ICMCTF2000 Session D4/E5: Properties and Applications of Diamond, Diamondlike and C-BN Coatings

Wednesday, April 12, 2000 8:30 AM in Royal Palm Salon 4-6

Wednesday Morning

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8:30 AM D4/E5-1 Structure and Mechanical Properties of TiC/Amorphous Hydrocarbon Nanocomposite Coatings
W.J. Meng, R.C. Tittsworth (Louisiana State University); L.E. Rehn (Argonne National Laboratory)
Using the techniques of reactive magnetron sputtering and inductively coupled plasma (ICP) assisted hybrid physical vapor deposition (PVD)/chemical vapor deposition (CVD), we have synthesized a wide variety of metal-free amorphous hydrocarbon (a-C:H) and Ti-containing hydrocarbon (Ti-C:H) coatings. Coating mechanical properties such as elastic modulus and hardness have been measured by the technique of nanoindentation and correlated to Ti and hydrogen concentrations, measured by electron probe microanalysis (EPMA) and elastic recoil detection (ERD). The microstructure of the Ti-C:H coatings is further characterized by x-ray diffraction (XRD), transmission electron microscopy (TEM), extended x-ray absorption fine structure (EXAFS), and x-ray absorption near edge structure (XANES). We demonstrate that the solubility limit of Ti in amorphous hydrocarbon network is between 1 and 2.5 at. %. Beyond the Ti solubility limit, precipitation of TiC nanocrystal occurs and Ti-C:H coatings are in fact TiC/a-C:H thin film nanocomposites. We demonstrate that the consideration of both metal and hydrogen concentrations is important in understanding the mechanical property variations of TiC/a-C:H nanocomposite coatings. Connections to other thin film nanocomposite systems will be made.
9:10 AM D4/E5-3 The Deposition and Properties of Me-DLC Coatings Deposited by DC Magnetron Sputtering
C.V. Cooper (United Technologies Research Center); C. Specht (Fraunhofer Institute für Schicht- und Oberflächen Technik, GERMANY); K. Bewilogua (Fraunhofer Institute für Schicht- und Oberflächen TechnikSurface Engineering and Thin Films, Germany); B.D. Hansen (Sikorsky Aircraft)
Metal-containing, carbon-based coatings have been deposited via DC magnetron sputtering onto coupon substrates composed of the high-speed steel, AISI M50, using sputtering targets composed of elemental W, Ti, and Nb. The objective of the study has been to deposit carbon-based coatings having high hardness, good adherence, smooth surface morphology, and a thickness ranging from 0.5 to 5 µm. The composition of the deposited coatings has been varied by control of the mass flow rate of C@sub2@H@sub2@ and the ratio of the flow rates of C@sub2@H@sub2@ and Ar. Substrate bias has been applied during deposition from floating potential to -500 V DC to effect variations in coating hardness and adherence. Following deposition, the Me-DLC coatings have been characterized using the experimental techniques of scanning electron microscopy, electron probe microanalysis, secondary ion mass spectrometry, surface profilometry, static indentation adherence, nanoindentation hardness, and sliding and abrasive wear. The major results of this study indicate that the hardness and adherence of the coatings depend strongly on the metal constituent, on its concentration, and on the magnitude of the applied bias voltage. Hydrogen concentration, as measured using SIMS, shows a clear dependence on the metal constituent, with W-containing coatings exhibiting lower H concentrations than Ti-containing coatings. High hardness, low abrasive wear rate, and excellent coating adherence have been achieved by the use of W sputtering targets, by applying a substrate bias voltage of -300 V DC, and by varying the ratio of C@sub2@H@sub2@ to Ar to achieve a metal content of approximately 15 atomic percent. Complete results from this systematic experimental study will be presented and discussed.
9:30 AM D4/E5-4 Applications of Carbon-Based Coatings Prepared by Physical and Chemical Vapour Deposition Processes
L. Schaefer, J. Brand, A. Hieke, R. Wittorf, J. Gaebler, S. Mulcahy (Fraunhofer Institute for Surface Engineering and Thin Films, Fraunhofer IST, Germany)
Abstract Carbon-based coatings can be optimized for different applications by modification of deposition technology, growth conditions and incorporation of additional elements during growth, leading to the variation of properties like morphology, electrical conductivity, surface energy, friction and wear resistance. Carbon films can thus meet a variety of requirements imposed by different load spectra under service conditions. The large spectrum of developments and applications will be demonstrated by prototypes as well as products now entering the market. New machining as well as material developments increase the tribological requirements on components and tools for future applications and products. To meet these requirements, different carbon coatings are used for tools and machine components. Depending on the load spectrum for a product, carbon coatings are optimized with respect to high wear resistance, low friction and anti-sticking properties. Highest wear resistance is provided by polycrystalline CVD diamond films. Low friction coefficients combined with wear resistance is achieved by amorphous carbon films. Incorporation of additional elements allows the optimization of sticking behaviour. The performance of carbon coated products and prototypes will be demonstrated for driving elements, motor components, forming tools, cutting and grinding tools. The extremly high chemical resistance of diamond as well as highest overpotentials in water are utilized by conductive, boron doped diamond films for electrochemical applications. Utilizing the extraordinary electrochemical properties, new and highly efficient processes are possible. Diamond coated electrodes on industrial relevant materials and dimensions have been used for waste water treatment and purification of drinking water. Despite their high doping levels the diamond films are completely stable even for high current densities needed for productive conversion rates in electrochemical processes.
