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Pohyb železničních vozidel po infrastruktuře je ovlivňován množstvím aspektů. Mezi ty důležité patří bezpečnost, spolehlivost a také poskytnutí komfortu cestujícím. Nanášením tuhého maziva na určité místo okolku železničního kola ovlivňujeme při jízdě železničních vozidel všechny výše uvedené aspekty. Proto má oblast experimentálního zjišťování, analyzování a rozvoje problematiky mazání okolku velký význam. Tato práce se věnuje problematice experimentálního zjišťování vlivů přítomnosti maziva v kontaktu kola a kolejnice na zkušebním kladkovém stavu. K provedení experimentů je součástí této práce i doplnění zkušebního stavu o držák maziva, naměření adhezních charakteristik pro jednotlivé vzorky maziva a jejich vyhodnocení. Práce pak poskytuje souhrnnou představu o provedených měřeních a vyhodnocení vlivu maziva., The movement of railway vehicles on the infrastructure is affected by many aspects, among which undoubtedly belongs safety, reliability or providing comfort to passengers. By applying lubricant into the area of wheel flange, we affect all mentioned aspects and because of that, area of experimental findings, analysis and development of wheel flange lubrication has its meaning. This thesis addresses issues of experimental findings of lubricant presence between wheel and rail contact by applying a sample of lubricant used on tram wheel roller rig. For conducting experiments, this thesis also includes assembly of holder, which is needed for application of lubricant. Measurements of adhesion characteristic for each lubricant's samples and their evaluation. As a result, this thesis provides a comprehensive overview of conducted measurements and evaluation of the lubricant's effect on the contact between wheel and roller while applying on test tram wheel. As a result, this thesis provides a comprehensive overview of conducted measurements and evaluation of the lubricant's effect., Dopravní fakulta Jana Pernera, Student přednesl obhajobu své diplomové práce.  Odpověděl na dotazy vedoucího, oponenta práce a zkušební komise., Dokončená práce s úspěšnou obhajobou

Graphene oxide (GO), chemically expanded graphite (CEG) and graphite were evaluated as solid lubricant for ultrahigh molecular weight polyethylene composites. Under dry conditions, the addition of all solid lubricants increased the coefficient of friction by up to 38%. For the composites corrugated stick–slip features were observed which correlate with a decrease in matrix degree of crystallinity. GO had the lowest effect on the crystallisation, resulting in the lowest relative increase in friction coefficient of only 13%. Under water lubrication, GO, CEG and graphite were equally effective in reducing friction and wear. The highest friction for the neat matrix was found to be due to a transfer film, which was suppressed by the addition of the solid lubricants., Validerad;2023;Nivå 2;2023-06-26 (hanlid)

This thesis aims to investigate the coefficient of friction between steel on steel contacts with the addition of solid lubricants such as h-BN, WS2, MoS2 in powder form, in dry conditions and wet conditions. More specifically, the purpose is to enhance the sliding between the piston rings and cylinder block in a modern high temperature steam engine developed by RANOTOR. The friction test was carried out as a linear sliding test with determined loads and sliding speed. Hertzian contact theory was deployed to calculate contact pressure and shear stresses to make sure the contact was elastic, alternatively plastic. It was found that WS2 and MoS2 lowered the coefficient of friction quite heavily in dry conditions, acting as a thin protective-lubricating film. h-BN performed rather poorly, increasing the coefficient of friction. In a water slurry, none of the powders managed to decrease the COF due to the particles not interacting with the surfaces.The solid lubricants tested should be further tested as coatings since they acted like it in dry conditions., Denna rapport syftar till att undersöka friktionskoefficienten i stålkontakter med tillsats av fasta smörjmedel som h-BN, WS2, MoS2 i pulverform, under torra och våta förhållanden. Mer specifikt är syftet att förbättra glidningen mellan kolvringarna och insidan av cylindern i en modern högtemperatur-ångmotor utvecklad av RANOTOR. Friktionstestet genomfördes som ett linjärt glidtest med bestämda belastningar och glidhastighet. Hertzian-kontaktteorin användes för att beräkna kontakttryck och skjuvspänningar för att säkerställa att kontakten var elastisk alternativt plastisk. Det visade sig att WS2och MoS2 kraftigt sänkte friktionskoefficienten under torra förhållanden genom att agera som en tunn skyddande-smörjfilm. h-BN presterade dåligt och ökade friktionskoefficienten. I vattenblandning lyckades inget av pulverna minska friktionskoefficienten eftersom partiklarna inte interagerade med ytorna. De testade fasta smörjmedlen bör vidare testas som beläggningar eftersom de fungerade som dessa under torra förhållanden.

