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  • 1.
    Aiso, Toshiharu
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Wiklund, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Kubota, Manabu
    Nippon Steel & Sumitomo Metal Corporation.
    Jacobson, Staffan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Effect of combined additions of Si, Mn, Cr and Al to carbon steel on material transfer in a steel/TiN coated tool sliding contact2017In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 388-389, p. 9-17Article in journal (Refereed)
    Abstract [en]

    Material transferred from steel work materials onto the cutting tools largely affects tool life and machining performance. This material transfer is strongly influenced by the steel composition, and different alloying can have very different effects. Crossed cylinders sliding tests can be used to simulate the contact between the chip and the tool in machining. In this work such a test is used to evaluate material transfer and friction characteristics of a TiN coated tool sliding against five model steels. These model steels are especially designed to study the effects from specific combination of alloy elements, i.e. the steels, containing 0.55 mass% C and 1 mass% Si, are alloyed with one or more of 1 mass% Mn, Cr and Al. When using the steels alloyed without Al, Si-rich oxide layers are formed on the coating, resulting in a low friction coefficient. When using the steels alloyed with Al, almost pure Al–O layers are formed, resulting in a higher friction coefficient and rapid coating cracking. Essentially, the most easily oxidized alloy element is most strongly enriched in the oxide and decides the main mechanism of the material transfer and friction behavior.

  • 2.
    Aiso, Toshiharu
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Wiklund, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Kubota, Manabu
    Nippon Steel & Sumitomo Metal Corporation.
    Jacobson, Staffan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Effect of Si and Al additions to carbon steel on material transfer and coating damage mechanism in turning with CVD coated tools2016In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 368-369, p. 379-389Article in journal (Refereed)
    Abstract [en]

    Material transfer from the work materials to the tools strongly influences machining performance and tool life. The influence of Si and Al additions to carbon steel on the material transfer and coating wear in turning with CVD coated carbide tools is investigated. Three model steels are specifically designed to separately study the effects of the individual alloying elements: one reference steel with C as the only alloying element (Base steel), and two steels alloyed also with 1 mass% Si or Al. In the region around the depth of cut on the rake face, where the outside edge of the chip passes over the tool surface, the coating is worn mainly by abrasion when cutting the Base steel. When cutting the Si alloyed steel, an almost pure Si–O transfer layer covers the coating surface, which protects it from wear. When cutting the Al alloyed steel, an almost pure Al–O transfer layer forms on the coating. This layer promotes steel transfer and associated adhesive wear of the coating, which rapidly results in coating detachment and eventually causes notch wear. In the crater region, only the Al alloyed steel results in a transfer layer, an AlN layer that reduces the crater wear.

  • 3.
    André, Benny
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Lewin, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry, Inorganic Chemistry.
    Jansson, Ulf
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry, Inorganic Chemistry.
    Wiklund, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Friction and contact resistance of nanocomposite Ti-Ni-C coatings2011In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 270, no 9-10, p. 555-566Article in journal (Refereed)
    Abstract [en]

    Ceramic nanocomposite coatings in the Ti-Ni-C were deposited using PVD and studied with respect to tribological properties and contact resistance. It was shown that coatings could be deposited combining of a low contact resistance and a low friction coefficient against silver, making them suitable for use in high performance electrical contacts.Nine coatings with different amounts of C and Ni were deposited. Coatings on flat Ni plated copper substrates were tested in a tribological ball-on-disc setup against ball bearing steel balls. Depending on primarily the amount of carbon the coatings showed very different friction coefficient and wear rate. The coatings were also deposited on cylindrical Ni plated copper substrates. Using geometrically identical silver plated cylinders as counter surface these were evaluated in a test setup better resembling a real life electrical contact. For most coatings a low electrical contact resistance was measured. The evolution of friction coefficient and contact resistance was correlated to wear marks and contact tracks, with their generated tribofilms, as examined after testing using electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy.

  • 4.
    Angserud, Jenny
    et al.
    Sandvik Mining.
    From, Anna
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Wallin, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Jacobson, Staffan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Norgren, Susanne
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    On a wear test for rock drill inserts2013In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 301, no 1-2, p. 109-115Article in journal (Refereed)
    Abstract [en]

    In this work wear of cemented carbide rock drill inserts is evaluated by using a rotating rock cylinder as counter surface. The influence on wear rate and degradation mechanisms from varying dry and wet conditions, cemented carbide grade, abrasive particle type and size as well as load is studied. The used abrasive media are alumina and silica.

    Test results show high repeatability and the three tested cemented carbide grades can be differentiated, even though their relative difference in sample hardness is modest. The loads used, 100–200 N, are sufficiently high to cause fracture and wear of the granite rock. The degraded microstructure of inserts tested under wet and dry conditions as well as with added silica particles is similar to field worn inserts. Hence, the same wear mechanisms occur and the test successfully mimics rock drill wear. Typical insert wear includes cracking and fragmentation of WC grains, depletion of Co binder phase and adhered material originating from the rock.

    Tests under dry conditions always cause less measured wear than tests under wet conditions.

    Addition of alumina particles, which are harder than the used cemented carbide samples, causes a significant wear rate increase but does not provide wear similar to rock drilling.

  • 5. Anmark, Niclas
    et al.
    Bjork, Thomas
    Ganea, Anna
    Olund, Patrik
    Hogmark, Sture
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Karasev, Andrey
    Jonsson, Par Goran
    The effect of inclusion composition on tool wear in hard part turning using PCBN cutting tools2015In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 334, p. 13-22Article in journal (Refereed)
    Abstract [en]

    This work reports on hard part turning of carburizing steels using a PCBN cutting tool in fine machining. Emphasis is on the link between composition of the inclusions in work material and wear mechanisms of the cutting tool. A Ca-treated machinability improved 20NiCrMo steel was included together with three other carburizing steels with different inclusion characteristics. Machining tests were conducted to examine cutting tool life and its balance between excessive flank wear and crater wear. The wear mechanisms were examined using a scanning electron microscope (SEM) equipped with an energy dispersive X-ray spectrometer (EDS) and a secondary electron (SE) detector. The longest tool life was obtained when cutting the Ca-treated steel. The improved machinability is linked to the deposition of complex (Mn,Ca)S and (Ca,Al)(O,S) protective slag layers that form on the rake face of the cutting tool during machining. Cutting in this steel also resulted in a typical ridge formation in the tool edge crater. Transfer of workpiece material to the rake face crater is characteristic in hard part turning of steel with high cleanliness. This is suggested to be related to the lack of the sulfides that lubricate conventional machinability treated steels, and that the crater wear of low-sulfur steel is more pronounced than for steels with higher sulfur content.

  • 6. Beste, Ulrik
    et al.
    Jacobson, Staffan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    A new view of the deterioration and wear of WC/Co cemented carbide rock drill buttons2008In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 264, no 11-12, p. 1129-1141Article in journal (Refereed)
    Abstract [en]

    WC/Co cemented carbide is a material developed for highly demanding applications. The unique combination of hardness and toughness makes it especially suitable for wear resistant parts of tools for rock drilling. The wear of cemented carbide rock drill buttons has been the focus of numerous studies, and a large amount of wear data has been published. However, the broad range of possible wear mechanisms, the large number of rock types of very different character, and finally the large local property variations even within a single drill hole, has made it difficult to sort out a good general understanding. One conclusion stands out very clear: the wear data for one rock drill in one rock type is unique to that particular situation and should not be expected to apply to other rock drills in other rock types. Even so, some general wear mechanisms can be observed. Against this backdrop, this paper seeks to present a new, more comprehensive, view on the deterioration and wear mechanisms of cemented carbide rock drill buttons. The new view combines some of most important aspects, including two life limiting factors, five classes of mechanisms of deterioration and five classes of material removal mechanisms. The view is based on careful high resolution investigations of worn rock drill buttons selected from drilling of different rock types. The deterioration includes a fundamental change of material and properties due to intermixing of rock material and cemented carbide in the surface layer of the button. It further includes corrosive decay and oxidation of WC and formation of large-scale cracks in a reptile skin pattern.

