ICMCTF2004 Session E4-1: Tribology of Diamond, Diamond-like and Related Carbon Coatings/Thin Films

Thursday, April 22, 2004 8:30 AM in Room California

Thursday Morning

Start	Invited?	Item
8:30 AM	Invited	E4-1-1 An Overview on the Tribological Behavior of DLC in Technical and Medical Applications R. Hauert (EMPA, Switzerland) Diamond-like carbon (DLC), also known as amorphous hydrogenated carbon (a-C:H), is a class of material with variable properties. Depending on the deposition conditions and the setup used in tribological experiments, varying and even controversial results are obtained. Additionally, hydrogen, oxygen and the relative humidity have a crucial influence on the tribological behavior. The amorphous nature of a-C:H opens the possibility to introduce different amounts of other elements into the coating and still maintain the amorphous phase of the coating. By this technique film properties such as thermal stability, hardness, tribological properties, electrical conductivity, surface energy and biological reactions of cells in contact with the surface can be tuned within a certain range. Commercial applications of DLC and alloyed DLC are for example: Magnetic storage media, diesel injection pumps, sliding bearings, car valve rockers, gears, tappets of racing motorcycles, laser barcode scanner windows in supermarkets, VCR head drums, textile industry parts. DLC has excellent tribological properties in technical applications, however the literature shows contradicting results on the wear behavior of DLC coated hip joints.
9:10 AM		E4-1-3 Microstructure of Amorphous Diamond-like Carbon Thin Films and Changes during Wear E. Sutter, J. Goldsmith, J.J. Moore, B. Mishra (Colorado School of Mines); M Crowder (Maxtor Corporation) Using scanning and transmission electron microscopy, we investigate the microstructure of diamond-like carbon (DLC) thin films deposited in electron-cyclotron resonance plasma. During pin-on-flat wear experiments, the amorphous DLC films are found to be a source for formation of transfer film and wear track debris with composite microstructure. The transfer film represents a composite that consists of an amorphous matrix with dispersed microcrystalline and tubular particles. The debris from the wear track represent separated bundles of aligned tubular particles and clusters of microcrystalline particles. We relate the lowering of the coefficient of friction measured during the wear experiments to the formation of the composite transfer film and its steady-state low value to the possibility that the randomly oriented tubular particles from the transfer film engage in rolling friction in the process of their organization into aligned bundles.
9:30 AM		E4-1-4 Tribological Analysys of Amorphous Carbon Coatings for Valve Train Components M. Moronuki, K. Tsuji, A. Yoshimoto, A. Ishibashi, A. Kunimoto (Riken Corporation, Japan) Fuel economy is becoming a more important development target. The valve train can contribute a substantial part to mechanical friction, especially at low speeds where fuel economy is most important. Two different valve train layouts are commonly used. One is a valve train with direct acting mechanical bucket tappets (MBT), and another one with roller finger followers (RFF). The latter is often used to achieve the least possible friction, but unfortunately the costs are much higher than for the bucket tappet design. In order to exploit the advantage of the mechanical bucket tappet valve train in terms of cost, performance, an attempt has been made to use a hard coating to compensate for the friction losses inherent in this design. The friction tests were carried out on an externally driven engine head by using gas nitrided, Cr-N coated and newly developed amorphous carbon coated tappets. Newly developed amorphous carbon allows bucket tappets to achieve roller finger follower levels. In 5W-30 oil, the friction loss of newly developed amorphous carbon coated tappets was 50% less than that of tappets with Cr-N. But the friction behavior was quite different between 5W-30 and 5W-20 oils. Using this type of carbon coating, fuel consumption has been improved, and exhaust reduction is expected.
9:50 AM		E4-1-5 Tribological Performance of DLC at Elevated Temperatures S.V. Hainsworth (University of Leicester, United Kingdom) DLC coatings are used in a variety of applications to improve tribological performance. Many of the tests to assess friction and wear rate of the coatings are carried out at room temperature despite the fact that in service the coatings are often used at higher temperatures. The performance of a tungsten carbide-doped DLC coating (WC/C) deposited by physical vapour deposition onto a steel substrate has been characterized as a function of temperature using scratch testing, multi-pass scratch testing, micro-abrasion wear testing and pin-on-disk wear testing. Additionally, measurements of friction torque as a function of temperature have been made in an experimental cam-tappet rig with an oil-based lubricant. The mechanical properties of the coating have been assessed using nanoindentation testing. The deformation and wear modes have been characterised using scanning electron microscopy. The results indicate that the tribological performance of DLC coatings is sensitive to temperature, even with relatively modest temperature increments.