The increasing global demand for innovative and environmentally friendly lubricants can be met through the use of solid lubricants. By switching from conventional lubricants such as various oils or grease to solid lubricants, new scopes of application can also be opened up. The main requirements for solid lubricants are a reduction in the coefficient of friction (CoF) and an increase in wear resistance. Due to the favourable material properties, molybdenum (Mo) coatings fulfil the tribological requirements and are therefore promising solid lubricants which can be applied via physical vapour deposition (PVD). In this work, the impact of substrate temperature on the hot hardness of deposited Mo coatings was determined. The specimen with the highest hot hardness was then tribologically examined both at the micro and nano level. Through an analysis of the wear tracks by means of nanoindentation and scanning electron microscopy (SEM), it was possible to detect the influence of the tribological load separately from that of the thermal loads. The results showed that the tribological load influenced the Mo coating by significantly increasing its hardness. This was achieved due to the work hardening of the Mo layer leading to an increase in the wear resistance of the coating.

Due to a growing energy problems in the last decades, different ideas and methods for saving energy and efficiency improvement become more and more requested. Taking into account that almost half of the energy losses in machines and mechanisms occur in frictional processes thus the importance of improving tribology performances in different machine elements is rather clear. Machine elements such as gears, rolling and sliding bearings in various applications are usually operating with different lubricants in order to reduce friction and wear of their contacting surfaces. Besides surfaces in contact cannot be conventionally lubricated due to legal and environmental restrictions or physical limitations, in applications in food, textile, paper or medical industry as well as limitations due to ultra-clean conditions, extreme temperatures, radiation or vacuum, solid lubricants gain more and more attention due to the possibility to maintain essential lubrication properties. MXenes are a novel class of new two-dimensional materials, derived from well established MAX phases such as Ti3AlC2, which have the ability for a wide use in fields and applications due to their unique structure and properties. The distinct structure, low shear resistance, and easy-to-modify ability endow MXenes with particularly superior lubrication potentials. Authors of the paper present an overview synthesis and variety of MXenes, their mechanical and frictional properties dealing with ideas for possible applications in several machine elements aimed to reduce friction, wear rate and improve their performances making longer working life.

In the quest for decreasing fuel consumption and resulting gas emissions in the aeronautic sector, lightweight materials such as Carbon Fiber Reinforced Polymers (CFRPs) and Ti-6Al-4V alloys are being used. These materials, with excellent weight-to-strength ratios, are widely used for structural applications in aircraft manufacturing. To date, several studies have been published showing that the use of metalworking fluids (MWFs), special tool geometries, or advanced machining techniques is required to ensure a surface quality that meets aerospace component standards. Conventional MWFs pose a number of environmental and worker health hazards and also degrade the mechanical properties of CFRPs due to water absorption in the composite. Therefore, a transition to more environmentally friendly cooling/lubrication techniques that prevent moisture problems in the composite is needed. This research shows that lubricated LCO2 is a viable option to improve the quality of drilled CFRP and titanium aerospace components compared to dry machining, while maintaining clean work areas. The results show that the best combination of tool geometry and cooling conditions for machining both materials is drilling with Brad point drills and lubricated LCO2. Drilling under these conditions resulted in a 90 % improvement in fiber pull-out volume compared to dry machined CFRP holes. In addition, a 33 % reduction in burr height and a 15 % improvement in surface roughness were observed compared to dry drilling of titanium.

In this work, self-lubricating composites containing MoS2 and graphite dispersed in an iron matrix were produced by powder metallurgy and sintering. Previous studies demonstrate that MoS2 reacts with iron matrixes during sintering, making the production of Fe-MoS2 composites rather difficult. Therefore, this study focused on a potential solution to avoid or reduce this reaction, whilst still providing good tribological properties. Our results show that the addition of graphite retards the reaction of MoS2 with iron and that the combination of MoS2 + graphite results in composites with an optimized coefficient of friction associated with a low wear rate both in nitrogen and air atmospheres. Through adequate control of the lubricant’s particle size, composition, and processing parameters, self-lubricating iron-based composites with a low dry coefficient of friction (0.07) and low wear rate (5 × 10−6 mm3·N−1·m−1) were achieved., In this work, self-lubricating composites containing MoS₂ and graphite dispersed in an iron matrix were produced by powder metallurgy and sintering. Previous studies demonstrate that MoS₂ reacts with iron matrixes during sintering, making the production of Fe-MoS₂ composites rather difficult. Therefore, this study focused on a potential solution to avoid or reduce this reaction, whilst still providing good tribological properties. Our results show that the addition of graphite retards the reaction of MoS₂ with iron and that the combination of MoS₂ + graphite results in composites with an optimized coefficient of friction associated with a low wear rate both in nitrogen and air atmospheres. Through adequate control of the lubricant’s particle size, composition, and processing parameters, self-lubricating iron-based composites with a low dry coefficient of friction (0.07) and low wear rate (5 x 10⁻⁶ mm³ .N⁻¹.m⁻¹) were achieved., Conselho Nacional de Desenvolvimento Científico e Tecnológico, Brazil

In this preliminary study, a set of self-lubricating copper-tungsten disulfide (Cu-WS₂) composites are prepared via a powder metallurgy route to analyze the effects of solid lubricant concentration on their tribological, electrical and wettability properties. An extensive characterization is performed to preliminarily assess the potential application of these metal matrix composites (MMCs) in sliding electrical contacts working under harsh conditions. The experimental results reveal the beneficial effect of WS₂ on the wear behavior of the prepared composites, as demonstrated by friction coefficient, specific wear rate and wear coefficients results. A second phase content in the 10–15 wt% range appears to guarantee the better combination of the desired features.

