ICMCTF2007 Session E1-3: Friction and Wear of Coatings: Lubrication, Surface Effects and Modelling

Tuesday, April 24, 2007 1:30 PM in Room California

Tuesday Afternoon

Start	Invited?	Item
1:30 PM		E1-3-1 Fretting Wear of Soft Noble Coatings for Electrical Application P.J. Jedrzejczyk, S. Fouvry (Ecole Centrale de Lyon, France) The fretting wear in electrical contacts is a serious problem in many applications especially in the widely understood automotive industry but also in other machines exposed to vibrations. It introduces serious electrical distortions, mainly the high electrical resistance of connectors and finally electrical installation malfunctions. Need of improvement of functional properties of mentioned elements led to the development of numerous non noble and noble materials consisting of pure metallic materials, doped ones as well as of soft coatings. To reproduce the environmental conditions of car engine a specific fretting test machine has been designed and built. With this apparatus, most of the physical conditions like relative humidity range, temperature level, frequency range, relative displacement range and force applied to the contact can be precisely controlled to simulate all loading factors. The evolution of the friction coefficient as well as electrical resistance is measured and registered during all tests. In this work, one couple of noble soft coatings under fretting conditions was examined to see the influence of the fretting regime and environmental parameters on its electrical behavior. A quantitative variable has been introduced to estimate the electrical durability of the studied materials.
1:50 PM		E1-3-2 Melt Lubrication of Sliding Electrical Contacts P.Y. Hsieh, G. Ghosh, M.E. Fine, Y.W. Chung, J. Wang (Northwestern University) Unlike organic lubricants, liquid metals offer high electrical conductivity and better thermal stability over a wide temperature and pressure range. A thin fusible-alloy coating can lower both electrical contact resistance and static friction in a sliding electrical contact through melt lubrication. Liquid bismuth-based alloys were assessed for potential use in high-power sliding electrical contacts through simultaneous measurement of friction force and electrical contact resistance as a function of load, current density, and temperature. Liquid bismuth lubricants have potential applications to replace conventional lubricants in high-speed generators and alternators.
2:10 PM		E1-3-3 Characterization and Modeling of the Wear and Subsurface Microstructure Evolution of Metal Single Crystal Surfaces C.C. Battaile, S.V. Prasad, J.R. Michael, P.G. Kotula (Sandia National Laboratories) Surface treatment and modification are commonly used to engineer friction and wear behavior. Recent experiments have demonstrated that wear-induced evolution of the subsurface material can yield an in-situ surface treatment of sorts. In the present work, extensive plastic deformation and mechanical mixing near the surfaces of Ni single crystals, worn at 1 N load with a 1/8 inch diameter SiN ball, created microstructures which substantially modified the wear deformation mode and altered the frictional properties of the surface. Furthermore, these phenomena were strongly influence by the crystallographic orientation of the surface relative to the wear geometry. On the {110} surface of Ni worn along the <211> direction, particularly large deformations led to the formation of ultra-fine-grained material at the surface, which in turn served to reduce the measured friction coefficient by a factor of two or more. Other crystallographic orientations did not strongly exhibit this behavior. These experiments will be described, and the characterization of the worn material will be detailed. Our model of the wear process, based on dislocation plasticity, subgrain formation, and ultra-fine-grain rotation, will be presented and validated in the context of the experimental observations.
2:30 PM	Invited	E1-3-4 Thermally Activated Friction: Macroscopic Evidence W.G. Sawyer, M.A. Hamilton (University of Florida) Solid lubricants used in aerospace applications must provide low friction and a predictable operation life over an extreme range of temperatures, environments and contact conditions. There are a number of coatings that are used for friction and wear management on moving mechanical assemblies that must operate under this temperature range. Recent experiments with macroscopic tribometers and atomic force microscopes suggest that solid lubricants may be interfacially sliding, and the activation barriers to sliding may be linked back to the nature of the bonding across the interface. Variable temperature data with PTFE, MoS₂, and DLC films will presented. Results show a monotonic increase in friction coefficient as sample surface temperature was decreased from 317°K to 173°K for all samples. The behavior of hard coatings that are not solid lubricants do not show this trend. Intentionally grown films of ice had a friction coefficient around µm=0.25. All of the data together suggests that there are limits to thermally activated friction, where the coefficients of friction become so large that material wear becomes the mechanism that provides velocity accommodation.
