ICMCTF2004 Session E4-2: Tribology of Diamond, Diamond-like and Related Carbon Coatings/Thin Films

Thursday, April 22, 2004 1:30 PM in Room California

Thursday Afternoon

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1:30 PM E4-2-1 Triboemission of Electrons, Ions and Photons from Diamond Like Carbon Films and Generation of Tribomicroplasma
K. Nakayama (National Institute of Adv. Industrial Sci. & Tech., Japan)

Various curious physical and chemical phenomena, which cannot be explained with frictional temperature rise, have been reported. This has suggested the existence of some unknown high energetic states generated at a sliding contact. On the other hands, the author has systematically investigated triboemission phenomena of electrons, ions and photons on various solids and gases under dry and lubricated sliding conditions. From the systematic investigation, it has been concluded that a tribomicroplasma, in which electrons, ions and photons are emitted, is generated by discharging of the surrounding gas due to intense electric fields caused by tribocharging. Recently, the author has successfully been able to take the images of the tribomicroplasma generated in a gap of sliding contact. The intensity of the tribomicroplasma increases with the electric resistivity of solids.

In a hard disk driver (HDD) simulation experiment of a diamond pin sliding on a soda lime glass substrate, the author found also the tribomicroplasma. During the sliding contact of the diamond pin on hydrogenated (H-film) and nitrogenated (N-film) carbon films, triboemission of electrons, ions and photons were observed with and without perfluoropolyether (PFPE) lubricated sliding conditions. The triboemission intensity was increased first gradually and then exponentially at a certain hydrogen and nitrogen content in the H- and N-films with the electric resistivity of these DLC films. The H-film emitted electrons more intensely than the N-film. This was explained with that the H-film has a higher electric resistivity than the N-film. This reveals that N-film has better tribological performances than H-film concerning decomposition of lubricant. It is known that organic molecules are decomposed in extremely high energetic plasma. Then PFPE molecules are decomposed by the tribomicroplasma to shorten the life of the HDD.

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); K. Itou, M. Fujioka, Y. Funaki (NDK, Incorporated, Japan)

DLC coatings with excellent tribological properties have attracted much attention in the automobile 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 technologies for them. However, conventional DLC coating is not widely used in the automobile 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 the DLC-Si coating was designed, and the DLC-Si coating 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 automobile industry.

