AVS2001 Session TR+MM-TuP: Poster Session

Tuesday, October 30, 2001 5:30 PM in Room 134/135
Tuesday Afternoon

Time Period TuP Sessions | Topic TR Sessions | Time Periods | Topics | AVS2001 Schedule

TR+MM-TuP-2 Investigations on Anisotropic Friction Factor
V.V. Tarasov, A.V. Trubachev (Institute of Applied Mechanics of Ural Branch RAS, Russia)
The anisotropy effect is caused by the difference in the microgeometry characteristics of the surface and its physico-mechanical properties, depending on the direction of tracks of a tool, left after mechanical processing of the surface. In the common case in the presence of the anisotropic friction, in contrast to the isotropic one, the body moves at a certain angle to the direction of the application of the disturbing (imposed) force. With the orthotropic friction (M. Guber) there are two directions on the surface of the body; when the isotropic body is moving in these directions it is possible to know maximal and minimal values of friction coefficient, respectively. We place the axes X and Y in these directions, and designate the corresponding friction coefficients as К and k. The mathematical model was suggested for description of the body motion due to anisotropic friction for the constituents of the friction force along the axes X and Y. At the report the a mechanical simulation model is schematically presented for visual study of the peculiarities of friction and motion of the couple of bodies "anisotropic - isotropic surface". For real pairs of friction are more then 0.6, and technologically it is difficult to realize its further decrease. The appearance of the materials with controlled friction characteristics will allow better use of the properties of anisotropic friction in various tribo-conjuctions. The experiments, conducted with the use of the mechanical model, have confirmed both qualitative and quantitative correspondence of experimental and calculated results. The experiments with the use of special samples were carried out for the pairs "isotropic - anisotropic surface" without lubricant. Thus, when the steel plate was used for the experiment, the limiting coefficients were determined: from 0.123 to 0.005. The experiments with the use of special samples were carried out for the pairs "isotropic - anisotropic surface" without lubricant.
TR+MM-TuP-3 Friction Properties of Cobalt-based Diamond Materials under Metallic Sliders
A.S. Alwatban (Riyadh Technical College, Saudi Arabia)
The frictional properties of cobalt based diamond containing different size of diamond particles both in air and in vacuum were studied. In both cases a group of a metallic sliders were used. The coefficients of friction tend to increase with the increasing of the diamond particle size. The coefficient of friction in air is lower than that in vacuum. As a results of increasing the number of traversals, significant wear of the diamond composites by metallic sliders (stainless steel) was observed although the coefficient of friction was decreasing. Scanning electron microscopy studies revealed the wear track that and the wear debris formed during the friction tests. One of the significant factors for the reduction of friction could be the embedded fragmented diamond particle in the metallic sliders.
TR+MM-TuP-4 Measurement of Rolling Friction for MEMS Applications
T.-W. Lin, D. Wendland, B. Shapiro, R. Ghodssi (University of Maryland)
Friction has been a major concern in addressing MEMS reliability. The friction force is expected to be less when only rolling friction exists between two relatively moving components in MEMS devices. This concept is examined by a proposed experimental system using 300 µm diameter ball bearings to characterize static and dynamic rolling friction. The system consists of a servomotor, linkages, a platform, sliding rails, a CCD camera, and silicon specimen. The motor combined with the linkages provides the platform with a linear oscillating motion. A silicon plate (stator), 1cm*1cm*500µm, attached on the platform, has two parallel micromachined v-grooves on its top surface. Equal numbers of stainless steel micro-balls are placed in each of the v-grooves. Another silicon plate (slider), identical to the stator, rests on the micro-balls. The gap between two plates is designed to be 3 µm. The micro-balls are in contact only with the walls of the stator and slider v-grooves. The rolling friction at the contact points causes the slider to move along the direction of oscillation of the stator. The camera is used to record the slider's positions over time to determine velocity and acceleration of the slider. The dynamic coefficient of friction is computed by dividing the acceleration of the slider with the acceleration due to gravity. A curve for the instantaneous coefficient of friction is derived. Preliminary results for rolling friction of micromachined silicon surfaces in contact with stainless steel micro-balls will be presented.