3:10 PM		E1-3-6 Study on the Mechanical Properties of CNT Film Produced by Surface Decomposition of SiC Y. Tsukiyama, T. Tokoroyama (Nagoya University, Japan); M. Kusunoki (Japan Fine Ceramics Center, Japan); H. Usami (Meijo University, Japan); N. Umehara (Nagoya University, Japan) Since the discovery of carbon nanotubes (CNTs) by Iijima, the remarkable structural, electrical and mechanical properties as carbon material have attracted many researchers, and the synthesis of high quality CNTs using various method such as arc discharge, laser vaporization, pyrolysis, plasma-enhanced or thermal chemical vapor deposition (CVD) has been studied. In 1999, Kusunoki et al. have reported that CNTs with high-density and high-alignment are formed vertically on a silicon carbide (SiC) surface by annealing the substrate at 1700°C in a vacuum furnace. In this process called surface decomposition method, the CNTs have grown without any catalytic help of metals or gases. This high dense and high aligned CNTs on SiC substrate (CNT film) could be used for promising tribomaterial as high friction or wear proof materials because each CNT is covalently bound to the SiC substrate. Thus, we have studied about wear property and wear mechanism of CNT film by tribotesting using AFM (atomic force microscopy) and micro-scratching test. It was found that CNTs showed interesting tribological behavior. By micro scratching test (tip radius was 5 µm) which measured the critical load when films are removed, longer CNTs are removed under lower normal load than shorter CNTs. And each CNT was not worn but broken away from its root. Considering the influence of the length of CNTs, wear mechanism of the CNT film was discussed.
3:30 PM		E1-3-7 Evaluation of Wettability, Mechanical, Tribological Properties of Super Hydrophobic Coatings Based on Organic-Inorganic Hybrid Coatings R.P. Ayalasomayajula, S. Santucci (University of L'Aquila, Italy); D. Di Claudio (CASTI, CNR-INFM Regional Laboratory, Italy) Organic-inorganic hybrid materials can offer multifunctional properties tailoring from submicrometer to nanometer length scales in various applications such as micro and nano photonic devices including, waveguides, light emitting devices, quantum dot devices, photonic band gaps and holographic materials. In the present investigation, hybrid materials based on polydimethoxy silane, perfluorolky silanes and fluorine based polymers were spin coated on to different substrates glass, quartz, and polycarbonate substrates at room temperature. The deposited films have been cured under UV irradiation for better polymerization followed by annealing at 100°C (polycarbonate), 200°C and 300°C for 30 min. To improve the scratch resistance properties of these coatings nanoscale Silica colloidals have been incorporated into the matrix by sol-gel process. UV-visible spectroscopy (UV-vis), Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD) have been used for optical absorbance, vibrational and stretching bands, and phase formation of the deposited of the films, respectively. The deposited films are transparent, hard, scratch resistance and in particular hydrophobic. Friction coefficient measurements have been carried out by using steel and Al₂O₃ as counter bodies. Adhesion strength failure and hardness measurements on plastic substrates were examined by using scratch resistance tester and nanohardness tester, respectively.
3:50 PM		E1-3-8 Improvement of Lubrication by Surface Microtexturation using Ultrashort Laser Pulses L. Mourier, D. Mazuyer (Ecole Centrale de Lyon, France); A.A Lubrecht (INSA Lyon, France); C. Donnet (Université Jean Monnet and University Institute of France) The use of ultrashort laser pulses for the microtexturation of metallurgical surfaces and coatings undergoes nowadays a continuous growth. In the field of tribology, the objective is to reduce friction and wear in various lubrication regimes. The use of femtosecond laser pulses improves the achievable quality of the microstructures on any kinds of materials, in comparison to nanosecond laser pulses because of the minimized heat affected zone. In this paper, the transient lubrication phenomena induced by circular micro-cavities passing through an elastohydrodynamic (EHD) contact are analyzed. A 52 100 steel ball was micro-machined using a femtosecond pulse laser, and is tested with an EHL tribometer. The experiments are simulated numerically with a 2D-multigrid solver. Under rolling sliding conditions, the film thickness distribution is modified, and two opposite effects are observed. Deep micro-cavities induce an oil film decrease. On the contrary, a shallow micro-cavity (in the micrometer range or less) locally generates a large increase in the film thickness. When the ball surface is the slowest, the propagation velocity of the local oil film reinforcement increases.
