Papers

ICMCTF2007 Session G2-2: Coatings and Automotive Applications

Friday, April 27, 2007 8:00 AM in Room San Diego

Friday Morning

Start	Invited?	Item
8:00 AM		G2-2-1 Surface Modification Technologies for Piston Rings T. Sekiya (RIKEN Corporation, Japan) Piston rings reciprocate at high speed in engines and they have three functions. The first one is gas seal, the second is oil control and the third is transferring piston heat to cylinder. In order to maintain these functions, base materials for piston rings require high elasticity, anti-wear property and thermal conductivity. The tribological performance of the sliding surface of piston ring is especially important. Therefore, various surface modifications have been applied for piston rings depending on the performance of engine. On this occasion, we will outline the transition and features of material and surface modification development, which includes Cr plating, thermal spray, gas-nitriding and PVD coating. In recent years, the Cr-N coated piston rings produced by vacuum arc ion plating have been employed increasingly. In the initial stage of development, the Cr-N PVD coating was applied only for high load diesel engines, but now these coating is expanding usage for gasoline engines. With tighter control on exhaust emissions from diesel engines, piston rings require high durability, high abrasion resistance and anti-scuffing resistance. To meet these requirements, we found that thick Cr-N coating was very effective for diesel application. And we succeeded in the mass production of thick Cr-N coating of around 50 microns. In addition, the Cr-N coating reveals low friction in engine oil and this is very attractive for fuel economy. For gasoline engine application, the combination of thin Cr-N coating and low-alloy ring material is available now. Above mentioned features and future challenge on PVD coating for piston rings are presented in detail.
8:40 AM		G2-2-5 Structural Characterization of Selflubricating Nanocomposites Designed for Engine Applications B. Pécz (Hungarian Academy of Sciences, Hungary) There are hard coatings available for several applications and also other coatings exist with low friction. However, there is a challenge to combine their properties in one coating, what is realized with less success. A coating with both of the above properties would be very advantageous for the car industry and could be used for example on piston rings. This talk reports on several nanocomposite coatings, all of them are prepared in order to get a two-phase material. Model systems of metallic grains in amorphous carbon, or in fullerene-like CNx layers are discussed. Model experiments have shown, that the crystalline grains dispersed in the matrix should be below 10 nm size. Cr-B-N and CrC-C coatings are studied in details. The layers are prepared by magnetron sputtering and transmission electron microscopy is used to characterize the microstructure of the layers at the nanometer scale (also by elemental mapping), or even at atomic level. Sputtered Cr-B-N thin films consist of crystalline grains of hard CrB2, or CrN depending on the nitrogen added during reactive sputtering. Hexagonal BN lubricant phase was expected as well, but instead of that an amorphous matrix was observed, which was proved to be predominantly BN. Cr-C/a-C:H coatings showed a two phase nanocomposite structure with about 2-8 nm size metallic grains situated in an amorphous carbon matrix. The metallic grains were identified as fcc-CrC with some additional Cr. High resolution images show a quasi-periodic sequence of a-C and nanocrystalline grains, which could be a consequence of a self-organizing separation process during deposition.
9:20 AM		G2-2-3 Nanocomposite Coatings for Piston Rings C. Mitterer, G. Gassner, K.P. Budna (University of Leoben, Austria) Present requirements of the automotive industry are clean and resource-efficient combustion engines, with reduced fuel consumption as well as CO₂, CH_x and fine dust emission. To achieve this goal, piston/liner systems are required which are capable of running dry under high pressure and temperatures. Thus, a combination of high wear resistance with low friction is desired, which is not fulfilled by the electroplated Cr and PVD CrN coatings presently applied to piston rings. Promising candidates for wear-resistant and self-lubricious coatings can be synthesized using nanocomposite approaches, where hard wear resistant phases like CrN and CrC are used together with lubricious phases like amorphous hydrogenated carbon (a-C:H) and hexagonal boron nitride (h-BN). The present talk focuses on the development of sputtered self-lubricious coatings for piston rings based on the nanocomposite systems CrC/a-C:H and CrN/CrB₂/h-BN. Application-oriented properties like hardness, elastic modulus, friction and wear behaviour as well as thermal stability are presented and discussed. High-temperature X-ray diffraction, X-ray photo-electron spectroscopy and Raman spectroscopy data are used develop a detailed understanding of the response to elevated temperatures. While coatings in the system CrN/CrB₂/h-BN seem to lack self-lubricious properties, it was found that CrC/a-C:H coatings show superior friction coefficients (below 0.1 against alumina in ball-on-disc testing) and wear resistance (abrasive wear coefficient, 7^.10^-16 m³/Nm), thus outperforming the commercially available arc-evaporated CrN and sputtered WC:C coatings.
