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  • 1.
    Almqvist, Andreas
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Hardell, Jens
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Selected papers from those presented at the 3rd International Tribology Symposium of IFToMM2014In: Lubrication Science, ISSN 0954-0075, E-ISSN 1557-6833, Vol. 26, no 5, p. 273-275Article in journal (Refereed)
  • 2.
    Bara, Özlem
    et al.
    Faculty of Engineering, Department of Mechanical Engineering, Erzincan University.
    Efeoğlu, İhsan
    Faculty of Engineering, Department of Mechanical Engineering, Erzincan University.
    Hardell, Jens
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Adhesion and tribological properties of TiTaBN coatings with a graded interlayer deposited by pulsed DC biased and continuous dc biased magnetron sputtering2015In: Journal of Adhesion Science and Technology, ISSN 0169-4243, E-ISSN 1568-5616, Vol. 29, no 18, p. 2006-2019Article in journal (Refereed)
    Abstract [en]

    The properties of TiBN-based coatings are significantly affected by adding alloying elements and coating parameters. Therefore, in this study, TiTaBN coatings with graded interlayer (CWGIL) were deposited on D2 steel substrates by pulsed DC biased (PDCB) and continuously DC biased (CDCB) closed field unbalanced magnetron sputtering (CFUBMS). The structural, mechanical, adhesion and tribological properties of the coatings were analysed with EDS, SEM, XRD, microhardness, scratch testing and a pin-on-disc tribo-tester (under various atmospheric conditions). TiTaBN CWGIL deposited by PDCB magnetron sputtering (MS) had a very dense microstructure, high hardness and a high critical load value. TiTaBN CWGIL deposited by PDCB MS had a lower friction coefficient, the wear rate and the penetration depth in all atmospheric conditions. In conclusion, the application of a PDCB substrate instead of a CDCB one dramatically increases the performance of CFUBMS-deposited TiTaBN coatings.

  • 3.
    Courbon, Cedric
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Fallqvust, M.
    R&D Materials and Technology Development, Seco Tools AB, Fagersta.
    Hardell, Jens
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    M'Saoubi, R.
    R&D Materials and Technology Development, Seco Tools AB, Fagersta.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Adhesion tendency of PVD TiAlN coatings at elevated temperatures during reciprocating sliding against carbon steel2015In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 330-331, p. 209-222Article in journal (Refereed)
    Abstract [en]

    This work focussed on assessing the contact conditions driving the adhesion tendency of PVD TiAlN coated cemented carbide during reciprocating sliding against a normalized AISI 4137 carbon steel. A special emphasis is given to the surface topography of the coating. Results are analysed in terms of friction and material transfer over a large range of temperatures (up to 800 °C) and contact pressures. The post-test surface analysis of the specimens is conducted in order to understand the tribological behaviour and elucidate the formation mechanisms of transfer layers. A numerical model is developed to assess the amount of heat effectively transmitted into the first bodies and the temperature of the surfaces in contact.Whereas temperatures close to 400 °C ensure the formation of a stable tribofilm reducing friction, the highest temperatures lead to unstable frictional behaviour. Coating surface topography has been seen to be a major parameter driving material transfer during the first stages of the contact and the formation of a transfer layer. Thin and homogeneous layers are almost instantaneously formed with a polished surface whereas some time is required with a rougher one to form a film. A large amount of the frictional power is dissipated into these layers and high temperatures can be reached at the surface due to frictional heating. Contact pressure is found to be a parameter promoting transfer and oxidation

  • 4.
    Courbon, Cedric
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Fallqvust, M.
    R&D Materials and Technology Development, Seco Tools AB, Fagersta.
    Hardell, Jens
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Saoubi, R.M.
    R&D Materials and Technology Development, Seco Tools AB, Fagersta.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Influence of temperature and surface topography on friction and adhesion tendency of PVD TiAIN coating2014Conference paper (Refereed)
  • 5.
    Das, Sanjeev
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Pelcastre, Leonardo
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Hardell, Jens
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Effect of static and dynamic ageing on friction and wear behaviour of aluminium 6082 alloy2012In: 15th Nordic Symposium on Tribology - NordTrib 2012: 12 - 15 June 2012 - Trondheim, Norway, Trondheim: Department of Geography, Norwegian University of Science and Technology, 2012Conference paper (Refereed)
    Abstract [en]

    In recent past, warm forming processes have been used successfully to increase the strength of age-hardenable alloys by dynamic precipitation. However, the influence of dynamic age hardening on the wear and friction behaviour of age-hardenable aluminium alloy is not clear. Therefore, in the present investigation the effect of static and dynamic ageing on the friction and wear behaviour of aluminium 6082 alloy (AA 6082) sliding against tool steel (TS) surface has been studied. The aluminium samples used in the present study were in as-cast, solitionised and peak aged conditions. Optical microscope revealed the presence of dendritic structure in both as-cast and solitionised samples. Scanning electron microscope analysis of the debris and worn surfaces revealed the wear mechanism and role of precipitates on the friction and wear results. At low temperature (40 C), the frictional behaviour of as-cast, solitionised and peak aged samples were similar. The wear rates at 40 C increased with increase in the amount of strain inside the specimens due to fine precipitations. At 180 C, a significant variation in the frictional behaviour of different specimens was observed. The wear rate of solitionised specimens at 180 C is higher compared to as-cast and aged specimens. The absence of hard phases at initial stage of the test and subsequent dynamic precipitates restricted to a thin layer were responsible for the increase in wear rate.

  • 6.
    Das, Sanjeev
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Pelcastre, Leonardo
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Hardell, Jens
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Effect of static and dynamic ageing on wear and friction behavior of aluminum 6082 alloy2013In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 60, p. 1-9Article in journal (Refereed)
    Abstract [en]

    In the present investigation the effect of static and dynamic ageing on the wear and friction behavior of aluminum alloy (AA 6082) sliding against tool steel (TS) surface has been studied. The AA 6082 alloy samples used in the present study were in as-cast, solutionized and peak aged conditions. Scanning electron microscope analysis of the debris and worn surfaces revealed the role of precipitates on the dry sliding wear behavior. Frictional behavior varies significantly for all the conditions at elevated temperature (180 °C) compared to room temperature (40 °C). Such response was attributed to the dynamic precipitations during elevated temperature test.

  • 7.
    Deng, Liang
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Mozgovoy, Sergej
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Hardell, Jens
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Oldenburg, Mats
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Development of a Tribological Test Programme Based on Press Hardening Simulations2017In: Tribology letters, ISSN 1023-8883, E-ISSN 1573-2711, Vol. 65, no 2, article id 43Article in journal (Refereed)
    Abstract [en]

    Press hardening is widely utilized to form ultra-high-strength steels characterized by a high strength-to-weight ratio for automotive components. Press hardening processes include heating boron–manganese steels to austenite phase, forming the steels at a high temperature, and cooling the formed blanks until the martensite phase is reached . However, press hardening processes lead to severe contact conditions between the blank and the tools including contact pressure, relative sliding, and high temperatures, which result in tool wear and increased maintenance cost. The contact conditions that occur in the stamping tool are difficult to study on site. Additionally, simplified tests, such as pin on disc and ball on disc, are insufficient to reproduce press hardening conditions in laboratory environments . The aim of this study includes developing a tribological test with press hardening conditions in which tool steel pins continuously slide on fresh and hot boron–manganese steel strips. The test programme mimics press hardening conditions with respect to sliding distance, sliding velocity, contact pressure, and surface temperature that were studied based on finite element (FE) simulations of a press hardening experiment. Furthermore, a FE simulation of the tribological test is established and it provides contact temperature in the pin tip with a high accuracy. A tribological test is used to study friction and mass loss with variational pressures and velocities that represented typically variational contact conditions in the press hardening. The tribological test is also used to obtain correlations between the tribological behaviours and process parameters in press hardening including pressure and sliding velocity.

