rights reserved.
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34.
  • Olsson, Mikael, et al. (författare)
  • Surface degradation mechanisms of cemented carbide drill buttons in iron ore rock drilling
  • 2017
  • Ingår i: Wear. - : Elsevier BV. - 0043-1648 .- 1873-2577. ; 388-389, s. 81-92
  • Tidskriftsartikel (refereegranskat)abstract
    • The wear behavior of cemented carbide rock drill buttons is influenced by many factors, which include the composition and microstructure of the cemented carbide material, the nature of the rock material, and the conditions of the rock drilling operation. Depending on the type of rock and on the drilling procedure used, the cemented carbide is exposed to substantially differing mechanical and thermal conditions. In the present study, the surface degradation and wear mechanisms of cemented carbide drill buttons exposed to iron ore rock drilling have been characterized based on a combination of high resolution scanning electron microscopy (SEM), focused ion beam cross-sectioning (FIB), energy-dispersive X-ray spectroscopy (EDS) and electron back scatter diffraction (EBSD).The results show a significant difference in surface degradation and wear between the front and peripheral buttons of the drill bits. While the front buttons display a relatively smooth worn surface with shallow surface craters the peripheral buttons display a reptile skin pattern, i.e. plateaus, 200-300. μm in diameter, separated by valleys, typically 40-50. μm wide and 15-30. μm deep, The reptile skin pattern is obtained in regions where the peripheral buttons are in sliding contact against the drill hole walls and exposed to high surface temperatures caused by the frictional heating. The results indicate that the reptile skin pattern is related to friction induced thermal stresses rather than mechanical contact stresses, i.e. the reptile skin pattern is formed due to thermal fatigue, rather than mechanical fatigue, caused by the cyclic frictional heating generated at the cemented carbide button/iron ore interface.
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35.
  • Pejryd, Lars, 1955-, et al. (författare)
  • Process monitoring of wire drawing using vibration sensoring
  • 2017
  • Ingår i: CIRP - Journal of Manufacturing Science and Technology. - : Elsevier BV. - 1755-5817 .- 1878-0016. ; 18, s. 65-74
  • Tidskriftsartikel (refereegranskat)abstract
    • Automating the detection of processing conditions that may lead to defects in the wire during the wire drawing process is of high interest to the industry. Current practise is based primarily on operator experience. Increasing demands on product quality and process robustness emphasises the need for development of robust in-process detection methods. This work is focusing on investigating the potential of using vibration monitoring to detect process deficiencies or variations that may lead to defects in the product. Wire drawing of a carbon steel in different lubricating situations was used to investigate vibration signal response together with force measurements and surface investigation of the wire product. The results show that vibration measurement is capable of detecting loss of lubrication that leads to poor surface quality of the wire.
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36.
  • Prosek, Tomas, et al. (författare)
  • Effect of chloride-to-chromate ratio on the protective action of zinc surface films under atmospheric weathering conditions
  • 2007
  • Ingår i: Corrosion. - : National Assoc. of Corrosion Engineers International. - 0010-9312 .- 1938-159X. ; 63:3, s. 258-267
  • Tidskriftsartikel (refereegranskat)abstract
    • The formation and the corrosion protection of newly formed chromium-rich layers on bare zinc surfaces were studied to model the conditions in defected areas of both organic and conversion chromate coatings that are in contact with water environments contaminated with different amounts of chloride ions. Composition of the layers was identified with Fourier transformed infrared spectroscopy (FTIR), x-ray absorption near-edge structure (XANES), and secondary ion mass spectroscopy (SIMS). The presence of chloride in the range from 0.06 mM to 1,000 mM in the chromate treating solution had almost no effect on the amount of chromate adsorbed on zinc. Three independent technique showed that a more than 4-order increase in chloride concentration results in the drop of the chromate content in the surface film only by 20% to 25%. Cr(VI)-to-total Cr surface ratio was close to 0.3 and constant under present experimental conditions. More chromium was detected in the outer region of the film, whereas chloride accumulated in the inner region. As a result of the linear increase of the surface chloride concentration with the chloride concentration in the chromate treating solution, the chloride-to-chromate surface molar ratio increased sharply. The rate of reduction of Cr(VI) to Cr(III) and the corrosion rate of zinc exposed to atmospheric weathering conditions increased significantly with the chloride-to-chromate ratio. The chromate coatings showed good stability and a high level of corrosion protection, up to the ratio of approximately 2. It represented a threshold value below which relatively low rates of the chromate reduction and zinc corrosion were observed, since the significant part of the chloride ions was inactivated in the first hours of exposure by the formation of insoluble corrosion products. A negative effect of the increasing chloride-to-chromate surface molar ratio on corrosion can be seen in the increasing ability to reduce oxygen on the zinc surface measured by the scanning Kelvin probe (SKP) technique. Inhibition of the cathodic reaction by chromate was less effective at higher ratios.