10:10 AM		E4-1-6 Effects of High-temperature Hydrogenation Treatment on Sliding Friction and Wear Behavior of Carbide-derived Carbon Films A. Erdemir, A. Kovalchenko (Argonne National Laboratory); M. McNallan, A. Lee (University of Illinois at Chicago); Y. Gogatsi, B. Carroll (Drexel University) In this study, we investigated the effects of a high-temperature hydrogenation treatment on sliding friction and wear behavior of carbide-derived carbon (CDC) films in dry nitrogen and humid air environments. These films are produced on the surfaces of metal carbides by reacting the carbide with chlorine or chlorine-hydrogen gas mixtures at 600 to 1000°C in a sealed reactor. The typical friction coefficients of CDC films in open air are in the range of 0.1 to 0.25, but in dry nitrogen, the friction coefficients vary a great deal, typically ranging from 0.05 to 0.3, depending on process temperature and gas mixtures. In an effort to achieve lower friction in inert gas or vacuum environments, we developed a special hydrogenation process that was proven to be very effective in lowering friction of CDC films produced on SiC substrates. The results of sliding friction and wear tests on hydrogenated CDC films revealed a close correlation between the measured friction coefficients and the degree of hydrogenation of the CDC films. Specifically, these results showed that the films that were post-hydrogen treated exhibited friction coefficients as low as 0.03 in dry nitrogen, while the friction coefficients in humid air were in the order of 0.1. Similar correlations were observed on wear rates of the films and the counterface silicon nitride balls. Detailed mechanical and structural characterizations of the CDC films and sliding contact surfaces were done using a series of analytical techniques and these findings were correlated with the friction and wear behaviors of as-produced and hydrogen-treatd CDC films.
10:30 AM		E4-1-7 Tribological Characterization of Amorphous Hard Carbon (ta-C) Coating at Room Temperature; Effect of Counterbody Materials and Humidity H.-J. Scheibe, V. Weihnacht (Fraunhofer Institute of Material and Beam Technology, Germany); D. Klaffke (Bundesanstalt fuer Materialforschung und-pruefung, Germany) Using high-current pulse-arc techniques (Laser-Arc, HCA), ta-C films of about 3 µm thick-ness and hardness up to 60 GPa have been deposited onto steel substrates. The films are characterized with respect to their density, elastic modulus, adhesion, surface roughness. The friction and wear behaviour was studied with oscillating sliding motion (gross slip fretting) with a ball-on-flat configuration at room temperature. Since the tribological behaviour of car-bon coatings can depend sensitively on the counter body material the coatings were tested against balls of different materials (bearing steel 100Cr6, alumina Al₂O₃ , silicon nitride Si₃N₄). The effect of moisture content on friction and wear was investigated in the range of 3 % to 100 % R.H.. Running in effects were separated from the stationary behaviour by tests with two different number of cycles (105 and 106). In all tests the friction was determined during the test, the wear (loss of material) was deter-mined after the test for the ball and for the coated disk. The wear behaviour depends on the counter body material and on relative humidity of surrounding air. Against steel and alumina a high wear resistance is found in all environments the coating tends to fail in dry air against silicon nitride
10:50 AM		E4-1-8 Tribological Behavior of Diamond-like Carbon Films in Aqueous Environment S.J. Park, K.R. Lee (Korea Institute of Science and Technology, South Korea); D.H. Ko (Yonsei University, South Korea) For the application of the diamond-like carbon (DLC) coating to the protective layer of an artificial hip/knee joint, tribological property of DLC film in biological environment such as saline solution is the most important properties. In the present work, tribological behavior of the DLC film in saline solution was investigated. Tribological properties of pure DLC film (a-C:H) and Si-DLC were compared. Pure DLC films of different bond structures were also prepared by changing the self bias voltage. In aqueous environment, the friction coefficient of pure DLC film was low and stable, same as the friction coefficient in ambient environment though the transfer layer didn't exist in the aqueous environment. However, the adhesive wear occurred in the case of pure DLC film. This adhesion problem resulted from the instability of DLC film in water environment. On the other had, tribological properties of the Si-DLC film showed high wear resistance even in aqueous environment. The effect of water on the tribological behavior will be discussed in terms of the tribochemical reactions between the film, water and the counterface materials.
11:10 AM		E4-1-9 Nano-impact Testing - an Effective Tool for Assessing the Resistance of Advanced Wear-resistant Coatings to Fatigue Failure and Delamination B.D. Beake, J.F. Smith (Micro Materials Ltd., United Kingdom) Thin films and coatings can fail by fatigue at lower loads than predicted by static tests. The nano-impact technique is an accelerated low load wear test capable of revealing marked differences in performance that can be used to optimize the design of new coated systems for improved durability. Instead of simply characterizing the new generation of advanced coatings and thin films, their actual tribological performance under in service conditions can now be assessed. Detailed evaluation of their mechanical reliability under repetitive stress will be critical in their acceptance to replace existing coatings. This paper introduces the concepts behind the nano-impact technique and presents results on a wide range of advanced DLC and amorphous carbon coatings where the results have been used to improve design and final performance where results of other nano-scale characterization tools, such as nanoindentation, are insufficient.