ICMCTF2003 Session E4-2: Tribology of Diamond, Diamond-like and Related Carbon Coatings/Thin Films

Tuesday, April 29, 2003 1:30 PM in Room California

Tuesday Afternoon

Start	Invited?	Item
1:30 PM	Invited	E4-2-1 Various Applications of DLC Including DLC-Coated Rubber Components T. Nakahigashi (Nippon ITF, Inc., Japan) DLC (Diamond Like Carbon) as a hard carbon film has such features as the lowest friction coefficient among various ceramics coating materials, high hardness, and less aggressiveness to other parties. Because of these features, its practical use for sliding is in progress. However, people now call other films DLC too even though they are different from those defined in ‘80s. Moreover, new manufacturing methods such as spatter method and arc method are now used in addition to the conventional ones like radio frequency (r.f.) plasma assisted chemical vapor deposition (PACVD) and ionized deposition. Another topic in these days is a flexible DLC film that uses rubber as radical material in stead of the formally used radical materials such as metal and ceramics. We thought that three issues have to be resolved. (1) Low heat resistance of the polymer materials such as rubber and resin. (2) Pollution of the polymer material surface by oil, fat, resin, and oxidation prevention agents, etc., and (3) Transformation of the polymer materials. To resolve these possible problems: (1) We have developed a processing method by using the Amplitude-Modulated RF Plasma Chemical Vapor Deposition method which enables coating at lower temperature (below 80 degree C) and does not allow the processing temperature to rise any higher. (2) To prevent the pollution, we decided to clean the polymer surface by plasma. (3) To prevent the transformation, the film should be flexible enough to absorb the polymer material transformation. We have modified the DLC film structure to permit expansion and contraction. This new DLC film is applied as a coating of ‘O’ ring for 35 mm zoom camera. This paper reports a technological trend of various applications of the recent DLC films and an example of sliding use of the ruber radical material.
2:10 PM		E4-2-3 Investigation of DLC-Si Coatings in Large Scale Production Using DC-PACVD Equipment K. Nakanishi, H. Mori, H. Tachikawa (Toyota Central R&d Labs. Inc., Japan); Y. Funaki, K. Itou (NDK, Inc., Japan) DLC coatings with excellent tribological properties have attracted much attention in the automotive industry. Friction control of automotive sliding parts and dry machining without lubricants have become more important for energy saving. DLC coating is one of the key technology for them. However, conventional DLC coating is not widely used in the automotive industry because of their low productivity and adhesion of the coatings. The new methods of the DLC-Si (silicon-containing DLC) coating by DC-PACVD, and improving of adhesion of the coating were developed in our laboratory. The throwing power of the new coating method is excellent compared with that of sputtering or RF-PACVD, and the coating for the parts loaded in three dimensions is possible. The large-sized DC-PACVD equipment (φ800x1500mm) for DLC-Si coating was designed, and DLC-Si coatings in large scale production was investigated. In this report, it will be revealed that the new coatings and the productivity of the coating method newly developed have enough potential for application to automotive industry.
2:30 PM		E4-2-4 A Study of the Tribological Behaviour of Three Carbon-Based Coatings, Tested in Air, Water and Oil Conditions at High Loads J. Stallard, D. Mercs, M. Jarratt, D.G. Teer (Teer Coatings Ltd, United Kingdom); P.H. Shipway (University of Nottingham, United Kingdom) Diamond-like carbon (DLC) coatings exhibit excellent low friction and wear protection properties in dry sliding conditions. Two recently developed carbon based coatings have very good wear resistance (e.g. specific wear rate as low as 1x10^-17 m³N^-1m^-1) and low friction under high applied loads, both dry and oil-lubricated. A comparison of the friction and wear properties of hydrogen free and hydrogenated amorphous carbon coatings (Graphit-iC and Dymon-iC respectively) and a benchmark commercially available DLC is presented in this paper. The coatings, on tool steel substrates, were characterised by their tribological performance, tested in dry, water and oil-lubricated conditions against a range of technologically relevant counter surface materials. Graphit-iC coatings were deposited in an industrial closed field unbalanced magnetron sputter ion plating (CFUBMSIP) system and the Dymon-iC coatings were deposited using a hybrid magnetron sputtering/plasma enhanced chemical vapour deposition (PECVD) system. The benchmark commercial DLC coatings were produced elsewhere by plasma assisted chemical vapour deposition (PACVD). The adhesion, friction and wear resistance of the coatings were determined using scratch adhesion and Pin-on-Disc testing. A Fischerscope H100 Ultramicrohardness tester measured the composite and coating hardness. Optical microscopy was used to observe all the effects of the testing conducted on the samples. A scanning electron microscope (SEM) was used to examine surfaces and the coating /substrate interface. X-ray diffraction (XRD) and reflection high energy electron diffraction (RHEED) techniques were used to identify coating structure, both before and after tribological testing. The results show how substrate surface roughness, counterface material hardness and changes in environmental conditions affect the formation of a transfer layer and subsequently influence the friction and wear performance of the coatings.
