Friction measurements between two contacting B4C surfaces in airand UHV at room temperature using 0.10-0.13N loads are reported. A novel pin (radius=0.005m) on flat device allowing for interchange in UHV is used. The tribological surfaces can be examined using scanning Auger and XPS in the same UHV system. The coefficient of friction for air exposed surfaces is found to vary between air (0.20-0.25) and UHV (1.2-1.8). Stick-slip behavior, indicating strong adhesion, is observed in UHV while only a smooth friction value is measured in air. Air pressures ≥ 100Pa are necessary toreduce the friction from the high value in UHV. The friction between the clean surfaces in UHV initially is 0.8-1.3, but following mechanical conditioning at a higher velocity the friction drops to 0.17-0.25. In situmechanical conditioning is necessary to obtain reproducible friction values for the clean surface. Exposing the clean surfaces to oxygen (103Pa) while conditioning results in an increase in friction (1.0-1.2). Auger line scans through the scar made using the clean surfaces show enhanced B and reduced C. Similar Auger scans for oxygen exposed surfaces indicate that tearing of the oxide layer may be the reason for the high friction. The friction for a clean pin and an in situ nitrogen-implanted flat (10keV, saturation dose) is 0.70-0.80. Film transfer to the pin is observed.

A system for the continuous lubrication of ceramic surfaces at high temperatures by a carbon formed exclusively at the wear surfaces is described. Thelubricant is delivered as a simple gas, ethylene, which is catalytically transformed. No reaction products are left which contain bearing surface material and the only non-volatile product is lubricating carbon. One of the wearing surfaces must contain or have an overlay of nickel (about 1000 A thick in this work) and, preferably, a coating of nickel oxide on top to reducenickel wear during startup. Since the carbon is formed only on nickel and the oxide is worn only in the weartrack, only the wear track is lubricated. The laboratory system consisted of a sapphire pin on a nickel-coated rotating alumina disc. Ethylene was delivered only to the conjunction region, which was surrounded by air. Contact pressures were about 200 MPa, linear speeds between 3 and 9cm/sec. Friction coefficients dropped from 0.6 to 0.06 when ethylene was delivered to the contact at 500°C. Wear rateswere not measureable under operating conditions. Cases other than ethylene and catalysts other than nickel will be explored in further work.

Composite ceramic coatings of alumina (A1203) containing some molybdenum disulfide (MoS2) were electro-codeposited on to Al metal substrates by a combination of anodic sparks deposition of A1203 and electrophoresis of MoS2. The microstructures were characterized by XRD, XPS, SEM, EDS, SNMS,TEM, SAD and relative wear resistance measurements. The coatings consisted mostly ofa-A1203 with some γ and βpresent as well. The coatings were porous and microcracked. SEM showed them to consist of circular “splats” which had rapidly crystallized from the molten state in areas ofdielectric breakdown in the coating. In the TEM the microstructure was seento contain “sets” of parallel, elongated grains having a single crystallographic orientation. The grains were separated by dislocated, low angle grain boundaries or microcracks. The sets intersected at irregularly curved interfaces and were mechanically interlocked. Quantitative SNMS indicated that up to 26 wt% MoS2 was incorporated in coatings fabricated from 5g\1 solutions. SEM\EDS as well as TEM\SAD\EDS identified 1-3μm particles of MoS2 incorporated into the 5g\1 solution derived coatings. These coatings exhibited a 50% lower wear rate than pure alumina coatings deposited under the same conditions.

In order to better understand the chemical bonding forces which control lubricating film stability and adhesion, the binding of lead and tin atoms on the ceramics alumina and silica was investigated by laser induced thermal evaporation combined with mass spectrometric detection of the evaporated species. The interaction between lead or tin and alumina and silica was studied as a function of coverage. The sticking probability for the interaction was measured and found to be temperature and coverage dependent. At low coverage the binding energy of lead to alumina and silica was determined as 237and 246 KJ mol1 respectively, while the binding energy of tin to alumina and silica is 313 and 331 kJ mol1, respectively. A binding energy model based on thermochemical and crystallographic data was used to predict corresponding values which agree with the experimental values.