  • 8.
    Deng, Liang
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Mozgovoy, Sergej
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Hardell, Jens
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Oldenburg, Mats
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Implementation of wear models for stamping tools under press hardening conditions based on laboratory tests2014In: Advanced Materials Research, ISSN 1022-6680, E-ISSN 1662-8985, Vol. 1063, p. 339-342Article in journal (Refereed)
    Abstract [en]

    Tool wear occurring in press hardening processes receives insufficient attention since its corresponding measurements and full-scale experiments are complicated and expensive. This paper presents a study of tool wear in press hardening based on laboratory experiments and FE-simulations. Two experimental laboratory setups depending on the contact conditions in press hardening build the base for the wear models implemented in the FE-simulation to predict wear depths. The highest wear depth is found at the radius of the stamping tool and the discrepancies in wear predictions based on the two different laboratory test setups are analyzed.

  • 9.
    Deng, Liang
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Mozgovoy, Sergej
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Hardell, Jens
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Oldenburg, Mats
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Numerical study of contact conditions in press hardening for tool wear simulation2017In: International Journal of Material Forming, ISSN 1960-6206, E-ISSN 1960-6214, Vol. 10, no 5, p. 717-727Article in journal (Refereed)
    Abstract [en]

    In the press hardening industry, industrial and academic efforts are being directed toward predicting tool wear to realize an economical manufacturing process. Tool wear in press hardening is a tribological response to contact conditions such as pressure and sliding motion. However, these contact conditions are difficult to measure in-situ. Furthermore, press hardening involves high temperatures, and this increases the complexity of the tribo system. The present work investigated the contact conditions of press hardening with a commercial FE code (LS-DYNA) as a base for tool wear simulation. A press hardening experiment was established in industrial environments and evaluated through FE simulations. The numerical model was set up so as to approximate the manufacturing conditions as closely as possible, and the sensitivity with respect to the friction coefficients was examined. The influence of numerical factors such as the penalty value and mesh size on the contact conditions is discussed. The implementation of a modified Archard’s wear model in the FE simulation proved the possibility of tool wear simulation in press hardening. Finally, a comparison between the tool wear simulation and the measured wear depth is presented. 

  • 10.
    Deng, Liang
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Mozgovoy, Sergej
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Hardell, Jens
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Oldenburg, Mats
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Press-hardening thermo-mechanical conditions in the contact between blank and tool2013In: 4th International Conference Hot Sheet Metal Forming of High-performance Steel CHS: June 9-12, Luleå, Sweden : Proceedings / [ed] Mats Oldenburg; Braham Prakash; Kurt Steinhoff, Auerbach: Verlag Wissenschaftliche Scripten , 2013, p. 293-300Conference paper (Refereed)
  • 11.
    Deng, Liang
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Mozgovoy, Sergej
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Hardell, Jens
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Oldenburg, Mats
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Validation of tool-wear simulations based on a full-scale press hardening experiment2015In: Hot Sheet Metal Forming of High-Performance Steel 5th International Conference: May 31-June 3, Toronto, Canada : Proceedings / [ed] Kurt Steinhoff; Mats Oldenburg; Braham Prakash, Auerbach: Verlag Wissenschaftliche Scripten , 2015, p. 121-128Conference paper (Refereed)
    Abstract [en]

    To extend the service life of stamping tools for press hardening processes, tool wear prediction gradually becomes an important topic of concern in industry. However, wear simulations based on the finite element method are mainly developed in laboratory and the lack of validation of full-scale experiments restricts the proposal of an accurate wear model. The work presented in this paper aims at validating the used wear models for stamping tools through a full-scale press hardening experiment. The wear model in conjunction with finite element (FE) simulations are dependent on contact mechanics and the corresponding wear data is obtained from laboratory tests, where the test parameters are specified in ranges that accord with the contact conditions of press hardening. The full-scale press hardening experiment producing a dog-bone shaped part is run for 200 continuous strokes. Geometry updating of the stamping tool is used to investigate the influence of shape change on the pressure occurring on the tool. The results have shown that the geometry change of the stamping tool, after producing a large number of parts, causes changes in the contact pressures and therefore affects the wear simulation. In the end, the wear simulation results are compared to the preliminary result of the full-scale press hardening.

  • 12.
    Deng, Liang
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Oldenburg, Mats
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Mozgovoy, Sergej
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Hardell, Jens
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Wear Observations on Uncoated Tool and Workpiece Surfaces from a Full-Scale Press Hardening Wear Test2017In: Advanced High Strength Steel and Press Hardening / [ed] Zhang, Y; Ma, M, Singapore: World Scientific, 2017, p. 433-437Conference paper (Refereed)
    Abstract [en]

    Tool wear in press hardening has attracted researchers' attention and recently several papers have focused on the wear observations in the laboratory tests mimicking the press hardening conditions. However, the wear observations and quantification in full-scale press hardening tests are rare in view of high costs and longtime requirements. In this work, the wear behavior in a full-scale press hardening wear test has been studied in order to understand the wear mechanisms occurring in the stamping tool. Furthermore, the wear depths in the real stamping tool were measured by using a coordinate measurement machine (CMM) that can provide the quantified wear result and serve as a base to validate the possible wear model. The present study also includes the wear observations in both the counterparts i.e., the blank (workpiece) and the stamping tool with the aim of studying the transfer material/wear particles. Two common tool steels were used in the full-scale press hardening wear test and the differences in the wear severities were observed. Since abrasion and adhesion are major wear mechanisms previously in many laboratory tests, the present study identifies the wear evolution and mechanisms on uncoated tool and workpiece surfaces in the press hardening wear test.