2:30 PM E4-2-4 On the Microstructure and Mechanical Behaviour of Metal-containing Amorphous Hydrogenated Carbon Coatings (me-c:h): the Role of the Deposition Conditions.
N.J.M. Carvalho, J.Th.M. De Hosson (University of Groningen, The Netherlands); C. Strondl (Hauzer Techno Coating BV, The Netherlands); V. Rigato (Istituto Nazionale di Fisica Nuclearey, Italy)
Metal-containing amorphous hydrogenated carbon (Me-C:H) coatings offer unique high wear resistance and low friction coefficient properties that make them very desirable for a wide range of tribological applications. Series of Me-C:H coatings were prepared by unbalanced magnetron sputtering using tungsten, tungsten carbide and boron carbide as target materials in a plasma containing argon and acetylene. The substrate materials used were stainless, tool steel and silicon wafers. The influence of the substrate rotation speed, flow of acetylene gas and the ion beam energy on the microstructure, chemical composition and mechanical behaviour of the different Me-C:H coatings have been investigated. Their structural characterization has been performed with atomic force microscopy, transmission electron microscopy and ion beam analysis (Rutherford backscattering spectrometry and elastic recoil detection analysis). The residual stress state was measured by wafer curvature experiments, elastic stiffness and hardness by nanoindentation, friction properties against steel by a pin-on-disc apparatus, and adhesion on substrates by scratch testing with an acoustic emission detection. Further, focused ion beam has been used to mill cross-sectional transmission electron microscopy specimens from the indentations contact site, allowing the assessment of the microstructural aspects controlling the fracture behavior of the coatings. The observations indicate that the target material, substrate rotation speed, and ion beam energies influence the architecture of the coatings, thereby changing significantly the abrasive wear and fatigue resistance. A direct correlation was found between the metal- and hydrogen-to-carbon ratios and the hardness, elastic modulus, and friction coefficient. Specifically, a high metal content increased the hardness and elastic modulus, whereas an increase in hydrogen content promoted the reduction of the friction coefficient and compressive residual stress.
2:50 PM E4-2-5 Controlled Humidity Friction Coefficient Measurement of Sulfur Stabilized Hydrogenated Carbon Films
C.A. Freyman, Y.W. Chung (Northwestern University)
Hydrogenated carbon films have been deposited on Si substrates and stainless steel ball bearings by Ar magnetron sputtering technique. The resulting films are known for their very low friction properties in inert environments, but loose this property in the presence of water. Because practical applications of low friction films will take place in ambient air, the surface must be stabilized against water degradation. Sulfur gas has been introduced as a surface poison in attempt to prevent the degradation of the low friction properties. A ball on flat friction tester was enclosed in a controlled humidity chamber to precisely test the effect of humidity on the friction coefficient of the sulfur poisoned hydrogenated carbon films at different humidity values. The lowest coefficient of friction was optimized in relation to the amount of hydrogen and sulfur in the precursor gas along with the sputtering parameters of deposition. Other surface poisons might also be investigated.
3:10 PM E4-2-6 Tribological Behavior of WC/DLC/WS2 Nanocomposite Coatings
J.H. Wu, D.A. Rigney (Ohio State University); M.L. Falk (University of Michigan); J.H. Sanders, A.A. Voevodin, J.S. Zabinski (Air Force Research Laboratory)
Conventional DLC coatings do not perform well in sliding applications in certain environments, e.g., vacuum. Nanocomposite coatings developed at the Air Force Research Laboratory are designed for operation in environments ranging from humid air to the vacuum of space, as required for aerospace applications. A magnetron sputter-assisted pulsed laser deposition process was used to produce coatings with a matrix of DLC and nanoparticles of both WC and WS2. Coatings were tested on a pin/disk tribometer equipped with an environmental chamber and an in situ Kelvin probe. Low friction and wear were achieved in both air and vacuum. Post-test characterization of disk wear tracks, pin wear scars and debris involved the use of SEM/EDS, FIB/TEM, XPS and Raman spectroscopy. Surface material with mixed components dominate the tribological behavior of these coatings in both air and vacuum. Molecular dynamics (MD) is being used to model an amorphous material containing crystalline nanoparticles. Preliminary results suggest that soft particles (e.g., WS2) tend to mix with the matrix material rather than spreading on the surface as a separate layer. This is consistent with experimental observations.
3:30 PM E4-2-7 Friction and Wear Behaviour of Chromium Nitride Supported Carbon Coatings by Reactive Magnetron Sputtering
M. Diesselberg, H.-R. Stock, P. Mayr (Stiftung Institut fuer Werkstofftechnik, Germany)
Due to their low friction coefficient and high wear resistance amorphous hydrogenated carbon (a-C:H) films are suitable as protective dry lubricant for gears. Such a-C:H films were deposited on polished discs of carburised steel at temperatures below 200°C by sputtering from carbon targets and reactive deposition from acetylene. To improve adhesion the substrate was coated with a transition layer prior to deposition of the a-C:H film. This transition layer with a thickness of about 2 µm was produced by successively increasing the carbon cathode power while simultaneously decreasing the chromium cathode power and the nitrogen gas flow. The resulting graded multilayer consisting of chromium nitride (CrN) and amorphous carbon (a-C) acts as support for the subsequent a-C:H film. The main focus of this work was the effect of different ratios of sputtered to reactively deposited carbon on the friction and wear behaviour of the coating. Pin-on-disc tests were performed by sliding the coated samples against 100Cr6, sapphire and DLC-coated 100Cr6 balls in ambient air under an applied load of 100 N. It was found that increasing the a-C:H to a-C ratio enhances the self-lubricating properties and therewith reduces friction. However, if an optimal acetylene fraction was exceeded, it resulted in very soft films and increased wear which lead to partial coating failure after a short sliding distance. The optimal plastic hardness for this coating system, depending on the sp2/sp3 carbon binding ratio, was found to be 13 GPa resulting in steady state friction coefficients of 0.07 against DLC-coated balls and 0.15 against the other examined counter materials. Coating adhesion, determined using scratch adhesion tests, depended on the chemical composition and thickness of the underlying CrN/a-C transition multilayer and showed values up to 100 N. These tribological tests illustrate the potential of a-C:H films to effectively reduce friction and wear of gears.
3:50 PM E4-2-8 Superior Friction Properties of Carbon Nanotube Coatings in Air and in Ultrahigh Vacuum, a Spacelike Environment.
K. Miyoshi, R.L. Vander Wal (NASA Glenn Research Center); A. Sayir (Case Western Reserve University); S.C. Farmer (NASA Glenn Research Center)
A new two-layered nanotube coating (nanotube topcoat/iron bondcoat/quartz substrate) with superior friction properties in air and in ultrahigh vacuum, a spacelike environment, has been developed for aerospace applications, including the development of micro-machines. These systems have contacting surfaces in relative motion. Friction contributes performance, energy consumption, wear damage, maintenance, short lives or catastrophic failure, and reliability of the mechanical systems. The coefficient of friction for the new nanotube coating in contact with 440C stainless steel is one fourth of that for quartz or iron coating on quartz in air. In an ultrahigh vacuum the coefficient of friction in contact with alumina-based oxide ceramics is one third of that for quartz or for an iron coating on quartz. The coating can dramatically improve the stiction (or adhesion) and friction of the contacting surfaces, a major issue for micro-machines.
4:10 PM E4-2-9 Correlation between Plasma Characterization and Growth of Fullerene-like Cnx Thin Films Deposited by Pulsed Laser Ablation
H. Riascos (Universidad Tecnologica de Pereira, Colombia); G. Zambrano (Universidad del Valle, Colombia); A. Devia (Universidad Nacional, Colombia); H. Galindo, C. Power, J. Gonzalez (Universidad de los Andes, Venezuela); P. Prieto (Universidad del Valle, Colombia)

