ICMCTF2008 Session G2: Coatings and Automotive Applications

Tuesday, April 29, 2008 1:30 PM in Room Sunset

Tuesday Afternoon

Start	Invited?	Item
1:30 PM	Invited	G2-1 PVD Coatings for Automotive Components T. Krug, R. Tietema (Hauzer Techno Coating BV, Netherlands) PVD coatings are already used for some automotive components with great success. For example, there is almost no Diesel passenger car without PVD coatings to provide wear protection in the injection system and there is no Formula 1 race without such coatings. Wear protection and more recently reduction of friction to reduce internal losses in the engine will further increase the demand for PVD coatings in future to develop the so called one liter car (consumption of 1 liter per 100 km, or about 200 miles per gallon). In this paper, first an overview of today’s coatings and their application in series products are given. As in many cases today not the technical performance however the production (coating) costs are the limitations to use PVD in series cars, cost calculations are presented and technical attempts are discussed to reduce manufacturing costs in total.
2:10 PM		G2-4 On the Relationship Between Mechanical and Tribological Properties of DLC and Performance in Automotive Engine Applications S.D.A. Lawes (University of Leicester, United Kingdom); M.E. Fitzpatrick (Open University, United Kingdom); S.V. Hainsworth (University of Leicester, United Kingdom) Operating conditions in automotive engines are changing owing to increased demand for high efficiency and low environmental emissions. Some of these changes are leading to a harsher operating environment for some engine components. A number of methods are used for increasing the wear resistance of components, including the use of diamond-like carbon coatings. DLC coatings can be produced that offer a wide range of attractive mechanical, physical and tribological properties such as extreme hardness (>90 GPa), low coefficients of friction against a number of counterfaces and low wear coefficients. In this work three different types of DLC have been investigated, a hydrogen free DLC (a-C), a hydrogenated DLC (a-C:H) and a silicon doped hydrogenated DLC (a-C:H:Si) for a variety of substrate surface finishes. The coating structure and composition was identified by Raman spectroscopy and energy dispersive X-ray analysis. Mechanical and tribological properties were evaluated by nanoindentation, scratch and wear testing. The coatings were also tested in an instrumented cam-tappet testing rig to determine the friction and wear performance in a practical engine application. Scanning electron microscopy and atomic force microscopy have been used to evaluate the deformation and wear mechanisms that were observed. The hydrogenated DLC performed best on the cam-tappet test rig although conversely did not give the best performance in laboratory testing. Further optimisation of the coatings for this application continues. Results are discussed in terms of understanding how the results of laboratory test procedures enable selection of coatings for engine applications.
2:30 PM		G2-6 In-Line Atmospheric Plasma Deposition of Silicon Organic Coatings on Automotive Aluminum Housings A. Knospe, T. Beer (Plasmatreat GmbH Research and Development Center, Germany); Z. MacKay (Plasmatreat North America, Canada) An in-line, atmospheric plasma coating process has been used to overcome corrosion problems in automotive assembly and is currently in full production for a major manufacturer. By forming a homogeneous barrier layer on aluminum, bond line corrosion has been prevented around the lid of electric motor housings. Using reflective electron microscopy at 50,000x magnification, 100μm coatings were observed to be pore-free and act as passive protective layer, providing much greater longevity than were a sacrificial treatment used. The coating is hexamethyldisiloxane-based, and a silicon-organic layer is deposited by introducing the precursor into an RF plasma stream created at 19kHz. The substrate is first pretreated using air plasma (also at 19kHz) and this cleans and prepares the surface for coating adhesion. No solvent or other chemical is required for the process other than the glue which bonds with the coating interface. Evaluation of both 96-hour direct salt spray testing and 750-hour SWAAT (Sea Water Acetic Acid Test) showed no signs whatsoever of corrosion on low-carbon aluminum alloys. This same coating process can be adapted for application to other substrates including most polymers to provide similar results.