  • 13.
    Deng, Liang
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Pelcastre, Leonardo
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Hardell, Jens
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Oldenburg, Mats
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    A Tribological Test under Press Hardening Conditions for Galling Research2017In: 6th International Conference Hot Sheet Metal Forming of High-Performance Steel CHS2: June 4-7 2017, Atlanta, Georgia, USA : proceedings / [ed] Mats Oldenburg, Braham Prakash, Kurt Steinhoff, Warrendale, PA: Association for Iron & Steel Technology, AIST , 2017, p. 453-460Conference paper (Refereed)
  • 14.
    Deng, Liang
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Pelcastre, Leonardo
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Hardell, Jens
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Oldenburg, Mats
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Experimental Evaluation of Galling Under Press Hardening Conditions2018In: Tribology letters, ISSN 1023-8883, E-ISSN 1573-2711, Vol. 66, no 3, article id 93Article in journal (Refereed)
    Abstract [en]

    Severe adhesion, also referred to as galling, is a critical problem in press hardening, especially in stamping tools used for hot forming of Al–Si-coated ultra-high strength steel. Galling is known to develop rapidly on the tool surface and it negatively affects the quality of the formed products. Earlier research on this topic has focused on the galling initiation. However, studies on the galling development during extended sliding and the corresponding quantitative measurement still lack depth. In the present study, a tribological test is established to study the galling development under press hardening conditions. The tribological test set-up aims to simulate extended sliding between the Al–Si-coated boron steels and the tool die material. The contact conditions in the interface are studied by a numerical model of the tribological test. The friction coefficients and material transfer are discussed taking into account the variation of the different test conditions. Using the results from the tribological tests, the galling simulation is performed in the numerical model. A geometry-updated sample based on the galling (transferred material build-up) height is simulated and the consequent pressure fluctuation is obtained in the numerical model. This contributes to the explanation of the severe transferred material accumulation during the test.

  • 15.
    Efeoglu, Ihsan
    et al.
    Atatürk University.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Hardell, Jens
    Interfacial scratch adhesion behavior of multilayered Ti(BN):Ti(MoS2) based PVD coatings2009Conference paper (Other academic)
    Abstract [en]

    Interfacial adhesion is critical property of multilayered thin films used in micro-electromechanical systems, ceramic capacitors, wear resistant coatings. In the present investigation, Ti(BN)+Ti(MoS2) solid multilayered composite solid lubricant coatings were deposited by magnetron sputtering from separate Ti, TiB2, and MoS2 target. X-ray diffraction, microhardness tester, and scratch tester were used to evaluate structural, mechanical and interfacial adhesion properties. In the work, described here changes in the adhesion of intercoat exhibited by nine different coatings deposited under variants of deposition parameters have been investigated. It is found that the crack propagates alternatively between the two interfaces with thinning of the interlayer.

  • 16.
    Gebretsadik, Daniel
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Hardell, Jens
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Efeoğlu, Ihsan
    Atatürk University.
    Prakash, Braham
    Tribological properties of composite multilayer coating2010In: 14th Nordic Symposium on Tribology: NORDTRIB 2010 : Storforsen, Sweden, June 8-11, 2010, Luleå: Luleå tekniska universitet, 2010Conference paper (Refereed)
    Abstract [en]

    The use of surface coatings is emerging as one of the most important approaches in reducing friction and wear in various tribological applications. Even though single layer coatings have a wide range of applications, the performance of the single layer alone may not always be adequate to meet the desired tribological property requirements. Hence, coatings consisting of multi-layers to meet different property requirements in demanding applications are required. In this study, the tribological properties of a graded composite multilayer coating with a specific layer sequence of MoS2:Ti/MoS2:TiBN/TiBN/TiB2/Ti deposited on tool steel substrate have been investigated at temperatures of 40°C and 400°C respectively. The experimental results from the tests at 40°C have shown that the friction coefficient value rangesbetween 0.02 and 0.034. It was found that the deposition parameters influenced the friction and durability of the coatings. Higher substrate bias was found to result in higher friction and the coating deposited at high substrate bias and low N2 flow showed the lowest durability. The friction coefficient and durability of the coatings were found to be highly dependent on temperature. At high temperature, the friction coefficient increases almost three fold and the durability decreases significantly.

  • 17.
    Gebretsadik, Daniel
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Hardell, Jens
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Efeoğlu, Ihsan
    Faculty of Engineering, Department of Mechanical Engineering, Atatürk University, Erzurum, Turkey.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Tribological properties of composite multilayer coating2011In: Tribology - Materials, Surfaces & Interfaces, ISSN 1751-5831, E-ISSN 1751-584X, Vol. 5, no 3, p. 100-106Article in journal (Refereed)
    Abstract [en]

    The use of surface coatings is emerging as one of the most important approaches in reducing friction and wear in various tribological applications. Even though single layer coatings have a wide range of applications, the performance of the single layer alone may not always be adequate to meet the desired tribological property requirements. Hence, coatings consisting of multilayers to meet different property requirements in demanding applications are required. In this study, the tribological properties of a graded composite multilayer coating, with a specific layer sequence of MoS2/Ti‐MoS2/TiBN‐TiBN‐TiB2‐Ti deposited on tool steel substrate, have been investigated at temperatures of 40 and 400°C respectively. The experimental results from the tests at 40°C have shown that the friction coefficient value ranges between 0�02 and 0�034. It was found that the deposition parameters influenced the friction and durability of the coatings. Higher substrate bias was found to result in higher friction, and the coating deposited at high substrate bias and low N2 flow showed the lowest durability. The friction coefficient and durability of the coatings were found to be highly dependent on temperature. At high temperature, the friction coefficient increases almost threefold, and the durability decreases significantly.

  • 18.
    Gebretsadik, Daniel
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Hardell, Jens
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Embeddability behaviour of some Pb-free engine bearing materials2016Conference paper (Other academic)
    Abstract [en]

    An important requirement on engine bearing materials is its ability to embed dirt/abrasive particles onto the bearing surface and minimize damage to the expensive crankshaft. This property is achieved by applying an overlay onto the lining. In this work, a journal bearing test rig that operates under steady loading condition has been employed to investigate the embeddability behaviour of selected multi-layered Pb-free engine bearing materials in the presence of contaminant/abrasive particles in engine oil. Test materials include Pb-free bearing materials with overlay compositions of Sn, Bi, PAI containing MoS2 and graphite. Pb-based overlay has also been studied as a reference. Embeddability behaviour in terms of wear and changes in surface topography has been investigated. The damage on the shaft and the bearing surfaces were studied in order to elucidate the mechanisms involved. It has been possible to distinguish between the embeddability characteristics of different materials.

  • 19.
    Gebretsadik, Daniel
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Hardell, Jens
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Friction and wear characteristics of different Pb-free bearing materials in mixed and boundary lubrication regimes2014Conference paper (Refereed)
    Abstract [en]

    Traditional bearing materials contain different amounts of lead (Pb) due to its friction reducing properties. However, in view of the negative health and environmental impact of Pb, there are new directives that limit the usage of Pb in engine bearings. Owing to this, new bearing materials that provide at least comparable tribological performance to that of Pb containing alloys are emerging and manufacturers have already started manufacturing Pb-free bearing materials. It is, however; still unclear how these new engine bearing materials would perform in mixed and boundary lubricated conditions. In this study, a block-on-ring test setup was employed to investigate the tribological performance of several bimetal and multi-layer Pb-free bearings with different compositions of lining and overlay materials. Pb-containing bearing material was also studied as a reference material. Friction and wear properties of these bearing materials were investigated and their wear mechanisms under lubricated conditions have been analysed.

