ICMCTF1998 Session E5/D4: Properties and Applications of Diamond, Diamondlike and c-BN Coatings

Thursday, April 30, 1998 8:30 AM in Room California

Thursday Morning

Start	Invited?	Item
8:30 AM	Invited	E5/D4-1 Tribological Fundamentals of Polycrystalline Diamond Films M.N. Gardos (Hughes Aircraft Company) SEM tribometry was performed with polished, mostly C(100)-textured and acid-cleaned polycrystalline CVD diamond films heated and cooled to and from 950°C in -1 x 1-^-5 Torr vacuum, followed by similar testing in 0.2 ±0.1 Torr partial pressures of 99.999% H₂ (hsub 2) and in 0.2 Torr partial pressure of 99.997% O₂ (P₀₂) to observe the surface chemistry-controlled tribological behavior of the films. In vacuum, all tests showed the characteristic stepfunction-with-trough coefficient of friction (COF) curves previously hypotehsized as footprints of wear- and thermal desorption-induced generation of dangling o bonds, which re(de)construct on continued heating and cooling to eventually become passivated by the residual water vapor in the SEM column. In the P_H2 and P_O2 atmospheres, all wear tracks showed the stepfunction-like COF curves caused by adsorbate de(re)sorption on heating and cooling, although a distinct re(de)construction trough could be duplicated during sliding in the same track in selected tracks only (P_H2), or during only the first test on the same track subjected to repeated testing (P_O2). In ther other tracks during the P_H2 tests, either the presence (but without duplication), or only a hint or a complete absence of these troughs was observed, despite of attempts to increase the highest possible temperature of the sliding surfaces (I.e., the magnitude of the activation energy needed for reconstruction) by lowering the P_H2 in the specimen chamber. The presence of the COF troughs in all three atmospheres lends strong additional support to the hypothesized re(de)construction of diamond surfaces tribostressed under thermally ramped conditions, their residual surface disorder after polishing notwithstanding. The repeatable occurrence of the final COF reduction in the step-function on cooling, even without the trough, represents the footprint of tribocatalytically enhanced dissociative chemisorption of molecular hydrogen and oxyten on polycrystalline diamond surfaces. The persistent absence of the troughs after the first in P_O2 and the occasional absence of the trough in P_H2 may indicate that the gas molecules or their reactive intermediates (especially oxygen) prevent reconstruction of the dangling surface bonds by some gas-phase interaction, even at the highest temperatures.
9:10 AM		E5/D4-3 Tribological Characteristics of Nanocrystalline Diamond Films W.D. Drawl (The Pennsylvania State University); T.O. Overt (The Pennsylvania State University); A. Badzian (The Pennsylvania State Unversity) For several years, diamond has been thought a promising material regarding its tribological properties. Its high hardness and low coefficient of friction have lead many to believe that bearings and others wear parts could be improved by applying diamond coating. Several studies have been conducted and provide insight to problems associated with polycrystalline diamond films as bearing surfaces. The majority of these studies involve the testing of relatively rough diamond films under high loads. paragragh This work will describe tribological results from studies conducted on smooth nanocrystalline diamond films at relatively low loads. Coating will be obtained using microwave plasma enhanced chemical vapor deposition techniques. These films will be characterized by Raman spectroscopy and SEM as well as for surface roughness. The tribological properties of the films will be evaluated using an atmosphere controlled reciprocating ball on flat test device.
9:30 AM		E5/D4-4 Friction and Wear of DLC-based Multilayer Nanocomposite Coatings K. Miyoshi (NASA Lewis Research Center); J.S. Zabinski, J.H. Sanders, A.A. Voevodin (Air Force Research Laboratory); R.L.C. Wu (K Systems Corporation) Nanocomposite films consisting of amorphous diamondlike carbon (a-DLC or a-C) layers and a gradient Ti-TiC-DLC underlayer were produced by the hybrid of magnetron sputtering and pulsed laser deposition on 440C stainless steel substrates. Also, hydrogenated DLC (a-C:H or H-DLC) films with a thickness of 800 nm were produced on the Ti-TiC-DLC underlayer by the direct impact of an ion beam (composed of a 3:17 mixture of Ar and methane) at an ion energy of 1500eV. They had a 0.5 -2 microns total thickness of DLC layers on the gradient Ti-TiC-DLC underlayer. The resultant DLC films were characterized by Raman spectroscopy, x-ray photoelectron spectroscopy, Auger electron spectroscopy, scanning electron microscopy, and surface profilometry. Sliding friction experiments were conducted with 440C stainless steel and silicon nitride balls in sliding contact with DLC films in ultrahigh vacuum and in humid air. The coefficient of friction and wear rate of DLC films are strongly dependent on the hydrogen content and sliding friction conditions such as environment and counterpart material
9:50 AM		E5/D4-5 Tribological Behaviour of Amorphous Hard Carbon Films Against Zinc Plated Steel Sheets M. Murakawa, N. Koga, S. Watanabe, S. Takeuchi (Nippon Institute of Technology, Japan) Zinc plated steel sheets have been extensively used in the automotive industry because they are very effective in preventing formation of ruster on various parts particularly on body parts which are usually made by stamping processes such as deep drawing and blanking. The materials, however, are known to have a very poor deep drawing capability, and often cause heavy adhesion onto the tool without use of heavy lubricants which are detrimental to the earth environment. Accordingly, this study has been performed in an effort to provide a solution to this problem by finding a suitable tool material and/or a possible modification method of it by use of protective coatings so as to enable us to use lubricants such as, e.g., water soluble lubricants which are of much lower viscosity and more friendly to the earth, yet very poor in their lubricating capability. We have found from the tribological tests that hard carbon coatings including a DLC coating and a WC containing hard carbon coating could be potential candidates for the modified deep drawing tool material.