In addition, temperature programmed desorption and\or decomposition (TPD) was used to investigate the thermal and\or chemical stability of MoS2 films on molybdenum supports. The TPD spectra for S2 from MoS 2 were analyzed, and activation energies were found to be dependent on the film application technique. The binding energy model also provided a useful approximation to the experimental activation energies for the S2 production from MoS2 films. Water and carbon impurities were shown to contribute to the decomposition of MoS2 producing SO2 and CS2. The TPD spectra of S2, SO2, and CS2 provide a measure of the onset of lubricant decomposition.

The goal of tribo-material development is to produce materials which can beused to construct tribo-elements for use in mechanical systems and which will perform in a predictable manner. Tribo-element performance is critical in determining mechanical system reliability. In addition, tribo-elements are among the most severely taxed mechanical system elements, and require a high level of geometric accuracy and stability. Because of the wide variety of operating variables and environments, there are no universal test procedures to determine the efficacy of materials for tribological applications. Tribo-material evaluation is complex, important, and not well understood.

This paper discusses the primary environmental operating variables for different tribo-elements, the rationale for their importance and will survey how they are normally included in tribo-material evaluation. The paper will also distinguish between tribomaterial evaluation for known well defined applications as compared with the evaluation of potential tribo-materials for which the relevant application is unknown. The objective of the material scientist, in either situation, is to select and use the evaluation program involving minimum time and cost consistent with generating results leading to design decisions with confidence.

The role and nature of the many available “bench tests” will be discussed as will be the role and sophistication of thorough tribo-system simulation.

As in many areas of materials development, it is appropriate for tribo-material development to paraphrase the well known adage; “the proof of the tribo-material is in the using.”

Five different slip modes have been identified for bundles of copper fiberssliding on a smooth copper substrate in atmospheric air, argon and nitrogenat pressures from atmospheric to 0.01 Torr. These are stick-slip, variable sliding, intermittent stick sliding and two kinds of smooth sliding, one apparently a basic property of clean surfaces and the other due to contaminants. These forms of sliding are rather persistent once established, and they follow some trends. Specifically, low-pressure smooth sliding is coordinated with a value of the coefficient of friction (μ) near 0.15 and is seen when the surface film is exceptionally thin, while intermittent stick sliding appears to be due to “pads” on the substrate surface,and variable sliding to small particles caught in between the fibers and the copper substrate. However, the five slip modes are erratic in that under the same conditions one or another or yet a third may be observed, even though the electrical contact resistance (R) depends rather reproducibly on time, load, velocity, ambient atmosphere and pressure. That dependence indicates an equilibrium between film destruction through sliding and film formation, overwhelmingly through the presence of oxygen. In the stick-slip mode the difference between pst tic and ųK itic appears to be roughly proportional to ų 0.15, i.e. tfiee xcess of e average value of the friction coefficient above 0.15, being about 20% for ų 0.3 andvanishing near ų =0.15. During slip episodes, R spikes roughly in proportion to their magnitude. Some tentative interpretations are offered, based on the concept that ų consists of three additive components, namely due to the bulk (ųBulk), due to debris (ųDebris), and dueto scoring of surface films (ųFilm).At any rate, the conclusion that the results contradict all previous models of “adhesive” wearis inescapable.

A number of bolted-type tin-plated copper connectors commonly used for distribution transformers were examined using Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Analysis (EDX). The connectors studied had been removed from service because of unsatisfactory performance under normal operating conditions as manifested either by overheating or instability.Detailed examination revealed the presence of extensive fretting damage in thecontacting surfaces. The fretting debris was composed mainly of tin oxide and oxidized base-metal particles. Localized melting and wear of the tin plating were also observed.

The Z,X coordinates of the fracture surfaces of TNT have been measured witha stylus profilometer. The fracture surfaces of the material under study are obtained by accelerating prepared samples in anultracentrifuge. When the tensile or shear strength is exceeded a fracture surface is obtained. Usingdiamond and sapphire styli the topography of the fracture surface has been studied from a wavelength of 1.0 micron to nearly 1.0 centimeter. The powerspectra have been calculated from the data using a prolate spheroidal data window in the horizontal space domain prior to the employment of the fast Fourier transform algorithm. The power spectra are found to decrease with increasing spatial frequency. Peaks are observed in the low frequency region of the power spectra and indicate that much of the fracture is occurring atgrain boundaries.

We report a surface science study of fluorinated and hydrogenated ethers adsorbed at a metal surface. Fluorinated ethers bond less strongly to ruthenium surfaces than the hydrogenated analogs, both for atomically-smooth and atomically-rough surfaces. For the hydrogenated ethers, 0.03 to 0.17 monolayers undergo decomposition, while fluorinated ethers do not decompose significantly.