  • 20.
    Gebretsadik, Daniel
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Hardell, Jens
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Friction and wear characteristics of different Pb-free bearing materials in mixed and boundary lubrication regimes2014Conference paper (Refereed)
    Abstract [en]

    Traditional bearing materials contain different amounts of lead (Pb) because of its friction reducing properties. However, in view of the negative health and environmental impact of Pb, there is growing emphasis on restricting the usage of Pb in engine bearings. Owing to this, new bearing materials that provide at least comparable tribological performance to that of Pb containing alloys are being developed and some new Pb-free materials are being already used in engine bearing applications. It is, however, still unclear how these newengine bearing materials would perform in mixed and boundary lubricated conditions. In this study, a block-on-ring test setup was employed to investigate the tribological performance of several bimetal and multi-layer Pb-free bearing materials with different compositions of bearing lining and overlay plating. Pb-containing bearing material was also studied as a reference material. Friction and wear properties of these bearing materials wereinvestigated and their wear mechanisms under lubricated conditions have been analysed. Bearing material with overlay of Polyamide-Imide with graphite and MoS2 exhibited better friction and wear properties than Pb-based and Al-Sn based materials. Pb-containg bearing material shows higher wear and Al-Sn based material has shown higher friction.

  • 21.
    Gebretsadik, Daniel
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Hardell, Jens
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Friction and wear characteristics of different Pb-free bearing materials in mixed and boundary lubrication regimes2015In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 340-341, p. 63-72Article in journal (Refereed)
    Abstract [en]

    Traditional bearing materials contain different amounts of lead (Pb) because of its friction reducing properties. However, in view of the negative health and environmental impact of Pb, there is growing emphasis on restricting the usage of Pb in engine bearings. Owing to this, new bearing materials that provide at least comparable tribological performance to that of Pb containing alloys are being developed and some new Pb-free materials are being already used in engine bearing applications. It is, however, still unclear how these new engine bearing materials would perform in mixed and boundary lubricated conditions. In this study, a block-on-ring test setup was employed to investigate the tribological performance of several bimetal and multi-layer Pb-free bearing materials with different compositions of bearing lining and overlay plating. Pb-containing bearing material was also studied as a reference material. Friction and wear properties of these bearing materials were investigated and their wear mechanisms under lubricated conditions have been analysed. Bearing material with Polyamide-Imide based overlay containing graphite and MoS2 exhibited better friction and wear properties than Pb-based and Al-Sn based materials. Pb-containing bearing material shows higher wear of material and Al-Sn based material has shown higher friction compared with the other test materials.

  • 22.
    Gebretsadik, Daniel
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Hardell, Jens
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Investigations into Seizure Behaviour of Pb-free Engine Bearing Materials Under Dry Condition2015Conference paper (Other academic)
    Abstract [en]

    Due to new environmental regulations, Pb-free engine bearing materials are becoming more common and there is a need for studying their tribological performance. Under severe and nonideal operating conditions, failure due to seizure can occur in engine bearings. In this work, seizure behaviour of different multi-layered engine bearing materials has been studied by using a block-on-ring test set up. These materials included Al-Sn based lining with no overlay, bronze lining with Polyamide-imide (PAI) based overlay containing MoS2 and graphite, bronze lining with two overlays of Al-Sn based and PAI based overlay, bronze based lining with Sn-based overlay and bismuth (Bi) containing bronze with Sn-based overlay. Tests were performed by progressively increasing the load in a stepwise manner at a constant speed under unidirectional dry sliding conditions. Bronze based lining with a PAI based overlay containing MoS2 and graphite did not exhibit seizure up to a load of 475 N. For Al-Sn based lining without overlay, seizure occurs at relatively lower load of 125 N. In most cases, there is material transfer onto the counter surface test ring. The test materials, counter surfaces and the wear debris were analysed using SEM incorporating EDS with a view to explain the seizure mechanisms.

  • 23.
    Gebretsadik, Daniel
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Hardell, Jens
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Seizure behaviour of Pb-free engine bearing materials under dry condition2018In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 232, no 2, p. 106-116Article in journal (Refereed)
    Abstract [en]

    Due to new environmental regulations, Pb-free engine bearing materials are becoming more common and there is a need for studying their tribological performance. Under severe operating conditions, failure due to seizure can occur in engine bearings. In this work, seizure behaviour of different multi-layered engine bearing materials has been studied by using a block-on-ring test setup under dry condition. These materials included Al–Sn-based lining with no overlay, bronze lining with polyamide-imide-based overlay containing MoS2 and graphite, bronze lining with two overlays of Al–Sn-based and polyamide-imide-based material, bronze-based lining with Sn-based overlay and bismuth (Bi)-containing bronze with Sn-based overlay. The tests were performed by gradually increasing the load at a specific time interval and in a stepwise manner and at a constant speed under unidirectional dry sliding conditions. The test materials, counter surfaces and the wear debris were analysed using SEM with a view to understand the seizure mechanisms. Bronze-based lining with a polyamide-imide-based overlay containing MoS2 and graphite does not exhibit seizure up to a load of 475 N. For Al–Sn-based lining without overlay, seizure occurs at a relatively lower load of 125 N. The Al–Sn-based lining with no overlay shows higher friction and the polyamide-imide-based overlay containing MoS2 and graphite shows lower friction during the seizure test. In most cases, there is material transfer onto the test ring counter surface. Material transfer onto the counter surface either due to severe adhesion or wear debris adhered and smeared on it. Al–Sn-based lining and an exposed Al–Sn-based overlay show severe adhesion that causes seizure. On the other hand, exposed Pb containing lining and Bi containing lining seize due to mechanical interlocking caused by the adhered wear debris on both surfaces.

  • 24.
    Gebretsadik, Daniel
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Hardell, Jens
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Seizure behaviour of some selected Pb-free engine bearing materials under lubricated condition2017In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 111, p. 265-275Article in journal (Refereed)
    Abstract [en]

    Under severe operating conditions seizure can occur in engine bearings. Therefore it is important to study seizure behaviour of selected Pb-free bearing materials that may replace the conventional Pb-based materials. Seizure tests were carried out using a block-on-ring test configuration by stepwise increasing applied load at a constant rotational speed using base oil and also fully formulated engine oil respectively. The bearing materials are ranked in terms of friction and seizure load. Al-Sn based lining without overlay shows higher friction and lower seizure load in both oils. Polyamide-imide based overlay containing MoS2 and graphite and Pb-based material show no sign of seizure. For Sn-based overlay plated materials seizure load is higher in fully formulated engine oil than in base oil.

  • 25.
    Gebretsadik, Daniel
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Hardell, Jens
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Tribological performance of tin-based overlay plated engine bearing materials2015In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 92, p. 281-289Article in journal (Refereed)
    Abstract [en]

    A block-on-ring test setup is employed to investigate tribological performance of Sn-based overlay plated bearing materials under mixed and boundary lubrication condition. Pb-containing bearing material is also studied as a reference. Sn-based and Pb-based overlays have shown similar transition in friction when rotational speed is varied. Under relatively longer test duration, Sn-based overlays exhibit comparable friction and wear properties with that of Pb-based overlay. It takes longer time to obtain steady-state friction for Sn-based overlay than Pb-based overlay. Wear behaviour of tested samples are also similar except for tests in the mixed lubrication regime where Sn-based overlays show better wear resistance. In the Sn-based overlays main wear mechanisms are adhesive and abrasive wear leading to exposure of the Ni interlayer.

