ICMCTF2001 Session E1-1: Reduction of Friction Through Coating/Surface Modification

Wednesday, May 2, 2001 8:30 AM in Room California

Wednesday Morning

Start	Invited?	Item
8:30 AM	Invited	E1-1-1 Studying Friction in MEMS: Test Structure, Metrology and Lubrication Choices M.P. de Boer, J.M. Redmond, J.A. Knapp, T.M. Mayer (Sandia National Laboratories) Tribological issues such as poorly controlled adhesion and friction are limiting the growth of microelectromechanical systems (MEMS) in the wider market place. To address this problem, a MEMS-based technological infrastructure is being developed. Deflection curves of simple test structures sensitive to adhesion and friction are measured by interferometry at the nm scale, and properties are determined by comparing measurement results to mechanics models. In this presentation, we will show the sophisticated functionality MEMS devices can acccomplish, describe test structure and metrology considerations for achieving a tribology lab on a chip, demonstrate that silane coupling agent monolayers significantly reduce friction, and explore the limitations of these coatings.
9:10 AM	Invited	E1-1-3 Physical and Chemical Polishing of Steel by Ceramic Coatings S.J. Harris, G.G. Krauss (Ford Research Laboratory) We have shown previously that over the course of thousands of cycles, the abrasiveness (or polishing ability) of carbon-containing films falls drastically in ball-on-disk experiments using steel balls, and that the rate of this fall can be characterized by a single parameter. In this work we provide evidence that this polishing is due to both chemical and physical aspects of the contact. We discuss the implications of these results for how best to apply ceramic coatings to protect machine parts against fatigue.
9:50 AM		E1-1-5 The Influence of Surface Roughness on Friction and Wear of DLC Coatings F. Svahn, @Ao A@ . Kassman Rudolphi (Uppsala University, Sweden) The use of low friction coatings like amorphous carbon and metal doped amorphous carbon coatings on machine elements is constantly increasing. Most often, a surface treatment e.g. grinding/polishing and/or surface hardening is required for optimal performance of the coated machine element. Since such treatments can be very time-consuming and expensive it is important to investigate the influence of different substrate conditions on the tribological behaviour of the coated component. In this study the effect of surface roughness on friction and wear of the coating and the counterpart was examined. Ball bearing steel plates were grinded to different surface roughnesses and coated with a thin metal doped amorphous carbon coating (WC/C) by a reactive magnetron sputtering process. In a ball-on-disc test, the ball diameter and the applied load were varied to study the influence of contact area and contact stress, respectively, on the tribological behaviour for a given surface roughness. All tests were conducted in humid air and in oil. The results indicate a clear influence of surface roughness on the tribological properties of a coating.
10:10 AM		E1-1-6 Hydrogen Effects on the Friction Mechanism of Diamond-Like Carbon Films C. Donnet (Ecole Centrale de Lyon, France); A Grill (IBM Research Division, T.J. Watson Research Center, NY); J. Fontaine, T Le Mogne (Ecole Centrale de Lyon, France) The structure and properties of Diamond-like carbon films strongly depend on the hydrogen content and nature of carbon-hydrogen bonds, which can be now accurately controlled by the deposition process. The objective of the present work is to highlight the role of hydrogen on the friction mechanism of DLC films, both as a constituent of the carbonaceous film and as a gaseous species introduced in the surrounding environment during the friction process. Two films with different hydrogen contents were selected. The friction experiments were performed in ultrahigh vacuum or in an atmosphere of pure hydrogen or argon. Two typical friction regimes are identified. High steady-state friction in UHV (friction coefficient of 0.6) is observed for the lowest hydrogenated and mostly sp2-bonded DLC film. Superlow steady-state friction (friction coefficient in the millirange) is observed both for the highest hydrogenated film in UHV, and for the lowest hydrogenated film in an atmosphere of hydrogen (10 hPa). Superlow friction is corellated with a hydrogen saturation across the shearing plane through weak van der Waals interactions between the polymerlike hydrocarbon top layers. This regime is observed during the steady-state period if the film contains enough hydrogen incorporated during deposition. If this condition is not satisfied (i.e. for the film with the lowest hydrogen content), the limited diffusion of hydrogen from the film network towards the sliding surfaces seems to be responsible for a superlow running-in period. The superlow friction level can be reached over longer time periods by suitable combinations of temperature and molecular hydrogen present in the surrounding atmosphere during friction.
