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  • 151.
    Mozgovoy, Sergej
    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.
    High Temperature Friction and Wear Studies on Tool Coatings under Press Hardening Contact Conditions2015Conference paper (Refereed)
  • 152.
    Mukerji, J.
    et al.
    Central Glass and Ceramic Research Institute (CGCRI), Calcutta.
    Bandopadhyay, S.
    Central Glass and Ceramic Research Institute (CGCRI), Calcutta.
    Wani, M. F.
    Indian Institute of Technology, New Delhi.
    Prakash, Braham
    Friction and wear behaviour of hot pressed sialon sintered without externally added liquid1990In: 3rd International tribology conference: Selected papers, Tokyo: Japan Society of Tribologists , 1990, Vol. 3, p. 1401-1406Conference paper (Refereed)
  • 153.
    Mukerji, Joydeb
    et al.
    Central Glass and Ceramic Research Institute (CGCRI), Calcutta.
    Prakash, Braham
    Wear of Nitrogen Ceramics and Composites in contact with Bearing Steel under Oscillating Sliding Conditions1998In: Ceramics International, ISSN 0272-8842, E-ISSN 1873-3956, Vol. 24, no 1, p. 19-24Article in journal (Refereed)
    Abstract [en]

    The wear of nitrogen based ceramics in contact with bearing steel balls (SAE 52100) was investigated under reciprocating sliding conditions at a velocity of 0.1 m/s, and 20 N, 40 N and 100 N load. Three types of ceramics were studied: viz. hot pressed silicon nitride (HPSN) sintered with selected liquid in the system yttria-aluminium nitride-silica and composites of HPSN with BN and TiC; SiAlON formulated with different amounts of alumina and silica; and aluminatitanium nitride composite having 60 mol% TiN. Among the HPSN composites, HPSN 15vol% TiC had the lowest average wear factor (K) of 2.0 × 10- 5mm3/m/ N. The SiAlONs, in general, had the highest K and this increased with increasing O concentration. The lowest K value for SiAlON ceramic was 6.9 × 10-5mm3/m/N. The high K value of SiAlON is attributed to O substitution, which promotes adhesive wear resulting in mutual material transfer. The lowest wear of all the ceramics tested was found for the alumina-titanium nitride composite, the wear factor being of the order of 4.4 × 10-7mm3/m/N, which is one order of magnitude lower than the other nitrogen ceramics. In the case of HPSN and alumina-titanium nitride composites, abrasive wear and wear due to microfracture were the main wear mechanisms. Wear of the steel ball was lowest when in contact with HPSN---TiC composites, being almost equal to that of the ceramic, whereas the alumina-titanium nitride composite wore away the steel almost 20 times faster than the ceramic and will thus be unsuitable as a counterface material for 52100 steel.

  • 154.
    Muramoto, K.
    et al.
    Chiba Institute of Technology.
    Prakash, Braham
    Hiratsuka, K.
    Chiba Institute of Technology.
    Influence of wear particles removal on friction and wear of metals2000In: Proceedings of the International Tribology Conference: : ITC Nagasaki 2000 ; October 29 - November 2, 2000, Tokyo: Japanese Society of Tribologsts , 2000, p. 363-366Conference paper (Refereed)
  • 155. Murthy, D. V. S.
    et al.
    Singh, P.
    Bansal, R. K.
    Tewari, U. S.
    Indian Institute of Technology, New Delhi.
    Prakash, Braham
    Modified polycarboxylate cement for dental applications1995In: Proceedings of the Conference on Prosthetics: Biomaterials and Implants (CEPROBIM), 1995Conference paper (Refereed)
  • 156. Nilsson, Daniel
    et al.
    Isaksson, Patrik
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Effects of area ratio and nature of surfaces on scuffing in lubricated contacts2008Conference paper (Other academic)
  • 157.
    Nilsson, Daniel
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Isaksson, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Effects of area ratio and nature of surfaces on scuffing in lubricated contacts2009In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 223, no 3, p. 445-455Article in journal (Refereed)
    Abstract [en]

    Heavily loaded moving machine components encounter severe tribological problems. Typical examples include piston and cylinder contacts in a hydraulic motor. Piston and cylinder bore contacts invariably operate in boundary lubrication regime and the risk for seizure of these contacts is high particularly when lubricated with low-viscosity lubricants. The piston assembly in a radial piston hydraulic motor has conformal (area) contact. In this work, these contacts have been simulated in the laboratory by using a thrust washer test configuration. The influence of area ratio, nature of contacting surfaces, and speed on scuffing has been investigated by using a factorial design of experiments approach. The influence of area ratio on wear at lower speed has also been studied. The results have revealed that the surface power, or μpv-value, at scuffing varies by 3-4 times when the area ratio was increased from 8 to 72 per cent. The running-in wear tests have shown that running-in of the upper and lower specimens also varies with the area ratio. During the first 30 s the upper specimen is polished with low area ratio, whereas the lower specimen is polished with high area ratio. The surface temperature was estimated by using finite-element calculation and it was found to be similar prior to scuffing for both 8 and 72 per cent area ratios at 1.7 m/s sliding speed. The comparison of the results with the actual motor tests shows that an area ratio of 24 per cent seems to simulate the piston-cylinder contact better.