  • 26.
    Hardell, Jens
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    High temperature tribology of high strength boron steel and tool steels2007Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    There are many tribological interfaces that are exposed to elevated temperatures. Typical examples are the interfaces of various moving assemblies, for examples in aerospace industry, power generation and metalworking processes. The exposure of materials to elevated temperatures results in highly complex interfaces due to changes in morphology, microstructure and mechanical properties coupled with the occurrence of oxidation and diffusion. All of these changes will influence the tribological behaviour of materials at elevated temperatures. Another major concern is lubrication at elevated temperatures since conventional lubricants do not perform at temperatures above ~300ºC. High strength steels are commonly used as structural reinforcements or energy absorbing systems in automobile applications due to their favourable strength to weight ratios. The high strength of these steels leads to several problems during forming such as poor formability, increased spring back, and tendency to work-harden. In view of these difficulties, high strength steels are usually formed at elevated temperatures with a view to facilitating forming and simultaneous hardening by quenching of complex shaped parts. A review of published literature has revealed that only a few studies pertaining to high temperature tribology (including those of hot metalworking) have been carried out so far. The understanding of the high temperature tribological behaviour of high strength steels and tool steel pairs is also highly inadequate. The aim of this work is therefore to obtain a better understanding of the friction and wear mechanisms of tool steel and high strength boron steel tribological pairs at elevated temperatures. The experimental studies were carried out by using a high temperature version of the Optimol SRV reciprocating friction and wear test machine. The tribological studies were performed at temperatures ranging from 40ºC to 800ºC. The experimental materials were tool steels of three different alloying compositions (with and without nitriding) and high strength boron steel (unhardened, hardened, with and without Al-Si coating). The results have shown that both friction and wear of tool steel and high strength steel pairs are temperature dependant. An increase in temperature has resulted in lower friction for all the material pairs. Tool wear increased when the temperature increased from 40 to 400ºC during sliding against uncoated high strength steel but remained unchanged when the temperature increased further to 800ºC. When sliding against Al-Si coated high strength steel, tool wear increased with increasing temperature. Plasma nitriding of tool steels has been effective in reducing friction as well as in providing protection against severe adhesive wear. The Al-Si coating on the high strength steel has resulted in high friction at low temperatures and low friction at elevated temperatures. It has also shown an increased wear resistance at elevated temperatures. The coating undergoes significant surface morphological changes when exposed to elevated temperatures which are likely to influence its tribological behaviour. Hardening of the high strength steel has resulted in decreased friction at all temperatures. It led to higher tool wear at low temperatures and lower tool wear at elevated temperatures

  • 27.
    Hardell, Jens
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Tribology of hot forming tool and high strength steels2009Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Tribological research pertaining to moving machine components operating at elevated temperatures has so far received only limited attention despite the fact that many technological applications encounter high-temperature conditions. Examples of such applications can be commonly found in the aerospace, power generation and hot metal working industries. In the metal working field, thermo-mechanical forming of high-strength steel components has grown very rapidly in recent years. The increased usage of such components has its driving forces in improved crashworthiness, reduced fuel consumption and conservation of natural resources. These processes, invented about 30 years ago in northern Sweden, enable the forming of complex shaped components at elevated temperatures and the simultaneous control of complex microstructures. Despite the fact that more than 30 years of research has gone into developing and optimising these thermo-mechanical processes there are several aspects which have not been adequately studied or understood. One of these aspects is the tribology of the tool-workpiece interaction at the high temperatures encountered during hot metal forming. This is where tribological research can contribute greatly in improving the hot sheet metal forming processes. The main tasks involved are the understanding, prediction and control of friction as well as wear during the interaction of tool and workpiece at elevated temperature. Future research also needs to consider the tribology of rapidly emerging surface engineering technologies that have potential for high temperature applications such as hot metal forming. This work has focussed on investigating the friction and wear characteristics of different tool steels during sliding against ultra high strength boron steel at different temperatures ranging from room temperature to 900 °C. Tribological studies have also been conducted on surface treated/coated tool steels during sliding against coated workpiece material with a view to explore the potential of surface engineering in controlling friction and minimisation of wear at elevated temperatures.The results have shown that friction and wear characteristics of these material pairs are temperature dependant and generally the tribological interaction of the tool-workpiece pair at elevated temperatures result in reduced friction and increased wear of the tool material. The main wear mechanisms at elevated temperatures are adhesive and abrasive and interaction with oxidised wear debris has a significant influence on the tribological behaviour of the system. Plasma nitriding of the tool steel has resulted in reduced and more stable friction and also improved resistance against severe adhesive wear at elevated temperatures. The best wear resistance has been achieved by applying a duplex surface modification system on the tool steel (nitriding + PVD coating). Application of a surface coating on the ultra high strength boron steel, Al-Si or Al-Si with graphite, has been shown to have a much greater effect on the frictional behaviour compared to that on the tool surface. This, however, has an effect on tool wear owing to the abrading action of the hard intermetallic layer formed on the Al-Si coated UHSS surface when exposed to high temperatures.

  • 28.
    Hardell, Jens
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Almqvist, Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Neville, Anne
    School of Mechanical Engineering, University of Leeds.
    Liśkiewicz, Tomasz W.
    School of Mechanical Engineering, University of Leeds.
    Editorial2014In: Tribology - Materials, Surfaces & Interfaces, ISSN 1751-5831, E-ISSN 1751-584X, Vol. 8, no 2, p. 55-56Article in journal (Other academic)
  • 29.
    Hardell, Jens
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Efeoğlu, Ihsan
    Atatürk University.
    Prakash, Braham
    Tribological degradation of MoS2-Ti sputtered coating when exposed to elevated temperatures2009Conference paper (Other academic)
  • 30.
    Hardell, Jens
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Efeoğlu, Ihsan
    Atatürk University, Faculty of Engineering, Department of Mechanical Engineering, Erzurum.
    Prakash, Braham
    Tribological degradation of MoS2-Ti sputtered coating when exposed to elevated temperatures2010In: Tribology - Materials, Surfaces & Interfaces, ISSN 1751-5831, E-ISSN 1751-584X, Vol. 4, no 3, p. 121-129Article in journal (Refereed)
    Abstract [en]

    The use of solid lubricants is an effective way to control friction and wear in applications where traditional lubricants such as oils and greases cannot be used. MoS2 is a popular solid lubricant which has been widely used in many applications, especially space applications in view of its good performance in vacuum. Recent developments in physical vapour deposition technology have led to the development of sputtered MoS2 films doped with different metals to improve their durability and reduce the detrimental effects of oxidation and humidity on their tribological performance. In this work, a MoS2-Ti coating deposited on a hot forming tool steel substrate has been studied at ambient and elevated temperatures. The objective was to investigate how the friction and durability of the MoS2-Ti coating are affected after exposure to elevated temperatures. The results have shown that low friction values of ∼0·02 were obtained at room temperature and low relative humidity of 25%. An increase in relative humidity to 40% led to an increase in friction by almost 100%. There was a very significant degradation in frictional characteristics as well as durability after the MoS2-Ti coating was exposed to 400°C. The wear of the counter surface also increased when sliding against the MoS2-Ti coating exposed to elevated temperatures. This has been attributed to interaction of the counterbody with hard abrasive molybdenum oxides formed on the MoS2-Ti coating due to exposure to elevated temperatures.

