ICMCTF2000 Session E5/Dr: Properties and Applications of Diamond, Diamondlike and Related Coatings
Thursday, April 13, 2000 8:30 AM in California
E5/Dr-1 Comparative Study of the Tribological Behaviour of Diamond Coatings Obtained by Combustion Flame Process and Other Usual Methods
D. Paulmier, M. Schmitt, T. Le Huu (LPMM-ERMES, CNRS-UMR 7554, France)
With its excellent mechanical and chemical properties (low wear rate, hardness, chemical inertness), diamond coatings asserted themselves in many industrial applications, and more particularly in the cutting tools field. @paragraph@ Most of the used diamond coatings are obtained by Chemical Vapour Deposition (CVD) assisted by plasma and RF, but their low growth rate (1µm/h) remained a major disadvantage ; it was therefore necessary to find a more efficient process. In spite of some drawbacks, the combustion flame process became then attractive because it offers a high growth rate and can easily be realised.@paragraph@ The tribological behaviour of the thus obtained diamond coatings shows significant differences compared with the properties of other diamond coatings ; these variations depend on the elaboration conditions and processes, on the crystallographic structures and on the environment. @paragraph@ The aim of this paper is to highlight some parameters from which originated these differences. The crystals orientation, the surface reactivity linked to the presence of dangling bonds, the nature of the counterface are some of theses factors influencing the tribological behaviour. @paragraph@ The friction coefficient evolution, versus the time, depends on the gases quantities present in the lattice, and on the ability of this latest to release these gases. @paragraph@ The transferred layer from the counterface to the diamond coating, whom sight depends on the roughness of this one, can play the role of a protective film, and can improve the coating lifetime in the case of cutting tools applications. @paragraph@ The morphology and composition modifications of both the diamond coating and the counterface are highlighted by Scanning Electron Microscopy observations and Energy Diffraction Spectroscopy and Raman Spectroscopy analyses.
E5/Dr-3 Modified ta-C Films with Low Friction in Dry Atmospheres
J. Koskinen, H. Ronkainen, K. Holmberg, S. Varjus (VTT Manufacturing Technology, Finland); T. Sajavaara (University of Helsinki, Finland)
Hydrogen free diamond-like tetrahedral amorphous carbon (ta-C) films with high content of sp@super 3@ bonds have a very high hardness and elastic modulus (up to 600 GPa). They have also excellent tribological properties in atmospheres that contain humidity ( 50 % RH) or also when submerged in water. However, in dry atmospheres the co-efficient of sliding friction against bearing steel, for instance, increases to values of over 0.7. In this paper ta-C films were modified in various ways by adding hydrogen to the film. The ta-C films were grown by using non filtered pulsed vacuum arc deposition in the ambient of hydrogen and hydrocarbon gases. A novel layered structure containing titanium layers which contain hydrogen and carbon have also been grown by using filtered metal arc in combination with the pulsed carbon arc. The hydrogen content and the composition of the films were measured by using forward recoil spectroscopy (FRES). The tribological performance of the coatings were determined by using pin-on-disk tests. The counter part material was steel (AISI 52100), the normal load applied 5 N and the sliding velocity 0.02 m/s. In the modified films the hydrogen content was up to 15 at.% in ta-C and about 16 at.% in the titanium layers. A co-efficient of friction of about 0.2 at dry nitrogen atmosphere was measured. The role of hydrogen in the sliding contact will be discussed.