  • 158.
    Nilsson, Daniel
    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.
    Friction and wear of some selected polymeric materials for conformal tribopairs under boundary lubrication conditions2012In: 8th International Fluid Power Conference (8. IFK): March 26 - 28, 2012 in Dresden; [conference proceedings], Dresden: Dresdner Verein zur Förderung der Fluidtechnik e.V , 2012, Vol. 2, p. 217-231Conference paper (Refereed)
  • 159.
    Nilsson, Daniel
    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.
    Influence of different surface modification technologies on friction of conformal tribopair in mixed and boundary lubrication regimes2011In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 273, no 1, p. 75-81Article in journal (Refereed)
    Abstract [en]

    Moving machine assemblies are generally designed to operate in full film lubrication regime to ensure high efficiency and durability of components. However, it is not always possible to ensure this owing to changes in operating conditions such as load, speed, temperature etc. The overall frictional losses in machines are dependent on the operating lubrication regimes (boundary, mixed or full-film). The present work is thus aimed at investigating the role of different surface modification technologies on friction of a sliding bearing/roller tribopair both in boundary and mixed lubrication regimes. A special test rig comprising of two bearings was built for the experimental studies. Tribological tests were conducted in a wide speed range to enable studies in boundary and mixed lubrication regimes. The influence of application of different surface modification technologies on both the sliding bearing and the roller surfaces on friction has been studied. The rollers used in these studies were provided with five different coatings (hard DLCs and a soft self-lubricating coating). Additionally, two uncoated rollers having different surface roughness were also studied. Uncoated bearings were used in all tribopairs except two. These two bearings were coated with DLC and phosphate coatings respectively and uncoated rollers were the mating counterparts. Friction measurements were made on the new as well as the previously run-in surfaces. It was found that the rollers with self-lubricating coating resulted in lowest boundary friction closely followed by the rollers with the hardest DLC coatings. The DLC coating applied on to the bearing showed lower boundary friction after running-in. Mixed friction has been found to be mainly dependent on the surface topography characteristics of both the original and the run-in surfaces of bearings and rollers. The harder DLC coatings and the phosphated bearing showed the lowest mixed friction due to an efficient running-in of the bearing surface.

  • 160. Nilsson, Daniel
    et al.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Influence of surface modification technologies on friction of conformal tribopair in boundary and full film lubrication regimes2010In: 14th Nordic Symposium on Tribology: NORDTRIB 2010 : Storforsen, Sweden, June 8-11, 2010, Luleå: Luleå tekniska universitet, 2010Conference paper (Refereed)
    Abstract [en]

    Moving machine assemblies are generally designed to operate in full film lubrication regime to ensure high efficiency and durability of components. However, it is not always possible to ensure this owing to changes in operating conditions such as load, speed, temperature etc. The overall frictional losses in machines are thus dependent on the operating lubrication regimes (boundary, mixed or full-film). The present work is thus aimed at investigating the role of different surface modification technologies on friction of a conformal tribopair both in boundary and full film lubrication regimes. The conformal pair chosen is a hydrodynamic bearing with some hydrostatic lift.A special test rig comprising of two bearings was built for the experimental studies. Tribological tests were conducted in a wide speed range so as to enable studies in all lubrication regimes i.e., in boundary, mixed and full-film lubrication.The influence of application of different surface modification technologies on friction has been studied. In all, rollers with five coatings (four hard DLC coatings and one self-lubricating coating) and two rollers without coating having different surface finish. Friction measurements were made on the new as well as the previously run-in components. The different coatings exhibit different levels of boundary friction, with the self-lubricating coating having lowest boundary friction, closely followed by those with hard DLC coatings. The softer amongst the hard DLC coatings showed similar boundary friction compared to that with uncoated rollers. The lift-off speed, i.e., the transition between full-film to mixed and boundary lubrication mainly governed by the surface topography characteristics. A smooth surface finish can be achieved either by polishing before the test or by effective running in of the new surface. The effectiveness of running-in of surfaces was influenced by the surface roughness and hardness of the interacting surfaces.