  • 7. Beste, Ulrik
    et al.
    Jacobson, Staffan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Targeting micro-sectioning: A technique to study subsurface features in worn specimens2008In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 264, no 11-12, p. 1152-1156Article in journal (Refereed)
    Abstract [en]

    Traditional preparation of metallographic cross sections by cutting, polishing and etching has a long and successful history of revealing grain sizes, phase composition, gradients, etc. However, the technique is limited with respect to precision in the positioning of the cross section, and it also tends to inadvertently remove brittle constituents and conceal cracks and small details close to ductile phases, that may become smeared out by the polishing. The present paper presents an alternative cross sectioning technique for worn surfaces, developed to automatically reveal weak zones in the surface layer of a material, without the need of precise positioning, and also avoiding inadvertent removal of brittle phases. The technique is applicable to materials that exhibit brittle fracture, and is normally used for characterisation of unworn materials. It is primarily intended for studies in the SEM, since the cross sections produced typically exhibit too coarse topography to be sharply pictured in the light optical microscope. The simple and rapid preparation technique is described and examples from worn cemented carbide rock drills and hot rolls are presented to illustrate some of the capabilities of the technique.

  • 8. Beste, Ulrik
    et al.
    Jacobson, Staffan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Hogmark, Sture
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Rock penetration into cemented carbide drill buttons during rock drilling2008In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 264, no 11-12, p. 1142-1151Article in journal (Refereed)
    Abstract [en]

    In percussive and rotary percussive rock drilling, the rock is crushed into small fragments by the repeated hard impact of the drill bit, and subsequently removed by flushing water or air. To avoid excessive wear, the steel drill bit is equipped with a set of cemented carbide buttons that protrude from the bit to take the actual impact. The severe contact against the rock results in some wear of the button, but also in formation of surface layers of rock material and penetration and impregnation of rock material into the cemented carbide structure. This situation, with serious implications for the wear and fracture of the buttons, have previously not been reported. The present findings represent a significantly new understanding of the wear of the rock button material. The deterioration mechanisms are described in detail, using examples from a range of real drilling applications in different rock types. During operation, material in the surface layer of the drill button shifts from that of the original cemented carbide into an uncontrolled composite. This composite is formed by the WC carbide hard phase and a binder consisting of a mixture of cobalt and rock. This new material should be expected to exhibit properties significantly different from the original cemented carbide.

  • 9.
    Braceras, Inigo
    et al.
    Tecnalia Res & Innovat, Mikeletegi Pasealekua 2, San Sebastian, Spain.
    Ibanez, Inigo
    Tecnalia Res & Innovat, Mikeletegi Pasealekua 2, San Sebastian, Spain.
    Taher, Mamoun
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Mao, Fang
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    del Barrio, Andres
    Tecnalia Res & Innovat, Mikeletegi Pasealekua 2, San Sebastian, Spain.
    Saenz De Urturi, Saioa
    Tecnalia Res & Innovat, Mikeletegi Pasealekua 2, San Sebastian, Spain.
    Berastegui, Pedro
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Andersson, Anna M.
    ABB AB, Corp Res, Insulat & Mat Technol, SE-72178 Vasteras, Sweden.
    Jansson, Ulf
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    On the electro-tribological properties and degradation resistance of silver-aluminum coatings2018In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 414, p. 202-211Article in journal (Refereed)
    Abstract [en]

    Contact materials in sliding electrical applications must possess low electrical contact resistance, low friction and wear coefficients, and high degradation resistance to the surrounding media. Silver coatings are commonly used in such applications despite their shortcomings. This work has focused on the study of alternative silver-aluminum coatings deposited by PVD. The main findings include the strong dependence of the tribological performance on the concentration of Al and hence the phases present in the coatings. Besides, the wear mechanism was found to be affected by the working media, either on air or insulating oil. Results have shown that for full HCP phase coatings (Ag67Al33), wear rates are lowest, with no adhesive wear and good surface sulphidation resistance, though with some proclivity to oxidation, coupled with a moderate increase in the electrical contact resistance.

  • 10. Casas, B.
    et al.
    Wiklund, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Lanes, L.M.
    Hogmark, Sture
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Adhesion and abrasive wear resistance of TiN deposited on electrical discharge machined WC-Co cements rbides2008In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 265, no 3-4, p. 490-496Article in journal (Refereed)
    Abstract [en]

    Electrical discharge machining (EDM) is a non-traditional machining method extensively used to manufacture complex geometries of hard and brittle materials such as WC-Co cemented carbides (CC). Although the thermal action of the EDM process is known to yield a relatively poor surface integrity in these materials, it may be minimized through the implementation of multi-step sequential EDM and post-EDM surface treatments. Particularly, hard coating application has been demonstrated to be effective for decreasing the EDM-induced mechanical degradation. However, additional studies are required on such coating-EDMed substrate systems to determine other crucial properties in terms of applications, e.g. adhesion and micro-scale wear behaviour. In this work the adhesion strength and the microabrasive wear resistance of TiN deposited on EDMed substrates have been evaluated by means of scratch and crater grinder testing, respectively. The results indicate that both critical load for decohesion of the coating from the substrate and coating specific wear rate increase with finer-executed EDM, reaching values close to those measured for a TiN coating deposited on a ground and polished substrate.

  • 11.
    Elo, Robin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Heinrichs, Jannica
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Jacobson, Staffan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Wear protective capacity of tribofilms formed on combustion engine valves with different surface textures2017In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 376-377, p. 1429-1436Article in journal (Refereed)
    Abstract [en]

    The valve system controls the flow of gases into and out of the cylinders of combustion engines. As the combustion chamber is repeatedly filled with air and emptied from combustion residues, the contacting surfaces of the valve and valve seat insert (VSI) are exposed to high temperatures, high speed impacts, corrosive environment and high closing forces. Since the expected wear life of the components is hundreds of millions of operational cycles, the wear rate has to be extremely low. Previous studies have shown that this is accomplished by the continual formation of protective tribofilms on the surfaces, formed from oil additive residues. For some stationary gas engines, seemingly random occurrence of severe wear, i.e. without correlation to special running conditions, calls for an improved understanding of the wear protective abilities of these tribofilms. Further, the potential of making the protection more robust by using simple textures on sealing surfaces is investigated. Real valves and VSI's were therefore run in a dedicated test rig, previously shown capable of forming tribofilms similar to those found in real engine valves. Two surface textures, turned or ground, were tested. After a running in phase where fully covering tribofilms were formed, the tests were continued without adding the oil residues needed for replenishing the tribofilm. The flow of oil residues was either completely stopped or only intermittently open. The resulting wear was monitored during testing and after finishing the tests remaining tribofilms were analysed with SEM and EDS. The severity of the wear was graded and the presence of tribofilm and localization of wear was correlated. The endurance of the tribofilms was surprisingly high for both textures. Typically the tribofilms exhibited better wear resistance than the underlying metals. Once fully formed, the tribofilms can therefore endure for a long time without addition of new tribofilm forming material. Both textures showed the first sign of wear after roughly the same time and then followed the same progression, when the flow of oil residues was cut. With the intermittent oil residue supply, both textures performed even better. Especially the turned texture showed only slow, mild wear.