2:50 PM		E4-2-5 Changes in Wear and Friction Mechanisms of Polycrystalline Diamond in Different Environments J. Andersson, S. Jacobson (Uppsala University, Sweden) Diamond and diamond like carbon coatings have been demonstrated to have very interesting friction and wear properties. However, the mechanisms of friction and wear, and specifically the very strong influence from the environment on these properties, are not yet fully understood. The present investigation aims at adding some understanding to this area. Both rough and smooth polycrystalline diamond surfaces, grown in a hot filament CVD reactor, are worn in a ball-on-flat set-up. The experiments are conducted using diamond flat against diamond ball in normal air, water and inert atmospheres. Micro-spot XPS analysis is used to map surface chemical effects, which are related to friction as well as wear in the different environments. The evolution of surface roughness due to the process of wear is investigated with high resolution SEM and AFM. Preliminary results show dramatic changes in the evolution of surface topography and friction. In water, wear consists of a mild chemical polishing as well as, in the rough surface case, severe cracking of diamond grains. In the inert case, friction is clearly elevated and wear is dominated by the substantial generation of debris in the nanometer range.
3:30 PM		E4-2-7 Microstructural Evolution in As-deposited and Worn W-DLC Coatings Deposited by Magnetron Sputtering C.V. Cooper (United Technologies Research Center); J.C. Jiang, W.J. Meng (Louisiana State University); A.G. Evans (University of California at Santa Barbara) A detailed microstructural characterization of W-containing diamond-like-carbon (W-DLC) coatings, deposited onto spur gears via magnetron sputtering, has been conducted using transmission electron microscopy (TEM) in plan- and cross-sectional orientations. W-DLC-coated spur gears were tested in a POE oil at relatively low oil film thickness and examined via TEM in both the as-deposited and tested conditions. High-resolution microscopy clearly shows the presence of nanometer-scale structural/compositional modulation within the W-DLC coatings and further reveals the existence of a micrometer-scale columnar structure and intercolumnar defects within the coating. Defect morphologies were examined and related to the failure mechanisms of coated gears. Interestingly, the defects within the intercolumnar domains proved to be stable, and their presence was observed to play no role in the degradation of the coating.
3:50 PM		E4-2-8 The Coefficient of Static Friction of Silicon Containing Diamond-like Carbon Films U. Müller, R. Hauert (Swiss Federal Laboratories for Materials Testing and Research (EMPA), Switzerland) Diamond-like carbon films are well known for their outstanding tribological properties, which has been shown in many studies. Because of their extreme hardness, low coefficient of sliding friction (often after some running-in time) and especially their ability to form a transfer layer on the counter-body of the frictional pair these coatings have found many areas of application. There are many different types of these coatings on the market depending on the deposition process and on the deposition parameters used. This variability allows to tailor certain film properties to specific applications. Additionally, alloying with different elements allows further adaptations. One special tribological problem is found in applications where almost no or only little motion takes place and therefore no transfer layer can build up. In this case a special coating is needed which has a low coefficient of friction already at the very beginning of any motion. A similar situation is found in low load applications where neither a transfer layer is created nor the transformation of the topmost surface layer into a more graphitic-like state takes place. In this study silicon containing diamond-like carbon films are produced in a r.f. plasma-activated chemical vapor deposition system. A mixture of acetylene and an organosilicon gas is used to deposit silicon containing diamond-like carbon films onto hardened steel sample plate. On top of a supporting coating a 20 nm thick diamond-like carbon layer with varying silicon content is deposited using different selected self-bias voltages. The coefficient of static friction against a hardened stainless steel surface is then measured in dependence of the silicon content and of the self-bias used. The films display a constant coefficient of static friction even after many single measurements. The results are compared to results obtained for pure diamond-like carbon films.