  • 161. Nilsson, Daniel
    et al.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Investigation into the seizure of hydraulic motors2010In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 43, no 1-2, p. 92-99Article in journal (Refereed)
    Abstract [en]

    Despite its practical significance, the occurrence of seizure in tribological systems has not been fully understood. In this work, extensive actual tests on hydraulic motors under extreme operating conditions of low viscosity, high pressure and speed have been conducted with a view to investigate and understand the seizure mechanism. Some of the motors failed and they were stopped at different stages of progressive seizure. Based on these investigations, a three stage seizure process has been suggested. Stage 1 involves the breakdown of hydrodynamic oil film between roller and piston which leads to increased friction, thermal expansion and increased leakage. In stage 2, scuffing is initiated either between roller and piston or between piston and cylinder. During stage 3 scuffing propagate to several pistons.

  • 162.
    Nilsson, Daniel
    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.
    Static/dynamic friction and wear of some selected polymeric materials for conformal tribo-pairs under boundary lubrication conditions2013In: Friction, E-ISSN 2223-7690, Vol. 1, no 3, p. 232-241Article in journal (Refereed)
    Abstract [en]

    This work is aimed at investigating the friction and wear performance of different polymeric materials having potential for hydraulic system components under lubricated sliding conditions against a steel counter face. A pin-on-disc test configuration was used for the experimental study. The different polymeric materials selected for these studies were commercial polyimides (PI), polyether ether ketone (PEEK), and flouropolymers. Some of these materials were bulk materials whereas others were used as coatings applied on to the cast iron substrate. The tribological characteristics of the polymers were compared with a reference grey cast iron. The frictional characteristics were evaluated in both static and dynamic conditions. The results have shown that by using polymeric materials it is possible to reduce breakaway friction by an order of magnitude compared to grey cast iron. However, the breakaway friction increased significantly after the wear tests. The polymeric materials having lowest breakaway friction have shown the highest wear with the exception of the PEEK-PTFE coating which showed low wear. PI with graphite fillers also showed low wear but it resulted in relatively high friction. The carbon fibre reinforced materials resulted in unstable friction as well as higher wear compared to the PI materials with graphite fillers

  • 163.
    Oldenburg, Mats
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Steinhoff, KurtUniversity of Kassel.Prakash, BrahamLuleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Hot sheet metal forming of high-performance steel, CHS2: 2nd international conference, June 15-17 2009, Luleå, Sweden. Proceedings2009Collection (editor) (Other academic)
  • 164.
    Oldenburg, Mats
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Steinhoff, KurtUniversity of Kassel.Prakash, BrahamLuleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Hot sheet metal forming of high-performance steel, CHS2: 3rd international conference, June 13-17 2011, Kassel, Germany. Proceedings2011Collection (editor) (Other academic)
  • 165.
    Oldenburg, Mats
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Steinhoff, KurtUniversity of Kassel.Prakash, BrahamLuleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Proceedings: 4th International Conference Hot Sheet Metal Forming of High Performance Steel June 9 - 12, 2013, Luleå, Sweden2013Collection (editor) (Other academic)
  • 166.
    Pelcastre, Leonardo
    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.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Tribological behaviour of Al-Si-coated ultra-high-strength steel during interaction with tool steel at elevated temperatures: Influence of tool steel surface topography parameters on galling2015In: Proceedings of the Institution of mechanical engineers. Part B, journal of engineering manufacture, ISSN 0954-4054, E-ISSN 2041-2975, Vol. 229, no 8, p. 1373-1384Article in journal (Refereed)
    Abstract [en]

    Galling is a severe form of adhesive wear encountered in metal forming operations. In hot stamping, an Al-Si coating is normally applied onto the ultra-high-strength steels to prevent decarburisation and to improve the corrosion resistance of the steel. Material transfer occurring from the coated ultra-high-strength steel to the tool surface has been identified as major issue in hot stamping. This transferred material impairs the quality of the produced parts and at the same time, it increases the costs of maintenance of the tools. This work focuses on the understanding of surface topography parameters and their effect on galling. Surface roughness level and orientation of the surface lay on tool surface have been studied. The results showed that a single parameter of the surface topography is not enough to describe the resistance to galling. Parameters such as Rv, Rp and Rsk are also important to consider in order to rank the galling resistance of the surface. The sliding direction with respect to the surface lay also had a significant influence on galling; sliding in the direction parallel to it resulted in substantially reduced material transfer.