  • 12.
    Elo, Robin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Jacobson, Staffan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Formation and breakdown of oil residue tribofilms protecting the valves of diesel engines2015In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 330-331, p. 193-198Article in journal (Refereed)
    Abstract [en]

    The contacting surfaces of modern valve systems experience a complex contact situation with repeated micro sliding at high temperatures and pressures. The wear rate of the surfaces has to be extremely low to fulfill the high demands on engine efficiency during its entire life-time-wear will cause valve recession and thus make the combustion less efficient. In addition to this, legislation requires reduced particulates in the emissions, which leads to aggravating conditions for the valves. Studies of field samples from well-functioning engines have shown that a protective tribofilm is formed on the contacting surfaces of the valve. This tribofilm is primarily built up from combustion residues of the engine oil and fuel, making its composition sensitive to their additives. Since the low wear rate is dependent on the formation of a tribofilm based on oil residues, while future legislation will demand even cleaner emissions, a deepened understanding about the formation and dynamics of these tribofilms is needed. How quickly are they formed, how quickly do they wear, do they require constant supply of "building material", can they efficiently protect the surfaces also when substantially less building material is available? In the present study, the formation and breakdown mechanisms of this type of protective tribofilms have been investigated in a specifically designed valve rig. This rig uses real engine components and allows controlled addition of oil mist (in the present case from a fully formulated engine oil) into a hot air stream, passing the operating valve. Four phases were identified in the tribofilm dynamics. In the first-formation-phase, oil residue particles become trapped on the sealing surfaces of the valve, and then smeared out between the closing surfaces to form a covering tribofilm. In the second-equilibrium-phase, the tribofilm coverage is stable, meaning that the addition of new particles is balanced by wear of the film. Two types of films form, one thick carbon-based film and one thinner additive-based film. If the supply of oil is cut off, the third-breakdown-phase commences. Here the carbon-based film is quickly removed while the additive-based film keeps protecting the valve surface for numerous closing cycles. When also this film become worn through, the final phase-wear of exposed valve material -commences, involving severe wear and oxidization. Interestingly, it was found that the breakdown was slower if the equilibrium phase was longer, indicating that the additive-based tribofilm becomes more durable by being more worked.

  • 13.
    Fallqvist, M
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Olsson, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Influence of CVD Al2O3 coated tool surface micro topography on the tribological characteristics in metal cutting – Part I2012In: Wear, ISSN 0043-1648, E-ISSN 1873-2577Article in journal (Refereed)
  • 14.
    Fallqvist, M
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Olsson, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Influence of CVD Al2O3 coated tool surface micro topography on the tribological characteristics in metal cutting – Part II2012In: Wear, ISSN 0043-1648, E-ISSN 1873-2577Article in journal (Refereed)
  • 15.
    Fallqvist, Mikael
    et al.
    Högskolan Dalarna, materialvetenskap.
    Olsson, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    The influence of surface defects on the mechanical and tribological properties of VN-based arc-evaporated coatings2013In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 297, no 1-2, p. 1111-1119Article in journal (Refereed)
    Abstract [en]

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

  • 16.
    Forsberg, Peter
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Gustavsson, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Hollman, Patrik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Jacobson, Staffan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Comparison and analysis of protective tribofilms found on heavy duty exhaust valves from field service and made in test rig2013In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 302, no 1-2 SI, p. 1351-1359Article in journal (Refereed)
    Abstract [en]

    Increasing demands from environmental legislations are changing the conditions that the valve system is exposed to in heavy duty engines. Increased pressures, higher temperatures and lower amounts of particulates which can build up a protective film are some of the increasing challenges which the system has to endure. Thick protective tribofilms found on heavy duty exhaust valve surfaces have been analysed with SEM, TEM, EFTEM, STEM-EDS, Nano-indenter and XPS in order to get a better understanding for the tribofilms properties. Two analysed samples are presented in this paper, from a field service truck and another from atest rig which uses vaporised engine oil to simulate the particle flow. The tribofilms are built upfrom several layers with varying compositions. Most of the material originates from oil additives, but also metallic oxides and other carbon compounds produced in the combustion system. The similarities between the rig generated tribofilm and the tribofilm found on the field tested valve verify the test rig behaviour and opens up for realistic wear testing where the importance ofthe protective tribofilm can be investigated in detail that is not possible in motor tests. 

  • 17.
    Forsberg, Peter
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Gustavsson, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Renman, Viktor
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Hieke, André
    Jacobson, Staffan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Performance of DLC coatings in heated commercial engine oil2013In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 304, no 1-2, p. 211-222Article in journal (Refereed)
    Abstract [en]

    Multilayer Diamond Like Coatings (DLC) are widely used to protect highly loaded components from wear and/or to reduce the friction losses in combustion engines. The uppermost layer of the coating controls the chemical situation in the contact and is therefore a very important part of modern multilayer coatings. To examine the individual performances and assess differences and potentials of modern DLC coatings, four commercially available DLCs designed for automotive components with different doping elements together with an uncoated reference were tested in high performance engine oils heated to 90 °C at two different initial contact pressures. The coefficient of friction generally was higher in the tests with the lower initial contact pressure (approximately 20% for all combinations) and the specific wear rate was also up to 100% higher for some combinations. It was also found that a used motor oil showed up to 30% higher friction than when fresh and at the same time reduced the wear in most cases. The tungsten doped coating showed the highest wear, but also the lowest coefficient of friction. The Si doped coating showed the best wear results, most probably due to the ability to make use of the additives in the oil to form a protecting tribofilm.

  • 18.
    Forsberg, Peter
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Hollman, Patrik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Jacobson, Staffan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Wear mechanism study of exhaust valve system in modern heavy duty combustion engines2011In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 271, no 9-10, p. 2477-2484Article in journal (Refereed)
    Abstract [en]

    The increasing demands from environmental legislations are changing the conditions that the valve system is exposed to in heavy duty engines. Increased pressures, higher temperatures and lower amounts of soot which can build up a protective film are some of the increasing challenges which the system has to endure.

    Three pairs of valves and valve seat inserts with the same material and design properties but with different service condition have been analyzed with a variety of analytical instruments to gain information of how the wear occurs.

    The wear mechanisms found were a combination of oxidation, where many different oxides were found, adhesive wear, which was seen both in form of material transfer and flow lines. On top of Sample Mild and Hard there were tribo films of thickness varying from 1 to 5 mu m consisting of Ca, O, P, S and Zn. The film has in all cases protected the underlying surface from wear but in some cases seems to have a corrosive impact instead.

  • 19.
    Gerth, Julia
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Larsson, Mats
    Wiklund, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Riddar, Frida
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Hogmark, Sture
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    On the wear of PVD-coated HSS hobs in dry gear cutting2009In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 266, no 3-4, p. 444-452Article in journal (Refereed)
    Abstract [en]

    A hob is an advanced gear cutting tool usually made of homogenous high-speed steel (HSS) and coated by physical vapour deposition (PVD). It is designed for regrinding and recoating many times. However, hobs of today suffer from unpredictable wear making it difficult to schedule when they should be taken out for reconditioning. This investigation is aimed to contribute to the fundamental knowledge of the wear mechanisms and wear propagation of hobs used in dry gear cutting. Two AlCrN-coated hobs, used in actual gear cutting, were investigated by scanning electron microscopy (SEM) to study the tool topography, light optical microscopy (LOM) to study metallographic cross-sections and by X-ray photoelectron spectroscopy (XPS) for surface analyses.

    It is concluded that the high potential of PVD-coated HSS as tool material is not taken full advantage of. The main reason is a combination of a poor surface preparation prior to coating and excessively high compressive residual stresses, making parts of the coating detach along the edge line even on unused cutting teeth. During cutting, the high intrinsic stresses in combination with droplets and defects in the coating facilitated its fragmentation through decohesion and detachment. Simultaneously, the rake face is gradually covered by a thin oxide layer dominated by Fe, Cr and Mn in about equal amounts, and also with a significant content of Si. It is believed but not proved that this layer is beneficial.

