Papers

ICMCTF2004 Session E1-1: Friction and Wear of Coatings I: Lubrication and Surface Effects

Tuesday, April 20, 2004 8:30 AM in Room Royal Palm 1-3

Tuesday Morning

Start	Invited?	Item
8:30 AM		E1-1-1 Lubrication with Water: Learning Lessons from Nature N. Spencer (Swiss Federal Institute of Technology, Switzerland) Although nature manages to lubricate many sliding interfaces with water-based lubrication systems, this approach is unusual in industrial applications. There are a number of reasons for this, not least the inability of water to increase its viscosity significantly as a function of applied pressure. This property accounts for the outstanding performance of oil in elastohydrodynamic lubrication. Water is, on the other hand, an attractive candidate as a lubricant, since it is non-toxic, environmentally compatible, non-flammable, and an excellent heat-transfer medium. An approach that has been effectively used in our laboratories in recent years is the adsorption of brush-like molecules onto surfaces, which function as local viscosity enhancers, thus leading to improved film-forming capability under low-speed conditions. Additionally, these additives appear to dramatically reduce friction under nanotribological conditions.
9:10 AM		E1-1-3 Tribological Properties of Adsorbed Water Layer on Silicon Surfaces with Different Hydrophilicity under Various Humid Environments D. I. Kim, H.S. Ahn (Korea Institute of Science and Technology, South Korea) Tribological properties of adsorbed water layer on solid surface in sliding contact have not yet been fully understood. We aimed to better understand how water vapor pressure and surface hydrophilicity influence the tribological behavior of adsorbed water-mediated microcontact. Friction and interfacial shear strength of the silicon surface with different water affinity against a glass sphere was examined under various water vapor pressures in a wearless sliding condition (low contact pressure). Friction behavior with high contact pressure was also investigated to identify the influence of water layer on friction mechanism. The friction of hydrophilic surface decreased as the vapor pressure increased. Less hydrophilic surface showed stable and low friction force regardless of relative vapor pressure. However, more hydrophilic surfaces with high relative vapor pressure exhibited lower shear strength than less hydrophilic surfaces independent of capillary effect. It was also shown that the prolonged stable friction state is influenced by the surface water affinity and the water vapor pressure. These behaviors were explained in terms of capillary wetting and the role of confined water layer in the contact area.
9:30 AM		E1-1-4 Friction of Thin Coatings on Three Length Scales D. Drees (Falex Tribology NV, Belgium); J.-P. Celis, S. Achanta (Katholieke Universiteit Leuven, Belgium) Friction at different length scales has been a matter of investigation in the field of tribology. The present work is an approach to cover the entire range of testing parameters that are used in evaluating friction on different scales. Since friction is omnipresent in every situation ranging from nanoscale to macroscale its dependence on many operational parameters makes it very difficult to analyse. Hence the study of friction at different length scales will provide a good basis for understanding the underlying mechanisms or its origin. Also the length scale measurements can be used in demarcating the vital parameters that influence the phenomenon. It illustrates size effect on the friction behaviour that aids in understanding the friction occurring at different application scales (atomic, micro and macroscale). This work facilitates the verification of theoretical models that exist for this phenomenon. All the results and conclusions are based on experimental evidence obtained by testing coatings like DLC, TiN and MoSi₂ with silicon nitride counter body with varying diameters, depending on the equipment and pressure-displacement range. The experiments were performed with identical contact parameters (contact pressure, speed and environment etc.) so as to make a comparative study of the results. All the pressure calculations were done using the Hertzian contact model (ball on flat) and all the experiments were carried out over the widest possible range of experimental parameters, using available testing equipment like the Lateral Force Microscope, a Basalt precision tester and the MTM fretting mode I equipment. This work shows the overlap of the different tribological equipment covering an entire range of displacements and pressures, thus enables to bridge the gap between nano, micro and macrotribology. There are also some pressure scales pertaining to microtribological systems that may be quite relevant to the microelectronic devices.