  • 167.
    Pelcastre, Leonardo
    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.
    Herrera, Natlia
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Investigations into the failure mechanisms of form fixture hardening tools2011In: Proceedings, 3rd International Conference Hot Sheet Metal Forming of High Performance Steel: June 13 - 17, 2011, Kassel, Germany / [ed] Mats Oldenburg; Kurt Steinhoff; Braham Prakash, Auerbach: Verlag Wissenschaftliche Scripten , 2011, p. 93-103Conference paper (Refereed)
  • 168.
    Pelcastre, Leonardo
    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.
    Galling mechanisms during interaction of tool steel and Al-Si coated ultra-high strength steel at elevated temperature2013In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 67, p. 263-271Article in journal (Refereed)
    Abstract [en]

    Occurrence of galling in hot forming is detrimental to the quality of produced parts and process economy. Material transfer from Al-Si coated work-piece to the tool material has been studied in this work. PVD coatings (AlCrN, TiAlN and DLC) on tool steel substrate have been considered as well as plasma nitriding and their tribological behaviour was compared to the case of an untreated tool steel. Galling initiates through accumulation and compaction of wear debris when untreated tools are used whereas the PVD coatings resulted in increased galling due to adhesion. Plasma nitrided tool steel showed negligible galling due to formation of glaze layers and the formation of such layers depends on the occurrence of wear of the nitrided tool steel.

  • 169.
    Pelcastre, Leonardo
    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.
    Influence of die Temperature on the Tribological Response During Interaction with Al-SI Coated Ultra-High Strength Steel2017In: 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. 461-469Conference paper (Refereed)
  • 170.
    Pelcastre, Leonardo
    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.
    Influence of temperature on friction behaviour of tool steels sliding against Al-Si coated UHSS2016In: Proceedings of the 17th Nordic Symposium on Tribology : Nordtrib 2016, 2016Conference paper (Refereed)
    Abstract [en]

    In the automotive industry, a significant amount of components are formed using hot stamping. This process allows formation of complex shapes whilst controlling microstructure and mechanical properties of the end product. There are different tribological challenges encountered within the process due to the elevated temperature. The current studies focused on the tribological behaviour of different tool steels sliding against Al-Si coated steel (typically used in hot stamping) at different temperatures. It was observed that the tool steel temperature and the work-piece material temperature had a direct effect on friction level and stability and on the wear mechanisms; particularly in the occurrence of adhesive wear and material transfer onto the tool steels. In general, larger amount of material transfer and higher friction was observed with lower temperatures on the tool steel (~200˚C) and higher temperature of the work-piece material (~900˚C). The presence of oxides on the tool steel reduced the severity of material transfer and stabilised friction. However, the tool steel composition also affected the effectiveness in the stabilisation of the friction coefficient

  • 171.
    Pelcastre, Leonardo
    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.
    Influence of temperature on friction behaviour of tool steels sliding against Al-Si coated UHSS2016Conference paper (Refereed)
    Abstract [en]

    In the automotive industry, a significant amount of components are formed using hot stamping. This process allows formation of complex shapes whilst controlling microstructure and mechanical properties of the end product. There are different tribological challenges encountered within the process due to the elevated temperature. The current studies focused on the tribological behaviour of different tool steels sliding against Al-Si coated steel (typically used in hot stamping) at different temperatures. It was observed that the tool steel temperature and the work-piece material temperature had a direct effect on friction level and stability and on the wear mechanisms; particularly in the occurrence of adhesive wear and material transfer onto the tool steels. In general, larger amount of material transfer and higher friction was observed with lower temperatures on the tool steel (~200˚C) and higher temperature of the work-piece material (~900˚C). The presence of oxides on the tool steel reduced the severity of material transfer and stabilised friction. However, the tool steel composition also affected the effectiveness in the stabilisation of the friction coefficient.

  • 172.
    Pelcastre, Leonardo
    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.
    Influence of tool steel surface topography on galling during hot forming of Al-Si coated ultra high-strength steels2012In: 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]

    Galling is a severe form of adhesive wear encountered in metal forming operations. In hot stamping, an Al-Si coating is normally applied onto the ultra high strength steels (UHSS) to prevent decarburisation and improve the corrosion resistance of the steel. Material transfer occurring from the coated UHSS to the tool surface has been identified as major issue in hot stamping. It is a known problem as this transferred material impairs the quality of the produced parts as well as increases the costs of maintenance of the tools. The present work focuses on the understanding of surface topography parameter and their effect on galling. Surface roughness level and orientation of the roughness marks (lay) on tool surface have been studied. The results showed that a single parameter of the surface topography is not enough to describe the resistance to galling. Parameters such as Rp, Rv and Rsk are also important to consider in order to rank the galling resistance of the surface. The sliding direction with respect to the surface lay also had a significant influence on galling; sliding in the direction parallel to it resulted in substantially reduced material transfer.