    To improve service life and reliability of gear cutting hobs, precautions should be taken for the grinding–polishing preparation prior to PVD-coating to ensure a smooth substrate free from burning damage and other defects. Also, the edge radius and coating thickness has to be matched with the magnitude of compressive residual stresses in the coating.

  • 20.
    Gerth, Julia
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Werner, Mathias
    KTH.
    Larsson, Mats
    Wiklund, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Reproducing wear mechanisms in gear hobbing: Evaluation of a single insert milling test2009In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 267, no 12, p. 2257-2268Article in journal (Refereed)
    Abstract [en]

    Gear hobbing is a widely used method in industrial gear manufacturing. The most common type of hob is made of homogenous HSS and protected by a PVD coating. In order to increase the reliability and tool life of these milling tools, further developments of the tool surfaces and cutting edges are necessary.

    A single tooth milling test, using a HSS insert in a conventional milling machine, has been developed with the aim to reproduce the wear mechanisms seen on real HSS gear hobbing teeth. The benefits of such a test, compared to actual gear hobbing tests, are primarily accessibility and reduced costs for both design and production of test specimens (inserts).

    The main goal of this study was to verify that the wear mechanisms in the developed test correspond with the wear mechanisms obtained in real gear hobbing. Once this was verified, the influence of surfaces roughness on the performance of TiAlN coated HSS inserts was evaluated by using the tool as delivered or after polishing the tool surfaces. Parameters considered were tool wear, cutting forces and the quality of machined surfaces. The polished inserts, yielded less adhered work material and reduced flank wear but no significant difference in cutting forces as compared to the unpolished inserts.

  • 21.
    Gerth, Julia
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Wiklund, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    The influence of metallic interlayers on the adhesion of pVD TiN coatings on high-speed steel2007In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 264, no 9-10, p. 885-892Article in journal (Refereed)
    Abstract [en]

    In nearly all applications the adhesion of the coating to the substrate is crucial for the components performance and length of life. To enhance the adhesion it is common to use a metallic interlayer, most often titanium. In this study seven different metallic interlayers, namely W, Mo, Nb, Cr, Ti, Ag and Al, have been evaluated with respect to their influence on the adhesion of PVD TiN coatings to polished high-speed steel, ASP 2060. The purpose of this work is to investigate how some physical properties of a metal affect its capability to function as an adhesion interlayer. Samples were prepared using dc magnetron sputtering for the interlayer and reactive dc magnetron sputtering for the TiN coating. The deposition process included both pre-treatments and in situ treatments of the substrate surface in order to eliminate possible contaminations. The adhesion of the coatings was investigated with two different methods: scratch testing and Rockwell adhesion testing. The results indicate that differences in hardness between the metallic interlayers influence the practical adhesion more than differences in E-modulus. Furthermore, in order to optimize adhesion, the hardness of the interlayer should be close to the hardness of the substrate. It was also suggested that stresses, both in the TiN coating and in the metallic interlayer, affect the adhesion properties negatively. In addition, the necessity of interlayer in TiN on HSS can be questioned as the reference samples, without interlayer, showed adhesion properties comparable to the highest ranked interlayer containing samples in our assessment.

  • 22.
    Grandin, Martina
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Wiklund, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Friction, wear and tribofilm formation on electrical contact materials in reciprocating sliding against silver-graphite2013In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 302, no 1-2 SI, p. 1481-1491Article in journal (Refereed)
    Abstract [en]

    In this study nanocomposite coatings mating silver-graphite were investigated for sliding electrical contact applications with the aim to optimize tribological and electrical properties. Apart from two different Ti–Ni–C nanocomposite coatings, brass, steel and TiN were also tested against a commercial silver-graphite at varying load and current. Friction, wear and contact resistance were measured in reciprocating sliding in ambient air. It was concluded that the wear of the silver-graphite was increased by current, for TiN and steel as much as four times, at a 5 N load. A tribofilm, with properties differing from the silver-graphite, formed on the coating/metal surface in all cases. This resulted in a very similar coefficient of friction, 0.3, for all mating materials. However, different load and current gave rise to slightly different thickness and morphology. A too low load was detrimental, as the coating became damaged, while a too high load was not favorable for tribofilm formation. In tests with varying current, a specific current could be identified that best governed the build-up of a well conducting and stable tribofilm. The largest differences were observed in the initial stages of testing, since once the tribofilm was built up, the contact resistance approached that of self mated silver-graphite, 40 mΩ. Experiments showed that the load and the current can be optimized to minimize wear of the silver-graphite which in turn would allow for lower maintenance costs.

  • 23.
    Grandin, Martina
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Wiklund, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Wear and electrical performance of a slip-ring system with silver-graphite in continuous sliding against PVD coated wires2016In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 348, p. 138-147Article in journal (Refereed)
    Abstract [en]

    Sliding electrical contacts transferring current between stationary and rotating components are also tribological systems. Although low contact resistance and noise are prioritised, lower wear rates reduce material usage, and lower friction reduce energy loss. In this paper a slip-ring assembly with wires contacting a silver-graphite ring is investigated with the aim to optimize the wire material to displace all wear to the ring. Uncoated wires and wires coated with nanocomposite Ti-Ni-C or TiN are tested at 100 mA current. Tribofilms, consisting mainly of silver and carbon, form on the wires and a contact resistance of around 0.5 Omega is measured for all wire materials. The properties of the tribofilms control the overall performance and the similarity between them, regardless of wire material, is the reason for the similar contact resistance. The Ti-Ni-C coating wear least on the silver-graphite. Both coatings degrade and wear off during testing, exposing the steel substrate. The steel itself also wears, although not at a rate excluding it as a possible wire material. None of the three surfaces fully displaces wear to the ring only. Considering the performance of the uncoated steel wire, coatings cannot be motivated on behalf of either improved electrical performance or wire protection.

  • 24.
    Grandin, Martina
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Wiklund, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Wear phenomena and tribofilm formation of copper/copper-graphite sliding electrical contact materials2018In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 398-399, p. 227-235Article in journal (Refereed)
    Abstract [en]

    Copper-graphite composites of different compositions sliding against copper are investigated with regards to friction, wear and contact resistance. We find that comprehensive studies including the tribological as well as electrical aspects are rarely found in the literature. We combine friction, wear and contact resistance measurements with thorough surface analysis to complete the understanding. We find that including graphite in the composite greatly reduce the coefficient of friction. However, increasing the vol.% of graphite above 74 will not continue to reduce the friction. We conclude that the coefficient of friction is slightly lower when testing is performed without current than at 5 A current. A comparison of the specific wear rate for the tested composites shows that the one with 74 vol.% of graphite gives the lowest wear rate. In general, the wear rate is higher when tests are performed without current. Chemical analysis of the tribofilm that forms on the copper surface shows that it consists of graphite as well as Cu2O. It is also shown that the amount of graphite in the tribofilm correlates to the composition of the copper-graphite. Novel cross-section images of the tribofilm contribute to a deeper understanding of how sliding electrical contact surfaces are affected by current and sliding motion.