A vacuum chamber was designed for studying tribological properties of materials under pressures of 5xlO8 Torr to one atmosphere. The chamber is equipped with a pin-on-disk tribometer, in-situ Auger\X-ray photoelectron spectroscopies, a sputter-ion gun and a windowless solid-state X-ray detector. In this paper, we present results of a study using 52100 steel balls sliding on flat disks of the same material in vacuum and in dry air as a function of normal load. The contacts were lubricated with a synthetic hydrocarbon oil (poly-a-olefin). Failure is defined as the point at which the coefficient of friction increases rapidly above the steady state value.

As expected, failure occurs much sooner in vacuum than in dry air. Surface analysis (Auger and XPS) shows direct evidence of the occurrence of high temperature flashes on the surface, which allows the formation and maintenance of a thick oxide in the presence of an adequate supply of oxygen. In addition, a brown film is formed in the vicinity of the wear track for tests performed in dry air, while this film is absent in vacuum. The brown film appears to be a combination of iron oxide and oxidized hydrocarbon from XPS measurements. Results of these studies suggest that the maintenance of an oxide is associated with extended contact life in these studies.

In this paper we are concerned with the morphology of the polymers adsorbedon surfaces, in particular di-block copolymers. Our work is motivated by the experimental findings of Fladziioannou et al. [1] on the steric forces between two adsorbed layers of di-block poly(vinyl-2-pyridine)\ polystyrene (PV2P\ PS) copolymer on mica surfaces. The PV2P block binds strongly on the mica surfaces and the PS block extends into thesolvent toluene (good solvent for PS). Hadziiouannou et al. found that the repulsive forces between the two surfaces start at a distance 1) larger than 10 times the radius of gyration RG of a free P' in toluene. Furthermore, the starting distance D increases with increasing degree of polymerization N of PS in a fashion I) ~ Na with a close to I. We,tudy the adsorption of di-block copolymer with Monte Carlo simulations. The Monte Carlo simulations are especially powerful in dealing with kinetics which is important in systems where hysteresis is observed II1 and cannot be appropriately taken into account by analytical (or numerical) calculations based onequilibrium assumptions.

Wear has been found in the Hertz tracks of fluid lubricated, high quality angular contact ball bearings which spin too slowly to generate an elastohydrodynamic lubricating film. Often a taper section or profile of the track shows a “W” or a “U” shaped groove. A mechanism is proposed to account for these shapes.

This wear has been detected by destructive long term life tests in expensive bearings. A bench test is described which gives accelerated results on easily rejuvenated plates. Connections between the ball on plate tester and any angular contact bearing are outlined.

Ball on plate tests using two perfluorinated and one synthetic hydrocarbon lubricant are interpreted in terms of a slow buildup of an electrically insulating, chemically derived film on the Hertz track. Details of the film buildup and its wear protection ability are specific to each lubricant.

The scuffing resistance of materials under lubricated high-speed sliding was analyzed based on the thermalelastic instability (TEl) model. The model was used to select and rank scuffing-resistant materials.

The scuffing resistance was also determined experimentally by the Falex 6 thrust washer wear tests. There was good agreement between the experimental results and the analytical predictions.

In this paper the computer controlled methodology and the testing apparatus were developed and designed to study seizure as a destructive wear. The seizure testing methodology is based on obtaining the power losses information in testing zone during any time of testing period. These losses are dueto the different friction coefficient in the area of load and sliding zone.They can be automatically recorded and recomputed into the friction force and\or friction coefficient. The friction force and\or friction coefficient - sliding distance relationship can be plotted and the starting point of mass transfer which results in increasing the friction coefficient can be detected. The test results are presented using developed methodology as well as traditional optical microscope and surfanalyzer.

A new wear tester for temperatures up to 1100ºC is introduced. Firstresults of sliding wear tests are shown and discussed. Due to enhanced tribooxidation at 550ºC the wear rates of one-phase materials are lower compared to those measured at 25ºC. The wear rates of hard phase containing alloys increase with temperature, because the metal matrices loose their capability of supporting the hard phases bringing about additional abrasion.