  • 173. Pelcastre, Leonardo
    et al.
    Hardell, Jens
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Prakash, Braham
    Investigations into the occurrence of galling during hot forming of Al-Si coated high strength steel2010Conference paper (Other academic)
  • 174.
    Pelcastre, Leonardo
    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 the occurrence of galling during hot forming of Al-Si-coated high-strength steel2011In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 225, no 6, p. 487-498Article in journal (Refereed)
    Abstract [en]

    Galling is a severe form of adhesive wear associated with both cold and hot metal forming operations. In hot sheet metal forming of Al-Si-coated ultrahigh-strength steel (UHSS), transfer occurs from the coated UHSS to the tool surface. This leads to poor quality of produced parts, damage of expensive tooling, and increased downtime for maintenance of the tools. This study thus aims at identifying the salient mechanism(s), which give rise to initiation/occurrence of galling at elevated temperatures. This has been accomplished by analysing actual hot forming tools and through systematic parametric tribological investigations in the laboratory. The analysis of the actual tools has shown that the transferred layer consists of Al, Si, and Fe. The structure of the transferred materials is composed of sintered/compacted wear particles. The parametric study has shown that galling is dependent on the operating conditions. A strong relationship between the contact pressure and material transfer has been observed. The severity of galling is lower for smoother surfaces at low contact pressure. However, at high contact pressure, the influence of roughness under these conditions is insignificant. It has also been observed that hard-tool steel substrates reduce the severity of galling, particularly, at high contact pressure.

  • 175.
    Pelcastre, Leonardo
    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.
    Micro-mechanisms of galling at elevated temperatures2012In: International Colloquium Micro-Tribology 2012, Warsa, 2012, p. 29-30Conference paper (Refereed)
  • 176.
    Pelcastre, Leonardo
    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 behaviour of Zn coated UHSS sliding against hot-work tool steel at high temperatures2017In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 376-377, no Part-A, p. 423-432Article in journal (Refereed)
    Abstract [en]

    The increasing demands for light-weight components in vehicles contribute to the global expansion of hot sheet metal forming technologies. Structural components are typically produced using hot stamping of ultra-high strength steel (UHSS). This process allows forming of complex shapes whilst enabling control of the mechanical properties of the end product. Interest in zinc coated UHSS has increased in recent years in view of the corrosion protection it provides to the final components. There is a need for increased understanding of its tribological behaviour during the interaction with tool steel at elevated temperatures. In this work, tribological studies have been carried out in a novel hot strip tribometer. The aim was to study the effect of different operating conditions on the tribological behaviour of zinc coated UHSS sliding against a hot-work tool steel under un-lubricated conditions. The parameters studied in this work were; temperature, ranging from 400 °C to 700 °C; and contact pressure, from 5 to 30 MPa. The UHSS was initially heated up to austenitising temperature (840 °C) and then cooled down to the testing temperature. Upon stabilisation of temperature, the load was applied and sliding was carried out for a total of 1500 mm at 100 mm/s. The results showed a trend towards decreasing average coefficient of friction as temperature and contact pressure increased. Unstable friction behaviour was observed at low temperature (400 °C) and high contact pressure (30 MPa) whilst higher temperatures (600 °C) facilitated the development of a low and stable friction behaviour. It is proposed that the friction behaviour is controlled by the properties of the zinc phases in the coating developed during heating of the UHSS. The combination of high temperature and sliding conditions result in the removal of the uppermost oxide layer and the phases beneath control the friction behaviour.

  • 177.
    Pelcastre, Leonardo
    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.
    Rolland, Anthony
    Exchange Student LTU.
    Influence of microstructural evolution of Al-Si coated UHSS on its tribological behaviour against tool steel at elevated temperatures2014Conference paper (Other academic)
    Abstract [en]

    The usage of the hot stamping process is of great importance due tothe high demands for production of ultra-high strength steels (UHSS).An Al-Si coating is normally applied to the steel to preventdecarburisation and scaling during heating and to improve thecorrosion resistance of the final component. During heating, the Al andthe Si from the coating combine with the Fe from the steel substrate toform hard intermetallic phases. Little is known about the influence ofthe heating conditions on the tribological behaviour of the Al-Sicoating during interaction with tool steels. The present workinvestigated different heat treatment parameters and the influencethey had on the microstructure of the coating and the gallingbehaviour. With low alloying temperatures (700C), severe gallingoccurred and increasing the alloying temperature to 900C resulted inalmost negligible material transfer. The reduction in galling wasassociated to the development of Fe2Al5 and FeAl2 at the surface.