Polytetrafluoroethylene (PTFE) has shown an outstanding lubricity as a solid lubricant, but its application is limited due to its low-mechanical strength and high-wear rate. In this study, core-shell nanoparticles were synthesized using PTFE as the core and polymethylmethacrylate (PMMA) as the shell. The formed core-shell nanocomposites by leveraging the core-shell nanoparticles as basic structural units exhibit remarkable enhancement on uniformity, tensile strength, and wear resistance, compared to mechanically mixed composites with the same composition. Our experiments demonstrated the following results: (1) Owing to the excellent uniformity, the maximum tensile strength of core-shell nanocomposites was 62 MPa, three times higher than that of mechanically mixed composites. (2) The composite matrix formed by PMMA shell had better reinforcement and protection effect on inner PTFE phase, resulting in a reduced wear rate of 0.3 × 10−5 mm3/(N m), one order of magnitude lower than that of mechanically mixed composites. (3) The friction coefficient and interfacial mechanical properties of the core-shell nanocomposites at different temperatures have been systematically studied to get insights into lubrication mechanisms. It is proved that the temperature can decrease the modulus and increase the interfacial adhesion as well as the loss tangent of the core-shell nanocomposites, thus affecting the lubrication properties in multiple ways., QC 20201209

The potential use of two-dimensional (2D) materials as solid lubricants in micro-and nano-scale mechanical systems draws significant attention, mainly due to the fact that liquid based lubrication schemes fail at such small length scales. Within this context, the lamellar material molybdenum disulfide (MoS2), in the form of a single or few layers, emerges as a promising candidate for the solid lubrication of small-scale mechanical systems.Motivated as above, this thesis focuses on the nanotribological properties of mechanically exfoliated MoS2, explored via state-of-the-art atomic force microscopy (AFM) experiments. First, the dependence of friction force on sliding speed is investigated for single-layer and bulk MoS2 samples. The results demonstrate that (i) friction forces increase logarithmically with respect to sliding speed, (ii) there is no correlation between the speed dependence of friction and the number of layers of MoS2, and (iii) changes in the speed dependence of friction can be attributed to changes in the physical characteristics of the AFM probe. The direction dependence (i.e. anisotropy) of friction on MoS2 is studied next. In particular, high-resolution AFM measurements conducted by our collaborators at McGill University lead to the direct imaging of atomic-scale ripples on few-layer MoS2 samples, allowing to explain the various symmetries for friction anisotropy that are observed in our experiments as a function of scan size. Finally, the nanotribological properties of Re-doped MoS2 are studied, revealing a surprising, inverse dependence of friction force on number of layers, in contradiction with the seemingly universal trend of decreasing friction with increasing number of layers on 2D materials. Attempts are made to uncover the physical mechanisms behind this striking observation by way of roughness and adhesion measurements.In summary, the results reported in this thesis contribute to the formation of a comprehensive, mechanistic understanding

A dynamic model based on mass balance of fine aerosol particles was developed in order to tackle the problem of accurate quantification of mechanically stimulated particle emission (MSPE) from nanofunctionalized and solid lubricating materials. In contrast to the conventional approach, the model accounts for the effect of air turbulization caused by moving parts of the experimental tribological setup on the enhancement of particle deposition velocity. The increase of the velocity of the moving parts results in an increase of the deposition velocity that leads to a significant underestimation of experimentally measured particle emission rates. The developed model was experimentally verified using natural and artificial nanoparticle aerosols. Finally, the new methodology of particle emission rate quantification was employed for the analysis of fine particle emission produced when the solid lubricating materials were tested against a sliding steel surface. The developed method paves the way for defining a standard method of experimental assessment of nanoparticle triboemission enabling the experimental results obtained in various laboratories to be compared. It also bridges the gap between the phenomenological models and experimental measurements.

Nowadays, hydropower plants are forced to have more frequent power control and the self-lubricated bearings used in the applications are one of the most critical components affected by the continuously changing operating conditions. In this study, microstructure and composition of two commercially available bearing materials (Orkot TXM Marine and Thordon ThorPlas) used in hydropower turbines were studied. In addition, the influence of sliding speed and applied pressure on the friction and wear behavior of the materials was investigated systematically for dry sliding conditions. The bearing materials were characterized using X-ray microtomography, Nuclear Magnetic Resonance (NMR) spectroscopy and Inductively Coupled Plasma–Sector Field Mass Spectrometry (ICP-SFMS) techniques. Friction and wear tests were carried out with a polymer pin sliding against a stainless steel (SS2333) plate with a linear reciprocating motion. Test conditions were: room temperature, 9–28 MPa pressure and 10–40 mm/s sliding speed ranges. Surface analysis of the polymer pins and the wear tracks were performed by optical profilometry, Scanning Electron Microscope (SEM) and Energy Dispersive Spectroscopy (EDS) techniques. Test results show that, for both materials, the coefficient of friction (COF) is decreasing at higher pressures. Surface analysis reveals higher concentrations of solid lubricants in the transfer layers formed at higher pressures, explaining the decrease in COF. Furthermore, the specific wear rate coefficients are increasing at higher sliding speeds, especially at lower pressures. Results of this study demonstrate that, under dry sliding conditions, changes in sliding speed and pressure have a significant influence on the tribological behavior of these bearing materials., Validerad;2018;Nivå 2;2018-05-02 (andbra)