E5/Dr-4 Synthesis of Superlow Friciton Carbon Films From Highly Hydrogenated Methane Plasmas
A. Erdemir (Argonne National Laboratory); O.L. Eryilmaz, I.B. Nilufer (Istanbul Technical University, Turkey); G.R. Fenske (Argonne National Laboratory)
In this study, we investigated the friciton and wear performance of diamondlike carbon films (DLC) produced from increasingly hydrogenated methane plasmas. The films were deposited on steel substrates by a plasma-enhanced chemical vapor deposition process at room temperature and the tribological tests were performed in dry nitrogen. The tribological tests revealed a close correlation between the hydrogen content of carbon source gas and the friction and wear coefficients of the DLC films. Specifically, films grown in plasmas with higher hydrogen-to-carbon ratios had much lower friction coefficients and wear rates than did films derived from source gases with lower hydrogen-to-carbon ratios. The lowest friction coefficient (0.003) was achieved with a film derived from 25% methane-75% hydrogen, while a coefficient of 0.015 was seen in films derived from pure methane. Similar correlations were observed for wear rates. Films derived from hydrogen-rich plasmas had the least wear, while films derived from pure methane suffered the highest wear. The lifetime tests were also performed to determine the durability of each film. We used a combination of surface analytical methods to characterize the structure and chemistry of the DLC films and worn surfaces
E5/Dr-5 Sliding Friction and Wear Performance of Hydrogen-free to Highly-hydrogenated Dlc Coatings in Vacuum
A. Erdemir (Argonne National Laboratory); J. Fontaine, C. Donnet (Ecole Centrale de Lyon, France); O.L. Eryilmaz (Istanbul Technical University, Turkey); R.E. Erck (Argonne National Laboratory)
In this study, we investigated the sliding friction and wear performance of hydrogen-free to highly hydrogenated DLC films in dry nitrogen and high-vacuum. We found a close correlation between friction coefficient and the degree of hydrogenation in DLC films that were produces in gas discharge plasmas consisting of essentially no hydrogen to very high hydrogen (i.e., up to 75%). Specifically, results showed that the films grown in source gases with higher hydrogen had lower friction coefficients in both the dry nitrogen and vacuum test environments than films grown in source gases with low-to-no hydrogen. The lowest friction coefficients (0.003 and 0.01) were achieved with a film derived from 25%methane + 75% hydrogen. Similar correlations were observed on wear rates. Specifically, the films derived from source gases with low or no hydrogen were worn out rather quickly and the substrate material was exposed, while the films derived from highly hydrogenated methane plasmas remained intact and wore at rates that were nearly two to three orders of magnitude lower than the hydrogen-free films. In-situ and ex-situ characterizations of the films and sliding contact surfaces were done using XPS, AES, SEM, TEM, and UV-Raman spectroscopy and the results were correlated with friction and wear performance.
E5/Dr-6 Deposition and Tribological Characterization of Highly Wear-Durable ECR-Sputtered Carbon Films
S. Umemura (Chiba Institute of Technology, Japan); S. Hirono (NTT AFTY Corporation, Japan); T. Hayashi (NTT Lifestyle and Environmental Technology Laboratories, Japan); R. Kaneko (Wakayama University, Japan)
In the present high-density magnetic recording technology, the protective film thickness of magnetic heads has been reduced to below 10 nm. For such ultrathin films, improvement of inherent wear durability and adhesion characteristics of the films are critical in determining the film design and its tribological performance. Furthermore, to realize such ultrathin protective films, an evaluation method which can evaluate independently their inherent wear durability and adhesion characteristics is needed. We proposed the such an evaluation method for ultrathin films using an AFM nanowear test @footnote 1@. @paragraph@ By applying the proposed method, we clarified the deposition conditions for the highly wear-durable carbon films prepared by electron-cyclotron-resonance (ECR) plasma sputtering. The wear durability of the ECR-sputtered films was far superior to that of the RF-sputtered films. ECR-sputtered films made with high energy ion irradiation showed the highest wear resistance, nearly comparable with that of bulk diamond @footnote 2@. We attribute this high durability to selective etching of the weakly bonded carbon atoms by the high-energy ion irradiation. Furthermore, we also clarified the most suitable deposition conditions of an adhesion layer for the ECR-sputtered carbon films by applying the proposed method. @paragraph@ Therefore, the highly wear-durable ECR-sputtered carbon films and the proposed method will have important roles in the head-media interface design for the next generation of high-density magnetic recording technology. @FootnoteText@ @footnote 1@ S. Umemura, et al, IEICE Trans. on Electronics, E81-C, 337 (1998). @footnote 2@ S. Hirono, et al. IEEE Trans. Mag., 34, 1729 (1998).
