ICMCTF2005 Session D2-2: Special Forum World Market Perspective of Diamond and Diamond-Like Carbon

Thursday, May 5, 2005 1:30 PM in Room Royal Palm 1-3

Thursday Afternoon

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1:30 PM D2-2-1 Industrial Applications of DLC Coatings in the Automotive Industry
C. Strondl, T. Krug, R. Tietema (Hauzer Techno Coating BV, Netherlands)
PVD coatings are increasingly being used in the automotive sector. There are mainly two driving forces for this. The first one is to lower wear of components. For example, the power output of engines have increased dramatically the last 10-20 years leading to higher loads and as a consequence increased wear of these components. The second driving force is a stronger environmental legislation and the need to reduce emissions and fuel consumption. Typical demands in tribological applications are: 1) Low wear of the coated part, 2) Low wear of the counter part adn 3) Low coefficient of friction. DLC coatings typically fulfil the above mentioned requirements. Two main categories of DLC coatings can be distinguished, metal doped and metal free DLC coatings. The metal doped DLC coatings are typically produced by reactive unbalanced magnetron sputtering of a metal target using a hydrocarbon/argon gas mixture. For producing the metal free DLC coatings, sputtering from graphite targets or various PA-CVD based techniques are used. To get the best performance out of the different coatings, it is always necessary to engineer the coatings to the application. This means that the wear mechanism of the application has to be considered and an appropriate coating system selected. The specific know-how to control the different coating properties in the selected coating system is especially important. A few examples of coating properties that can be modified for metal doped DLC and some examples of industrial applications will be presented.
2:10 PM D2-2-3 Diamond-Like Carbon Materials- Applications, Markets, Research and Development in Taiwan
D.-Y. Wang (Institute of Material and System Engineering, Mingdao University, Taiwan)
Amorphous carbon films with diamond-like properties are potential candidates for tooling and biomedical applications because of their high hardness, chemical inertness, and excellent corrosion resistance. Major techniques for synthesis of diamond-like carbon (DLC) films include chemical vapor deposition (CVD) and physical vapor deposition (PVD) processes assisted by vacuum arc, laser ablation, mass selected ion beam, RF, or pulsed sputtering. Several industrial applications taking advantage of the DLC technology have emerged recently. This presentation reviews the development of a series of nano-composite and multilayered DLC coatings, such as Cr-C:H, Ti-C:H, Zr-C:H, Cr-C and Ti/C, synthesized by cathodic arc activated deposition (CAAD) and unbalanced magnetron sputtering systems. It is essential to have an intermediate layer of Ti, Zr, Si, or Cr to improve the adhesion between the coating and substrate. In addition, the properties of DLC can be favorably influenced by doping with either metals or ceramic compounds. The synthesis of DLC films by CAAD can be viewed as a hybrid PVD and CVD process. In Taiwan, DLC films have been prepared for mechanical, tooling, semiconductor, and decorative industries. Industrial applications and market development in Taiwan will also be addressed.
2:50 PM D2-2-6 A Comparative Study on the Performance Testing of Diamond Coated Micro-Drills used in Nanotechnology Applications
G. Cabral, N. Ali, V.F. Neto, E. Titus, J. Gracio (University of Aveiro, Portugal); A.A. Ogwu (University of Paisley, United Kingdom)
In this paper, we report results obtained from a comparative study investigating the performance and lifetime of diamond-coated WC-Co micro-drills during hole-drilling procedures carried out on graphite medium. The three types of diamond coatings used in this study were deposited onto the micro-drills using bias-enhanced-growth (BEG), conventional CVD and time-modulated CVD (TMCVD) processes. SEM was used to characterize the film morphologies and also determine the flank wear of the micro-drills after undergoing the drilling procedures. The performance of diamond coated micro-drills was determined by considering the area of flank wear, which was observed on the key cutting edges after the different number of drillings into the graphite. As a comparison to the un-coated micro-drills, it was found that by applying a diamond coating to the micro-drill, this improved the performance and the lifetime of the tool. The diameters of the holes formed on the graphite material were measured from both the top end and the bottom end of the graphite block material. BEG and TMCVD processes produced nano-scale diamond films, whereas, the conventional CVD process deposited polycrystalline diamond coatings displaying the columnar growth mode. The different modes of growth involved with the different deposition processes will be discussed. Raman spectroscopy was used to determine the quality of the diamond films, in terms of diamond carbon phase. The adhesion behavior observed in the different films has been explaining in terms of multi-layer structures and mechanical interlock at the drill/film interface.
3:10 PM D2-2-7 Nanocrystalline Diamond/Amorphous Carbon Composite Films for Applications in Tribology, Optics and Biomedicine
C. Popov, W. Kulisch (University of Kassel, Germany); M. Jelinek (Institute of Physics, ASCR, Czech Republic)