Mechanical components operating at elevated temperatures can be identified in the aerospace industry as well as in metal forming. Hot stamping is a metal forming technique utilized for manufacturing high strength lightweight components for the automotive industry. Three types of Ni-based hardfacings doped with solid lubricants were manufactured using laser cladding. An additional hardfacing was also manufactured using the Ni-based alloy only as a reference. Solid lubricants added were Ag+WS2, WS2 and Cu+MoS2. These hardfacings were manufactured and tribologically evaluated for potential application in hot stamping tooling. Direct diode laser was used for the cladding process. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were used for characterization of the microstructure after deposition. Tribological testing was done using a reciprocating pin-on-disk tribometer under dry sliding conditions at temperatures in the range between RT and 600°C. Bearing steel ball and a flat pin made of the same material were used as counterbodies. Wear volume loss was measured using a 3D optical interferometer. For identification of the wear mechanisms SEM/EDS techniqueswere used. Formation of a lubricious CrxSy phase was detected after deposition, additionally encapsulation of silver particles by CrxSy was also observed. Reduction of friction coefficient was observed for every self-lubricating hardfacing compared to the reference. Lowest friction coefficient (0.23-0.3) was observed when the testing temperature was set to 400°C using a pin-on-flat configuration. Lowest wear rate was observed at 400°C, with the coating containing Ag and WS2 having a specific wear rate of 3.04 · 10−5mm3/Nm. The lubricity of the self-lubricating hardfacings was attributed to the CrxSy phase observed on the worn surface. At low to moderate temperatures abrasive wear is the main wear mechanism. At the highest testing temperature, oxidative wear was dominant.

The increased use of high and ultra-high strength steel and materials with a high adhesion tendency leads to higher demands regarding the wear resistance of forming tools. A promising approach addressing both challenges is to apply MoS2 dry film lubricant coating systems to the tool surface. These coatings reduce friction and the use of drawing oils and can also be used as an abherent. Once these coatings are exhausted, they can be chemically removed and reapplied. However, the tool life of the coatings cannot be predicted properly, due to their inhomogeneous wear behavior which depends on the forming parameters and differs locally. Moreover, there are carryover effects of MoS2-particles to already ablated areas. Given the unpredictability of the wear of dry film lubricant coatings, it is not possible to plan the recoating cycles appropriately and thus, the potential of these coatings for commercial applications is limited. In this research, the wear behavior of MoS2-layers in deep drawing processes was investigated on a test stand with DP800+Z coil material which ensures realistic load conditions at the draw ring radius. Firstly, the wear pattern was determined and locally different contact pressures were recorded and assigned to respective wear areas. Due to bending effects of the sheet material, there are two major areas of wear on the draw ring radius. During wear tests, the wear-dependent coating thickness during wear initiation was determined by using 3D laser scanning microscopy and the friction force was evaluated. © 2017 The Authors.

We thank G. Glasser, G. Scha¨fer, T. Schuster and M. Wagner for technical support, and K. Varanasi, T. Kajiya and G. Auernhammer for stimulating discussions, and J. Pham for carefully reading the manuscript. Financial support from SPP 1420 (H.J.B.), COST1106 (D.V.), and ERC grant SuPro (H.J.B.) is gratefully acknowledged., For a liquid droplet to slide down a solid planar surface, the surface usually has to be tilted above a critical angle of approximately 10°. By contrast, droplets of nearly any liquid “slip” on lubricant-infused textured surfaces – so termed slippery surfaces – when tilted by only a few degrees. The mechanism of how the lubricant alters the static and dynamic properties of the drop remains elusive because the drop–lubricant interface is hidden. Here, we image the shape of drops on lubricant-infused surfaces by laser scanning confocal microscopy. The contact angle of the drop–lubricant interface with the substrate exceeds 140°, although macroscopic contour images suggest angles as low as 60°. Confocal microscopy of moving drops reveals fundamentally different processes at the front and rear. Drops recede via discrete depinning events from surface protrusions at a defined receding contact angle, whereas the advancing contact angle is 180°. Drops slide easily, as the apparent contact angles with the substrate are high and the drop–lubricant interfacial tension is typically lower than the drop–air interfacial tension. Slippery surfaces resemble superhydrophobic surfaces with two main differences: drops on a slippery surface are surrounded by a wetting ridge of adjustable height and the air underneath the drop in the case of a superhydrophobic surface is replaced by lubricant in the case of a slippery surface., European Commission, Depto. de Ingeniería Química y de Materiales, Fac. de Ciencias Químicas, TRUE, pub