2:50 PM		G2-7 Magnetron-Sputtered nc-ZrC/a-C:H Coatings for the Application in Hydraulic Displacement Units K. Bobzin, N. Bagcivan (RWTH Aachen University, Germany); N.A. Goebbels (Aachen University, Germany) In this work ZrC coatings were deposited by low temperature (<160 °C) reactive magnetron sputtering using metallic zirconium targets in the presence of a low pressure argon and acetylene atmosphere. They were investigated regarding plasma characteristics of deposition process and coating’s structural, mechanical and tribological properties. Plasma characteristics were acquired using optical emission spectroscopy and Langmuir wire probe and compared both with process parameters such as bias voltage or reactive gas flow and coating’s properties. Pending upon suitable process parameters nanocrystalline (nc) zirconium carbide particles are formed and embedded in an amorphous hydrocarbon (a-C:H) matrix. Crystallite sizes of zirconium carbides were calculated using the Debye-Scherrer method based on X-Ray diffraction analysis and verified by TEM investigations. The nanocomposite coatings exhibit hardness of up to 16 GPa, excellent friction behaviour against materials typically used for hydrostatic displacement units e.g. C45E (friction coefficient 0,05 in air) determined using a ball-on-disc tribometer. Fatigue behaviour of nanocomposite coatings was investigated by impact testing and correlated with H/E ratio.
3:10 PM		G2-8 Tribological Behaviors of MoN_x-Cu and -Ag Nanocomposite Coatings Under Boundary Lubricated Sliding Conditions A. Erdemir (Argonne National Laboratory); M. Urgen (Istanbul Technical University, Turkey); O. Eryilmaz (Argonne National Laboratory); K. Kazmanli, V. Ezirmik (Istanbul Technical University, Turkey) Recent experimental studies have confirmed that not all hard coatings can provide low friction under boundary lubricated sliding conditions. Mechanistically, it is thought that active anti-friction and –wear additives in oils do not react well with such coatings and hence there is no tribochemical boundary film providing low friction and wear. Currently there is an urgent need to develop lubricant-friendly or -responsive hard coatings for use in a range of automotive applications. Using a recently proposed crystal-chemical model as a guide [1], we formulated and produced a number of nanocomposite coatings consisting of a hard MoN and/or Mo₂N phase and a soft metal phase such as Cu, Ag, etc. Because of the very high ionic potentials of the complex oxides, sulfides, and phosphates (which result from tribochemical reactions during lubricated sliding), these nanocomposite coatings can reduce friction by as much as 80% and at the same time increase resistance to wear and scuffing under boundary lubricated sliding regimes. In this paper, we will present the very close relationship between ionic potentials and shear rheology of various tribo-films that were detected on sliding surfaces of MoN_x-Cu and -Ag coatings. The major implications of this study is that using such a fundamental approach one can formulate better tribological coatings providing not only superior wear resistance but also high lubricity during lubricated sliding conditions.
3:30 PM		G2-9 Electrical Behaviors of Tin, Silver and Gold Thin Coatings Under Micro-Fretting Loadings: Impact of Sliding Conditions and Gaseous Atmospheres P. Jedrzejczyk, S. Fouvry (Ecole Centrale de Lyon, France) Microdisplacements at the contact interface (fretting) of electrical connectors damage the contact area and disturb the electrical signal. Such phenomenon is widely observed in automotive application. To increase the connector endurances numerous thin soft coatings are applied. However due to the complexity of the phenomena it is still very difficult to compare and predict their respective durability. A specific device to test microcontacts with low normal forces and very small displacement amplitude has been developed. The electrical contact resistance as well as the wear is measured. Non noble tin, noble gold and semi-noble silver coatings have been tested. A strong relationship between the fretting sliding condition and the electrical behavior is found. Under partial slip conditions the stick zone maintains a very good conductance independently of the coatings. Under larger sliding conditions, involving gross slip conditions, the electrical conductance of the contact is highly connected to the wear and debris properties. For noble coatings, wear through of the coating rules the electrical behavior since the debris are not oxidized. For non noble coatings the electrical endurance is drastically reduced since the electrical behavior is directly related to the oxidized third body formation. It is shown that silver displays an equivalent behavior than gold under common atmosphere conditions. However under sulfur gaseous ambient, the noble properties of silver are drastically decayed and the electrical performances reduced to the plain tin material. A quantitative methodology is developed to calibrate the potential interest of silver compared to tin and gold materials.