9:50 AM D4/E5-5 Tribological and Corrosion Properties of Ultra Thin Overcoats Deposited by PECVD
M.L. Wu, K.J. Grannen (Seagate Technology Corporation)
C:H and C:H:N overcoats at thickness below 5 nm were synthesized by plasma-enhanced chemical vapor deposition (PECVD). The preliminary results show that the tribological performance of these PECVD films are superior to the magnetron sputtered films. The contact start-stop (CSS) test at ambient environment showed low stiction performance of the overcoats at over 10K cycles without significant wear. The corrosion protection performance will also be studied. The PECVD technique is investigated as a promising technique for overcoats synthesis in magnetic hard disk industry.
10:30 AM D4/E5-7 Low Stress Diamond Like Carbon (dlc) Films Deposited using Filtered Cathodic Arc
B. Druz, Y. Yevtukhov (Veeco Instruments, Inc.); C. Hwang (IBM); V. Novotny (Terastor); I. Zaritskiy (Veeco Instruments, Inc.); G. Moutchaidze (IBM)
Low stress DLC films were deposited on various substrates using filtered cathodic arc process. Deposition process of 2-80 nm thick films exhibited very good thickness run to run repeatability with standard deviation < 0.25 nm. Ununiformity of the 5 nm thick film was less than 5% (H-L/H+L, H-highest thickness, L-lowest thickness) over a 15 cm diameter area. Mechanical, optical (refraction index, absorption coefficient vs wavelength, Raman spectra), and electrical properties of films were investigated. Coatings demonstrated high hardness 45-65 GPa and Young’s modulus 230-300 GPa, excellent elastic recovery, and surface smoothness. Stress of films was as low as 2.5-3.5 GPa. Transparency and resistivity of the low stress films showed significant decrease compared with high stress films. Raman graphite peak (about 1550 cm@super -1@) of low stress films was more pronounced than the one for the films with high stress. In addition, high anisotropy (several orders) of electrical resistivity was observed for resistivity measured in normal and parallel directions to the surface. High corrosion resistance of the coatings was exhibited. An explanation of changes in the film properties was based on the assumption that basic characteristics of the deposited films were determined by the relative proportion of two complementary kinds of bonds, the tetrahedral sp@super 3@ leading to stiff three dimensional networks and the trigonal sp@super 2@ bonds corresponding to mainly two dimensional bonded arrangements close to fullerene-like, or nanotube-like structures.
10:50 AM D4/E5-8 Friction and Wear Properties of ta-C Coated Plasma Nitrided Steel in Unidirectional and Reciprocating Sliding
B. Podgornik, J. Vizintin (University of Ljubljana, Slovenia); H. Ronkainen, K. Holmberg (VTT Manufacturing Technology, Finland)
In recent years the use of nitrided substrates for hard coatings has been widely reported. The majority of work refers to the coating of high alloy steels with a thin nitrided case, in order to achieve higher wear resistance and better adherence of the hard coating. These composite systems are mostly used as cutting tools. Beside that a lot of research work has been done on investigating tribological properties of DLC films, which were deposited on ‘hard’ substrates like ceramics. However, requirements for machine parts are quite different from those for tools. In addition to a hard, wear and fatigue resistant surface with good frictional characteristics, a tough, fracture resistant core is necessary. In the contrast to high alloy steels such as tool steels, hardened and tempered low alloy steels have high fracture toughness. Unfortunately, due to poor load carrying capacity of the steel substrate and very thin nature of the hard coating, hard-coated engineering low alloy steels would fail at high surface pressures, especially in the case of DLC coatings. On the other hand high hardness and internal compressive stresses of the case formed by plasma nitriding can lead to increased load carrying capacity as well as to improved coating adhesion, fatigue strength and tribological properties of coated parts. Undoubtedly, optimisation of the entire coating-substrate system is necessary. Properties obtained by the combination of plasma nitriding with hard-coating would allow function sharing between the core material, the hardened case and the surface, which is of special interest for application in complex stressed machine components. @paragraph@The intention of the present work was to open the possibility of using hard DLC coatings in the field of machine elements. Therefore, samples made of AISI 4140 steel pre-treated by plasma nitriding and coated by a hydrogen-free hard carbon coating were investigated with respect to the microhardness, residual stress, scratch adhesion and the dry sliding wear resistance. Wear tests in which duplex treated pins were mated to hardened ball bearing steel discs were performed under unidirectional and reciprocating sliding. In order to determine the influence of the nitrided zone on the tribological properties of coating-substrate composite coating was deposited on hardened as well as on plasma nitrided samples, nitrided under different nitriding conditions. @paragraph@The results of the investigation showed improved mechanical and tribological properties of plasma nitrided hard-coated specimens compared to un-coated and pre-hardened ones, observed for both unidirectional and reciprocating sliding. Furthermore, compound layer was found to act as an intermediate hard layer leading to superior tribological properties.