10:30 AM		E1-1-7 Preparation by Pulsed Vacuum arc Deposition and Characterization of DLC/MoS₂ Nanocomposite Thin Films M.P. Delplancke-Ogletree (Universite Libre de Bruxelles, Belgium); O.R. Monteiro (Lawrence Berkeley National Laboratory) The mechanical and tribological properties of amorphous carbon films have been extensively investigated. The lubrication performances of non-hydrogenated DLC are limited in absence of moisture. The incorporation of clusters of a solid state lubricant like MoS₂ in a matrix of DLC could provide interesting tribological properties to this nanocomposite. In this paper, we prepared nanocomposite thin films by mixing C⁺ and Moⁿ⁺ plasma streams originated in filtered cathodic arc plasma sources in presence of a CS₂ or S vapor. The results obtained with these two precursors were compared in terms of purity, bonding states, and control of carbon and sulfur incorporation. The S vapor was selected for further studies. The influence of the sulfur concentration in the films and of the substrate bias on the structure and properties of the nanocomposites were studied by TEM, XPS, AES, and ball-on -disk wear tests. The paper is presenting a comparison with other systems like tungsten and titanium doped DLC. .
10:50 AM		E1-1-8 Tribochemical Effects Between Diamond-Like Carbon Coatings and Antiwear and Friction-modifying Additives J. Fontaine, C. Donnet, J.M. Martin, M Belin (Ecole Centrale de Lyon, France) The tribological properties of some Diamond-Like Carbon (DLC) coatings make them suitable for wear protection in automotive engines. However, the lubricants used in such engines contain several additives and particularly antiwear and friction modifiers, w hich are known to form so-called "tribofilms" on metallic surfaces. We investigated the tribological behavior of DLC/steel and DLC/DLC contacts in boundary lubrication with base oil and with various additives, like zinc dithiophosphate (ZnDTP) and molybd enum dithiocarbamate (MoDTC). A significant reduction of friction was found for the DLC/steel contact with Mo-containing lubricant additives, compared to DLC/DLC contact and moreover to base oil. Finally, TEM observations of wear debris as well as XPS and AES analyses inside wear scars were performed to track the tribofilm formation and to elucidate the tribochemical interactions between DLC coatings and additives.
11:10 AM		E1-1-9 Vacuum Tribology Studies of WC-Ag and TiC-Ag Composite Coatings Deposited by Sputtering and Laser Ablation J.L. Endrino, J.E. Krzanowski (University of New Hampshire); J.J. Nainaparampil (Systran, Inc.) There is a recent need for new coating materials that can provide both low friction and reduce wear for rolling and sliding components in vacuum service. Carbide coatings are well known to be very effective in improving hardness and wear properties, however, they have high friction coefficients in vacuum environments. Soft solid lubricants, such as silver are effective in reducing friction but may not provide good wear resistance. Our research shows that advanced composite ceramic-silver coatings greatly decrease the friction coefficient and could be used in vacuum environments to reduce lubrication problems. In this study, tungsten carbide-silver and titanium carbide-silver films of a thickness of 750 nm were deposited by magnetron co-sputtering and by magnetron sputtering-pulse laser deposition (MSPLD) to study their friction properties. X-ray diffraction (XRD) was used to determine their structural properties. Energy dispersive x-ray analysis (EDX) was used to determine silver content and the pin-on-disk friction test was performed under vacuum to obtain the friction coefficients. SEM images from the surface of the films were taken and studied to further understand the morphology of this type of composite ceramic coatings. The significance of silver as a friction reducing agent was demonstrated for both TiC-Ag and WC-Ag. For example, a WC film deposited at 275ËšC by magnetron sputtering has a friction coefficient in vacuum of 0.7, while a WC-Ag (with 10% silver) film deposited at the same temperature has a friction coefficient of 0.25. Comparison of the friction coefficient of films deposited at 275ËšC and at 150ËšC indicate a strong relationship between friction and crystallite size.