10:30 AM		E5/D4-7 Wear Behavior of Diamond-like Nano-composite Coatings D.J. Kester (Advanced Refractory Technologies, Inc.); I.L. Singer, R.N. Bolster (U.S. Naval Research Laboratory) Diamond-like Nanocomposites (DLN) are a family of amorphous thin film coatings with high hardness, low friction, low stress, and good ad hesion to a variety of substrates. The coatings contain C, H, Si, and O; in addition, metal atoms can be incorporated into the coatings. Coatings 1-2 μm thick were deposited onto Si substrates. Continuous indentation testing gave hardness values from 9 - 30 GPa and modulus values from 50 - 300 GPa. Sliding wear tests were performed with a WC ball against DLN-coated Si. Wear rates ranged from 3 - 15 x 10^-8 mm³/N-m. Raman spectroscopy was used to study the chemistry of the coatings and of the transfer films generated by sliding wear; the transfer film was found to have a chemistry different from that of the coatings. Abrasive wear tests were performed using 3 micron diamond paste; wear resistance, determined using mass loss measurements, was more than twice that of single crystal sapphire. Correlations between hardness, chemistry, and sliding and abrasive wear will be presented.
10:50 AM		E5/D4-8 Comparison of Tribological and Mechanical Properties of DLC-Coatings Deposited with Different CVD-and PVD-Techniques A. Schroeer, E. Jeanpetit, E. Pflueger (CSEM Centre Suisse d'Electronique et de Microtechnique SA, Switzerland); C. Schuerer (Gesellschaft fuer Fertigungstechnik und Entwicklung Schmalkalden e.V., Germany) Diamond-like carbon (DLC) coatings are used nowadays for many different applications. Contrary to coating systems like titanium nitride, the quality of DLC-coating properties have a much wider spread depending on deposition techniques and their specific parameters. Differences in the wear resistance of orders of several magnitude were found. For this reason, it is necessary to examine the limiting parameters of DLC-coatings obtained by different deposition techniques. In this study, adhesion effects, roughness, hardness, wear and friction behavior are compared and discussed. DLC-coatings deposited with chemical (CVD) and physical vapor (PVD) deposition techniques like plasma deposition, plasma-enhanced chemical vapor deposition, sputtering and pulsed arc deposition were investigated. For the plasma deposition process, a detailed description of the influence of deposition parameters on coating properties will be presented.
11:10 AM		E5/D4-9 Time-dependant Changes in the Mechanical Properties of Diamond-like Carbon Films S.J. Bull, S.V. Hainsworth (University of Newcastle, United Kingdom) A number of workers have reported the degradation of hydrogenated diamond-like carbon films at elevated temperatures - generally graphitisation rapidly occurs at temperatures above 250^oC. However, changes in properties due to structural relaxation at lower temperatures have been much less well studied. In the past we have observed that the residual stress measured in an ion beam assisited DLC film is much greater just after deposition, than when remeasured some months later. This would imply that structural relaxation is occurring in the film which could result in changes in other properties. In this study we have performed nanoindentation and residual stress measurements on DLC films produced by ion beam assisted deposition and plasma assisted chemical vapour deposition within a few weeks of coating and have then repeated the measurements after allowing the coatings to age for several years. Changes in Young's Modulus have occurred but these are not accompanied by changes in hardness. The observed changes are probably due to a gradual graphitisation of the film (i.e. conversion of sp3 to sp2 bonds) during storage. The differences between films deposited by different methods will be highlighted.
11:30 AM		E5/D4-10 Fretting Wear Behavior of DLC Films Produced from Methane and Acetylene O.L. Eryilmaz (Istanbul Technical University, Turkey); A. Erdemir (Argonne National Laboratory); K. Kazmanli (Istanbul Technical University, Turkey) The ball on disc wear behavior of DLC coatings against various materials was well investigated in different environments. In this study the fretting wear behavior of DLC produced from methane and acetylene is investigated in open air (%30 RH) and dry nitrogen. The coatings were produced on flat H13 hardened steel and 52100 steel balls. The DLC films were characterized with respect to their hardness, Raman investigations were also conducted on these films.
11:50 AM		E5/D4-11 Effects of Nanoscale Morphology on the Abrasion of Steel by Diamondlike Carbon S.J. Harris (General Motors R&D Center) Ceramic coatings can improve the resistance to rolling contact fatigue by polishing or abrading the parts against which they rub. Thus, the abrasiveness of a coating is a property which can control its usefulness as a tribological coating. We use a ball-on-disk tribometer with a steel ball on 5 commercial and 1 in-house metal-containing DLC coatings, examining the abrasive wear on the steel. Abrasiveness of the coatings varies by 3 orders of magnitude. We show that the abrasiveness of a coating is an extraordinarily strong function of the nanoindentation hardness of the films. We show that small-scale surface morphology, on the order of 100 nm or less, is strongly correlated with abrasiveness; while larger scale morphology, on the order of 1 mm or greater, is not correlated with abrasiveness. The difference can be explained in terms of a model for abrasive wear. AFM measurements of the surface height distribution functions allow us to find a quantitative relationship between abrasiveness and asperity shape and height which cannot be observed with an optical profilometer. The abrasiveness of a coating decreases rapidly as the height distribution changes. We find a scaling relationship which shows that rates of loss of abrasiveness for all of the coatings are remarkably similar in spite of the large differences in the abrasiveness of the different coatings. These relationships allow us to predict the amount of abrasive wear in complex situations.