ICMCTF2005 Session E4: Tribology of Diamond, Diamond-like and Related Carbon Coatings/Thin Films

Wednesday, May 4, 2005 1:30 PM in Room California
Wednesday Afternoon

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Start Invited? Item
1:30 PM Invited E4-1 Different Carbon Based Thin Films and their Microtribological Behaviour in MEMS Applications
R. Bandorf, H. Lüthje, C. Henke, J. Wiebe, J.-H. Sick (Fraunhofer IST, Germany)

Amorphous Carbon based coatings are well known and typically used for high wear resistant and low friction in mechanical contacts. Since carbon based films can be fabricated at rather low temperatures < 150°C the application covers a broad variety of different metal, ceramic and to some extent also organic substrates. Especially for micro mechanical and micro electro mechanical systems (MEMS) dry lubricants are very essential for applications due to the absence of additional sticking and adhesion phenomena usually induced by liquid lubricants. Recent tribological developments in MEMS technology, application and characterization, using thin carbon based films are reviewed in this paper.

However, besides the development of thin tribological coatings further improvement of the frictional behaviour can be realised by optimizing the contact situation. Therefore an optimized topography and surface profile is generated by means of micropatterning. This novel results on micro structured surfaces coated with a-C:H and a-C films will be discussed. Furthermore an oscillating friction tester for the investigation of flat to flat contact, closing the gap between the common pin-on-disc tester and the single asperity investigations by means of AFM method will be presented. The perspectives and limitations of the micro areal tester as well as the behaviour of areal microcontacts and micro structured surfaces will be discussed.

The goal of the investigations was a further reduction of friction by use of microstructures and load-optimized contact areas. Therefore the resulting contact area, correlated with the resulting local pressure, was varied over three orders of magnitude by variation of both width and spacing of the micropattern in the range of 5-100µm. For optimised combination of sliding carbon film and micro patterned surfaces the friction coefficient was reduced by more than 30% compared to full area contact.

2:10 PM E4-3 Tribological Properties of Carbon and Titanium Carbide Multilayer Hard and Solid Lubricating Films
T.H Hashizume, S.M. Miyake, S. Watanabe (Nippon Institute of Technology, Japan); M.S. Sato (Oiles Corporation, Japan)
Nano period multilayer films, such as carbon / titanium carbide multilayer film show the characteristic improvement from which single film differs, and examination various now is performed. Carbon / titanium carbide multilayer film contains in the titanium carbide structure which shows wear resistance and the graphite structure which shows solid lubricant. Formation of a multilayer film formed the nano-period film by using magnetron RF sputtering equipment, generating Ar plasma, and carrying out sputtering of the target of carbon, carbon and titanium by turns. The sample which changed the nano-period cycle was created and by adjusting the formation time of each sputtering considered influence which a nano-period cycle has on the various characteristics. The tribology characteristic evaluation by the ball-on-disk tribotest, and the nano-indentation examination and micro wear characteristic evaluation using the atomic force microscope (AFM) were performed for evaluation of multilayer films. Moreover, an electron microscope and Raman spectrometer also performed analysis of multilayer films. As a result of examination, by changing a nano-period cycle, a friction coefficient and wear resistance changed and the multilayer film with the best characteristic was a 4nm period. And raman spectroscopic analysis, by changing a nano-period cycle, the shift of Id/Ig or a G-peak position was observed and the tendency changed with the nano-period cycle.
2:30 PM E4-4 Material Transfer Phenomena During Friction of Metal-Doped Ta-C
J. Fontaine, M. Belin (Ecole Centrale de Lyon, France); N. Benchikh, F. Garrelie, C. Donnet (University Jean Monnet, France)
Pulse laser deposition (PLD) processes are known to allow the deposition of tetrahedral diamond-like carbon films, often referred to as ta-C, exhibiting exceptionally high hardness, low friction coefficient together with very good wear resistance. However, these materials present also very high electrical resistivities, restricting their potential applications, especially for micro electro-mechanical systems. By using PLD technique in femtosecond mode with multiple targets, the growth of nanostructured metal doped ta-C has been possible. Films were produced with compositions of 0, 2, 5 and 15 at % of either nickel or tantalum. Their respective tribological behaviour in ambient air against steel has been investigated in a reciprocating sphere-on-flat tribometer, with spatially resolved friction force and electrical contact resistance measurements. Relatively low friction coefficient and low wear rates are reported for these metal-doped ta-C films. The addition of metal has a tendency to increase the friction coefficient while decreasing electrical contact resistance, with similar wear resistance. Depending on metal nature, material is either transferred from the coated flat to the steel pin (nickel) or from the steel pin to the coated flat (tantalum), controlling the evolution of friction during the experiments. These tribological phenomena are discussed with respect to metal incorporation and film nanostructure. Note: Requested an Oral Session.
2:50 PM E4-5 Tribology and Adhesion of Diamond-like Nanocomposite Coatings for MEMS Applications
S.V. Prasad, T.E. Scharf (Sandia National Laboratories)
Diamond-like nanocomposite (DLN) solid lubricant coatings grown by plasma enhanced chemical vapor deposition (PECVD) show promise as friction and wear reducing coatings for metal-based, microlithographic fabricated micrelectromechanical systems (MEMS). DLN coatings have an amorphous structure with mixed diamond-like (a-C:H) and quartz-like (a-Si:O) networks, and are well-known for their low friction behaviorin various environments. However, their tribological performance in load regimes relevant to MEMS operation is not well understood. In the current study, we have investigated the friction and wear behavior of DLN coatings deposited on silicon and nickel substrates in milli- and micro-newton load regimes using a sphere on flat unidirectional sliding tribometer and a nanomechanical test platform, respectively. Standard silicon nitride balls and specially fabricated MEMS tips were used as counterfaces for testing in ambient air and dry nitrogen environments. The fracture toughness and adhesion of the films to silicon and nickel substrates were also investigated with a micro-impact testing module on the nanomechanical test platform. The potential of DLN coatings to solve friction and wear issues in MEMS will be discussed in the light of the new tribological data.
3:10 PM E4-6 Effect of Counterface Materials on the Humidity Dependence of Tribological Behaviors of Diamond-like Carbon
S.-J. Park, K.-R. Lee, S.-C Lee, T.-Y. Kim (Korea Institute of Science and Technology, South Korea); D.-H. Ko (Yonsei University, South Korea)