TR+MM-TuP-5 Tribological Analysis of PET is blendas PET-PMMA for Test Pino-on-disk the Dry
M.S.B.P. Santos, F.J.B. Pinto, J.R.T. Branco (CETEC, Brazil)
The concern with the environment preservation has demanded increasing effort to recycle plastics. In a previous investigation we have reported the possibility to manufacture thermal sprayed coatings from recycled PET. Pin-on-disc data demonstrated that coatings had even better wear behavior than virgin PET. In the present work we have investigated the effects of PMMA content on the pin-on-disc and scratching behavior of PET-PMMA blends, in dry condition. AISI 52100 steel 6 mm balls, with and without TiN coatings were used as counterbody. The pin-on-disc wear testing were carried out under 1 and 10 N load. The scratching was performed with 1, 10, 50 and 100 N. Friction coefficient, volume and mass loss were monitored during testing. The paper also investigates on the effect of sliding speed.
TR+MM-TuP-6 Nanomechanical Response of Ultra High Molecular Weight Polyethylene Nanostructure
L. Riester (Oak Ridge National Laboratory); S.P. Ho, T. Boland, M. LaBerge (Clemson University)
Over the past three decades studies on patients with total joint replacement (TJR) prosthesis have shown that ultra high molecular weight polyethylene (UHMWPE) nanoscale wear debris causes osteolysis leading to subsequent aseptic loosening of the implant and total failure of the implant. At the nanoscale, UHMWPE is a semicrystalline material defined by a crystalline domain within an amorphous matrix. Previous work focused on determining the average mechanical properties assuming isotropy within the material proved insufficient for the consideration of failure analysis due to its composite-like anisotropic nanostructure. While several factors can influence the mechanical failure of a material, this study is limited to investigating the mechanical response of the nanostructure of UHMWPE insert in TJR prosthesis. In this study, the effects of sample preparation technique on the nanostructure and the nanomechanical response of compression molded UHMWPE nanostructure were investigated The nanostructure of UHMWPE samples prepared by ultramicrotoming, cryo-ultramicrotoming and etching techniques was studied using an atomic force microscope. The nanomechanical response of the nanostructure as a function of the sample preparation technique was studied using a Nanoindenter II with a diamond Berkovich indenter tip. The samples were indented using continuos stiffness method at a constant displacement rate for penetration depth range of 50-1000 nanometers respectively. This study shows that sample preparation techniques possibly introduced artifacts as illustrated by the changes in the morphology of UHMWPE, which was especially evident in polymers that were ultrasectioned above their glass transition temperature. It was also shown that the technique of etching a sample surface with a permanganate etchant to reveal the crystalline regions changed the neighboring boundary conditions, which in turn redefined the crystalline nanomechanical response to mechanical loading.
TR+MM-TuP-7 Single-Asperity Nanotribology and Nanorheology of Thin Poly(dimethylsiloxane) Films
S. Tan, G. Haugstad, W.L. Gladfelter (University of Minnesota)
The lubricating and non-stick characteristics of poly(dimethylsiloxane) (PDMS) have been exploited for years. As with many tribological systems, technological application led scientific understanding: experimental methods were not available to precisely control intersurface separation, contact geometry and loading conditions about individual surface asperities. In the last 15 years analytical tools have become available for this purpose. Uniquely, scanning force microscopy (SFM or AFM) employs a single microasperity and feedback-actuated tracking of surface topography. Thus "nanotribologists" now can investigate the fundamental unit of tribological systems: a single asperity with measurable radius of curvature, deforming into a material under measurable load, and sliding tangentially to the surface. Many SFM studies have involved simple systems, e.g. clean single-crystal inorganic surfaces or ordered ultrathin organic films lubricating such surfaces. Relatively little work has been on higher molecular weight, disordered films ranging in thickness from boundary lubrication (extremely thin) to bulk hydrodynamic (very thick). Yet real technological systems span this range. In the present work, SFM was employed to study nanotribology and nanorheology on poly(dimethylsiloxane) films varying from several to hundreds of nanometers thick. A wide range of molecular weights was examined, corresponding to bulk viscosities from 350 to 1,000,000 cS. Friction and pull-off forces were found to increase as a small fractional power of velocity over several decades. Similar, scaled-up behavior was observed using a cantilever-attached microsphere (R=10,000 nm) in place of the usual tip (R~10 nm). A dramatic increase in friction and adhesion was observed above a critical film thickness of approximately 3 Rg. Accompanying this increase was a qualitative signature of liquid-like behavior seen in force-versus-distance measurements.