In order to obtain the deterioration characteristics data of each sample exposed to ultraviolet radiation, atomic oxygen and radiation which is the orbital environment elements and the control data to estimate the effects of each orbital environment elements on the samples, ground control test and sample analysis before and after the experiments were carried out. Samples used were solid lubricants, CFRP (Carbon Fiber Reinforced Plastics), glass materials, polyimide, Teflon, and other. Analytical items were mass change before and after radiation, a change of surface optical characteristics and a surface analysis., 試料の軌道上環境要素である紫外線、原子状酸素および放射線による劣化特性のデータおよび軌道上での各環境要素が試料に与える影響を評価するための対照データの取得を目的として、地上対照試験および試験前後の試料の分析を実施した。使用した材料は、固体潤滑剤、CFRP(炭素繊維強化プラスチック)、ガラス材、ポリイミド、テフロンなどである。分析項目は照射前後の質量変化、表面光学特性の変化、表面分析である。

In this work, the effect of swirl to tumble ratio on homogeneity, turbulence and mixing in a generic heavy duty Diesel engine during compression, is investigated using Large-Eddy Simulations. The main conclusion is that the relative importance of dilatation (relative volume change) increases whereas the effect of tumble breakdown decreases with the swirl to tumble ratio. In detail, we show that an increase in tumble raises the peak turbulence level and shifts the peak to earlier crank angles, which in turn leads to higher dissipation. Moreover, maximum turbulence level at top dead center is obtained for a combination of swirl and tumble rather than for pure tumble. Furthermore, it is observed that the peak turbulent kinetic energy displays levels three times greater than the initial kinetic energy of the tumble motion. Thus, energy is added to the flow (turbulence) by the piston through generation of vorticity by vorticity-dilatation interaction. Also, the intermediate swirl/tumble ratios are found to introduce large non-uniformity in the flow field, leading to a non-solid body like rotation. Swirl/tumble (tilt) angles larger than 19°are necessary for complete mixing of the gas within the engine cylinder. Taken together, the combined effect of a combination of swirl and tumble turbulence during compression is investigated. This knowledge is important both for engine development as well as more theoretical aspects regarding the breakdown of large scale structures in an engine., QC 20151123

Práce je věnována hodnocení tuhých maziv pro kontaktní zatížení kolo-kolejnice. Navrhuje novou metodiku pro rychlou analýzu vybraných tuhých maziv. Práce se dále zabývá návrhem a hodnocením vhodných přípravků na zkoušku. Součástí je i provedení, vyhodnocení a posouzení vhodnosti zkoušek pro rychlé rozlišení rozdílů tuhých maziv., The work is dedicated to the evaluation of solid lubricants for contact wheel-rail loads. It proposes a new methodology for the rapid analysis of selected solid lubricants. The paper focuses on the design and evaluation of suitable preparations for the exam. It also includes the design, evaluation and assessment of the suitability test for the rapid resolution of differences solid lubricants., Katedra dopravních prostředků a diagnostiky, Student seznámil zkušební komisi se svojí bakalářskou prací, která byla věnována hodnocení tuhých maziv pro kontaktní zatížení kolo-kolejnice. V práci je navržena nová metodika pro rychlou analýzu vybraných tuhých maziv. Na otázky student zodpověděl vyhovujícím způsobem.

The results of the investigation of the peculiarities of formation of anti-friction coatings, capable of working in conditions of dry friction and high temperatures, which contain solid lubricants (C, CaF2, FemOn) are presented. The effect of thermal spray methods, type of spray material and the amount of solid lubricant on the phase composition, structure and properties of coatings is investigated.

As a result of studies, operating conditions of friction pairs of axial piston hydromachine parts were examined and real ways to use a number of tribological techniques to improve their performance were shown. It was found that the most simple methods that increase the performance of the friction units of axial-piston hydromachines, are using surfactants in hydraulic oil, creating conditions for the manifestation of the selective transfer with forming a thin copper film on the steel parts and using mobile insertions of active materials. A summary table with the main advantages of the considered unconventional methods that improve the running-in quality of axial-piston hydromachine parts and their friction units, which is of practical value for the operators and industrialists during repair works was given. The main advantages and disadvantages of unconventional methods, applicable for improving axial piston hydromachine durability were shown. So using surface active liquid additives increases wear resistance by 3 times, load-bearing capacity by about 2 times with the possibility to replace bronze with steel. Creating conditions for selective transfer provides smaller parameters that increase hydromachine performance and requires another liquid lubricating medium such as glycerin. A more efficient method is using special active solid lubricants, which allows not only to abandon hydrocylinder bronze blocks, replacing them with steel, but also enhance the durability up to 5 times, and fluid working pressure up to 400 atmospheres. This compensates for the costs, associated with manufacturing narrow pockets for a solid lubricant.

Solid lubricants are required in applications where traditional lubricants are precluded by challenging environmental conditions (e.g. space). However, the mechanisms that enable low friction and low wear sliding of these systems remain poorly understood. Recent studies have demonstrated low friction sliding is consistently accompanied by nanoscale tribo-films whose properties and contributions to friction reduction are unknown. The goal of this study was to elucidate the role of nanoscale tribofilms in friction and wear reduction by correlating macroscale tribological properties with the results of in-situ measurements of transfer film morphology, chemistry, and nanomechanical properties. The materials included molybdenum disulfide (MoS2) and polytetrafluoroethylene (PTFE), two very different but well studied and heavily used solid lubricants known for exceptional tribological characteristics. The tools used for the study included in-situ optical microscopy (morphology), interferometry (topography), and lateral force microscopy (tribology). A significant portion of the work was the development of a lateral force microscopy (LFM) calibration technique to enable quantitative and in-situ LFM measurements., The original document contains color images.