  • 25.
    Gustavsson, Fredrik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Jacobson, Staffan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Cavaleiro, Albano
    Polcar, Tomas
    Frictional behavior of self-adaptive nanostructural Mo-Se-C coatings in different sliding conditions2013In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 303, no 1-2, p. 286-296Article in journal (Refereed)
    Abstract [en]

    Sliding properties of Mo-Se-C coatings with two different carbon content deposited by magnetron sputtering were investigated in different sliding environments (argon, nitrogen, dry and humid air). Both coatings had a structure that was identified as randomly oriented structures of MoSe2 embedded into amorphous carbon matrix. The worn surfaces, i.e. the wear tracks and the wear scars of the balls, were analyzed by optical microscopy, Raman spectroscopy and scanning electron microscopy. The material transferred to the ball steel surfaces was almost exclusively MoSe2, whereas the wear tracks on the coatings were more complex, with areas rich in MoSe2 and areas similar to that of as-deposited coatings. The friction was lowest in argon (0.012 at a load of 10 N) and highest in humid air, but still remarkably low; as best 0.05 at 10 N load; however, the exceptionally low wear rate was almost identical. Thus, we focused our detailed analysis on these two examples to understand the mechanisms responsible for the difference between the friction coefficients. SEM, EDX, XPS, Raman and TEM with EELS and EDX were applied to investigate the composition and structure of localized spots of interest on the tested surfaces. In both cases, we observed well-ordered MoSe2 tribofilms with negligible amount of oxides. Carbon was not present in the sliding interfaces, although large amount of carbon was found outside the contacts on both surfaces. Based on our investigations, we suggest the increase in friction of Mg-Se-C in humid air is primarily due to the increase in shear strength of the MoSe2 structure by the presence of water molecules in the sliding interface

  • 26.
    Hammerström, Lars
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Jacobson, Staffan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Designed high-friction surfaces: influence of roughness and deformation of the counter surface2008In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 264, no 9-10, p. 807-814Article in journal (Refereed)
    Abstract [en]

    The present paper experimentally investigates the prospects of using surfaces with carefully designed topography to design contacts with a high level of static friction. All tests are run under boundary lubricated conditions. Specifically, very high static coefficients of friction (up to mu approximate to 1.2) are demonstrated for surfaces covered with sharp pyramids. The test surfaces were manufactured using micromechanical techniques based on photolithography and etching of silicon followed by deposition of CVD diamond. The technique results in exceptionally well-defined surface textures with very sharp and durable diamond pyramids. The possibilities of using such surfaces for gripping and various types of coupling applications are discussed in some detail. A good correlation between the achieved results and theoretical predictions of the ploughing component of friction is demonstrated. The technique showed to be very robust with only minor influence of surface roughness and counter surface deformation.

  • 27.
    Hanson, Magnus
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Stavlid, Nils
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Coronel, Ernesto
    Hogmark, Sture
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    On adhesion and metal transfer in sliding contact between TiN and austenitic stainless steel2008In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 264, no 9-10, p. 781-787Article in journal (Refereed)
    Abstract [en]

    Austenitic stainless steels are known to be very difficult to machine and form. This is due to their tendency to adhere to the tool material, which then initiates galling. In this paper, austenitic stainless steel has been tested against TiN in un-lubricated sliding contact. The interface between TiN and adhered stainless steel was investigated by transmission electron microscopy. An oxide layer, emanating from the stainless steel, was revealed to be present between the tool surface and the adhered stainless steel. It is concluded that the stainless steel oxide plays a major role for the sticky behavior of this material. To further investigate this phenomenon, austenitic stainless steel samples were also pre-oxidised before testing to examine if the oxide thickness and composition are important for the adhesion tendency. The test showed that the sample oxidised at 800 °C had less tendency to adhere than those oxidised at lower temperatures. The explanation is either its higher thickness, or its high content of Cr-oxide in its surface. The surface of the oxides formed at lower temperatures consists mainly of iron oxide.

  • 28.
    Hassila, Carl Johan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Harlin, P.
    Sandvik Mat Technol AB, Sandviken, Sweden.
    Wiklund, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Rolling contact fatigue crack propagation relative to anisotropies in additive manufactured Inconel 6252019In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 426-427, no Part B, p. 1837-1845Article in journal (Refereed)
    Abstract [en]

    Additive manufacturing is steadily gaining acceptance in certain industry segments as a process for the manufacturing of dense metallic components. The Ni-based superalloys belonging to the Inconel family have for many years been in focus for AM research and AM produced components are now becoming commercially available. However, it is still unclear how the microstructural anisotropy, inherent to most AM materials, affects the material performance in a given application. The anisotropy may e.g. influence the mechanical properties and the performance in certain tribological situations, such as when subjected to rolling contact fatigue. Like most AM methods, the powder bed fusion - laser beam process gives the produced components a relatively rough surface. To perform well in demanding tribological situations, the components are commonly machined to a smooth finish. In this work, Inconel 625 produced using PBF-LB is evaluated in a rolling contact fatigue test. Test cylinders (empty set 10 mm) have been produced using different build directions and scan strategies, resulting in varying microstructures and textures. In the rolling contact fatigue test, a cylindrical sample is mounted between two empty set 140 mm metal rollers, pulled together via a spring. After testing, the contact tracks are studied using SEM and EBSD to reveal cracks. Cracks were analysed with respect to the microstructure and anisotropies. It was found that the anisotropy influences both the nucleation and growth of cracks. The AM produced specimens were also found to be more prone to transgranular cracking than conventional Inconel 625, which predominantly displayed intergranular cracks.

  • 29.
    Heinrichs, Jannica
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Jacobson, Staffan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Laboratory test simulation of galling in cold forming of aluminium2009In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 267, no 12, p. 2278-2286Article in journal (Refereed)
    Abstract [en]

    Cold forming of aluminium is a group of very efficient methods, which are successfully used in a number of industrial applications. Two of the major factors limiting the tool life and restricting the shapes and sizes possible to produce, are galling, i.e. transfer of work material to the tool surface, and high stresses occurring when forming complex shapes. Both phenomena are closely related to the friction and adhesion in the tool to workpiece interface.

    The present paper investigates the influence of several surface parameters to the tendency to galling. This is done by forming aluminium using tool steel in a geometrically simplified lab test. The test scans over a wide load interval while monitoring the coefficient of friction. The corresponding transfer of work material to the tool surface is studied in the SEM after testing. The test is focused on the initial tool contact and also on the number of contacts before a critical friction level is reached.

    The test set-up comprises two crossed cylinders in sliding contact, one made of tool steel and one of work material. Three commercial tool materials were included, each prepared to two surface finishes. The aluminium workpiece cylinders of AA6082 were prepared by two different pre-treatments, solid lubrication followed by soft annealing and pickling, respectively.

    The respective importance of the tool material, preparation of the tool surface finish and the aluminium surface pre-treatment are compared with respect to initial galling tendencies and friction stability. The practical implications for real forming applications are discussed.

  • 30.
    Heinrichs, Jannica
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Jacobson, Staffan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    The influence from shape and size of tool surface defects on the occurrence of galling in cold forming of aluminium2011In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 271, no 9-10, p. 2517-2524Article in journal (Refereed)
    Abstract [en]

    Aluminium alloys are shaped in cold condition in a large number of industrial applications. Simple geometries can be produced to net shape in a single operation. Galling is an important factor limiting the tool life, the complexity of the shapes and the number of processing steps. A selection of ceramic coatings gives a strongly reduced tendency to galling, even without lubricant, as long as the coating surface is smooth. With rough coating surfaces there is no significant improvement compared to the conventionally used uncoated tool steels. The present investigation concentrates on the character of the surface roughness and its influence on galling. Here, surface defects including pyramidal indents and elongated scratches are introduced in a controlled manner and then characterised with optical microscopy and electron microscopy. After testing, the transfer of work material to the tool is studied using electron microscopy and surface analysis. The influence of the various types of local defects is studied with respect to galling tendencies and friction. The shape and extent of the surface roughness is important for galling resistance. Single indents, symbolizing occasional dents in the coating, initially pick up more aluminium than the surrounding coating but do not influence the galling and friction in total. This implies that the forming tools need fine polishing and gentle handling to avoid dents and initial aluminium pick up. The overall surface roughness level is of higher importance for galling and friction.