Tribological properties of the diamond-like carbon (DLC) film are sensitive to the test environment such as relative humidity. Recently, we investigated the tribochemical reactions between the film, counterface materials and the environment in order to understand the humidity dependence of the tribological behaviors@footnote 1@ . In the present work, uncoated and DLC coated steel ball was used to investigate the effect of the counterface materials on the humidity dependence. Tribological properties were investigated by using a ball-on-disc type tribometer in environment chamber. The DLC film was deposited on Si (100) wafer using benzene (C6H6) by r.f-plasma assisted chemical vapor deposition. The tribological test was performed in ambient air of relative humidity ranging from 0 to 90%. When using uncoated steel ball, the friction coefficient of DLC film increased from 0.025 to 0.2 as the humidity increased from 0% to 90%. In the case of DLC coated ball where the Fe-rich debris was not generated during sliding, the humidity dependence of the friction coefficient was much smaller: friction coefficient was 0.08 at the relative humidity of 90%. These results confirmed that the humidity dependence of the friction coefficient is related to the formation of Fe-rich debris by the wear of steel ball. The atomic bond structure of the transfer layer on the uncoated steel ball was much more graphitic than that on the DLC coated ball. These results suggest that the graphitic properties of the transfer layer are the major reason for the humidity dependence. Fe in the Fe-rich debris would enhance the formation of the graphitic transfer layer that is sensitive to the humidity.

footnote 1@ S.J. Park, J.-K. Kim, K.-R. Lee, D.-H. Ko, Diamond. Relat. Mater. 12 (2003) 1517.