4:10 PM		E1-3-9 Application of Nanodispersive Alumina in Antiwear Ni-P Composite Layers D. Ozimina, M. Madej (Kielce University of Technology, Poland); I. Piwonski (University of Lodz, Poland) The fabrication of layers having good antiwear properties and the enhancement of these properties by choosing appropriate lubricants are of crucial importance. The effectiveness and the operational reliability of tribological system strongly depend on the durability and reproducibility of antiwear top surface layer having fundamental role in activity of frictional contacts. Transformations of technological top surface layer are directly associated and depend on triboactive constituents in lubricant. This study presents the results of antiwear investigations of composite Ni-P-Al₂O₃ surface layers. Heterogeneous layers deposited on C45 and 100Cr6 stainless steel containing nanodispersive alumina (corundum) having particle size 2-4 nm were prepared with the use of electroless method. The structure of nanodispersive corundum powder as well as the technological surface layers were imaged with the use of atomic force microscopy (AFM) and scanning electron microscopy (SEM/EDS). Thickness of the layers and their micro- and nano- hardness were also measured. Tribological characteristics in macro- scale were performed on T-01M machine operating in pin-on-disc configuration in technical dry friction and boundary friction conditions. These measurements were realized in following model lubricants: mineral base oil, lubricant containing AW additives and high performance phosphazene synthetic oils. Measurements performed with the use of AFM were conducted in technical dry friction conditions. Comparative results analysis of the NiP and Ni-P-Al₂O₃ composites revealed that the presence of nanodispersive alumina phase enhance the mechanical and tribological properties of antiwear layers.
4:30 PM		E1-3-10 Friction and Wear of Titania and Alumina Ceramic Overcoats Under Unlubricated and Boundary Lubricated Conditions X. Li, M.L. Weaver (The University of Alabama) It becomes more promising to use modern fine ceramic coatings for better tribological performance under severe conditions. Among them, conformal oxide coatings are good candidates to effectively improve the reliability of MEMS devices with moving parts. Under unlubricated sliding contact conditions, self-mated oxide ceramics show a relatively high friction coefficient and low wear resistance. Limited data regarding successful lubrication of ceramics is available in the literature. Friction and wear of two promising candidates, titania and alumina overcoats, were studied in this report under unlubricated and lubricated conditions. Nanoindentation, friction and wear tests were conducted firstly under unlubricated conditions, and the correlation of mechanical properties to tribological behaviors were investigated. Two synthetic organic lubricants, a non-polar oil with a polyalphaolefin (PAO) structure, and a polar oil of poly(propylene glycol) monobutyl ether were selected. Boundary lubricated friction and wear tests were conducted by dip lubing the overcoat surfaces. Both friction coefficient and wear were decreased when using the polar ether lubricant, especially for the titania surfaces that have higher surface free energy. AFM and SEM/EDX were used to analyze the post-test wear tracks and wear debris. Combination of mechanics, wettablity and wear mode leads to a better understanding of tribology and lubrication of oxide ceramics.
4:50 PM		E1-3-11 Influence of Coatings on Oil-Out Performance of Rolling Bearings J.W. Eichler, A. Matthews, A. Leyland (University of Sheffield, United Kingdom); G.L. Doll (Timken Technology Center) The paper reports tests carried out using a newly-developed high cycle rolling contact test facility based on a thrust ball bearing configuration. The test machine is instrumented for temperature, torque, vibration and speed measurement. Our recent studies have focused on the "oil-out" performance using coated and uncoated counterfaces. The main coatings tested were carbon based and CrN based. Also we have investigated the influence of surface finish on friction and wear performance. Data is presented illustrating the benefits provided by coatings under these extreme operating conditions, and their ability to delay the onset of catastrophic bearing failure.