Microwave plasma chemical vapour deposition (MWCVD) has been used to deposit thin nanocrystalline diamond/amorphous carbon (NCD/a-C) composite films from methane/ nitrogen mixtures. It was established that at high methane concentrations (17%) and a substrate temperature of 770°C thick and smooth films can be prepared. The basic properties of the NCD/a-C coatings were thoroughly characterized by a variety of techniques: the composition by elastic recoil detection (ERD) analysis and X-ray photoelectron spectroscopy (XPS); the crystallinity by X-ray and electron diffraction; the morphology and topography by scanning electron microscopy (SEM) and atomic force microscopy (AFM); the bonding structure by electron energy loss spectroscopy (EELS), Raman and Fourier transform infrared (FTIR) spectroscopies, and XPS. In this contribution we report on the characterization of the application relevant properties of these films, especially the optical (refractive index, extinction coefficient, reflection, scattering), mechanical (hardness, friction, wear resistance, adhesion) and electrical characteristics (I-V and C-V curves), and the biocompatibility (cell tests). Their refractive index is between 1.95 and 2.1 in the visible region; the extinction coefficient reaches a value of about 0.1 while the optical band gap is around 1.4 eV. Concerning the mechanical properties it was found that the layers possess a hardness of about 40 GPa, a friction coefficient of 0.1 or even lower, good adhesion and a protective effect on silicon substrates. The results obtained showed that the application relevant properties of the NCD/a-C composite films are dominated to a great extent by the nature of the amorphous matrix rather than by that of the crystalline fraction, e.g. a relatively low refractive index, high absorption especially in the UV range, a narrow optical band gap and lower hardness compared to the bulk material.
3:50 PM D2-2-9 Hot Filament Chemical Vapour Deposition and Wear Resistance of Diamond Films on WC-Co Substrates Coated by PVD-Arc Deposition Technique
R. Polini, F. Pighetti (Universita' di Roma Tor Vergata, Italy); R. Valle, F. Casadei (Centro Svilippo Materiali SpA, Italy)
Diamond films are suitable for tools applications because of their hardness, large wear resistance combined with chemical inertness. However, the direct CVD diamond coating of Co-cemented tungsten carbide (WC-Co) substrates still represents a difficult task. In fact, the detrimental effects of the binder phase in the WC-Co substrate has to be inhibited either by Co etching or by interposing diffusion barrier layers. The removal of the binder by acid etching generates voids in the outermost layers of WC grains, thence to surface embrittlement of the cutting edge. This issue is particularly critical in interrupted cutting operations such as milling. The use of interlayers should provide both a strengthening of the cutting edge and a reduction of the film thermal stress. Moreover appropriate interlayers could help forming strong chemical bonds, thus increasing film adhesion. In this study we have investigated the properties of different interlayers prepared by PVD-arc deposition and their influence on the low temperature (650°C) Hot Filament CVD (HFCVD) of diamond coatings onto two different WC-Co grades (coarse grained WC with 6 wt.% Co and fine grained WC with 9 wt.% Co and 0.5 wt.% chromium carbide as grain growth inhibitor). The modifications of CrN, CrC, TiC, TiN, and Ti(C,N) interlayers, as well as CrN- and TiN-based multilayers under HFCVD conditions have been investigated by X-Ray Diffraction (XRD). The wear resistance of diamond coated WC-Co samples has been evaluated by tribological tests with alternative sliding motion. The tests were carried out by means of an Optimol SRV Tribometer and the results from uncoated, PVD-coated and diamond coated materials have been compared and discussed on the basis of interlayersâ?T modifications and substrate microstructure.
4:10 PM D2-2-10 CVD - Diamond Coated Cutting Tools
R. Cremer, O. Lemmer, D. Breidt (CemeCon AG, Germany)
CVD-Diamond tools are well established in machining graphite, green compacts and aluminum alloys. These achievements were possible not only by improving the technology but also by tailoring the CVD-diamond films to the specific applications. New challenges arise form new machining techniques, like high speed and dry cutting, as well as from novel high-tech materials, like fiber reinforced materials, that cannot be machined with conventional cutting tools. Extreme differences in thermal expansion coefficients and elastic constants of diamond and tool material lead to high stresses in the interface. This is disadvantageous esp. in interrupted cutting. On the other side, dry cutting gives increased adhesion of workpiece material and increased chemical wear, mainly oxidation, to the diamond itself. New features for CVD-diamond are introduced, that will overcome these difficulties: New adapted tool materials, improved surfaces and cutting edges, diamond multilayers with increased fracture toughness, pre-treatments for strengthening the interface, oxidation resistant coatings are elements to improve the system 'diamond coated tool' and will extent the applicability significantly. These new features can be used solely, combined with each other or together with the conventional CVD-diamond in respect to the specific applications. This will be illustrated by presenting cutting test results for different applications.
4:30 PM D2-2-11 Toward the World Best Performance of Diamond Coated Cutting Tools
H. Hanyu (Osg Corporation, Japan); S. Kamiya (Nagoya Institute of Technology, Japan); Y Murakami (Osg Corporation, Japan)

