ICMCTF2003 Session E4-1: Tribology of Diamond, Diamond-like and Related Carbon Coatings/Thin Films

Tuesday, April 29, 2003 8:30 AM in Room California

Tuesday Morning

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8:30 AM E4-1-1 Characterization of Carbon Coatings and Tribofilms with Resonant Raman Spectroscopy
A.C. Ferrari (University of Cambridge, United Kingdom)

Amorphous carbons are used in a wide range of tribological applications. Their properties vary enormously as a function of the deposition process and composition. Raman spectroscopy is a popular, non-destructive tool for the structural characterisation of carbons. It is a valuable tool to study the nature of the transfer layers and wear tracks in friction experiments. It is also commonly used to assess the quality of the carbon coatings for hard disk drives. Here we present a model for the interpretation of the Raman spectra, measured at any excitation energy for any carbon film1. Raman scattering from carbons is always a resonant process, in which those configurations whose band gaps match the excitation energy are preferentially excited. The Raman spectra of carbons consist of three basic features, the G and D peaks around 1600 and 1350 cm-1 and an extra T peak, for UV excitation, at ~980-1060 cm-1. The Raman spectra at any wavelength depend on 1) clustering of the sp2 phase, 2) bond length and bond angle disorder, 3) presence of sp2 rings or chains, and 4) the sp2/sp3 ratio. The G peak position increases as the excitation wavelength decreases. the rate of change of the G peak position is called dispersion. The G peak does not disperse in graphite. The G peak only disperses in disordered carbons and the dispersion is proportional to the degree of disorder. Combined Raman measurements at two different wavelengths, such as 514.5 and 244 nm, allow us to derive a wealth of information not accessible by visible Raman measurements alone. The G peak dispersion can be related with the main film properties, such as sp3 content, composition, density and elastic constants. Examples of application of resonant Raman spectroscopy to characterise carbon coatings will be discussed.

