ICMCTF2005 Session E1: Friction and Wear of Coatings I: Lubrication and Surface Effects

Wednesday, May 4, 2005 8:30 AM in Room California

Wednesday Morning

Start	Invited?	Item
8:30 AM		E1-1 Co-Sputtered Mo:S:C:Ti:B Based Coating for Tribological Applications I. Efeoglu (Ataturk University, Turkey) Composite structured hardened-solid soft lubricant films were deposited onto D2 tool steels by co-sputtering from MoS₂, C, Ti, and TiB₂ targets using closed-field unbalanced magnetron sputtering process (CFUBMS). The wear and friction properties of Mo:S:C:Ti:B based coating were investigated for tribological applications. The coated specimens were charecterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques. Reciprocating multi-pass and pin-on-disc wear tests were carried out to compare their friction and wear properties. Hardness measurements was performed by microindentation. Keywords: co-sputtering; Mo:S:C:Ti:B, friction, wear.
8:50 AM		E1-2 Growth, Structure, and Tribology of Atomic Layer Deposited Hard and Solid Lubricant Thin Films T.W. Scharf, S.V. Prasad, M.T. Dugger, P.G. Kotula, R.S. Goeke, T.M. Mayer, N.R. Moody (Sandia National Laboratories) Atomic layer deposition (ALD) is based on sequential introduction of gaseous precursors and selective surface chemistry to achieve controlled growth of a film at the atomic scale. Efficient transport of material into confined spaces at low pressure, and sequential introduction of reactants leads to inherently excellent control of film thickness and coverage of high aspect ratio structures. This makes it ideally suited for coating shadowed surfaces on the underside of micro-electromechanical systems (MEMS) and rolling element bearings (REB). The objective of our study was to study the synthesis and microstructure of highly conformal tungsten disulphide (WS₂) and ZnO solid lubricant thin films, and W/Al₂O₃ nanolaminate hard coatings. WS₂ is a well known solid lubricant coating traditionally grown by sputtering or pulsed laser deposition, however these techniques can not be applied to MEMS scale components since they are line of sight processes. A new catalytic route was established to promote nucleation and growth of WS₂ films on Si, thermally grown SiO₂, and stainless steel surfaces for MEMS and REB applications. Cross-sectional TEM with EDS spectral imaging, XRD, and Raman spectroscopy were used to determine the film morphology, composition, and crystallinity. The WS₂ films exhibited solid lubricating behavior with a steady-state friction coefficient of 0.02 to 0.04 under high loading stresses in a dry nitrogen environment, while ZnO films exhibited a friction coefficient of ~0.2. Furthermore, based on results showing high hardness for ALD tungsten and good adhesion and fracture resistance for ALD Al₂O₃, 32 and 64 bilayer nanolaminates were created from sequential deposition of W and Al₂O₃ films to a thickness of 200 nm on silicon substrates. These W/Al₂O₃ nanolaminates exhibited improved frictional response and film durability in comparison to their respective single layer films.
9:10 AM		E1-3 Lubrication of Multilayered and Composite Sb₂O₃ Doped MoS₂, DLC, and MoS₂/Graphite Coatings Grown by PVD: Performance and Mechanisms J.S. Zabinski, J.H. Sanders, B.S. Phillips, J.E. Bultman, J.J. Hu (Air Force Research Laboratory) Multilayer and composite coating architectures take advantage of strengthening mechanisms and multifunctionality derived from different components. In addition, solid lubricant performance is greatly improved through the use of dopants. Sb₂O₃, for example, is noted for improving the wear life and friction coefficient of MoS₂ even though it is not a solid lubricant itself. In carbon systems, Sb₂O₃ is used to help prevent oxidation. This paper explores the properties and lubrication mechanisms of Sb₂O₃ doped MoS₂ and DLC films grown by pulsed laser deposition and magnetron sputtering using Sb₂O₃/MoS₂ and Sb₂O₃/graphite targets. A mixture of all three materials is deposited to take advantage of the dry environment solid lubricant properties of MoS₂ and the moist environment properties of DLC/graphite. Tribological properties were measured in dry and moist conditions at temperatures to 350°C. Lubrication mechanisms were evaluated by wear track/debris analysis using cross section SEM/TEM, Raman and XPS spectroscopy, and scanning Auger microscopy. The role of composition, nanostructures, and self-layering of components in the determination of enhanced tribological properties will be discussed.