3:50 PM	Invited	G2-11 Automotive Precision Components - a Challenge for Job Coating Service Companies A. Hieke (IonBond Netherlands BV, Netherlands) Tribological coatings are an ever evolving component to a coatings supplier’s portfolio . Research and development in this area should be conducted by first evaluating the contact (tribological) characteristics and then translating that information to ideal coating properties. With this set of desirable properties a supplier can see which coating would make the best match or what can be modified in order to make that match. Regarding the choice of coatings, several parameters play a dominant role. It is important to differentiate between rolling, sliding, or mixed mode conditions. Also, the heat treatment conditions, the grinding operation after heat treatment and the resulting surface quality (e.g. roughness) of both contact partners should be taken in consideration. Post-treatments of vacuum deposited coatings are necessary in several occasions in order to avoid running-in failure modes. The drawback of a-C:H coatings ("DLC") is the sensitivity to crack initiation and crack propagation. Adequate support from base material, heat treatment, and base layers by PVD can avoid such cracking issues. The ongoing push for higher fuel efficiency, lower emission rates, higher power densities, lighter base materials, and longer warranty periods are drivers to increase the demand for surface enhancements of individual automotive components. The coatings prove their technical value, but the main challenge is to offer such coatings on an acceptable cost level.
4:30 PM		G2-12 Characterization of CrC-DLC Dual Core Coating for Automotive Applications E. Oeberg, A. Mueller, S. Eggenberger, A. Weibel, O. Massler (OC Oerlikon Balzers AG, Liechtenstein) So called dual core coatings consist of metal carbide or nitride supporting layer beneath a carbon based hard layer, i.e. diamond like carbon. This type of coating stack is widely used in automotive applications due to its superior performance. The main objective of this work was to obtain a CrC layer with good mechanical and tribological properties that can be applied to create an improved supporting layer for DLC coatings. In a first step CrC films were synthesized by reactive magnetron sputtering from a pure chromium target in a reactive Ar/C₂H₂ gas mixture onto steel and silicon samples. The influence of numerous deposition parameters was evaluated from results of layer characteristics such as hardness, adhesion and friction combined with XRD and REM measurements, as well as process analysis with a mass spectrometer. Layers with hardness up to 2700 HV_pl and still keeping friction at a low value to sustain a good wear reserve were produced. Adding a PECVD diamond like carbon layer on top of CrC layer improved performance which is shown by measurements of wear resistance and SRV tests. The overall results show a promising future for creating a reproducible process of a CrC-DLC coating with a supporting layer of high tribological performance and hardness.
4:50 PM		G2-13 Carbon Based Hard Coatings for Vaious Automotive Applications A. Mueller, R. Mertens, C. Pinero, M. Ante, O. Massler (OC Oerlikon Balzers AG, Liechtenstein) Thin diamond-like carbon films and other carbon containing coatings are nowadays widely used in automotive applications like e.g. Diesel injection. The main role of these coatings is to reduce wear and friction of the components but today each application has its own tailored layer structure and composition adapted to the customer specifications. This paper investigates the role of different carbon concentrations in the gas phase with respect to sliding and wear properties of the coatings. The deposition technique for the carbon based hard coatings is a PVD/PECVD process described in detail elsewhere [1]. For a specific carbon source measurements of partial pressures of carbon containing molecules have been carried out using a quadropole mass spectrometer. The comparison of sliding and wear properties for different carbon concentrations during deposition has been carried out by means of ball on disc test, SRV measurements and calo grinding under defined parameters. [1] EP1362931: Method and apparatus for fabrication of a DLC layer system