  • 31.
    Hardell, Jens
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Hernandez, Sinuhe
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Mozgovoy, Sergej
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Pelcastre, Leonardo
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Courbon, Cedric
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Effect of oxide layers and near surface transformations on friction and wear during tool steel and boron steel interaction at high temperatures2015In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 330-331, p. 223-229Article in journal (Refereed)
    Abstract [en]

    Recent years have seen a continuously growing interest in high temperature tribological research. A significant part of this is driven by the need for improved understanding and knowledge pertaining to friction and wear and their control in the context of hot forming of high strength steels. Friction and wear characteristics of a sliding system are highly dependent on the properties of the two interacting surfaces. At high temperatures, the surface and material properties become extremely important since these systems often operate under unlubricated conditions. High temperature tribological processes are highly complex as these involve changes in mechanical properties due to microstructural changes; thermal softening; surface chemical and morphological changes due to oxidation and diffusion; deterioration of the surface and bulk material as a result of adhesive/abrasive wear and thermal fatigue. Many of these changes occur on the surfaces and/or in the near surface region. The formation of surface oxide layers and near surface layers with a highly refined microstructure (nano-structured) has been reported to have a significant influence on the tribological behaviour. An improved understanding of these effects is a prerequisite in an attempt towards controlling friction and wear at high temperatures. The main aim of this work is to investigate the formation of oxide layers and near surface transformed layers during tool steel and boron steel interaction at elevated temperatures and their relation to the friction and wear response. The results from sliding wear tests showed that under favourable conditions of temperature and load, a reduction of wear by three orders of magnitude and reduced friction by 50% was obtained. This was attributed to the formation of a composite layer structure involving a refined workhardened layer and a protective oxide layer on top. In the case of three body abrasive wear of boron steel, a reduction in wear rate when temperature increased (100–200 °C) has also been found. This reduction in three-body wear is due to the formation of a workhardened layer with a mechanically mixed layer of wear debris and fragmented silica particles on top. At higher temperatures (>500 °C), the softer matrix due to recrystallisation and phase transformations was unable to maintain a lower wear rate despite the presence of embedded fragmented silica particles.

  • 32. Hardell, Jens
    et al.
    Kassfeldt, Elisabet
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Prakash, Braham
    Friction and wear behaviour of high strength boron steel at elevated temperatures of up to 800 °C2008In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 264, no 9/10, p. 788-799Article in journal (Refereed)
    Abstract [en]

    There has been a growing usage of high strength steels, particularly in automobile applications mainly as structural parts in view of their light weight and high strength properties. These materials are also being considered for dynamic applications. However, the understanding of their tribological behaviour vis-a-vis their hot forming and also as tribological materials is highly inadequate. The present work thus aims at creating new knowledge about the tribological characteristics of high strength steels and bridging this existing gap. High temperature tribological studies on different tool steels (with and without surface treatment) sliding against high strength boron steel (with and without coating) and studies on self-mated hardened high strength boron steel under dry reciprocating sliding conditions have been conducted. High temperature tribological studies keeping in view the hot metal forming aspects were conducted by using an SRV machine whereas a two-disc machine was employed for investigating their fundamental friction and wear behaviour. The results from the high temperature studies indicate that the friction is dependent on temperature since a reduced friction level was observed with increasing temperature. The wear of the tool steels increased with increasing temperature and nitriding of the tool steels provided better protection against severe wear. The results from the study on self-mated hardened high strength boron steel showed that sliding speed has a marginal effect on friction whereas the effect of contact pressure is more pronounced (decreasing friction with increased contact pressure). The specific wear rate decreased with increased sliding speed.

  • 33. Hardell, Jens
    et al.
    Kassfeldt, Elisabet
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Prakash, Braham
    High temperature friction and wear behavior of boron steel during rubbing against tool steel2006In: 12th Nordic Symposium on Tribology, NORDTRIB 2006: LO-skolen, Helsingør, Denmark, June 7-9 2006, Kongens Lyngby: Technical University of Denmark , 2006Conference paper (Refereed)
  • 34.
    Hardell, Jens
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Kassfeldt, Elisabet
    Prakash, Braham
    Högtemperatur-tribologi för verktygsstål och höghållfast borstål2007In: Svenska Mekanikdagar 2007: Program och abstracts / [ed] Niklas Davidsson; Elianne Wassvik, Luleå: Luleå tekniska universitet, 2007, p. 72-Conference paper (Other academic)
  • 35. Hardell, Jens
    et al.
    Kassfeldt, Elisabet
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Prakash, Braham
    Tribological properties of high strength boron steel self-mated pairs2006In: Nordtrib 2006, 12th Nordic Tribology Symposium, Denmark: [LO-skolen, Helsingør, Denmark, June 7 - 9 2006], Kongens Lyngby: Technical University of Denmark , 2006Conference paper (Refereed)
  • 36.
    Hardell, Jens
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Mozgovoy, Sergej
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Dube, Anshuman
    Ducom Instruments Pvt. Ltd..
    Oldenburg, Mats
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    A Novel High Temperature Tribometer for Hot Sheet Metal Forming Applications2014Conference paper (Refereed)
  • 37. Hardell, Jens
    et al.
    Pelcastre, Leonardo
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    High-temperature friction and wear characteristics of hardened ultra-high-strength boron steel2010In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 224, no 10, p. 1139-1151Article in journal (Refereed)
    Abstract [en]

    The usage of ultra-high-strength boron steel (UHSS) in automotive industry has increased rapidly in the recent past. Forming of UHSS components is performed at elevated temperatures, which also offers the possibility of hardening through quenching directly after forming. However, the influence of hardening on friction and wear during relative sliding between the tool and the workpiece is unclear. Therefore, the friction and wear characteristics at elevated temperatures of hardened and unhardened UHSS and tool steel pairs are investigated in this study. The results show that both friction and wear at all the investigated temperatures are affected by hardening of the UHSS. For uncoated UHSS, the hardening resulted in lower friction and the tool wear increased at low temperatures, but was not affected at elevated temperatures. This was attributed to the higher hardness after hardening combined with the presence of an oxide scale on the UHSS after heating and quenching. For Al-Si-coated UHSS, the hardening reduced friction and tool steel wear at elevated temperatures, and also reduced the wear of the Al-Si-coated high-strength steel at low temperature mainly owing to the formation of an intermetallic layer on the Al-Si-coated UHSS surface after exposure to elevated temperatures.