9:50 AM		E1-1-5 Room Temperature Deposition of Titanium Carbonitride Coatings by Pulsed Laser Deposition for Tribological Applications J.M. Lackner, W. Waldhauser, R. Ebner (JOANNEUM RESEARCH Forschungsgesellschaft GmbH, Austria); B. Major (Polish Academy of Sciences, Poland) Titanium carbonitride (TiCN) hard coating systems possess excellent tribological behaviour in metal punching and forming as well as in polymer processing contacts. In the present work TiC_xN_1-x coatings of various carbon (x) and nitrogen contents were deposited at room temperature by employing the pulsed laser deposition (PLD) technique. A pulsed Nd:YAG laser with 1064 nm wavelength was used for the vaporization of Ti targets in low-pressure N₂/C₂H₂ atmospheres. The highly ionized metal vapour was deposited onto polished substrates (molybdenum, AISI D2). The variation of the gas flow during deposition causes a change of the chemical composition, the texture and crystallinity of the coatings, and, consequently, the mechanical properties. Due to solid solution hardening of the TiN fcc lattice by low contents of carbon a strong increase in the hardness and elastic modulus was found. Higher carbon contents decrease both mechanical properties and the crystallinity too. Furthermore, the maxima in hardness and elastic modulus is corresponding with the minima in friction coefficients (~ 0.1 to 0.2) and wear rates of both the coated disc and the counterparts, AISI 52100 (DIN 100Cr6) ball-bearing steel balls and alumina balls, resp.. As an outstanding advantage of the TiCN coatings deposited at room temperature by the PLD process their excellent adhesion to the substrate can be pointed out, reaching the highest level (HF 1) in the Rockwell indentation test.
10:10 AM		E1-1-6 The Tribological Behaviour of CrN, Graphit-iC and Dymon-iC Coatings under Oil-lubrication J Stallard, D.G. Teer (Teer Coatings Ltd., United Kingdom) The use of hard ceramic coatings (especially CrN) in the field of machine components is now widely accepted. The development of low-friction wear resistant coatings that can run dry or in a minimum amount of oil is becoming increasingly more important. Two recently developed carbon based coatings (TCL Graphit-iC^TM and Dymon-iC) which have already been shown to exhibit very high sliding wear resistance and low friction in dry conditions, were compared to a CrN coating in oil lubricated conditions. In this paper, long term pin-on-disc tests using a chromium steel counterface ball were carried out on coated HSS test samples. All the coatings performed well with applied contact pressures exceeding 2 GPa, but the TCL Graphit-iC^TM and Dymon-iC coatings also exhibited the desirable characteristic of protecting the counterface material. Reasons for this behaviour are discussed.
10:30 AM		E1-1-7 Deposition and Characterization of nc-TiC/a-C Nanocomposite Coatings Y.T. Pei, D. Galvan, J.Th.M. De Hosson (University of Groningen, The Netherlands); A. Cavaleiro (Coimbra University, Portgual) Nano-structured coatings have recently attracted increasing interest because of the possibilities of synthesizing a surface protection layer with unique physical-chemical properties that are often unachievable in the bulk materials. On top of these coatings, amorphous DLC-based nano-composite coatings exhibit not only excellent wear resistance and high hardness but also low friction, which provide a solution to the stringent requirements on drive-line components in automotive industry such as prolonging the work life of the components and increasing the efficiency of the engines by reduction of friction. This paper will focus on the deposition and characterization of nano-crystalline TiC reinforced amorphous DLC (nc-TiC/a-C) composite coatings. Both balanced and closed field unbalanced magnetron-sputtering systems are used to deposit the nc-TiC/a-C nanocomposite coatings with hydrogenated or hydrogen-free DLC matrix, respectively. The contents of Ti and C in the coatings have been varied in the whole range of interest (5~45at.%Ti) by changing the configuration of the targets or by controlling the flow rate of ethylene gas. Different levels of BIAS and deposition pressure were used to control the nanostructure. The coatings exhibit hardness of 5~30 GPa, an H/E ratio around 0.1 and a friction coefficient of about 0.1. Detailed mechanical examinations, including nanoindentations, scratch and wear tests, have been performed on the coatings. Cross-sectional and planar (high resolution)TEM observations and energy filtered TEM together with EELS are employed to characterize the nanostructure, elements distribution in the coatings and chemistry of the carbon matrix, respectively. The influence of the volume fraction and size distribution of TiC nano-crystallites on the layers properties is inspected. Furthermore, the bonding characteristics of the C matrix (sp²-sp³) are determined and related to the layers performance.
10:50 AM		E1-1-8 Tribological Behavior of Metal Doped Ta-C Coatings Deposited by Laser Ablation - Respective Role of Ni and Ta J. Fontaine (Ecole Centrale de Lyon, LTDS, France); J.C. Orlianges (Universitát de Limoges, SPCTS, France); M. Belin, S. Mure (Ecole Centrale de Lyon, LTDS, France); C. Champeaux, A. Catherinot (Universitát de Limoges, SPCTS, France) Nickel and tantalum doped carbon films have been deposited under high vacuum by KrF laser ablation at ambient temperature. A computer controlled multi-target system allows predefined sequences of laser shots on the carbon and metallic targets respectively. Consequently, it has been possible to elaborate a wide series of metal (Me)/carbon (C) materials, ranging from a pure tetrahedral diamond-like carbon film (ta-C) up to pure metal, with explored compositions of 0%, 5%, 15%, 50% and 100% metal. The composition of the deposited layers has been checked, thanks to XPS surface analysis. The tribological behavior of these layers has been studied in a reciprocating steel sphere/plane configuration, in ambient air with spatially resolved friction measurements. All the coatings are found to resist high contact pressure (typically 0.8 GPa), indicating a fairly good adhesion to the substrate. Both friction coefficients, ranging from 0.08 to 0.45, and wear processes are found to be very dependent on the nature and concentration of metal. With tantalum, we observed the characteristic features for adhesive wear with some material transferred on the antagonist, even with low metal containing coatings. Some EDX analyses have confirmed the high metal content of this transfer patches, suggesting that some selective transfer occurred. The results are discussed in terms of the ability for the doping element to form carbide phases.