  • 31.
    Heinrichs, Jannica
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Mikado, H.
    YKK Corp, Machinery & Engn Grp, Tokyo, Japan.
    Kawakami, A.
    YKK Corp, Machinery & Engn Grp, Tokyo, Japan.
    Wiklund, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Kawamura, S.
    YKK Corp, Machinery & Engn Grp, Tokyo, Japan.
    Jacobson, Staffan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Wear mechanisms of WC-Co cemented carbide tools and PVD coated tools used for shearing Cu-alloy wire in zipper production2019In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 420, p. 96-107Article in journal (Refereed)
    Abstract [en]

    To form the individual elements, that together form a zipper, a pre-formed Cu-alloy wire is sheared using cemented carbide tools. The wear caused by the relatively soft copper alloy on the much harder tool is generally quite slow. However, millions of elements are to be sheared so eventually the wear becomes unacceptable and the tool needs to be exchanged. To improve product quality, as well as minimize down time and material consumption, the tool life needs to be prolonged. To achieve this the wear process needs to be better understood. Uncoated tools used for an increasing number of shearing events have been studied in detail using high resolution SEM and EDS, to map the propagating wear and get an insight into the wear mechanisms. Transfer of material from the Cu-alloy to the tool occurs and the wear is highly concentrated to specific areas. This wear occurs on a very fine scale, limited to within individual WC grains at each event. Tools coated with PVD CrC and PVD CrN have been studied for comparison with the uncoated cemented carbide. Both coatings successfully protect the cemented carbide tool from wear, however occasional flaking occurs and then the cemented carbide becomes exposed and subsequently worn. The differences in performance and wear mechanisms between the uncoated and coated tools are discussed, with focus on the capability of the coatings to prolong the tool life.

  • 32.
    Heinrichs, Jannica
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Olsson, M.
    Högskolan Dalarna.
    Jacobson, Staffan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Influence of tool steel microstructure on initial material transfer in metal forming-In situ studies in the SEM2013In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 302, no 1-2 SI, p. 1249-1256Article in journal (Refereed)
    Abstract [en]

    Metal forming constitutes a group of industrially important processes to form metallic components to net shape. When forming aluminium and other materials that tend to stick to the tools, problems associated with material transfer, e.g. galling, may occur. In a previous study by the present authors, in situ observations of aluminium transfer during sliding contact in the SEM revealed that the surface topography and chemical composition of the tool steel counter surface have a strong impact on the initial material transfer tendency. Even if carefully polished to a very smooth surface (Ra < 50 nm), transfer of aluminium was found to immediately take place on a very fine scale and preferentially to the surface irregularities presented by the slightly protruding M(C,N) particles (height 15 nm) in the tool steel. In contrast, the less protruding M6C carbides, as well as the martensitic steel matrix exhibited very little initial transfer. The mechanism behind the preferential pick-up tendency displayed by the M(C,N) particles was not fully understood and it was not possible to determine if the decisive mechanism operates on the microstructural scale, the nanoroughness scale or the chemical bonding scale. In the present study, these mechanisms have been further investigated and analysed by comparing the very initial stages of material transfer onto different types of tool steels in sliding contact with aluminium in the SEM. The tool steels investigated cover conventional ingot cast and powder metallurgy steel grades, selected to possess a range of different types, amounts and sizes of hard phase particles, including MC, M(C,N), M7C3 and M6C. The transfer mechanisms are investigated using high resolution SEM, and the differences between the different microstructures and carbide types are carefully analysed. The implications for real metal forming are discussed. 

  • 33.
    Heinrichs, Jannica
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Olsson, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences. Materials Science, Dalarna University, Sweden.
    Almqvist, Bjarne
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Jacobson, Staffan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Initial surface failure and wear of cemented carbides in sliding contact with different rock types2018In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 408-409, p. 43-55Article in journal (Refereed)
    Abstract [en]

    The initial wear, deformation and degradation of cemented carbide in contact with different rock types are studied using a crossed cylinder sliding test. The sliding distance is limited to centimetres at a time, interrupted by successive SEM analysis. This allows for careful studies of the gradually changing microstructure of the cemented carbide during the test. Five different rock types are included; granite, metal sulphide ore, mica schist, quartzite and marble. All rock types are very different in microstructure, composition and properties. The cemented carbide grade used for the evaluation contains 6 wt% Co and fine (~ 1 µm) WC grains, a grade commonly used in rock drilling. The results show that the cemented carbide microstructure becomes altered already during the very first contact with rock. The initial wear rate and wear character is highly influenced by the rock type. The initial wear of the cemented carbide is highest against quartzite and lowest against marble.

  • 34.
    Heinrichs, Jannica
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Olsson, Mikael
    Dalarna University.
    Jacobson, Staffan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Mechanisms of material transfer studied in situ in the SEM: Explanations to the success of DLC coated tools in aluminium forming2012In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, no 292, p. 49-60Article in journal (Refereed)
  • 35.
    Heinrichs, Jannica
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Olsson, Mikael
    Dalarna University.
    Jacobson, Staffan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    New understanding of the initiation of material transfer and transfer layer build-up in metal forming: In situ studies in the SEM2012In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 292-293, p. 61-73Article in journal (Refereed)
  • 36.
    Heinrichs, Jannica
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Olsson, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Jenei, Istvan Zoltan
    Jacobson, Staffan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Transfer of titanium in sliding contacts: New discoveries and insights revealed by in situ studies in the SEM2014In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 315, no 1-2, p. 87-94Article in journal (Refereed)
    Abstract [en]

    Titanium and its alloys generally display poor tribological properties in sliding contacts due to their high chemical activity and strong adhesion to the counter surface. The strong adhesion causes a high tendency to transfer and ultimately galling or build-up edge formation, resulting in severe surface damage. As a result, forming and machining of titanium and its alloys are generally associated with significant problems such as high friction, rapid tool wear and poor surface finish of the formed/machined surface. In the present study, in situ tests in a scanning electron microscope have been performed to increase the understanding of the mechanisms controlling the initial transfer of titanium (Grade 2) in sliding contact with tool surfaces. Tool materials included cover cold work tool steel, cemented carbide, CVD deposited Al2O3 and PVD deposited DLC. In these tests, a relatively sharp tip, representing the titanium work material, slides against a flat surface, representing the tool. The contact conditions result in plastic deformation of the work material against the tool surface, thereby simulating forming or machining. The limited and well-defined contact, along with the possibility to study the sliding in the SEM, makes it possible to correlate local surface variations to transfer of work material and frictional response. Post-test characterization of the contact surfaces was performed by high-resolution SEM, TEM, EDS and EELS. The initial friction was low and stable against all tested materials, but then gradually escalated against all surfaces except the DLC. The friction escalation was associated to increasing levels of transfer, while the DLC stayed virtually free from transfer. From these very initial sliding tests DLC is a promising tool coating in forming and machining of titanium. 

  • 37.
    Heinrichs, Jannica
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Olsson, Mikael
    Dalarna University.
    Staffan, Jacobson
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Surface degradation of cemented carbides in scratching contact with granite and diamond: the roles of microstructure and composition2015In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 342, p. 210-221Article in journal (Refereed)
    Abstract [en]

    Cemented carbides are composite materials comprising metal carbide grains in a more ductile metallic binder. This microstructure results in a combination of high hardhess and toughness, making them commonly used as rock crushing parts in rock drilling, where they usually show wear on a very fine scale. The hardness and toughness can ultimately be tuned for the application by adjusting the carbide grain size, binder fraction and composition. In the present investigation, the initial micro-scale deformation and wear of polished cemented carbide surfaces is studied by micro scratching with diamond and granite styli, and also by instrumented micro and nanoindentation. The deformation and wear is evaluated on the sub-micrometer scale using high resolution FEG-SEM and FIB cross sectioning. The selected microstructures include besides four cemented carbide grades that are commonly used in rock drilling also binderless and Ni containing grades. This wider range of cemented carbides is used to gain fundamental insights into the relations between microstructure and micro-scale deformation and wear. The results are discussed with respect to their significance for wear of cemented carbides in rock drilling operations.