  • 38.
    Hardell, Jens
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Prakash, Braham
    High-temperature friction and wear behaviour of different tool steels during sliding against Al-Si-coated high-strength steel2008In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 41, no 7, p. 663-671Article in journal (Refereed)
    Abstract [en]

    The recent years have witnessed an increasing usage of high-strength steels as structural reinforcements and in energy-absorbing systems in automobile applications due to their favourable high-strength-to-weight ratios. Owing to poor formability, complex-shaped high-strength steel components are invariably produced through hot-metal forming. The high-strength steel sheets are in some instances used with an Al-Si-coating with a view to prevent scaling of components during hot-metal forming. However, friction and wear characteristics of Al-Si-coated high-strength steel during interaction with different tool steels have not yet been investigated. With this in view, friction and wear behaviours of different tool steels sliding against Al-Si-coated high-strength steel at elevated temperatures have been investigated by using a high-temperature version of the Optimol SRV reciprocating friction and wear tester at temperatures of 40, 400 and 800 °C. In these studies both temperature ramp tests with continuously increasing temperature from 40 to 800 °C and constant temperature tests at 40, 400 and 800 °C, have been conducted. The results have shown that both the friction and wear of tool steel/Al-Si-coated high-strength steel pairs are temperature dependent. Friction decreased with increasing temperature whereas wear of the tool steel increased with temperature. On the other hand, the Al-Si-coated high-strength steel showed significantly lower wear rates at 800 °C as compared to those at 40 and 400 °C. The Al-Si-coated surface undergoes some interesting morphological changes when exposed to elevated temperatures and these changes may affect the friction and wear characteristics. The mechanisms of these changes and their influence on the tribological process are unclear and further studies are necessary to fully explain these mechanisms.

  • 39. Hardell, Jens
    et al.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Tribological performance evaluation of cold pilgering lubricants2010In: Tribology of manufacturing processes: proceedings of the 4th International Conference on Tribology in Manufacturing Processes, (ICTMP 2010) ; Nice, France, June 13th - 15th, 2010 / [ed] Eric Felder; Pierre Montmitonnet, Patis: Presses des Mines, 2010, p. 81-94Conference paper (Refereed)
  • 40. Hardell, Jens
    et al.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Tribological performance of surface engineered tool steel at elevated temperatures2010In: International journal of refractory metals & hard materials, ISSN 0958-0611, E-ISSN 2213-3917, Vol. 28, no 1, p. 106-114Article in journal (Refereed)
    Abstract [en]

    Tribological components operating at elevated temperatures can experience high wear, oxidation, thermal fatigue and changes in mechanical properties. In this work, the friction and wear characteristics of plasma nitrided and surface coated (CrN and TiAlN) tool steel during sliding against AISI52100 bearing steel have been studied at room temperature and 400 oC respectively using a ball on disc machine. Surface profiler and SEM/EDS techniques were used to characterise the surface topography and resulting surface damage of the test specimens. The results show that the friction of plasma nitrided tool steel during sliding against bearing steel ball is very high at room temperature and it drastically drops at 400oC. The wear is mainly abrasive at room temperature and adhesive at elevated temperatures. In case of CrN coated tool steel the friction is high but its wear is negligible at room temperature. At 400oC, the friction decreases marginally and transfer of bearing steel to the coated CrN coated disc has been observed. The TiAlN coating has shown relatively lower friction, compared to CrN and negligible wear at room temperature. At 400oC, the friction is very high and unstable and transfer of TiAlN coating to the mating ball occurs.

  • 41.
    Hardell, Jens
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Prakash, Braham
    Tribological properties of PVD coated and plasma nitrided hot forming tool steel during sliding against UHSS at elevated temperature2009In: Hot sheet metal forming of high-performance steel, CHS2: 2nd international conference, June 15-17 2009, Luleå, Sweden / [ed] Mats Oldenburg; Kurt Steinhoff; Braham Parkash, Auerbach: Verlag Wissenschaftliche Scripten , 2009, p. 349-357Conference paper (Refereed)
  • 42.
    Hardell, Jens
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Prakash, Braham
    Tribological studies on tool steel and ultra high strength boron steel pairs at elevated temperatures2008In: Conference Best in Class Stamping, June 16 - 18, 2008, Olofström, Sweden: [proceedings] / IDDRG, International Deep Drawing Research Group / [ed] Nader Asnafi, Olofström: Industriellt utvecklingscentrum i Olofström AB , 2008, p. 239-249Conference paper (Refereed)
    Abstract [en]

    The high strength to weight ratios of ultra high strength boron steels (UHSS) make them attractive for automotive applications in view of increasing emphasis on improved crashworthiness and fuel efficiency. However, these characteristics of UHSS also introduce certain difficulties in forming complex shaped structural components and energy absorbing systems. Most UHSS components are therefore produced through hot forming processes. One positive aspect of this hot forming is the opportunity for simultaneous hardening through quenching directly after forming. The success of a hot forming operation relies on many different factors and the majority of problems may be attributed to friction and wear. High wear of the tools leads to increased costs as well as higher rejection rates for manufactured components. Friction affects the forming of the workpiece and too low or high friction can impair the quality of the end product. Despite the clear need for knowledge concerning the high temperature friction and wear behaviour of these materials, work carried out so far in this field is very limited. The work at LTU aims at enhancing knowledge in the field of high temperature tribology in general and for tool steel and ultra high strength boron steel pairs in particular. This paper presents in brief the high temperature tribological studies conducted by employing both a reciprocating sliding friction and wear tester as well as a unidirectional sliding pin on disc machine. The results have shown that the operating temperature influences the friction and that an increase in temperature leads to a decrease in friction. Wear of the tool steel increases when the temperature increases from 40 deg C to 400 deg C but a further increase in temperature to 800 deg C does not influence wear. The UHSS exhibited lowest wear at 400 deg C due to the formation of wear protective layers. A surface coating on the tool steel provided better protection against wear but increased friction. The UHSS sheets are sometimes provided with an Al-Si coating. The studies have shown that Al-Si coating of UHSS sheets reduces friction at elevated temperatures but induces higher wear on the tool steel. The Al-Si coated surface also undergoes significant morphological and compositional changes when exposed to elevated temperatures

  • 43.
    Hardell, Jens
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Tribology of hot forming tool and high strength steels2013In: 4th International Conference Hot Sheet Metal Forming of High-performance Steel CHS: June 9-12, Luleå, Sweden . Proceedings / [ed] Mats Oldenburg; Braham Prakash; Kurt Steinhoff, Auerbach: Verlag Wissenschaftliche Scripten , 2013, p. 517-525Conference paper (Refereed)
  • 44.
    Hardell, Jens
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Prakash, Braham
    Steinhoff, Kurt
    University of Kassel.
    High temperature tribological studies on surface engineered tool steel and high strength boron steel2008In: Hot Sheet Metal Forming of High-Performance Steel: Proceedings, 1st International Conference, Kassel, Germany, October 22-24, 2008 / [ed] Kurt Steihoff; Mats Oldenburg; Braham Prakash, Bad Harzburg: GRIPS media , 2008, p. 69-76Conference paper (Refereed)
    Abstract [en]

    The popularity of hot sheet metal forming processes in the recent years has necessitated research efforts to improve tool life and control the friction level during hot forming operations. In this work, the tribological properties of tool steel and UHSS pairs at elevated temperatures have been studied by using a special hot sheet metal forming test rig that closely simulates the conditions prevalent in the real process. This test involves linear unidirectional sliding of a preheated UHSS sheet between two tool steel specimens where new workpiece material is continuously in contact with the tool surface. The study is aimed at investigating different surface treatments/coatings applied on either the tool or sheet surface or on both. The results have shown that it is possible to control the coefficients of friction through surface treatments and coatings of the tool and workpiece materials. The application of a coating on to the sheet material has a greater influence on the friction compared to changing the tool steel surface. After running-in, the investigated tool steel variants show almost similar frictional behaviour when sliding against the same sheet material. Even though coating the UHSS sheet reduces friction it abrades the tool surface and also results in transfer of the sheet coating material to the tool surface.