  • 178.
    Pelcastre, Leonardo
    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.
    Rolland, Anthony
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Influence of microstructural evolution of Al-Si coated UHSS on its tribological behaviour against tool steel at elevated temperatures2016In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 228, p. 117-124Article in journal (Refereed)
    Abstract [en]

    The usage of the hot stamping process is of great importance due to the high demands for production of ultra-high strength steels (UHSS). An Al-Si coating is normally applied to the steel to prevent decarburisation and scaling during heating and to improve the corrosion resistance of the final component. During heating, the Al and the Si from the coating combine with the Fe from the steel substrate to form hard intermetallic phases. Little is known about the influence of the heating conditions on the tribological behaviour of the Al-Si coating during interaction with tool steels. The present work investigated different heat treatment parameters and the influence they had on the microstructure of the coating and the galling behaviour. With low alloying temperatures (700˚C), severe galling occurred and increasing the alloying temperature to 900˚C resulted in almost negligible material transfer. The reduction in galling was associated to the development of Fe2Al5 and FeAl2 at the surface.

  • 179.
    Pelcastre, Leonardo
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements. Division of Machine Elements, Luleå University of Technology.
    Hardell, Jens
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements. Division of Machine Elements, Luleå University of Technology.
    Rolland, Anthony
    Division of Machine Elements, Luleå University of Technology.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements. Division of Machine Elements, Luleå University of Technology.
    Influence of microstructural evolution of Al-Si coated UHSS on its tribological behaviour against tool steel at elevated temperatures2014In: Society of Tribologists and Lubrication Engineers Annual Meeting and Exhibition 2014, Society of Tribologists and Lubrication Engineers , 2014, Vol. 1, p. 463-465Conference paper (Refereed)
    Abstract [en]

    In recent years, the usage of the hot stamping process has increased due to the high demands for production of ultra-high strength steels (UHSS). In particular, more studies are being carried out pertaining to the Al-Si coated UHSS to understand its behaviour during the forming process as well as the performance of the produced parts. The Al-Si coating is applied to the UHSS with the aim of reducing decarburisation and to avoid the formation of thick oxide scales on the work-piece during the heating stage. Usage of the Al-Si coating has the added benefit of greatly improving the corrosion resistance and paintability of the produced components [1,2].

  • 180.
    Pelcastre, Leonardo
    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.
    Vargas, Natalia Herrera
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Investigations into the damage mechanisms of form fixture hardening tools2012In: Engineering Failure Analysis, ISSN 1350-6307, E-ISSN 1873-1961, Vol. 25, p. 219-226Article in journal (Refereed)
    Abstract [en]

    In metal forming operations such as form fixture hardening, the interaction between the tools and the work-piece is strongly influenced by the tribological properties at the interface. Damage or excessive wear of the tools can be detrimental to the quality of the final component and it also has an impact on the process economy due to increased maintenance or more frequent replacement of tools. The objective of this study was to investigate the damage mechanisms encountered in real form fixture hardening tools in order to understand the causes of tool failure and ultimately to come up with possible solutions for this problem.Advanced techniques such as Scanning Electron Microscope (SEM), Energy Dispersive Spectroscopy (EDS) were used for obtaining an in-depth understanding of the different phenomena involved in the failure of form fixture hardening tools. Two different tools having different hardness values and microstructures that had been used in production were analysed.The damage mechanisms found included abrasive and adhesive wear, material transfer, corrosion and mechanical and thermal fatigue. The main damage mechanism was found to be cracking caused by mechanical stresses on the surface. Although both tools presented similar types of damage, the severity was different and it was strongly influenced by the microstructure.

  • 181.
    Pelcastre, Leonardo
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Heikkilä, Irma
    Swerea KIMAB, Stockholm.
    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.
    High Temperature Tribological Behaviour of Thermal-Spray Coated Toll Steels Sliding Against Al-Si Coated Ultra-High Strength Steel2017In: 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. 223-232Conference paper (Refereed)
  • 182.
    Persson, Håkan
    et al.
    Bodycote Material Testing AB.
    Hjertsén, David
    Bodycote Material Testing AB.
    Waara, Patric
    SSAB Oxelösund AB.
    Prakash, Braham
    Hardell, Jens
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Nötningskorrosion: Utvärdering av nötnings- och korrosionsbeständiga material2007Report (Other academic)
    Abstract [sv]

    Rapporten beskriver en utvärdering av nötnings- och korrosionsbeständiga material för en transportskruv för avfallsbränsle i en typisk miljö vid avfallseldade CFB-pannor. Utprovning har genomförts i både kontrollerad laboratoriemiljö och i verklig miljö vilket har gett en bättre förståelse för vilka konstruktionsmaterial som lämpar sig bäst i denna tuffa miljö och gett en modell för att i framtiden bättre kunna prediktera slitagehastigheten. De förändrade driftförhållanden, framförallt lägre varvtal, som den nya transportskruven har medfört (installerad i februari 2007 och med vilken fältproven har genomförts) har förskjutit nötning/korrosion förhållandet så att korrosionen är mer dominerande i nötningskorrosionen. Detta är tydligt då SS 2377 (rostfritt duplext stål), som är det mjukaste av de utvärderade materialen, uppvisar lågt slitage till följd av sitt goda korrosionsmotstånd. Konstruktionen av skruven har visat sig vara väldigt avgörande för nötningskorrosion