  • 38.
    Heldin, Magnus
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Wiklund, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Influences of load and temperature on groundwood pulping with well-defined tools2019In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 438-439, article id 203051Article in journal (Refereed)
    Abstract [en]

    Groundwood pulping is an industrial process with a high energy demand, although only a minor part of the energy is used for actually separating the fibres and the rest for working them. Traditionally, the separation process employs a grinding stone having particles embedded in a softer matrix. The position and distribution of the particles have been random, causing their interaction with the wood to also be random. This makes studies of the mechanisms during the separation process difficult. Knowledge of the mechanisms in the separation process helps when designing future tools aimed at energy efficiency or tailored fibre properties. Recently, grinding surfaces having diamond particles brazed to a steel backing at fixed positions have been developed and commercialised. In this work, individual particles are not positioned at the tool surfaces. Instead, well-defined structured diamond films, soldered to a backing, are used as grinding tools. The grinding asperities of such films can be tailored to shapes that are not possible to achieve by using particles. Using this kind of tool in a lab scale grinding equipment, confirms the well-known fact that increased load or increased temperature both lead to lower energy consumption for fibre separation and longer, less damaged fibres.

  • 39.
    Holmberg, Anders
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Andersson, Michael
    Hoganas AB, Bruksgatan 35, SE-26383 Hoganas, Sweden.
    Kassman Rudolphi, Åsa
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Rolling fatigue life of PM steel with different porosity and surface finish2019In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 426-427, no Part A, p. 454-461Article in journal (Refereed)
    Abstract [en]

    Gears made of PM steel are of interest for the automotive industry because they can be produced to near net shape with only a few processing steps. Automotive gears experience a complex contact situation with rolling as well as combined rolling and sliding. They also have to be able to withstand high loads and fairly high temperature variations. Earlier work show that the main limiting parameter of the contact fatigue life of PM steel is the porosity. A higher porosity/lower density will decrease the fatigue life of the PM component. In the present study, the pure rolling contact fatigue life of PM steel with different density and surface finish has been investigated. A rolling contact fatigue test rig, where rods of the tested material are mounted between two rolling wheels, was used. Two densities of PM steel, 6.8 and 7.15 g/cm(3) and a full density reference steel with two different surface finishes, centerless grinded and superfinished, were tested. The tests were run for a given number of load cycles or until failure (fatigue life). SEM was used to study the surfaces and cross-sections to reveal the mechanisms of crack initiation and propagation. The higher density PM steel (7.15 g/cm(3)) outperformed the lower density steel (6.18 g/cm(3)) by a factor of around 4 in fatigue life at the same surface pressure, regardless of surface finish. Cracks are initiated at a depth of around 100 mu m. These cracks propagate and eventually they reach the surface, causing surface damage and failure. For the low density PM steel, both sub surface crack initiation and failure occurred earlier (at a lower number of load cycles) than for the higher density PM steel. Severe surface damage or wear were not found until failure occurred. Still, some initial alteration of the surfaces was seen already after 0.5 million load cycles, in the form of removal of the highest asperity peaks on the centerless grinded surfaces, and opening of the surface pores on the superfinished surface. No effect of surface finish was found on the fatigue life. The difference in surface roughness could induce a difference in local stress concentrations at the surface, but in this test the cracks causing fatigue failure are initiated at a depth where the stress distribution is not affected by local surface stress concentrations. This means that for fairly smooth surfaces roughness, the surface of PM steel is not important when it comes to pure rolling fatigue life.

  • 40.
    Holmberg, Kenneth
    et al.
    VTT, Finland.
    Ronkainen, Helena
    Laukkanen, Anssi
    Wallin, Kim
    Hogmark, Sture
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Jacobson, Staffan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Wiklund, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Souza, M.
    Stahle, Per
    Residual stresses in TiN, DLC and MoS2 coated surfaces with regard to their tribological fracture behaviour2009In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 267, no 12, p. 2142-2156Article in journal (Refereed)
    Abstract [en]

    Thin hard coatings on components and tools are used increasingly due to the rapid development in deposition techniques, tribological performance and application skills. The residual stresses in a coated surface are crucial for its tribological performance. Compressive residual stresses in PVD deposited TiN and DLC coatings were measured to be in the range of 0.03-4 GPa on steel substrate and 0.1-1.3 GPa on silicon. MoS2 coatings had tensional stresses in the range of 0.8-1.3 on steel and 0.16 GPa compressive stresses on silicon. The fracture pattern of coatings deposited on steel substrate were analysed both in bend testing and scratch testing. A micro-scale finite element method (FEM) modelling and stress simulation of a 2 m TiN-coated steel surface was carried out and showed a reduction of the generated tensile buckling stresses in front of the sliding tip when compressive residual stresses of 1 GPa were included in the model. However, this reduction is not similarly observed in the scratch groove behind the tip, possibly due to sliding contact-induced stress relaxation. Scratch and bending tests allowed calculation of the fracture toughness of the three coated surfaces, based on both empirical crack pattern observations and FEM stress calculation, which resulted in highest values for TiN coating followed by MoS2 and DLC coatings, being KC = 4-11, about 2, and 1-2 MPa m1/2, respectively. Higher compressive residual stresses in the coating and higher elastic modulus of the coating correlated to increased fracture toughness of the coated surface.

  • 41. Iwai, Y.
    et al.
    Miyajima, T.
    Mizuno, A.
    Honda, T.
    Itou, T.
    Hogmark, Sture
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Micro-Slurry-jet Erosion (MSE) testing of CVD TiC/TiN and TiC coatings2009In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 267, no 1-4, p. 264-269Article in journal (Refereed)
    Abstract [en]

    Several different experimental techniques are normally used to evaluate tribological properties of thin hard coatings. However, most of the tests cannot assess properties of coating, substrate and interface independently. In this study, the potential of a Micro-Slurry-jet Erosion (MSE) test to swiftly evaluate the intrinsic wear properties of thin single layered and multilayered coatings is demonstrated. A slurry containing 1.2 mu m alumina particles was impacted at high velocity perpendicular to CVD TiC/TiN (TiN on top of TiC) and Tic coatings deposited on cemented carbide. In addition, nano-indentation and XRD, GDOES, AFM analyses were done for the original and worn surfaces. For the TiC/TiN coating, the wear depth of the TiN layer increased linearly until the Tic layer was reached. There after the wear occurred at a lower rate but tended to increase towards the TiC/substrate interlayer. The single layered Tic coating showed the same wear behaviour as the TiC layer of the TiC/TiN coating. The wear rate was constant within the individual TiN and Tic layers, but changed near the interfaces. The micro-topographies of the worn surfaces observed by AFM correlated to the difference in the wear rate of the individual layers and the change in wear rate at the interface to the substrate. The Tic layer proved to have about two times higher wear resistance than the TiN layer. Consequently, the MSE test can distinguish between small differences in the properties of the coatings and of the interlayer zones, and can be used as a screening test when evaluating multilayered as well as single layered coatings.