Diamond coating has been expected for the use of cutting applications. Although the anti-abrasive performance of diamond is extreme, there were many difficulties when coated on cutting tools since it is brittle and poorly adherent to the substrate. In order to realize high performance diamond coated cutting tools, the authors put a new emphasis on the fact that a coated cutting edge is a functional materials complex. A series of systematic improvements were made as in the following, for a total optimization of diamond coated cutting tools.

An adequate pretreatment for good adhesion was the first development to give them an acceptable level of performance. However it was not enough by itself for the durability in industry. To get the solution of this problem, authors further tried the total design of cutting edge together with the coating on it. With the optimum shape to minimize the stress in the cutting process, longer lifetime was achieved. Brittleness of diamond coating was overcome by developing finely crystallized diamond with doubled toughness in contrast to the coarse columnar grains in conventional diamond coatings. Fine crystals also dramatically reduced the roughness of coating surface, which opened new possibility for diamond-coated tools to be used as finishing tools for extremely abrasive materials and also to reduce the surface friction. By putting these developments altogether, one of the world highest performance of diamond-coated tools are currently produced.

Trials for a new horizon of diamond coated cutting tools are under progress. Boron doping was examined with successful results to improve the resistance against oxidation. Another promising possibility was confirmed by the recent development to combine diamond coatings with functional layers of different materials. Further improvement toward the world best performance is still going on.

4:50 PM D2-2-12 High Rate Deposition of DLC Based Hard Coatings on Grounded Flat Substrates
M. Weber, K. Bewilogua, R. Wittorf (Fraunhofer IST, Germany)
Metal containing (a-C:H:Me) and also metal free (a-C:H) diamond-like carbon (DLC) coatings can be prepared by reactive d.c. magnetron sputtering using acetylene as reactive gas. Due to their low friction coefficients and high wear resistance, DLC based coatings have a high potential for various applications. To achieve a sufficient hardness and a high wear resistance, commonly negative substrate bias voltages of 100 V and more will be applied in different power modes (d.c., radio frequency (r.f.) or medium frequency (m.f.)). On the other hand, the application of any bias voltage can be impossible, e.g. if grounded metal strips shall be coated in an in-line machine. Furthermore, for such an application additionally much higher deposition rates than usually achieved in batch coaters are required. Using a magnetron sputter arrangement with small target to substrate distances, a-C:H:Ti coatings were deposited with high rates (> 20 µm/h) on grounded metal substrates. The abrasive wear rates and also the adhesion of these coatings were comparable to those of "standard" a-C:H:Ti prepared with negative bias voltages in the range of 100 V and with rates between 2 and 3 µm/h. Composition and structure of both coating types were investigated in detail. Considering dependencies of deposition rate and substrate current vs. target to substrate distances, an interpretation of the experimental data was developed. Further process modifications, necessary to realize an in-line deposition process of DLC based coatings on metal strips and sheets, will be discussed.
Time Period ThA Sessions | Abstract Timeline | Topic D Sessions | Time Periods | Topics | ICMCTF2005 Schedule