11:10 AM D4/E5-9 Effects of Gas Pressure and Bias Voltage on the Properties of Amorphous Carbon and Carbon Nitride Films Produced by Plasma Enhanced CVD
F.J. Pino, E. Bertran, A. Canillas, E. Pascual, J.L. Andujar (Universitat de Barcelona, Spain)
Recently, amorphous carbon (a-C) and carbon nitride (a-CN@sub x@) films have attracted a great interest to be used as thin protective coatings for the improvement of the wear resistance magnetic hard disks and for IR optical surfaces.@paragraph@The present study discusses the effects of the technological parameters on the structural and vibrational properties of amorphous carbon and carbon nitride films obtained by Plasma Enhanced Chemical Vapour Deposition.@paragraph@The films were deposited on silicon and Corning glass substrates at room temperature by rf glow discharge decomposition of methane and nitrogen. The technological parameters were changed as follows: the rf-power between 1W and 200W, the bias voltage between -40V and -600V and the deposition pressure between 1Pa and 5Pa. In the amorphous carbon nitride series the gas mixture of methane and nitrogen was varied in order to control the stoichiometry of CN@sub x@.@paragraph@The compressive stress of the films ranged from 1Gpa and 5Gpa depending on both, the bias voltage and deposition pressure on the a-C and a-CN@sub x@ films. The films have been also analysed by Fourier-transform infrared spectroscopy, Raman spectroscopy and ellipsometry. The composition of the films of a-CN@sub x@ was studied with X-ray photoelectron spectroscopy.
11:30 AM D4/E5-10 CN@sub x@ and DLC Films with extremely low Roughness
K. Bewilogua, M. Keunecke (Fraunhofer Institute for Surface Engineering and Thin Films, Germany); A. Hieke (Fraunhofer Institute for Surface Engineering and Thin Films, Fraunhofer IST, Germany); I. Bialuch (Fraunhofer Institute for Surface Engineering and Thin Films, Germany)
For some applications, e.g. for protective layers on hard disks, very thin (< 10 nm) and hard films with a extremely smooth surfaces are needed. Promising candidates to fulfil these requirements are amorphous carbon based films. In our study carbon nitride (CN@sub x@) and amorphous hydrogenated carbon DLC) were compared, especially with respect to their roughness which was measured by Atomic Force Microscopy. CN@sub x@ was prepared by reactive DC magnetron sputtering from a graphite target in a nitrogen atmosphere. The DLC films were deposited by glow discharge techniques in hydrocarbon gases using different frequencies to excite the plasma. For CN@sub x@ a range of parameters (nitrogen flow, bias voltage) was found which allows the preparation of extremely smooth surfaces (RMS roughness < 0.2 nm). DLC films deposited with radio frequency glow discharges (13.56 MHz) exhibited clearly higher values (some nm). On the other hand the change to a frequency range of some 10 kHz allowed the deposition of DLC with the same low roughness (< 0.2 nm) like found for CN@sub x@. Beside the surface topography other interesting properties of the films like hardness, Young´s modulus, friction coefficients, wear rates and surface energies will be reported.
11:50 AM D4/E5-11 Design of W Buffer Layer for Adhesion Improvement of DLC Films on Tool Steels
K.-R. Lee, K.Y. Eun (Korea Institute of Science and Technology, Korea); J.-Y. Choi, Y. Jeon (J&L Tech., Ltd., Korea); I.K. Kim, J. Kim (Hanyang University, Korea)
Diamond-like carbon (DLC) films, also referred to as hydrogenated amorphous carbon, have superior physical and chemical properties such as high hardness, low coefficient of friction, high wear resistance and chemical inertness. However, the films have high residual compressive stress up to 10 GPa resulting in the limited coating thickness, beyond that the film is spontaneously delaminated from substrates. Especially, the poor adhesion on steels substrate is significantly limit the applications of the DLC films. Many attempts has been reported to improved the adhesion of the DLC films by choosing a suitable buffer layer and optimizing the pre-treatment of the substrate surface. @paragraph@ In the present work, we investigated the W buffer layer deposited by DC magnetron sputtering. SKD11 block of HRC 59 and rms roughness of 0.4µm was used as the substrate. Substrate was cleaned by Ar plasma at the bias voltage of -750V for 1h. W buffer layer was deposited by DC magnetron sputtering using Ar or mixture of Ar and CH@sub 4@ as the sputter gas. 2µm thick DLC film was then deposited by r.f.-PACVD using benzene as the precursor gas. The adhesion of the film was tested by conventional scratch method using CSEM REVETEST scratch tester. The composition and the structure of the buffer layer was investigated by RBS and high resolution TEM. We found that the adhesion of the film was strongly dependent on the properties and composition of the WC buffer layer. The result will be discussed in terms of the microstructure and mechanical properties of the buffer layer.
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