3:30 PM E4-7 Effect of Test Atmosphere on the Tribological Behavior of the Non-Hydrogenated Diamond-Like Carbon Coatings Against 319 Aluminum Alloy and Tungsten Carbide
E. Konca (University Of Windsor, Canada); Y.T. Cheng, A.M. Weiner, J.M. Dasch (General Motors R&D Center); A.T. Alpas (University of Windsor, Canada)
DLC coatings are promising candidates for dry machining of aluminum alloys since aluminum does not tend to adhere to the DLC surface in ambient conditions. Magnetron sputtered nonhydrogenated DLC coatings were produced and the effects of test temperature, test atmosphere and the counterface materials on the friction and wear behavior of these coatings have been studied. DLC coated M2 tool steel discs were tested against 319 Al pins, tungsten carbide (WC) and sapphire (Al2O3) balls using an environmentally controlled high temperature vacuum tribometer. The applied load was 4.9 N for all tests. Various sliding speeds and distances were employed. Tests were done at 25, 120, 300 and 400°C in ambient air. The wear resistance of this particular type of DLC has been found to be poor at elevated temperatures as low as 120°C. A surprising feature of this type of DLC was that it had higher wear rates against 319 Al alloy than that against tungsten carbide and sapphire. To elucidate the effect of test environment, the coatings have also been tested in vacuum (1.07x10-2 Pa) and inert gas (Ar and N2) atmospheres. The DLC coatings showed high coefficient of friction (COF) and wear rates in vacuum tests (0.52 ± 0.06, 4.05x10-4 mm3/m) compared to the ambient air tests (0.16 ± 0.04, 1.25x10-6 mm3/m). Tests were designed to study the effects of running-in in ambient air (i.e., initial wear) on the vacuum tribological behavior of the coatings. A very low COF regime (0.006-0.02) was observed under vacuum after a running-in period of sliding in ambient air to form a tribolayer on the contact surface of the 319 Al pin. The formation of this tribolayer on the counterface together with adsorption and dissociation of the atmospheric water on the sliding surfaces during sliding in ambient air were suggested as the mechanisms that create the subsequent very low COF regime under vacuum.
3:50 PM Invited E4-8 Application of DLCs and Other Carbon Based Nano-Particles for Aeronautics and Space Applications
K.W. Street, S.V. Pepper (NASA - Glenn Research Center); R.L. Vander Wal, A.J. Tomasek (National Center for Microgravity Research); W.R. Jones (Sest, Inc); M.J. Jansen (University of Toledo); V.N. Khabashesku (Rice University); R. Andrews (Center for Applied Energy Research)

The tribology program at NASA-Glenn is investigating diamond like carbon (DLC) films and carbon based nano-particles. The service conditions range from high temperature atmosphere to room temperature vacuum. Some of the lubricants and surface coatings of tribological significance that we have evaluated include neat nano-particles, both grown in situ and as bulk material deposited on the substrate, nano-particles dispersed in oils (nano-particulate based greases) and hydrogenated amorphous DLC films. These applications prove to be highly substrate dependent. The substrates we have considered for tribological couples include 440°C stainless steel (SS), quartz, sapphire and others coupled to similar material or one of the other substrates listed. In this presentation we will discuss results of our friction and wear testing for these systemin both a spiral orbit tribometer (SOT) and a unidirectional pin-on-disc (PoD) tribometer.

The SOT is a rolling contact tribometer which mimics the motion of a ball bearing. Our SOTs operate at ambient temperatures and in air, inert gas or vacuum. Typically SS on SS are the tribocouples lubricated with materials for space bearings such as low volatility oils or films such as DLC. The oil-nano-particle mixtures have the consistency of a grease. Nano-particles tested in Krytox 143AC include: nano-onions, single walled nanotubes, multi-walled nanotubes (MWNT) and fluorinated versions of these same base nano-carbons.

The PoD unit employed uses identical atmospheres to the SOT but is capable of high temperature operation. The majority of this testing uses a quartz disc with sapphire or SS pins. For bulk nano-particles, a thin layer (same materials as for the SOT) is deposited on the disc. Alternatively, we have grown MWNTs in situ by first depositing a thin metal catalyst layer and subsequently growing the MWNTs by chemical vapor deposition.

4:30 PM E4-11 Carbon Coatings with Optimised Sliding Behaviour for Precision Components in Industrial and Automotive Applications
O. Massler, M. Dippel, H. Eberle, M. Grischke, A. Ravagni (Balzers AG, Liechtenstein)

Modern mechanical machinery and engines have to run under high loads, speeds and temperatures and tighter tolerances and have to deliver smaller energy consumption, longer life and increased environmental friendliness. In many cases, the tribological systems and the materials choice are the performance- and lifetime limiting factors. Carbon based coatings play a very important role as an element for the design of those modern systems. In an industrial environment, a variety of coatings from this family of materials is being applied.

Hard diamond-like coatings will influence the counterbody, especially during early stages of operation. This can affect the performance of the tribosystem by reducing potential lifetime and friction benefits. A modular coating design for a metal-free hydrogenated diamond like carbon layer is proposed to avoid this circumstance. By suitable coating architecture and coating process, the counterbody surface is stabilized and system performance improved. The coating properties are demonstrated. The tribological behaviour of the coatings in several applications is being shown and benefits are being discussed.

Time Period WeA Sessions | Abstract Timeline | Topic E Sessions | Time Periods | Topics | ICMCTF2005 Schedule