4:10 PM		E4-2-9 Tribological Behavior of Si Incorporated DLC Film with Humidity Change S.J. Park, K.-R. Lee (Korea Institute of Science and Technology, South Korea); D.-H. Ko (Yonsei University, South Korea) Tribological behaveior of Si incorporated DLC film was investigated in various environments. The friction behavior was dependent on the relative humidity, even if the dependence was much smaller than that of pure DLC films. We focused on the tribo-chemical reaction and third body behavior in order to reveal the reason for the dependence. The tribological behaviors against steel ball and sapphire ball were compared. When using steel ball, the friction coefficient increased with increasing relative humidity. Wear rate of the ball and Fe concentration in the debris was also proportional to the relative humidity. The increase in the friction coefficient was correlated with the change in the debris composition from Si rich debris to Fe rich one. Friction coefficient against sapphire ball also increased with relative humidity. However, the increase was due to the changes in the transfer layer rather than a chemical reaction. These result shows that both tribo-chemical reaction and the transfer layer should be considered to understand the tribological behaviors.
4:30 PM		E4-2-10 Tribological Behaviour of DLC Coatings Operating under Different Lubrication Regimes B. Podgornik, J. Vizintin (University of Ljubljana, Slovenia); S. Jacobson, S. Hogmark (Uppsala University, Sweden) Analogously to the way as hard ceramic coatings (i.e. TiN, TiAlN,â€¦) became essential in the field of cutting tools, hard low-friction coatings (i.e. diamond and diamond like carbon coatings) are now becoming more and more important in the field of machine components. By both improving the wear resistance and giving excellent frictional properties, hard low-friction coatings certainly provide a great opportunity to improve durability and to reduce frictional losses of machine components. However, the demands on coatings for machine components are tougher than those on cutting tools. The expected life time is very long, both contact surfaces are of the same importance, the substrate hardness is rather low, and further the presence of the lubricating oil, originally designed for the steel/steel contact situation makes the selection and design even more complicated. The aim of the present work was to investigate the tribological behaviour of DLC coated surfaces, operating under different lubrication regimes. Tests were performed in a pin-disc and a load-scanning test rig, where DLC (WC-C) coated samples were loaded against coated and uncoated ones, while the steel/steel combination was used as a reference. All material combinations were tested under starved, boundary and EHD lubrication conditions, using four lubricants; pure poly-alpha-olefin oil (PAO), PAO mixed with commercial sulphur-based EP additive or ZDP-based AW additive, and fully formulated gearbox oil. Results of the investigation will be presented by means of the coefficient of friction, monitored as a function of time and load, wear and analyses of worn surfaces.
4:50 PM		E4-2-11 Diamond Like Coatings Prepared by the Filtered Cathodic Arc Technique for Minting Application M.-S. Leu (Industrial Technology Research Institute, Taiwan ROC); W. Lin (The Central Mint of China, Taiwan, ROC); S.-Y. Chen (Industrial Technology Research Institute, Taiwan, ROC) The wear resistance of diamond like coating (DLC) thin films prepared by filtered cathodic arc deposition technique are reported. Emphasis is placed on the lifetime of the DLC coatings on the proof minting dies, which can extend about 6 and 4 times corresponding to that of uncoated and hard chromium plating dies. The film thickness of DLC coatings are controlled only about 1 micrometer in order to maintain a high degree of surface smoothness onto the proof minting dies. Significant improvement of adhesion property, as evaluated by the scratch test was observed, as the thickness of the Ti interlayer was increased. The process offers a replacement of hard chromium plating and extended die lifetimes over conventional die surface treatments.