11:10 AM		E1-1-9 Tribological Behaviour of Thin a-C and a-C:H Films with Different Topographic Structure under Rotating and Oscillating Motion for Dry Lubrication R. Bandorf, H. Lüthje, C. Henke, J.-H. Sick (Fraunhofer IST, Germany) Fluid Lubrication can hardly be realized for microparts and MEMS components. Therefore coatings with low friction will be applied. Due to the small size of these parts only nanofilms are applicable. For further improvement of the microtribological behaviour we investigated the influence of a geometrical well defined surface structure. For standard characterization pin-on-disc-tests were performed. Beside the study of the friction coefficient under rotating motion also the microtribological behaviour of an areal microcontact was studied. A variation of width to spacing of concentric circles for the pin-on-disc-test showed the existence of an optimum contact area resulting in minimized friction coefficients. Microstructures of different shape and depth led also to a reduction of friction. In this case the resulting depth of the structures played a mayor role in tribological optimization. Shallow structures (d: 1,5 µm) showed only slight differences in the friction coefficient, while deeper structures (d: 4,5 µm) led to a significant reduction. Besides investigations on the microtribological behaviour under single asperity contact base on nanoindentation, we used an oscillating test for microstructured areal microprobes. First investigations on silicon micro-samples sliding against a silicon conterpart showed a linear dependence of sliding distance and resulting wear. Also a dependence of the friction coefficient on the roughness was observed. Therefore different roughnesses (polished, Ra= 50 nm, 200 nm) were investigated.
11:30 AM		E1-1-10 High Performance Chromium Based Coatings for the Application on Temperature Sensitive Machine Parts O. Knotek, E. Lugscheider, K. Bobzin, M. Maes (RWTH-Aachen, Germany); R. Cremer, G. Erkens, T. Rasa (CemeCon AG, Germany) Latest developments in machine performance have led to higher expectations in material design. Expectations in tensile strength, wear resistance, reduction of weight and friction can no longer be fulfilled by bulk materials. Therefore composite materials like multi layer carbon fiber structures, ceramics and high performance coatings gain more and more interest in an increasing number of applications. PVD coatings on machine parts offer a wide variety of desirable properties in wear resistance, running-in and oil off behavior as well as low friction. In this paper a development of an indusrial low temperature PVD process is presented for the use on machine parts. The deposited PVD-coating is a chromium based chromium aluminum nitride coating. In a first step, the potential of changing from DC to pulsed power supplies is shown. Improvement in coating structure as well as lower deposition temperatures are observed. Finally friction behavior was improved by adding oxygen as a reactive component in the last stage of coating process. The evaluation of the friction behavior was determined by pin on disc tests.
11:50 AM		E1-1-11 Tribological Properties Evaluation of AISI 1095 Steel Chromized at Different Temperatures J.W. Lee, S.J. Wang, C.L. Li, C.C. Lin (Tung Nan Institute of Technology, Taiwan, R.O.C.) Hard chromization process provides a surface modified coating on steel surface with high hardness, corrosion resistance and high temperature surface protection. AISI 1095 carbon steels were chromized to form chromium carbides and nitrides on surfaces by pack cementation process at 850°C - 900°C and 950°C for 1 to 9 hours, respectively. The nano hardness of the chromized steels were measured with a nanoindenter. The tribological properties were evaluated by pin-on-disk wear tests. Coefficients of friction of chromized steels were also measured. Rockwell-C adhesion quality tests were further conducted to evaluate the adhesion strength quality maps of chromizing layers. Surface morphologies of chromized coating layers and matrix after wear and adhesion tests were studied with an electron probe microanalyzer. Chipping and micro radial cracking failures were revealed on the chromized layers after the wear and Rockwell-C adhesion quality tests. It was concluded that similar surface hardness values could be achieved independent of chromizing temperature. Adhesion and anti-wear properties of chromized layers were enhanced as chromizing temperature and time increased.