TR+MM-TuP-8 Nanowear Patterning as an Activated Crazing Process
R.H. Schmidt (Lund University, Sweden); G. Haugstad, W.L. Gladfelter (University of Minnesota)
The friction and wear characteristics of nanoscale organic coatings are critical to new and emerging technologies (e.g. microelectromechanical devices). Fortunately the need to understand this behavior has coincided with the development of tools to measure shear forces on the nanometer scale, including the scanning force microscope (SFM). At the scientific frontier these methods have enabled careful studies of confinement effects on polymer dynamics, e.g. the glass transition. In contrast to traditional scientific disciplines like condensed matter physics and physical chemistry, the nanotribology community has only begun to examine the role of temperature in material response. The response of "soft" condensed matter to external forces can be dominated by entropic (temperature dependent) effects; further, nonequilibrium molecular conformations may introduce kinetic (rate dependent) effects. Rigorous studies of thin-film polymer nanotribology therefore must include methodologies to quantify the interrelated roles of temperature and rate. In the present work, wear on polystyrene films was studied via the commonly observed surface-patterning phenomenon, induced by raster scanning. This was examined in detail as a function of load, scan history (repetitions), scan line density, scan velocity, and temperature (40-115 ºC). Film response was highly linear with respect to load and the number of successive visits of the sliding tip. Results suggest that the scanning process induces damage in the film analogous to crazing in brittle bulk polymers. The temperature and rate dependences were analyzed within the Bingham-Voigt-Arrhenius model of plastic flow. Activation energies extracted from (a) surface roughening and (b) the spacing between scan-induced "bundles", were intermediate to known values for alpha and beta relaxations in the bulk polymer.
TR+MM-TuP-9 Decrease in Friction Force of Type 304 Stainless Steel in a Vacuum by Surface Roughness Modification
A. Kasahara, M. Goto, M. Tosa, K. Yoshihara (National Institute for Materials Science, Japan)
Surface modification of sliding motion materials is inevitable to reduce friction as well as outgassing in a vacuum. We therefore study the development of advanced vacuum motion materials by control of surface roughness on a submicron scale. The friction measurement was carried out on typical vacuum material as type 304 austenitic stainless steel sheet with such surface treatments as chemical polishing or electrochemical buffing after mechanical polishing. A frictional probe is a mechanically polished stainless steel ball of 3.18mm in diameter and was slided under load of 0.49N on surface of sheets with surface roughness from 40nm to 1000nm. Friction measurement in an atmospheric pressure showed little change in friction coefficients of sheets with chemical polishing or electrochemical buffing even by changing surface roughness, while friction measurement at the pressure of 1E-6Pa showed that friction coefficients of sheets increased largely except those of sheets with surface roughness around 100nm prepared by chemical polishing or electrochemical buffing. Stainless steel sheets modified only with surface roughness around 100nm can keep low friction coefficient of 0.1 both in an atmospheric pressure and in a high vacuum, which will help smooth sliding motion required for vacuum system.