During this program, we have worked to develop a fundamental understanding of the chemical and tribological issues related to the implementation of layered solid lubricants in aerospace mechanisms. The work has entailed chemical studies performed from a surface analytical approach, tribological measurements performed over a range of length scales, and the correlation of the two classes of information. Research activities have focused on the properties of single crystal MoS2 and PbS and the implementation of a UHV tribometer being used to explore the properties of MoS2 containing composite films.

Solid lubricant coatings with co-sputtered metal and MoS2 have shown favorable macrotribological properties at a wide range of contact stresses and humidity levels. These materials are also candidates for use in microcontacts and micro-electromechanical systems (MEMS), but their performance at this scale is poorly understood. For this study, microtribological properties of Au-MoS2 and Ti-MoS2 coatings, with varying metal additives of less than 15 at%, were examined using a nanoindentation instrument. Titanium and gold were chosen for this study as metal additives due to their different influence on the mechanical properties of the coating. The hardness and reduced modulus of the coatings increased with the addition of metal, when compared to pure MoS2. Reciprocating microscratch tests were performed with two spherical diamond tips (50 and 10//m radii) in dry air. A range of normal loads were used between 0.2 and 5.0 mN. Friction and wear measurements were analyzed with respect to the variation in the contact pressure and compared to literature studies performed at the macroscale. Correlations were found between the coating mechanical properties, tip-coating adhesion, interfacial shear strength, and the formation of transfer films and tribofilms., Originally published in Tribology Letters, v40 p199-211, 2010.

Hydrogen-free, hard carbon thin films are exciting material coatings candidates as solid lubricants. Two examples, ultrananocrystalline diamond (UNCD) and tetrahedral amorphous carbon (ta-C), are particularly promising, because their exceptional mechanical and tribological properties are combined with extremely smooth surfaces. However, their tribological performance can be seriously affected by variations in humidity. The mechanisms controlling the friction and wear of UNCD and ta-C are not well understood because of a lack of physical understanding of the surface interactions. The aim of this thesis is to elucidate the fundamental mechanisms of friction and wear in UNCD and ta-C films. An experimental protocol is defined to examine the relationship between the sliding environment, tribological performance, and mechanical and chemical changes to the films. Self-mated reciprocating tribometry in controlled environments measure UNCD and ta-C friction as a function of load and relative humidity (RH). Scanning white light interferometry measures the post-mortem height profile. Finally, chemical changes inside the wear track are characterized by x-ray photoelectron emission microscopy combined with near-edge x-ray absorption fine structure (X-PEEM-NEXAFS) spectromicroscopy. Results for ta-C and UNCD show that both films perform better at lower loads or with higher amounts of RH. Previous hypotheses for this suggested that lubrication for these films either comes in the form of graphitization (converting carbon from diamond-type bonding to graphite-like bonding) or by passivation (the termination of broken carbon bonds by species in the environment, such as water). All spectroscopic evidence shows no evidence of graphitization, but support the passivation hypothesis. Furthermore, the spectroscopy shows that the passivation is in the form of hydroxyl groups, most likely from water.

[EN] Can making is an enormous industry, and technical advances that improve the economy or environmental situation in this industry can have huge impact as a result. The use of polymer coatings on steel can result in successful ironing without any additional lubricants, and leads to reduction in volatile organic compound exhaust. This paper investigates the use of a three-layer polymer laminate coated steel, and demonstrates the good ironability that can be achieved, while presenting superior coatings for decoration. Two materials are investigated at a range of die angles, temperatures and speeds, and the resultant surface is evaluated to judge ironability. Consistent with previous results, good ironability is achieved with low die angles and cool tooling.

Microtribological measurements of a hydrogenated diamondlike carbon film in controlled gaseous environments show that water vapor plays a significant role in the friction coefficient. These experiments reveal an initial high friction transient behavior that does not reoccur even after extended periods of exposure to low partial pressures of H2O and O2. Experiments varying both water vapor pressure and sample temperature show trends of a decreasing friction coefficient as a function of both the decreasing water vapor pressure and the increasing substrate temperature. Theses trends are examined with regard to first order gas-surface interactions. Model fits give activation energies on the order of 40 kJ/mol, which is consistent with water vapor desorption., Published in Journal of Tribology, v131 article 032102, Jul 2009. Prepared in collaboration with Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, FL.