10:00 AM		G2-2-7 Synthesis of CrCN/C Nanocomposite Coatings for Piston Rings with a Novel PVD Process G. Wahli, G. Pannatier, E. Bergmann (Geneva School of Engineering, Switzerland); B. Pecs, L. Toth, E. Hegedus (Research Institute for Technical Physics and Material Science, Switzerland) Self Lubricating Ceramic Matrix NanoComposites, materials consisting of a hartstoff matrix with dispersed selflubricating nanoparticles are candidate coatings for Piston/Liner systems, where plasma sprayed microcomposites had been the state of the art before their substitution by PVD chromium nitride. A nocel PVD process for the synthesis of a SLCMNC coating consisting of a CrCN matrix with carbon inclusions is presented. The paper describes the deposition process, the structure and morphology of the coatings and their mechanical properties. Under apropriate process conditions almost isotropis nanocomposite coatings could be obtained. Their structure was analysed by Calotesting combined with LOM, and Transmission Electron Microscopy with low and high resolution combined with EFTEM.
10:20 AM		G2-2-8 Thin Layers in the Automotive Industry as a Challenge for Design and Development H. Meerkamm, A. Seitz, S. Tremmel (University of Erlangen-Nuermberg, Germany) Current developments in the automotive industry - especially in the field of combustion engines - are characterized by numerous efforts aiming for a reduction in energy consumption and pollutant emission. Simultaneously, increasing power enhancement and miniaturizing of components is observed. Associated with it are higher mechanical and thermal loads on the components and in particular on their surfaces. Coatings provide an opportunity to influence component properties at the place of action, thus the surfaces. They allow reducing friction and wear while increasing the degree of efficiency and the lifecycle of the entire power train. In addition, also environmental aspects, suitability for series production and costs are to be regarded. For tribologically highly-stressed components - taking all boundary conditions - into consideration the greatest potential is attributed to PVD-/PECVD-layers. This particularly applies to carbon-based layer systems. Within this group, a trend towards the hard ta-C layers is to be noticed. Layers are to be understood as design elements. They already need to be taken into consideration in the development process to enable a best-possible adaptation of the component and layer system to the existing strain collectives. In this article, various aspects of design for coating in reference to applications in the automotive industry are introduced, and possibilities and limitations of different layer systems are discussed. In addition to some universally valid approaches in selecting and dimensioning, typical applications such as, the coating of components for steering systems, Diesel injection systems, valve trains, or roller bearings are presented. Thereby, methods and tools of the development process are playing an equally important role as the chances for layer characterization do. Depending on the problem, they may range from numerical simulations through simple model experiments up to lifecycle forecasts on basis of component tests.