  • 45.
    Hardell, Jens
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Prakash, Braham
    Steinhoff, Kurt
    University of Kassel.
    High temperature tribological studies on surface engineered tool steel and high strength boron steel2009In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 80, no 9, p. 665-670Article in journal (Refereed)
    Abstract [en]

    The popularity of hot sheet metal forming processes in the recent years has necessitated research efforts to improve tool life and control the friction level during hot forming operations. In this work, the tribological properties of tool steel and ultra high strength boron steel (UHSS) pairs at elevated temperatures have been studied by using a special hot sheet metal forming test rig that closely simulates the conditions prevalent in the real process. This test involves linear unidirectional sliding of a preheated UHSS sheet between two tool steel specimens where new workpiece material is continuously in contact with the tool surface. The study is aimed at investigating different surface treatments/coatings applied on either the tool or sheet surface or on both. The results have shown that it is possible to control the coefficients of friction through surface treatments and coatings of the tool and workpiece materials. The application of a coating onto the sheet material has a greater influence on the friction compared to changing the tool steel surface. After running-in, the investigated tool steel variants show almost similar frictional behaviour when sliding against the same sheet material. Although coating the UHSS sheet reduces friction, it abrades the tool surface and also results in transfer of the sheet coating material to the tool surface

  • 46. Hardell, Jens
    et al.
    Quang, Hoai Le
    Luleå tekniska universitet.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Tribological performance of surface coated tool steel at elevated temperatures2008In: Proceedings of NORDTRIB 2008: 13th Nordic Symposium of Tribology / [ed] Jaakko Kleemola; Arto Lehtovaara, Tampere University of Technology, 2008Conference paper (Refereed)
    Abstract [en]

    In metal forming at elevated temperatures the tools are subjected to thermal cycling, increased oxidation and wear which will influence the lifetime of the tools and the quality of the produced parts. In addition to this, the frictional behaviour will also change with temperature and this can affect the performance of the forming operation itself. One way of controlling friction and reducing wear is to utilise the latest developments in surface engineering and modify or coat the tool surface with some thermally stable layer. However, in the open literature there are very few studies pertaining to the high temperature tribological properties of surface coatings applied on to the tool steels and sliding against actual workpiece material. This study thus aims at experimentally investigating the friction and wear characteristics of a surface coated tool steel during sliding against ultra high strength boron steel at elevated temperatures. The surface coatings applied on the tool steel in this work were of TiAlN and CrN respectively. The tribological studies were conducted by using both a reciprocating tribometer as well as a pin-on-disc machine at temperatures in the range from ambient to 800 ºC. A 3D optical surface profiler has been used for surface topography measurements and SEM/EDS have been used for investigating the resultant surface damage. The results have shown that the friction coefficient increases with temperature in unidirectional sliding. Wear of the coatings is negligible at room temperature but at 400 ºC the CrN disc is worn by abrading action of hard oxidised wear debris and the coating is removed to a large extent. In reciprocating sliding the friction also increases with temperature and the coatings are completely removed during sliding at 800 ºC.

  • 47.
    Hardell, Jens
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Yousfi, Amine
    Luleå University of Technology.
    Lund, Martin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Pelcastre, Leonardo
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Abrasive wear behaviour of hardened high strength2014In: Tribology - Materials, Surfaces & Interfaces, ISSN 1751-5831, E-ISSN 1751-584X, Vol. 8, no 2, p. 90-97Article in journal (Refereed)
    Abstract [en]

    Abrasive wear in industrial applications such as mining, materials handling and agricultural machinery constitutes a large part of the total wear. Hardened high strength boron steels are known for their good wear resistance and mechanical properties, but available results in the open literature are scarce. This work aims at investigating how different quenching techniques affect the two-body abrasive wear resistance of hardened high strength boron steels. Furthermore, the wear as a function of depth in thicker hardened high strength boron steel plates has also been studied. The material characterisation has been carried out using microhardness, SEM/energy dispersive spectroscopy and three-dimensional optical surface profilometry. The results have shown that water quenched and tool quenched high strength boron steel had similar wear resistance. The main wear mechanisms appear to be microcutting combined with microfatigue. Workhardening during the abrasion process has been found to affect the abrasive wear.

  • 48.
    Hardell, Jens
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Yousfi, Amine
    Luleå University of Technology.
    Lund, Martin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Pelcastre, Leonardo
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Abrasive wear behaviour of hardened high strength boron steel2013Conference paper (Refereed)
  • 49.
    Hernandez, Sinuhe
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Hardell, Jens
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Courbon, Cedric
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Winkelmann, H.
    AC²T research GmbH - Austrian Center of Competence for Tribology, Viktor-Kaplan-Straße 2 D, 2700 Wiener Neustadt.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    High temperature friction and wear mechanism map for tool steel and boron steel tribopair2014In: Tribology - Materials, Surfaces & Interfaces, ISSN 1751-5831, E-ISSN 1751-584X, Vol. 8, no 2, p. 74-84Article in journal (Refereed)
    Abstract [en]

    Tribological systems working under severe conditions like high pressures, sliding velocities and temperatures are subjected to different phenomena such as wear, oxidation and changes in mechanical properties. In many cases, there are several mechanisms occurring simultaneously.The predominating type(s) of wear mechanism(s) presented will depend on the materials in contact, operating parameters and surrounding environment. In this work, high temperature tribological studies of boron steel sliding against tool steel were conducted using a pin-on-disc machine under unlubricated conditions at five different temperatures ranging from 25 to 400C, three different loads: 25, 50 and 75 N (contact pressures of 2, 4 and 6 MPa respectively) and a sliding speed of 0.2 ms-1. Scanning electron microscopy/energy dispersive spectroscopy and X-ray techniques were used for analysing the resulting damage and tribolayers of the worn surfaces. Additionally, hardness measurements were carried out in a special hot hardness rig in the same temperature range as that used in pin-on-disc tests. The results have shown that for a given load, the wear rate of boron steel decreased as the temperature increased, reaching itslowest value at 400C at 50 N. In the case of the tool steel, it could be observed that at 200C and above, the wear rate decreased as the load increased. This behaviour is consistent with the formation of a protective oxidised layer initiated at 100C. At higher temperatures, such layers become more pronounced. The obtained data were finally used to construct a friction and wear mechanism map for this material pair that takes temperature and pressure into account.

  • 50.
    Hernandez, Sinuhe
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Hardell, Jens
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Courbon, Cedric
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Winkelmann, Horst
    AC²T research GmbH - Austrian Center of Competence for Tribology, Viktor-Kaplan-Straße 2 D, 2700 Wiener Neustadt.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Influence of load on friction and wear of tool steel - boron steel pair at elevated temperatures2013Conference paper (Refereed)
12 1 - 50 of 87
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