11:30 AM		E1-1-10 Wear Reduction- and Self-Lubrication Properties Of Substoichiometric Vanadium and Tungsten Oxide and Superstoichiometric Zirconium and Hafnium Carbide Coatings St. Bärwulf, E. Lugscheider, K. Bobzin, T. Hornig (University of Technology (RWTH) Aachen, Germany) The tungsten and vanadium oxides are promising to be usable as solid lubricants at elevated temperatures because of their ability to form non stoichiometric Magnéli-phases with reduced shear strength. So far they were mainly investigated as powdery material or as a component of ceramics for tribological or machining applications. As a matter of fact metal-oxides are interesting for tribological insets at atmospheric conditions because of their expected oxidation stability, hardness and low adhesion against the counterbody. For low temperature insets carbon containing coatings are meanwhile widely spread in numerous applications. Because of their phase generation / transition the zircon- and hafnium-carbon systems offer a very interesting possibilty to deposit graded coatings with self-adapting properties in dependance on the external mechanical load and the contact conditions. After a fundamental discussion about the deposition process development the self- adapting effect will be shown exemplarily for a hydraulic component after an inset under load in relative motion. The presentation will report about the mechanical and tribological properties of these coatings. Further possible ranges of applications will be deduced from the fundamental characterization and results of concrete insets (e.g. machining) shown. Therefore the coatings were analyzed by various testing methods to characterize the tribological, mechanical and structural properties, like contact angle measurements, SEM, scratch testing, nanoindentation, XRD and pin on disk.
11:50 AM		E1-1-11 The Role of Hydrogen in Tribological Properties of Hard Carbon Films A. Erdemir (Argonne National Laboratory) Extensive research on diamond and diamondlike carbon (DLC) films in our laboratory has led to the conclusion that the presence of hydrogen either within the film or in the test environment plays a major role in the tribological properties of these films. Specifically, it was found that a highly hydrogenated DLC film could provide friction coefficients from 0.001 to 0.005 in inert gas environments, while a hydrogen-free DLC providing friction coefficients of 0.3-0.6 under the same test conditions. Furthermore, the location and the type of hydrogen (protonic, atomic, or molecular) within these films are also critically important. Employing a combination of molecular dynamic simulation, surface and structure analytical techniques, it now became possible to better-understand the structural chemistry of the these DLC films and correlate these findings with their fundamental tribological mechanisms.
12:10 PM		E1-1-12 Composite Coatings with Improved Mechanical and Tribological Properties, Obtained by Implantation-Plasma Methods M.V. Atamanov, M.I. Guseva, Yu.V. Martynenko (Russian Research Center "Kurchatov Institute", Russia); V.S. Mitin (State Center of RF Allrussian Scientific and Recearch Institute of Inorganic Materials, Russia); A.V. Mitin (State Center of RF Allrussian Scientific and Recearch Institute of Inorganic Materials, Russian Federation, Russia); P.G. Moskovkin (Russian Research Center "Kurchatov Institute", Russia); S.A. Shiryaev (State Center of RF Allrussian Scientific and Recearch Institute of Inorganic Materials, Russia) Composite coatings of AlN, AlNC, TIN, TiNC, NbCN, TIAlZrN, TiCrWC kinds were manufactured by magnetron sputtering with ion implantation. The composition and thickness of the coating were investigated by RBS and SEM. The friction coefficient of some composite layers is < 0.5 and micro hardness > 40 GPa. Implantation of N⁺ and C⁺ ions with energy 40 keV results in oxygen concentration decreasing in coatings received by magnetron sputtering. The coatings have the thickness 5 - 15 µm and good adhesion.