Double oxide phases that combine a transition metal and a noble metal have recently become a subject of investigation as potential lubricious materials for high temperature tribological applications. Two selected double metal oxide phases, namely silver molybdates and tungstates, were produced in thin film and powder forms using magnetron sputtering and hydrothermal methods, respectively. The lowest frictional properties of these materials were measured at 600 degrees C to be 0.1 and 0.4 for the Ag2Mo2O7 and alpha-Ag2WO4 phases, respectively. Changes in the chemistry and crystal structure of these materials were investigated with increasing the temperature up to 600 degrees C using in-situ Raman spectroscopy, X-Ray diffraction and a differential scanning calorimeter. These tools revealed that the coatings went through a phase transition accompanied by a phase segregation of silver. Simulations performed to investigate the structural and thermal properties of these materials using ab-initio molecular dynamics (AIMD) method were in agreement with the experimental results. The structural and chemical information obtained using computational and experimental studies was correlated to their high temperature tribological performance. Moreover, a new double metal oxide based on the Ag-V-O system was created and tested at very high temperatures. This system was found to be lubricious (friction coefficient of 0.1) at temperatures as high as 1000 degrees C. This is a significant result given that this is the first solid lubricant that was found to perform well at these extreme temperatures. This finding will enable the design of new military machinery that operates at these high temperatures. Potential applications include solid lubrication for small caliber barrel and weapon action components, EM Gun rail materials, and helicopter engines., The original document contains color images.

Transmission and scanning electron microscopy studies of tungsten disulphide nanomaterials revealed nanotubes and onion-like structures. An electron diffraction pattern confirmed the lattice image of this nanotube. The tungsten disulphide nanomaterials exhibiting this kind of nanotubes will be useful as solid lubricant materials., The original document contains color images. All DTIC reproductions will be in black and white.

This program objective is to "Provide high purity optical materials for High Energy Lasers and Transparencies". Recent announcements by Japanese workers of poly crystalline ceramic high-energy laser media have expanded the horizons of possibility of solid state high energy lasers (HELs). The ceramic approach breaks bounds of size and cost previously imposed by the necessity of using only single crystals for lasing media., Submitted for publicaton in the Journal Composites Science Technology.

The U.S. Army Technology Exploitation/Exploration/Examination (TEX3) Program is funding efforts to determine how recent advances in nanotechnology can be of benefit to the military. One particular area of interest is nanocomposite thin films and coatings, a source of considerable study in recent years. Nanocomposites generally combine one or more nanocrystalline phases in a functional matrix to provide improved mechanical properties, corrosion resistance, and/or thermal stability. One example of this is the combination of a soft solid lubricating phase with a hard wear resistant matrix to provide improved wear resistance. Solid lubrication is of significant interest due to the significant problems posed by use of conventional lubricants in desert environments. The goal of this work is to determine how deposition conditions relate to the morphological evolution of the nanostructure of a specific CrN-Ag model nanocomposite system and how these nanostructures correlate to mechanical and adaptive lubrication properties.

Studies to explore the nature of friction, and in particular thermally activated friction in macroscopic tribology have lead to a series of experiments on thin coatings of molybdenum disulfide. Coatings of predominately molybdenum disulfide were selected for these experiments; five different coatings were used: MoS(2)/Ni, MoS(2)/Ti, MoS(2)/Sb2O3, MoS(2)/C/Sb2O3, and MoS(2)/Au/Sb(2)O(3). The temperatures were varied over a range from -80 deg C to 180 deg C. The friction coefficients tended to increase with decreasing temperature. Activation energies were estimated to be between 2 and 10 kJ/mol from data fitting with an Arrhenius function. Subsequent room temperature wear rate measurements of these films under dry nitrogen conditions at ambient temperature demonstrated that the steady-state wear behavior of these coatings varied dramatically over a range of K = 7 x 10(-6) to 2 x 10(-8) mm(3)/(Nm). It was further shown that an inverse relationship between wear rate and the sensitivity of friction coefficient with temperature exists. The highest wear-rate coatings showed nearly athermal friction behavior while the most wear resistant coatings showed thermally activated behavior. Finally, it is hypothesized that thermally activated behavior in macroscopic tribology is reserved for systems with stable interfaces and ultra-low wear, and athermal behavior is characteristic to systems experiencing gross wear., Published in Tribology Letters p1-6, 2008.

This report results from a contract tasking Kharkov Institute of Physics and Technology as follows: Development of new plasma deposition methods is critical for nanocomposite and nanostructured material growth. For example, to address the issues of ambient/space cycling, high-temperature lubrication, and reliability of space and air vehicles, new advanced coatings were developed by AFRL which need a combination of ceramic matrices and solid lubricant inclusions. This research project is directed to develop and optimize power supply for filtered vacuum arc generator located at AFRL/MLBT to enable the production of such unique composite coatings. In particular, the new power unit will provide a stable plasma filtering and delivery into synthesis chamber under conditions of strong magnetic fields for dielectric material growth. The commercially available technology is not capable of such task, due to a lack of understanding and control of the power supply current-voltage characteristics for non-metallic ionic current and density distributions in the arc plasma. This research project will tap the unique expertise of Ukrainian scientists in filtered vacuum arc technology, which was invented in Dr. Strelnitskiy's group. AFRL is currently evaluating the technology benefits for various tribological applications in both air and space vehicles. The new development suggested by this project will expand the range of materials to include insulating ceramic matrices, such as AL2O3 and ZrO2, for preparation of nanocomposite and nanostructured tribological coatings. This will provide a new capability for AFRL research in advanced wear and friction reducing coatings for aerospace. The project includes transfer of the research results, developed equipment, and technological procedures for the use in AFRL/MLBT research and development programs., The original document contains color images. STCU Registration No. P-251.