11:00 AM		G2-2-10 Reduction of Frictional Losses and Wear in Valve Train Systems - the Role of DLC Coatings M. Boghe, N.J.M. Carvalho (Bekaert Advanced Coatings, Belgium) Ever increasing government regulations, rising petroleum prices and international competition provides strong motivation to continuously improve motor vehicle performance. Reducing mechanical friction losses in engine components is a never-ending challenge for engine designers. Studies indicate that friction loss comprises the major percentage (15-20%) of the energy consumption generated within an internal combustion engine. Piston skirt friction, piston rings and bearings account for 66% of total friction losses, and the valve train accounts for 15-25% in the engine low speed range where the boundary and mixed lubrication dominate. Crankshaft, transmission and gears account for the remainder. The trend to use lower viscosity grade lubricants (e.g. 0W30 SAE) will help to reduce the friction losses, but it also leads to a reduced film thicknesses and potential durability problems. Over the last years an increasing number of DLC coatings have been brought to the market. Their combination of several exceptional qualities like self-lubricating, resistant to abrasive, adhesive, corrosive wear, and tailorability makes DLC an attractive solution to designers in improving the operational characteristics of valve train systems. In this paper focus is given to the most critical interface in the valve train that is between the cam and the follower, a contact that has proved difficult to lubricate effectively and is traditionally assumed to operate entirely in the boundary lubrication regime where, at least for parts of the cycle, surface interaction takes place. Two test apparatus have been used, a motored cylinder head and a laboratory reciprocating pin-on-disc, to study the influence of surface topography, treatment and hardness on the cam and follower performance. The right combination of DLC coating and surface finish results in a prevention of pitting and scuffing, and a friction reduction by 40%, which implies a reduction of the fuel consumption of the order of 1%.
11:20 AM		G2-2-11 Coatings for Automotive Components: Tribological Designs, Problems and Solutions A. Hurkmans (IonBond LLC) 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. In lubricated contacts, for example, coatings can be of help in all three areas of the Stribeck curve. Also, the heat treatment conditions and surface 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.
12:00 PM		G2-2-13 New Zinc-Based Automotive Steel Protection Technologies by PVD F.E. Goodwin (International Lead Zinc Research Organization, Inc.); F. Friess, A. Kovacs, G.K. Wolf (Limedion GmbH, Germany) Different approaches using ion beam assisted PVD for Zn-based steel protection were investigated: Multilayers consisting of a very thin interface layer, followed by a 4-5µm thick Zn-layer, also Zn-based coatings prepared by EG, followed by a 0,5-1µm PVD top coat. The interface layers consisted of Zn/Ti- or Zn/Cr-alloys, the base material was mainly high strength steel. For the deposition a 1,1m wide vacuum chamber equipped with two electron beam evaporators and an ECWR ion source were used. The source delivers ions of 0,5-1,5 keV and has a slit extraction of 1x30 cm. Steel samples of 3x1 cm and 10x10 cm were coated. The interface and top layers were deposited with ion beam assistance, the Zn-layer by pure evaporation or EG. Conclusions from preliminary results are the following: 1. Even on high strength steel it is possible to deposit Zn-based coatings with good adhesion by PVD. 2. The results of the salt spray test applied to specimen with interface modification can be arranged into 3 groups: a. A 5µm thick EG-Zn reference sample survives 40-50 h until red rust appears. b. 4 µm PVD-Zn samples with and without Cr interface layer last 40-90 h. c. Ti interface layers followed by 4µm PVD-Zn last 70-130 h. Mn or Mn/Zn top layers (0,5-1µm thick) on 5µm electrogalvanized Zn survive 3-5 times longer in the salt spray test than the reference without top layer.
12:20 PM		G2-2-14 Corrosion Protection Properties of Thin Plasma Electrolyte Oxidation Coatings on an Al-Si Alloy in E85 P. Zhang, D.O. Northwood, X. Nie (University of Windsor, Canada) In this study, thin aluminum oxide coatings with different thickness were deposited on Al-Si alloy substrates to provide corrosion protective films using plasma electrolyte oxidation (PEO) process. Potentiodynamic polarization tests and immersion corrosion tests of dissimilar material couplings were conducted to assess corrosion resistance of the coatings, Al-Si alloys, and cast irons in a commercial E85 (85% ethanol + 15% gasoline) medium for potential flex fuel vehicle (FFV) applications. Scanning electron microscopy (SEM) with energy dispersive X-ray (EDX) analysis and X-ray diffraction (XRD) were used to investigate the coating microstructure, thickness and chemical composition both before and after corrosion. The effect of PEO processing parameters and coating thickness on corrosion resistance was discussed.