1 A.C. Ferrari, J. Robertson, Phys. Rev. B 61, 14095 (2000); 64, 075414 (2001); B, 63, R121405 (2001).

9:10 AM E4-1-3 Microscratch Test of DLC Coating
D.H. Zaidi, A. Djamai, M. Nguyen (Universite de Poitiers, France)
The adherence characteristic of DLC coating on substrate was investigated by microscratch tests with the scratch tester ST-3001. The tests were made by Rockwell C indenter under progressive and constant normal load (5N ~ 200N) at low sliding speed. The tangential friction force and the acoustic emission during scratch testing were recorded according to the time and the load. The contact problem is also approached by three-dimensional modeling in coating surface and substrate. The resulting stresses are discussed for different values of the friction coefficient. The aim of this paper is firstly to present the experimental results of microscratch in DLC coating and determine the critical normal load that creates the cracks in the thin film as a surface failure. Then, the numerical study was realized to correlate it with the cracks experimentally obtained and microscopically measured.
9:30 AM E4-1-4 Dynamic Indentation Testing of Hard, Carbon-Based Coatings
J. Fernandez-Palacio, S.J. Bull (University of Newcastle, United Kingdom)
Carbon-based hard coatings such as DLC or CNx generally have amorphous microctructures and exhibit different deformation mechanisms from traditional crystalline hard coatings such as TiN. In particular, the H/E ratio is often very high for such carbon-based materials leading to highly elastic indentation behaviour. Also the mechanical properties of a fullerene-like CNx coating have recently been suggested to be like those of a superhard rubber. The structure of these materials suggests that time-dependent deformation mechanisms may be important in their mechanical response. In this paper the use of dynamic stiffness measurement in the nanoidentation assessment of a range of carbon-baesed coatings will be reported. The effect of frequency on loss and storage moduli will be presented and the implications of the time dependent deformation behaviour of the materials in tribological applications will be discussed.
9:50 AM E4-1-5 The Role of Gaseous Interactions in the Friction of Diamond-like Carbon Films
J. Fontaine, T. Le Mogne, J.L. Loubet (Ecole Centrale de Lyon, France); A. Grill (IBM T.J. Watson Research Center)
Amorphous hydrogenated carbon (a-C:H) films can achieve super-low friction coefficients in ultrahigh vacuum (UHV) for high hydrogen contents. Furthermore, friction experiments performed in gaseous hydrogen on a-C:H films with low hydrogen content have confirmed the lubricating role of hydrogen. It is believed that low Van der Waals interactions are thus promoted, allowing the reduction in friction. However, recent results stated that the viscoplastic behavior of a-C:H films is also correlated with super-low friction. It seems therefore that both physical chemistry and mechanics are involved in such friction regime. Model a-C:H films of known composition and mechanical properties were selected for their typical friction behavior in UHV. Friction experiments were then performed on these films in gases of increasing reactivity: helium, hydrogen and deuterium, oxygen. The respective roles of physicochemical interactions and mechanical properties in the super-low friction of amorphous hydrogenated carbon (a-C:H) are then discussed.
10:30 AM E4-1-7 Influence of the Substrate Properties on the Tribological Behaviour of Carbon Based Coatings
O.K. Massler (Balzers AG, Liechtenstein, Pricipality of Liechtenstein); E. Menthe (Daimler Chrysler Powersystems, Germany)
Carbon based coatings manufactured by PVD and PACVD-methods have reached a high level of acceptance for tribological applications. The reduction of friction and the prevention of surface- and friction related wear mechanisms are the main motivation for the application of the coatings to technical surfaces. An important role for the engineering of a coated surface are the demands of the application and the design of the tribosystem. The main steering parameters for the performance are the properties of the substrate material, the morphology of the surface, the boundary conditions of the tribosystem, the coating properties and -behaviour and the type of interaction between those parameters. The behaviour regarding frictional properties, and lifetime of a tribosystem are strongly depending on the loading, substrate hardness and roughness, the type of movement, but also coating type and coating thickness. The influence of the substrate heat treatment and nitriding prior to coating with two different carbon based coatings shows significant influences on the tribological behaviour of a tribosystem.
10:50 AM E4-1-8 Friction and Wear Behavior of Metal Doped DLC Coatings Studied by In Situ Raman Tribometry
T.W. Scharf, I.L. Singer (U.S. Naval Research Laboratory)
The friction and wear behavior of three (C:Ti, C:H:Ti, and C:H:W) metal containing diamond-like carbon (DLC) coatings in dry sliding contact has been investigated using a home-built in situ tribometer. Tests were performed under reciprocating sliding against sapphire and steel hemispheres in dry (~2% RH) and ambient (~50% RH) air at a contact stress of 0.7 GPa. In situ visual observations identified how third body processes affected the friction behavior of DLC coatings. For all test conditions, a transfer film began to form on the sapphire hemisphere during the first cycle, and the coefficient of friction dropped from ~0.2 to ≤ 0.1 during further buildup of the transfer film. Video analysis showed that most of the sliding motion took place between the transfer film (on the hemisphere) and the coating, indicating that the velocity accommodation mode was interfacial sliding. All three coatings had the same steady state friction coefficients: about 0.05 in dry air and ≥ 0.12 in ambient air. Both Ti-DLC coatings wore less than the W-DLC coating for all testing conditions. Humidity also contributed to the wear behavior: it increased the wear rate of the Ti-DLC coatings but decreased the wear rate of the W-DLC coating. Similar friction and wear behavior was seen with both sapphire and steel hemispheres. In situ Raman spectroscopy, ex situ FTIR and SEM/EDS analyses identified various tribochemical products (TiOx and WOx) and heterogeneities in transfer films. The role of the metal dopant in the wear of DLC will also be discussed.
11:10 AM E4-1-9 Characterization of Boron Containing Diamond Like Carbon Coatings
C. Strondl (Hauzer Techno Coating BV, The Netherlands); N.J.M. Carvalho, J.Th.M. De Hosson (University of Groningen, The Netherlands); G.J. van der Kolk (Hauzer Techno Coating BV, The Netherlands)
Two different types of metal containing diamond like carbon coatings (Me-DLC) have been produced by unbalanced magnetron sputtering. Sputtering from B4C targets has been used to form B-C:H coatings. The boron to carbon ratio has been altered to investigate changes in the mechanical and tribological properties. The microstructure of the coatings has been analyzed with cross-section SEM and high-resolution TEM and linked to the mechanical and tribological properties. Properties like coefficient of friction, hardness and E-modulus, impact fatigue and abrasive wear resistance have been investigated. A comparison of the mechanical and tribological properties to W-C:H coatings is also carried out.
11:30 AM E4-1-10 Magnetron Sputtered DLC and Nanocomposite with DLC Matrix Coatings of High Harness and Toughness for Tribological Applications
S. Zhang, X.L. Bui, Y.Q. Fu, H.J. Du (Nanyang Technological University, Singapore)
Hydrogen-free diamond-like carbon (DLC) and DLC nanocomposite coatings (TiC as a nanocrystalline phase) with the thickness from 1.5 µm to 3 µmm have been deposited by magnetron sputtering with graphite and Ti targets. The hardness of the coatings varied from 18 to 32 GPa. The plasticity during indentation deformation of the coatings is over 50%. Raman, XPS, XRD and TEM were utilized to investigate the chemical structure and composition of the coatings. Tribotests were carried out in dry, water and oil lubrication regimes. The graphitization was observed on both DLC and DLC nanocomposite coatings, which contributed much to the low coefficient of friction. The coatings show big potential for tribological applications on industrial scale.
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