E5/Dr-8 Tribological Behaviour of Diamond Coatings Sliding Against Al or Al Alloys
M. Schmitt, D. Paulmier, T. Le Huu (LPMM-ERMES, CNRS-UMR 7554, France)
A high hardness and a low wear rate combined to exceptional physical properties make diamond an ideal candidate for machining. It is particularly interesting for tooling aluminium and its alloys as it offers these soft materials a clean cutting and lets the shaving sliding on the tool surface. @paragraph@ It results from studies dealing with the diamond / aluminium friction that the tribological behaviour of this couple is greatly influenced by the presence of oxides, more particularly Al@sub2@O@sub3@, on the counterface surface. It was then necessary to better understand the role of these oxides during the cutting process, the way they modify the nature of the contact, their effects on the transferred layer formation. @ paragraph@ The tribological behaviour of diamond coatings obtained by combustion flame process, sliding against aluminium or aluminium alloys under different environments (vacuum, oxygen and water vapour) with a varying applied normal load is presented here ; the modifications of both the coating and the counterface, the friction coefficient evolution and the transferred layers are especially studied. @paragraph@ The surfaces changes are revealed by Scanning Electron Microscopy observations. Raman spectroscopy and Energy Dispersive Spectroscopy analyses were realised to highlight the observed phenomena.
E5/Dr-9 The Effect of High Humidity and Low Humidity on the Tribological Behavior of Diamond-like Carbon (DLC) Film Coated on WC-Co by Physical Vapor Deposition Method
Y. Ozmen (Pamukkale University, Turkey); A. Tanaka (MEL, Japan); T. Sumiya (Nanotec Co., Japan)
DLC film has been coated by PVD on WC-Co substrate with and without Si interface. They have been tested under low (~20%) and high (~80%) humidity conditions by reciprocating friction and wear apparatus. For ascertaining the wear mechanism from the topographies of DLC film, optical and SEM images of wear tracks have been taken. Wear debris particles behave as an abrasive agent depositing into the film and causing the start of failure. There have been multi wear mechanisms, such as fatigue, abrasion etc., existing simultaneously in the wear of DLC film in both cases. Wear rate decreases as the total wear way increases. At the same time for the case of DLC coating there is a well correlation between wear rate and friction coefficient. However, this harmony disappears for DLC/Si coating. Chemically activated process may be assumed for the controlling step in the micro crack propagation during the generation of a wear debris particle. Thus, the different tribological behavior of the DLC coatings at the different environmental conditions are tried to explain.
E5/Dr-10 Structural and Tribological Characterization of Multilayer ta-C Films Prepared by FCVA with Substrate Pulse Biasing
D. Sheeja, B.K. Tay, S.P. Lau (Nanyang Technological University, Singapore)
The filtered cathodic vacuum arc (FCVA) technique is reported to be an efficient method for producing high quality hard coatings, but has limitations for preparing thick tetrahedral amorphous carbon (ta-C) films. Multilayer approach is the only way to overcome this limitation, and is of great interest because it enables the fabrication of films having varied properties to suit the application. @Multilayer ta-C films, with thickness of around 1@micron@, are prepared on silicon substrates by alternate soft (25nm thick) and hard (125nm thick) layers of tetrahedral amorphous carbon. The compressive stress of the film measured using the radius of curvature technique is found to be around 5.4 GPa. The structural characteristics of the film are studied using Raman spectrometry and the film is observed to contain reasonably high sp@super3@fraction, with an I@subD@/I@subG@ratio of around 0.31. The friction and wear behaviour of the film is studied using a pin-on-disk tribometer. The wear rate of the multilayer ta-C film is investigated from the wear track, which is obtained from a surface profiler. The structural changes that occur due to the sliding are studied using Raman spectrometry and the results confirm the graphitisation of the ta-C film.@
E5/Dr-11 How Hard is CNx?
S.J. Bull, T. Malkow, I. Arce-Garcia (University of Newcastle, United Kingdom)
Thin CNx coatings deposited by magnetron sputtering and ion beam assisted deposition show very shallow residual impressions when investigated by Nanoindentation. The low work of indentation (i.e. small area enclosed by the loading and unloading curves} of these materials implies a very high hardness. However, analysis of the unloading curves by the Oliver and Pharr method generates hardness values which are often less than silicon. This raises the question of whether these materials are really hard at all. Measurements of Young's Modulus from the initial part of the loading curve, from Oliver and Pharr and from elastic wave measurements are all consistent. This implies that the material behaves like a very hard rubber which undergoes considerable elastic recovery on unloading but does not have a very high resistance to penetration on loading. The very low E/H values for CNx, particularly at high deposition temperatures would tend to confirm this view. In this paper we will discuss whether hardness or the ultimate resilience parameter is a better indicator of the properties of CNx.