  • 183.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Abrasive wear behaviour of Fe, Co and Ni based metallic glasses2005In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 258, no 1-4, p. 217-224Article in journal (Refereed)
    Abstract [en]

    Metallic glasses are a different category of materials that are characterized by their amorphous structure and metallic bonds. Owing to their disordered structure, metallic glasses possess several unique properties that make them attractive for tribological applications. This paper deals with an in depth investigation into the two-body abrasive wear behaviour of several compositions of Fe, Co and Ni based metallic glasses while rubbing against metallographic grade SiC abrasive papers. Identical studies have also been carried out on crystalline cold-rolled AISI 304 stainless steel for comparison. Two-body abrasive wear results indicate that wear characteristics of different metallic glasses are marginally superior or similar to that of stainless steel. The wear in Ni based metallic glass MBF 35 is significantly higher.than that in stainless steel. This is inspite of the fact that metallic glasses are considerably harder than stainless steel. Scratch indentation and acoustic emission studies (AE) were carried out with a view to understanding the mechanisms of occurrence of two-body abrasive wear in metallic glasses. Scratched surfaces of metallic glasses indicated the presence of arc-like features that in some cases extend well beyond the scratched groove edges. In the case of Ni based metallic glass MBF 35, cracking on the surface was clearly visible. In stainless steel, the grooves formed were neatly cut out and were free from the arc-like features. During scratch tests on metallic glasses, AE signals were obtained but no AE signals were generated during scratch tests on steel. Presence of arc-like features on scratched surfaces in metallic glasses are tensile micro-cracks formed due to brittle fracture owing to their poor ductility in tension. These results revealed that the abrasive wear of metallic glasses is not commensurate to their high hardness and occurrence of micro-cracking results in their poor abrasive wear resistance.

  • 184.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Current Trends in Tribology Research2013In: Proceedings of the International Conference on Smart Technologies for Mechanical Engineering (STME-2013), Excellent Publishing House, New Delhi, India , 2013, p. 4-Conference paper (Refereed)
  • 185. Prakash, Braham
    Friction and wear characteristics of advanced ceramic composite materials: (Chapter 11)1993In: Advances in Composite Tribology, Amsterdam: Elsevier, 1993, p. 405-449Chapter in book (Other academic)
  • 186.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    High temperature tribology in the context of hot sheet metal forming2011In: 6th China International Symposium on Tribology, August 19-22, Lanzhou, China, Lanzhou, China: State Key Laboratory of Solid Lubrication , 2011, p. 78-79Conference paper (Refereed)
  • 187. Prakash, Braham
    Interdisciplinary research and the role of Society of Advanced Science: a message to SAS Japan1991In: Journal of Advanced Science, ISSN 0915-5651, Vol. 3, no 1, p. 1-2Article in journal (Other academic)
  • 188. Prakash, Braham
    Investigations into the two body abrasion process of metallic glasses1998In: Proceedings of JAST tribology conference, Japan Society of Tribologists , 1998, p. 267-269Conference paper (Refereed)
  • 189. Prakash, Braham
    Tribotesting1993In: Monograph on Tribology in Engineering Design, Bangalore: Institution of Engineers, India , 1993, p. 152-165Chapter in book (Other (popular science, discussion, etc.))
  • 190. Prakash, Braham
    et al.
    Bandyopadhyay, Siddhartha
    Central Glass and Ceramic Research Institute (CGCRI), Calcutta.
    Mukerji, Joydeb
    Central Glass and Ceramic Research Institute (CGCRI), Calcutta.
    Friction coefficient of (a+b)-SiAlON composite against a steel and dense silicon nitride Tribopair1999In: Journal of The American Ceramic Society, ISSN 0002-7820, E-ISSN 1551-2916, Vol. 82, no 8, p. 2255-2256Article in journal (Refereed)
    Abstract [en]

    The friction characteristics of hot-pressed (α+β)-SiAlON, versus those of bearing steel and dense Si3N4 under dry sliding conditions, are reported. The coefficient of friction decreases as the alpha-SiAlON content increases and is double that of a metal-ceramic pair, in comparison to that of a ceramic-ceramic pair.