The last two decades have seen substantial progress in the development of physical vapor deposition processes and in ion implantation technologies to modify the surface properties of engineering materials. Surface modification to engineer surfaces for tribological applications has become possible. Hard coatings are now in wide commercial use in tooling applications both to reduce wear and to extend the product life. However, the use of wear resistant coatings in engineered parts and components is yet to become significant. Some of the problems inhibiting wider use of surface modification in tribological applications are discussed in this paper. Recent developments in arc coating to overcome the discrete interface problem associated with low temperature PVD are described. It is shown that the creation of graded interfaces is now feasible. Results from a study involving the multi-layer deposition of titanium and nickel from a single, composite cathode are presented and discussed. It is shown that the prospects for increased use of surface modification to improve the characteristics of tribological components have been enhanced.

CVD TiC coatings on steel bearing balls have been demonstrated to improve conventionally lubricated instrument bearing performance and life, particularly where wear mechanisms predominate. Lightly loaded, approximately 1,400 (200 ksi) MPa maximum Hertz stress, coated bearing balls have run billions of load cycles without coating integrity failure. Data is presented to characterize the behavior of TiC coated steel balls under heavy loads, to approximately 4,200 MPa (605 ksi) maximum Hertz stress, for 175,000 load cycles. As in the lightly loaded tests, there was no indication of coating integrity failure, ie. cracks or delamination. At loads of 2,500 MPa (364 ksi) and above, somewhat below the elastic limit of the 440C substrate, there was evidence of plastic deformation of the coated surface.

Diamond films have been deposited on Si, Mo and many other substrates by microwave and radio frequency plasma enhanced chemical vapor deposition. Although the adhesion between the diamond film and most of the metal substrates is poor due to residual thermal stress from the mismatch of thermal expansion coefficients, we have developed processes to promote the growth of uniform and continuous diamond films with enhanced adhesion to metal substratesfor tribological applications. The tribological properties of these films are measured using a ring-on-block tribotester. The coefficients of friction of diamond films sliding against a 52100 steel ring under the same experimental conditions are found to be significantly different depending on the morphology, grain size and roughness of the diamond films. However, under all cases tested, it is found that for uniform and continuous diamond films with small grain size of 1-3 micrometers, the coefficient of friction of thediamond film sliding against a steel ring under lubrication of a jet of mineral oil is about 0.04.

Different coatings were formed by galvanical deposition, thermochemical treatment, CVD, PVD or plasma spraying. Their wear behaviour was tested under various conditions so that adhesive and abrasive wear mechanisms predominated. The resistance of the coatings to adhesive failure and wear was examined with the pin and disc system under conditions of boundary lubrication. The discs were protected by different coatings while the pins were made of tool steel or alumina. For abrasive wear tests a grinding apparatus with grinding papers of flint, alumina or silicon carbide was used. From the resultsthe following conclusions can be drawn: -Thermochemically treated steels and nickel-phosphorus coatings have a high resistance to galling if the counterbody consists of steel or alumina. The couples plasma sprayed molybdenum against steel and tungsten carbide against alumina also have a high resistance against galling.

-The wear of most coatings is low if the counterbody is made of steel. By analumina counterbody the wear of the coatings isincreased. Alumina is worn less by the coatings than steel.

-The hard CVD- and PVD-coatings, the thermochemically formed iron boride andvanadium carbide coatings and the electroless nickel-phosphorus-diamond coatings have a high abrasive wear resistance.

In magnetic recording, the metallic magnetic media are protected from corrosion and wear by a thin sputtered carbon layer. The latter also acts as a self-lubricating film during the interaction of the media with the ceramic read \write head pad material. Since the surface energy of carbon is high, it tends to absorb and chemisorb environmental constituents such as oxygen, nitrogen, water vapor and hydrocarbons. These could then react with the head\media interface and form heterogeneous layers of “frictional polymers”. These changes in carbon lead to frictional instability and friction build-up. Low temperature gas plasma treatment of sputtered carbon layer was found to improve the surface properties and the frictional instability problems. Use of a mixture of argon and carbon tetrafluoride gases led to the formation of a very thin self-lubricating layer, probably a fluorocarbon. The surface also becomes smooth. This is because of thecombined reaction of chemical reaction, ion-diffusion, ion-penetration and plasma etching. This reaction product was found to be prominently present at the grain boundaries and other morphological inhomogeneities, thereby strengthening the weak areas and improving the tribo-performance of the media.