9:30 AM	Invited	E1-4 The Effect of Nitrogen and Hydrogen on Reducing Friction of Carbon-Based Coatings K. Koji, K. Adachi (Tohoku University, Japan) The Effect of Nitrogen and Hydrogen on Reducing Friction of Carbon-based Coatings. Diamond/Diamond of smooth surfaces shows high friction coefficientμof about 0.8 in high vacuum and 0.05-0.15 in humid air. High friction in high vacuum is understood as the result of strong bonding between dangling bonds of carbons on the rubbed diamond surfaces, and low friction in air as the result of termination of dangling bonds of carbon atoms by the contaminant species in humid air and the formation of lubricious materials by tribo-chemical reaction. In a similar mechanism, a-C/a-C of smooth surfaces of coatings gives high friction coefficient of μ about 0.7 in UHV and about 0.10 in humid air. However a-CH_x/a-CH_x of smooth surfaces of coatings shows low friction coefficient μ below 0.01 in high vacuum when x is larger than a certain value in the range of 34~40 at.%. Dangling bounds of carbon atoms are thought to be terminated by hydrogen atoms and viscoplastic tribo-films are thought to be formed. On the otherhand, Si₃N₄/a-CN_x shows high friction coefficient (μ0.2) in humid air, low friction coefficient (μ= 0.05) in vacuum and even lower friction coefficient (μμ -.01) in N₂ gas of one atmospheric pressure. N₂ gas of 2.8 atmospheric pressure reduces its friction coefficient down to μ=0.003. N₂ gas is effective to reduce friction of a-CN_x even when it is supplied to the contact interface in air, and μ=0.005 is obtained. In this paper, the lubricious effect of "Nitrogen and Hydrogen" on friction of carbon-based coating is reviewed and mechanisms are discussed.
10:10 AM		E1-6 Tribological Properties of Oriented Carbon Nanotube Coatings Produced by Plasma-Enhanced Chemical Vapor Deposition J.J. Hu, A.A. Voevodin (Air Force Research Laboratory); S.H. Jo, Z.F. Ren (Boston College); J.S. Zabinski (Air Force Research Laboratory) Carbon nanotubes (CNTs) received considerable research attentions because of the excellent mechanical properties, including both high strength and high elasticity, and the commercial availableness of high quality CNTs. Comparatively less research was done in the investigations of CNTs for tribological applications. In this paper, CNTs arrays and coatings were grown on stainless steel and silicon nitride substrates by plasma-enhanced chemical vapor deposition. Tribological properties of the CNTs samples were measured using a pin-on-disk tribometer in dry nitrogen and humid air environments. Friction coefficients were also measured for different CNTs geometries, comparing short (about 1 um) and long (about 6 - 8 um) CNTs in order to determine the influence of CNTs length on their tribological properties. Wear scars were further examined using scanning and transmission electron microscopes and micro Raman spectrometer. It was found that applied contact load can bend and orient nanotubes parallel to the sliding surface. However this critically depends on the contact load. At the loads below 10 mN, the CNTs could elastically restore after the contact was removed. The CNTâ?Ts orientation in the tribological contact and their graphitization had a pronounced effect on the sliding friction coefficient. The tribological behavior of CNTs coatings will be discussed in detail on the basis of experimental data.
10:30 AM		E1-7 Nano Tribological Properties of Perfluoropolyether-Coated Magnetic Disk Evaluated by Vertical and Lateral Vibration Wear Tests S. Miyake, M. Wang, S. Ninomiya (Nippon Institute of Technology, Japan) Perfluoropolyether (PFPE) lubricants are generally used in order to get good tribological properties of magnetic disks. This is done to protect the magnetic elements from corrosion and wear and to provide interface durability. In this paper, we present results of the nano tribological characteristics of two perfluoropolyether-coated (PFPE) magnetic diamondlike carbon (DLC) film disks with and without thermal cure. Lateral oscillation wear experiments were performed using lateral modulation friction force microscopy (LM-FFM) mode in the load range of 2280 nN, scanning speed of 3 Hz and the vibration frequency of 1 kHz, using a diamond tip of approximately 26 nm radius. The surface morphology of the PFPE-coated disks with and without thermal cure (PFPE films with and without cure) was examined by atomic force microscopy (AFM). The result showed that the frictional property of the PFPE film without cure was significantly improved compared with that of the PFPE film with cure due to the supply of free lubricant by tip sliding. Corresponding to this, the vertical oscillation wear experiments were performed under the same conditions and the result showed that the viscoelasticity of the PFPE film without cure increased, which gives the evidence of the supply of free lubricant on the PFPE film without cure.