  • 191. Prakash, Braham
    et al.
    Chawla, Anil K.
    DIFR, DRDO, Delhi.
    Influence of silicon addition on tribological performance in Zn‑Al alloy plain bearings1991In: Industrial tribology: 9th National conference : Selected papers and discussions, CMTI , 1991, p. B119-B126Conference paper (Refereed)
  • 192. Prakash, Braham
    et al.
    Chopra, P. K.
    Indian Institute of Technology, New Delhi.
    Awasthy, K. L.
    Indian Institute of Technology, New Delhi.
    A new device for monitoring of contaminants in engine lubricating oils1989In: The Journal of Condition Monitoring, ISSN 0950-9178, Vol. 2, no 4, p. 269-275Article in journal (Refereed)
  • 193. Prakash, Braham
    et al.
    Chopra, P. K.
    Indian Institute of Technology, New Delhi.
    Awasthy, K. L.
    Indian Institute of Technology, New Delhi.
    A new device for monitoring of contaminants in engine lubricating oils1987In: Synopsis of papers: 4th Tribology Conference / [ed] Gépipari . Tudományos Egyesület., Budapest: Gepipari Tudomanyos Egyesulet , 1987, p. 161-164Conference paper (Other academic)
  • 194. Prakash, Braham
    et al.
    Christensen, H.University of Trondheim.Sharma, J. P.Indian Institute of Technology, New Delhi.
    Proceedings / International Conference on Optimum Resources Utilization through Tribo Terotechnology and Maintenance Management (Tribo-Maint '81)1983Collection (editor) (Other academic)
  • 195.
    Prakash, Braham
    et al.
    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.
    Hardell, Jens
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    High temperature tribology research: needs and opportunities2013Conference paper (Refereed)
  • 196.
    Prakash, Braham
    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.
    Yang, Jun-Feng
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements. Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei.
    Fang, Qian-Feng
    Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei.
    Tribological properties of transition metal di-chalcogenide based lubricant coatings2012In: Frontiers of Materials Science, ISSN 2095-025X, E-ISSN 2095-0268, Vol. 6, no 2, p. 116-127Article in journal (Refereed)
    Abstract [en]

    Transition metal di-chalcogenides MX 2 (X = S, Se, Te; and M = W, Mo, Nb, Ta) are one kind of solid lubricant materials that have been widely used in industry. The lubricant properties of such lubricant coatings are dependent not only on microstructure, orientation, morphology, and composition of the coatings, but also on the substrate, the interface between substrate and lubricant coatings, and the specific application environment. In this review, the effects of parameters on tribological properties of such kind of lubricant coatings were summarized. By comparing advantages and disadvantages of those coatings, the special treatments such as doping, structural modulation and post-treatment were suggested, aiming to improve the tribological performance under severe test conditions (e.g. high temperature, oxidizing atmosphere or humid condition).

  • 197. Prakash, Braham
    et al.
    Hiratsuka, K.
    Chiba Institute of Technology.
    Sliding wear behaviour of some Fe, Co and Ni based metallic glasses while rubbing against bearing steel2000In: Tribology letters, ISSN 1023-8883, E-ISSN 1573-2711, Vol. 2-3, p. 153-160Article in journal (Refereed)
    Abstract [en]

    The sliding wear behaviour of several compositions of Fe-, Co- and Ni-based metallic glasses have been studied while rubbing against AISI 52100 bearing steel under reciprocating-sliding conditions. The wear resistances of Fe-based metallic glasses and Ni-based metallic glass (MBF 50) have been found to be superior to that of the mating AISI 52100 bearing steel. The examination of worn surfaces indicates that the superior wear resistance of metallic glasses is not merely owing to their high hardness but it is determined by phenomena of material transfer vis-à-vis the mating material and the formation of protective oxide layers on the metallic-glass surface during sliding.

  • 198. Prakash, Braham
    et al.
    Kumar, Brijesh
    Indian Institute of Technology, New Delhi.
    Influence of contaminant particle size on wear in journal bearings under boundary lubrication conditions1987In: International Tribology Conference: 1987 : preprints of papers, Barton: Institution of Engineers, Australia , 1987, p. 387-390Conference paper (Refereed)
  • 199. Prakash, Braham
    et al.
    Mathur, R. K.
    Gabriel India Limited, Parwanoo.
    Failure analysis of plain bearings1987In: National Seminar on Bearings, New Delhi: National Productivity Council , 1987, Vol. II, p. V-5/1-V-5/26Conference paper (Other academic)
  • 200. Prakash, Braham
    et al.
    Mukerji, J.
    Central Glass and Ceramic Research Institute (CGCRI), Calcutta.
    Kalia, S.
    Tribological properties of Al2O3-TiN composites1998In: American Ceramic Society Bulletin, ISSN 0002-7812, E-ISSN 1945-2705, Vol. 77, no 9, p. 68-72Article in journal (Refereed)
12345 151 - 200 of 245
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