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37.
  • Roizard, X., et al. (författare)
  • Insights into sliding wear and friction behavior of copper in ethanol containing alkylphosphonic acid molecules
  • 2016
  • Ingår i: Tribology International. - : Elsevier BV. - 0301-679X .- 1879-2464. ; 96, s. 141-148
  • Tidskriftsartikel (refereegranskat)abstract
    • In this work, the friction and wear behavior of bare copper was investigated for the first time under lubricated sliding conditions in diluted ethanol solutions of butylhosphonic (C4P), octylphosphonic (C8P), dodecylphosphonic (C12P), and hexadecylphosphonic (C16P) acids. The technique aims towards a more environmentally friendly lubrication to be used in shaping of copper sheets. Bare copper samples were subjected to unidirectional sliding using a tribometer with ball-on-disk contact geometry. Copper substrates (20 mm2×1 mm) were run against 100Cr6 ∅10 mm ball bearing counterbodies. All tests were conducted using the same sliding conditions with a normal load of 10 N, tangential velocity of 0.01 m/s, at room temperature of 20 °C. Worn surfaces were analyzed by Scanning Electron Microscopy, Optical Microscopy and White Light Interference Profilometry. When comparing to sliding tests in the pure ethanol solvent, significant decreases in terms of wear track dimensions, transferred material on the ball and friction coefficients are observed when active molecules are present in the solution. These form protective tribofilms exhibiting lubricating and anti-wear properties. Deeper studies on the tribological behavior of copper in C4P solution show that both low friction and low transfer of work material to the ball prevail in a specific range of low molecule concentration (5×10-4 M; 25×10-4 M). Even if the molecules are introduced during the test, after a few cycles, the tribological behavior improves, regardless of both friction level and copper surface degradation. Finally, specific friction tests were performed to further investigate the mechanisms. It was found that two mechanisms are involved; firstly molecules grafting onto the surface directly reduces friction, and secondly transformation of these grafted molecules into a tribofilm during the first mechanical contact cycles reduces it even further. 
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38.
  • Safara Nosar, Nima, 1982-, et al. (författare)
  • Influence of tool steel surface topography on adhesion and material transfer in stainless steel/tool steel sliding contact
  • 2013
  • Ingår i: Wear. - : Elsevier BV. - 0043-1648 .- 1873-2577. ; 303, s. 30-39
  • Tidskriftsartikel (refereegranskat)abstract
    • Transfer of work material to the tool surface is a common problem in many metal forming and metal working operations, especially in the case of work materials with a high adhesion tendency e.g. stainless steel, aluminum and titanium. In many operations, material transfer occurs already during the initial contact and with time it may result in degradation and roughening of the tool surface which will affect the surface quality of the formed or machined work material surface, e.g. problems related to galling in sheet metal forming. In the present study, the mechanisms behind the initial stages of material transfer between stainless steel and tool steel have been investigated under well controlled laboratory conditions and analyzed using optical surface profilometry and scanning electron microscopy.The results show that, independent of tool surface topography, transfer of stainless steel occurs already after a very short sliding distance. Depending on the tool steel surface topography, initial transfer occurs on two different scales. For a fine polished tool steel surface, fine scale transfer occurs in connection to protruding hard phase particles (carbides and carbonitrides) while for a ground rough surface large scale transfer occurs in connection to grinding scratches, where these act to mechanically scrape off material resulting in lumps off stainless steel on the tool steel surface. Also, sliding perpendicular to the grinding scratches results in more severe material transfer as compared with sliding parallel to the grinding scratches. Finally, the present paper illuminates the usefulness of combining optical surface profilometry and scanning electron microscopy as a powerful analytical tool when it comes to understanding the mechanisms controlling material transfer in a sliding contact on a μm-scale level.