10:50 AM		E1-8 Influence of Oxide Phase Formation on the Tribological Behaviour of Ti-Al-V-N Coatings K. Kutschej (Materials Center Leoben, Austria); P.H. Mayrhofer (University of Leoben, Austria); M. Kathrein (CERATIZIT Austria GmbH, Austria); P. Polcik (PLANSEE Ag, Austria); C. Mitterer (University of Leoben, Austria) Ti-Al-V-N coatings are potential candidates for dry machining applications due to the combination of superior mechanical properties of Ti_1-xAl_xN and the lubricating mechanisms of vanadium oxides (so-called Magneli phase oxides) which form in the temperature range between 500 and 700°C. During ball-on-disc tests against alumina at 700°C the friction coefficient is 0.27, whereas Ti_1-xAl_xN coatings without V show a friction coefficient of 0.8. After a certain sliding distance at 700°C the friction coefficient increases from 0.27 to 0.45. Here we show, using X-ray diffraction and Raman spectroscopy, that this increase in friction coefficient during high temperature ball-on-disc tests is directly related to different oxidation stages of the Ti-Al-V-N coating. The coatings were prepared by DC magnetron sputtering from a powder metallurgically produced Ti-Al-V target, containing 50 at.-% Al, 25 at.-% Ti, and 25 at.-% V, in an Ar + N₂ glow discharge. During the early sliding stages at 700°C, the Magneli phase V₂O₅ is formed in the wear track of the Ti-Al-V-N coating, providing low friction coefficients. Upon further increase of the sliding distance (i.e., increased thermochemical and abrasive exposure), an AlVO₄ phase is formed resulting in an increase of the friction coefficient and the wear rate. This work clearly shows the effectiveness of V containing oxides in influencing the tribological properties of hard coatings.
11:10 AM		E1-9 Superelastic (Cr,Al)N Coatings for High End Spindel Bearings L. Lugscheider, O. Knotek, K. Bobzin, M. Maes, C. Brecher, G. Spachtholz (Aachen University, Germany) Due to the increasing performance of machine parts, the surfaces of 100Cr6 ball bearings are highly stressed. High rotational speeds and machining forces arising from up-to-date production processes cause rising Hertzian pressures and - in consequence - rising wear. New composite materials are investigated to extend the limits of operation. Hybrid bearings are more and more applicated for an increasing number of purposes. In preliminary investigations cylinder roller bearings were successfully coated to reduce wear and friction within the mixed lubrication. As a follow up, these coatings are now investigated for EHD lubrication in spindle bearings. In this paper a Cr,AlN coating is presented, which is deposited to the raceways of spindle bearings at low deposition temperatures (<160°C) to avoid annealing. In a first step the coating and the coating design is investigated with respect to mechanical, elastic and tribological properties of the coating. In a second part the coated bearings are then evaluated in a spindle bearing test unit with respect to temperature rise and friction torque depending on rotational speed and axial loading.
11:30 AM		E1-10 Tribological Behaviour of Self-Lubrication Coating Deposited using Electrolytic Plasma Process L. Wang, A.T. Alpas, X. Nie (University of Windsor, Canada) 3xx.0 series cast aluminium alloys were increasingly applied in automotives as lightweight components. For improvement of surface hardness and wear properties of the alloys, studies on electro- and electroless plating, hard anodizing, thermal spraying, and vacuum depositions have been conducted. An emerging electrolytic plasma process (EPP) has been recently used to deposit a hard, thick alumina coating which however has a high coefficient of friction. This research was intended to synthesize a ceramic matrix-graphite particle composite coating on 319 and 390 cast Al alloys with the self-lubrication functionality. The temperature and liquid lubricant effects on tribological properties of the composite coating were investigated using a high temperature pin-on-disc tribometer. Scanning electron microscopy (SEM) with energy dispersive X-ray analysis system (EDX) was employed for study of coating morphology and wear mechanisms of the coating. It was found that graphite particles were embedded in the Al₂O₃-SiO₂ ceramic matrix. During the dry sliding wear, the film of graphite presented on the counterface as a result of graphite particles transferring from surface and subsurface. The friction and/or wear rate of the composite coating were significantly reduced compared with those in a single alumina oxide coating and the uncoated aluminium substrates.