Fullerene-like CNx thin films were synthesized by Pulsed Laser Ablation (PLA) of pyrolytic graphite (99.99%) target in nitrogen atmosphere using a Nd: YAG pulsed laser. The composition and structure of these films were analysed by RAIRS, XPS, and Raman spectroscopy and the morphology of the films surfaces by AFM. The RAIRS analysis of films deposited at different pressures show the presence of the 2229 y 2273 cm-1 stretching peaks associated to CN triple bonds of nitriles and isocyanides. On the other hand, the XPS study of the N 1s bonding energy region provided typical spectra of the CNx materials. The spectra present the energy peaks at 400.8 (P2) and 398.4 eV (P3), that usually are assigned to nitrogen that is bonded to sp2 and sp3 coordinated C atoms respectively. For a fullerene-like structure with developed basal planes, nitrogen is mostly bonded in an sp2 reach environment. In our conditions for films deposited at 5 mTorr the P2/P3 ratio is 1.2 indicating a fullerene-like structure. Finally, the Raman analysis of films produced at different pressures, shows the characteristic D and G peaks at 1360- 1370 cm-1 and 1580-1590 cm-1 relate to the bond length in sp3 or sp2 coordinated carbon respectively. The optical emission spectra from the PLA-plume show mostly the presence of the band heads of CN Violet vibrational rotational B2 Σ - X2Σ system and the characteristic C2 emission lines belonging to the Swan A3Πg - X´3Πu system. The OES plasma characterization allowed to correlate the concentration and vibrational temperatures of CN and C2 species present in the plasma with the fullerene like CNx film composition and bonding determined by XPS, IR and Raman spectroscopy.

Work supported by COLCIENCIAS, under the 1106-05-11457 research project.

4:30 PM E4-2-10 Improved Adhesion of Ultrananocrystalline Diamond Coatings to SiC Mechanical Seal Surfaces
A. Kovalchenko, J. Elam, O. Auciello, J. Hryn, D. Gruen, A. Erdemir, J. Carlisle (Argonne National Laboratory)
Mechanical shaft seals are necessary to prevent fluid leakage from rotating equipment. The performance of mechanical shaft seals can be greatly enhanced by applying coatings to the sealing surfaces that are hard, smooth and chemically inert. UNCD films are produced by microwave plasma chemical vapor deposition (MPCVD) in an argon/methane gas mixture. These UNCD films have a hardness of 97 GPa, an RMS roughness of approximately 20 nm, a coefficient of friction of 0.1 in air and display the same outstanding chemical resistance as natural diamond. Previously, UNCD coatings applied to SiC mechanical shaft seals decreased the frictional torque by a factor of 6-7 and showed negligible wear. Unfortunately, the films deposited in this previous investigation were prone to delamination from the SiC surfaces. In the present study, delamination was investigated as a function of the surface roughness of the initial starting substrate. UNCD films with a thickness of 1 µm were deposited using MPCVD at 850°C onto reaction bonded SiC seals with an outside diameter of 3 inches. Prior to the UNCD deposition, the SiC seals were polished to different initial surface roughnesses between 0.05 and 0.25 µm. The UNCD films were characterized using Raman microanalysis, SEM and optical profilometry. The coated seals were then subjected to wear testing in a dynamic seal testing machine at 3000 RPM and 100 psi for up to 10 days. The seals were periodically removed and inspected for wear using optical profilometry and Raman microanalysis. Delamination was evident in the SiC seals having smooth initial surfaces of 0.05 µm. However, delamination was absent for the rougher seals. In addition, the UNCD surfaces showed no measurable wear as compared to approximately 0.2 µm of wear for the untreated SiC surfaces. Ongoing experiments are investigating the effects of different seeding and nucleation methods on the UNCD adhesion.
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