  • 42.
    Jacobson, Staffan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Hogmark, Sture
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Surface modifications in tribological contacts2009In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 266, no 3-4, p. 370-378Article in journal (Refereed)
    Abstract [en]

    A characteristic of almost any type of dry or boundary lubricated tribological contact is that the composition and tribological properties of the original interface will change during use. The modifications include topography changes (smoothening or roughing), formation of micro-cracks, phase transformations, deformation hardening, formation of oxides, formation of solid films by reactions with lubricant additives, transfer of material from the counter surface, and so on. The thickness of these layers and films range from atomic monolayers (e.g., hydrogen termination of diamond surfaces) to tens of mu m (e.g., plastic deformation of metals). Since the tribological properties of tools, wear parts and mechanical components then are determined by these modified surfaces rather than by the original, they deserve attention and careful assessment. Without the knowledge about how these surface layers are formed and how they modify the tribosystem, it is not possible to predict the friction and wear properties of a material in a given tribological situation. Thus, post-test evaluation including microscopy and analysis of both surfaces and cross-sections is required. A number of surface modifications selected from a wide variety of tribosystems is briefly presented. The corresponding surface modifications range from the most well known and simple to the more complex and relatively unexplored. Finally, the potential of designing materials and lubricants for improved surface modification is discussed and examples are given of current research projects on promoting formation of protecting low-friction tribofilms in boundary-lubricated systems.

  • 43.
    Kassman Rudolphi, Åsa
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Jacobson, Staffan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Gross plastic fretting - examination of the gross weld regime.1996In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 201, no 1-2, p. 255-264Article in journal (Refereed)
  • 44.
    Kassman Rudolphi, Åsa
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Jacobson, Staffan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Gross plastic fretting - mechanical deterioration of silver coated electrical contacts.1996In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 201, no 1-2, p. 244-254Article in journal (Refereed)
  • 45.
    Kassman, Åsa
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Jacobson, Staffan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Surface damage, adhesion and contact resistance of siler coated plated copper contacts subjected to fretting motion1993In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 165, no 2, p. 227-230Article in journal (Refereed)
  • 46.
    Larsson, Elin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Andersson, Anna M.
    ABB Corporate Research, Västerås, Sweden.
    Kassman Rudolphi, Åsa
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Grease lubricated fretting of silver coated copper electrical contacts2017In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 376, p. 634-642Article in journal (Refereed)
    Abstract [en]

    Fretting of silver coated electrical contacts has been studied in a crossed cylinder contact model setup at varying displacement amplitude. The contacts have been tested dry (unlubricated) and lubricated with lithium complex (LiX) and polypropylene (PP) thickened greases. The same polyalphaolefin (PAO) base oil blend was used, hence the thickener is the only difference between the greases. At low displacement amplitude no large difference between dry and lubricated conditions was found. Contact welding occurs for all contacts, also the lubricated. The grease is ejected from the contact area after only a few fretting cycles and the contact welds. A positive effect of grease lubrication on friction and wear is primarily seen at high vibration amplitude, where gross slip is the prevailing fretting regime. For the LiX grease lubricated contacts, fretting at intermediate displacement amplitudes show to be the most critical and the wear marks show much surface damage. Here, the PP grease showed better lubricating effect than the LiX grease.

  • 47.
    Larsson, Elin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Olander, Petra
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Jacobson, Staffan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Boric acid as a lubricating fuel additive - Simplified lab experiments to understand fuel consumption reduction in field test2017In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 376, p. 822-830Article in journal (Refereed)
    Abstract [en]

    In field tests, a boric acid based fuel additive has led to reduced fuel consumption. The reduction was substantial, an average of 6 and 10% in passenger cars and diesel generators respectively. Aiming towards improved understanding of mechanisms behind the fuel saving, three methods to mimic the effect of the additive in the piston-ring/cylinder contact have been evaluated. A reciprocating cylinder/flat configuration with ball bearing steel against grey cast iron was used, and it was lubricated with base oil. The different methods were as following: A) repeated spraying of a small amount of the boric acid solution onto the surfaces, B) predeposition of a boric acid layer on the flat surface and C) a combination of method A) and B). The three methods all showed effects of the additive, spanning from about 20% to 50% reductions (in the latter case, from roughly 0.1 to 0.05 in coefficient of friction averaged over the stroke). The greatest potential of the additive was seen with local coefficient of frictions lower than 0.020 in tests at room temperature with Method C. This means a reduction of around 75% compared to the lowest levels measured for the reference tests run without the additive. The most stable friction test was Method A, where a small amount of boric acid solution was repeatedly sprayed onto the lubricated sliding surfaces. In this type of test, friction reductions of roughly 20% and 40% were found at 100 C and room temperature respectively. The tribological and chemical mechanisms of boric acid in this test configuration are yet not fully understood and more studies are needed. However, the observed poor stability of the tribofilms containing boron and oxygen complicates such activities.

  • 48. Lindholm, Per
    et al.
    Svahn, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Materials Science.
    Study of thickness dependence of sputtered-carbon coating for low friction valve lifters2006In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 261, no 3-4, p. 241-250Article in journal (Refereed)
    Abstract [en]

    This paper presents test and stress calculation results of two thicknesses (0.7 and 1.7 mu m) of amorphous a-C:Cr-coated standard rollers for a cam roller follower valve train mechanism in a diesel truck engine. The coated rollers were tested for 100 h on equipment simulating near-normal engine running conditions. For the thicker coating, the results show mainly polishing wear and low wear on the cam surface. The thinner coating delaminates and the cam shows higher wear. The delamination may be the product of high tensional stresses in the thinner coating, as determined by finite element calculations. These tensions allow surface cracks to propagate down to the chromium interlayer and vice versa.

  • 49.
    Lindquist, Mattias
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Wilhelmsson, Ola
    Jansson, Ulf
    Wiklund, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Tribofilm formation and tribological properties of TiC and nanocomposite TiAlC coatings2009In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 266, no 3-4, p. 379-387Article in journal (Refereed)
    Abstract [en]

    In a recent work a concept for self lubricating low friction TiC and nanocomposite TiAlC coatings was developed. Here we further investigate the mechanical and tribological properties of these coatings. Under identical deposition conditions, the addition of Al initiates the formation of a nanocomposite consisting of (Ti,Al)C grains in an amorphous carbon matrix. The coefficient of friction is lowered from 0.2 to below 0.1 in a pin-on-disc test against steel with unaffected coating wear rate. The lower friction is attributed to a more extensive formation of amorphous carbon and graphitisation on both the counter surface and in the coating wear track. The addition of Al also reduces coating hardness, Young's modulus and the residual stress, which can be explained by the weak carbide-forming ability of Al and the formation of a nanocomposite microstructure.

  • 50.
    Lindquist, Mattias
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Wilhelmsson, Ola
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry, Inorganic Chemistry.
    Jansson, Ulf
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry, Inorganic Chemistry.
    Wiklund, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Tribofilm formation from TiC and nanocomposite TiAlC coatings, studied with Focused Ion Beam and Transmission Electron Microscopy2009In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 266, no 9-10, p. 988-994Article in journal (Refereed)
    Abstract [en]

    This work demonstrate how two different carbide coatings respond very differently to tribological stress and their very different ability to provide low friction tribofilms in dry sliding against steel. Both coatings, TiC and TiAlC, were deposited by DC-magnetron sputtering, but while the TiC is a thermodynamically stable coating, the TiAlC is made metastable with the addition of Al, and therefore releases carbon upon tribological testing. Thus, the TiAlC coating is shown to be self-lubricating on the atomic scale which makes very low friction   achievable. The primary interest in this study is the differences in the tribofilms formed on the steel balls that have been sliding against  the two coatings. Cross-section samples for transmission electron  microscopy were extracted from the ball tribofilms using a focused ion beam instrument. X-ray photoelectron spectroscopy and Raman analysis were employed to provide information on the chemical and structural  characteristics of the tribofilms. It was shown that tribofilms on steel balls largely inherit the structure and composition that evolve   in the coating wear tracks, that the tribofilm microstructure greatly affects the friction level. It was also shown that tribofilm delamination, occurring with tribofilm growth, was initiated in weak ribbon like regions inside the tribofilm.

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