TR+MM-TuP-10 Friction Behavior of Third Element Incorporated Diamond Like Carbon Films in Various Environments
S.J. Park, K.-R. Lee, K.Y. Eun (Korea Institute of Science and Technology); A. Scholl, F. Nolting, A. Padmore (Lawrence Berkeley National Laboratory); D.-H. Ko (Yonsei University, Korea)
Tribological reaction between the steel ball and third element incorporated diamond-like carbon(DLC) film was investigated from the view point of tribochemical reaction. Si and W was selected for third element. Si incorporated DLC films were deposited using r.f. PA-CVD with mixtures of benzene and diluted silane gases. And W incorporated DLC films were deposited using hybrid DC magnetron sputtering system with methane and Ar. Si(100) wafer was used for substrate. Tribological test was performed using ball on disk type wear-rig. AISI52100 steel ball was used for the wear test. The test environments were dry air, humid air, and vacuum. In the case of the Si incorporated DLC film, it was observed that the debris were partly polymerized and finely dispersed when the Si concentration was larger than 5 at.%, which resulted in low and stable friction behavior in humid air. In dry air, the chemical bond structure of the debris was essentially the same as those in humid air. However, the debris of smaller size has more spherical shape. But in vacuum the debris at low Si concentration showed typical NEXAFS spectrum of a polymer. The polymeric component in the debris decreased as the Si concentration increased In W incorporated DLC films, it has lower friction coefficient but higher wear rate than a-C:H films made by PA-CVD. By analysis of the composition of debris, its friction behaviors were closely related to the formation of the silicon-rich oxide debris.
TR+MM-TuP-11 Structure Analysis of Tetrahedral Amorphous Carbon Films using Synchrotron Radiation Light Source
C.S. Lee, K.-R. Lee, K.Y. Eun (Korea Institute of Science and Technology); K.H. Yoon (Yonsei University, Korea)
Using energetic condensation of carbon ions from filtered vacuum arc plasma, tetrahedral amorphous carbon (ta-C) films were deposited on Si (100) wafers. During the deposition, a dc bias voltage ranging from 0 to -500V was applied to obtain films with various atomic-bond structures. Mechanical properties of ta-C films show the strong dependency on applied bias. The change of the atomic bond structure in ta-C film was analyzed by near edge x-ray absorption fine structure (NEXAFS). In the present work, we focused on the changes in NEXAFS spectrum in various deposition condition and post annealing processes. The relationship between peaks observed in the spectrum and the structural change in the film was identified in the conjunction with Raman and electron paramagnetic resonance spectroscopy (EPR). Based on these results, the suggested models on the atomic bond structure of ta-C film will be discussed.
TR+MM-TuP-12 Effects of Metal Dopant Content on Mechanical Properties of Ti-Me-N Films
H.K. Park (Sungkyunkwan University, Korea)
TiN coatings was applied for various application fields, because of a good wear-resistance and a high hardness. Typically, TiN thin films shows the hardness of 2200 kgf/mm2 and friction coefficient of 0.6. However, in many field, one is looking for a more improved tool which has low friction coefficient and high wear resistance. The main motivation of this study is to characterize the influence of various metal dopant content on TiN thin films. Ti-Me-N thin films were deposited onto steel substrates by PVD processing with a Ti target and various metal target. In this work, we synthesized titanium nitride films similar with reported typical titanium nitride films and synthesized Ti-Cu-N thin films with the addition of elemental copper which is measured improved hardness more than pure TiN films with copper content variables. This films has preferred oriented films of (111) direction. In addition, It was found that there is a strong correlation between content of various metal and film characteristics such as preferred orientation, grain size, hardness, and friction coefficient and so, in future study, improved mechanical properties of TiN films can be controlled and changed by selection and content of elements such as Sn and Ag modifying the film. The Ti-Me-N film will show apparent hardness characteristics and mechanical properties enhancement, when doping element is added onto TiN thin films. Film structure, chemical composition, mechanical properties were investigated by means of X-ray diffraction(XRD), scanning electron microscopy, X-ray photoelectron spectroscopy, wear resistance tester, hardness tester.
Time Period TuP Sessions | Topic TR Sessions | Time Periods | Topics | AVS2001 Schedule