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39.
  • Saketi, Sara, et al. (författare)
  • Influence of CVD and PVD coating micro topography on the initial material transfer of 316L stainless steel in sliding contacts : A laboratory study
  • 2017
  • Ingår i: Wear. - : ELSEVIER SCIENCE SA. - 0043-1648 .- 1873-2577. ; 388-389, s. 29-38
  • Tidskriftsartikel (refereegranskat)abstract
    • Austenitic stainless steels generally display poor tribological properties in sliding contacts partly due to their strong adhesion and transfer tendency to the counter surface. As a result machining of austenitic stainless steels is frequently associated with significant problems such as high stresses and high temperatures resulting in rapid tool wear. In the present study, the influence of coating micro topography on the initial material transfer of 316L stainless steel in sliding contacts has been evaluated using a scratch testing equipment. Coating materials include modem CVD Ti(C,N)-Al2O3-TiN and PVD (TLA1)N-(AI,Cr-2)O-3 coatings deposited on cemented carbide and pre- and post-coating grinding and polishing treatments were used to obtain different micro topographies of the coating surface. Pre- and post-test characterization of the surfaces was performed using high resolution scanning electron microscopy, energy dispersive X-ray spectroscopy and optical surface profilometry. The results show that the intrinsic topography of the as-deposited CVD and PVD coatings promotes material transfer. For the as-deposited CVD coating the nanoscale topography of the crystals controls the transfer while for the PVD coating the gm-scale droplets and craters control the transfer. Post-polishing of the coating, especially in combination with pre-polishing of the substrate, significantly improves the tribological performance of the surface reducing the friction coefficient and the material transfer tendency. However, the presence of gm sized droplets and craters in the PVD coating limit the possibility to obtain a smooth post-polished surface and its resistance to material pick-up. In contrast, post-polishing of the CVD coating does not suffer from intrinsic coating defects which results in low friction and a very high resistance to material pick-up.
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40.
  • Saketi, Sara, et al. (författare)
  • Influence of tool surface topography on the material transfer tendency and tool wear in the turning of 316L stainless steel
  • 2016
  • Ingår i: Wear. - : Elsevier. - 0043-1648 .- 1873-2577. ; 368–369, s. 239-252
  • Tidskriftsartikel (refereegranskat)abstract
    • Abstract The influence of tool surface topography on the initiation and build-up of transfer layers in the orthogonal turning of 316L austenitic stainless steel have been studied under well controlled conditions. Tool materials include CVD Ti(C,N)-Al2O3-TiN and PVD (Ti, Al)N-(Al,Cr)2O3 coated cemented carbide inserts prepared using different grinding and polishing treatments. Post-test characterization of the inserts was performed using high resolution scanning electron microscopy and energy dispersive X-ray spectroscopy. The results show that the transfer tendency of work material is strongly affected by the surface topography of the rake face. For both types of inserts, the initial transfer and the build-up of transfer layers are localised to microscopic surface irregularities on the rake face. Consequently, an appropriate surface treatment of the cemented carbide substrate before coating deposition and the as-deposited CVD and PVD coating can be used in order to reduce the transfer tendency and the mechanical interaction between the mating surfaces. Also, an improved surface finish was found to reduce coating wear and consequently the crater wear rate of the inserts investigated. This can most likely be explained by the reduced tendency to discrete chipping of coating fragments in the contact zone and the formation of a thin transfer layer composed of Al, Si, Ca, O with beneficial friction properties which are promoted by a smooth coating surface.
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