A new test rig is designed to evaluate the start-stop cyclic durability of high-temperature solid lubricant coatings applied to foil thrust bearing systems. This test rig also allows the characterization of low speed thrust bearing performance, augmenting existing high speed test capabilities. The Low-Speed Thrust Bearing Rig is designed to test foil thrust bearings at speeds up to 21,000 rpm and temperatures up to 540 deg C (1000 deg F), with variable thrust loads. Thrust bearings can be subjected to tens of thousand of start-stop cycles to simulate decades of service in a turbomachinery application. Initial testing has validated the rig capabilities by subjecting a bearing and thrust runner to more than two thousand start/stop cycles at a temperature of 430 deg C (800 deg F)., The original document contains color images.

Cold Spray or High-Velocity-Particle-Consolidation (HVPC) is a relatively new coating method for the deposition of metals, alloys, polymers, and composite powder-materials onto various substrates without significant heating of the spray powders or substrates. Due to the use of low temperatures and absence of in-flight oxidation and other chemical reactions, thermally vulnerable materials can be deposited without significant material degradation. Given these clear advantages, the objectives of the research detailed herein was to develop self-lubricating composite coatings by using HVPC. For the matrix phase, Nickel was selected due to its success against Ti, as well as its relatively high hardness and wear resistance. Molybdenum-disulfide (MoS2) and Boron Nitride (BN) were employed as the lubricants because of their excellent solid lubricating properties. Admixed, mechanically milled, and pre-coated lube particles were all studied as feedstock powders. The developed coatings were characterized for the distribution of lubricant and presence of porosity using microscopy; coatings with the highest and most homogeneous lubricant distributions were also analyzed for micro-hardness, wear, and bond-strength. Based on the above analysis, it was concluded that the HVPC process can be used for the development of Ni-BN composite coatings with comparable hardness and adhesive strengths relative to Ni coatings. Results indicated a slight reduction of friction that suggest greater amounts of lubricant are required in the coatings. This in turn suggests that, improved coatings may be best achieved by shrinking the size of the lubricant particle and increasing the thickness of the Ni coating. This was the major directive of the research detailed in Part II of this report.

This research in support of the Air Force Research Laboratory, Materials and Manufacturing Directorate was conducted at Wright-Patterson AFB, Ohio from 19 May 2003 through 30 November 2006. This task examined fretting wear that is an accumulation of damage that occurs at component interfaces that are subjected to high contact stresses coupled with low amplitude oscillation. In the titanium dovetail joints of turbine engines, fretting wear can be severe. Surface treatments, such as plasma sprayed coatings and solid lubricants, have been implemented to mitigate the fretting wear problem. However, the current coating systems are reliant primarily on the applied lubricant. Once the lubricant is worn away the soft plasma sprayed coating is exposed and can damage the mated Ti6Al4V surface. Therefore the blades using the current coating systems need to be replaced before the lubricants are worn completely away, which results in high maintenance costs from schedule based periodic blade replacement.

M-50 and carburized Pyrowear 675(registered) steel coupons deposited with commercially available physical vapor deposited (PVD) TiN, TiCN, TiAlCN, TiCrCN/TiB4C multilayer, electroless Ni (E-Ni) TiN, and E-Ni TiCN coatings were immersed in a branched perfluoropolyalklyether (PFPAE), Krytox AC(registered), in an oxidative environment at temperatures ranging from 315 to 360 deg C for a duration of 24 hours and compared to uncoated coupons. Coated and uncoated Pyrowear 675(registered) coupons demonstrated superior corrosion resistance compared to coated and uncoated M-50, respectively. The coatings most resistant to chemical attack in the PFPAE fluid were TiCN, E-Ni TiN, and E-Ni TiCN., Prepared in collaboration with Tribologix, Springboro, OH. Published in the Journal of Synthetic Lubrication, v24, n1, p1-17, Dec 2006.

This program has three sub-tasks: 1) Nitride Thin-Film Coatings, 2) Advanced Plasma Diagnostics, and 3) Studies of Charged-Particle Processes. The focus of Task 1 has been to develop amorphous carbon-nitride films utilizing controlled plasma-generated ions to increase the nitrogen concentration within the film. It is anticipated that development of films with higher concentrations of nitrogen will lead to properties similar to those theoretically calculated for crystalline β-C3N4. Successful development of this film will facilitate the creation of a smooth, extremely hard, thermally stable amorphous film. Applications can include hard-coating protection, solid lubricants, reduced friction and wear coatings, thermal heat spreaders, and high-temperature dielectrics. In Task 2 advanced diagnostics of plasmas with various operating conditions have been performed to gain a better understanding of the generated plasma fields. Task 3 has utilized Fourier Transform Mass Spectrometry (FTMS) to investigate gas-phase reactions of charged particles. Ion chemistries have been studied in selected compounds of great interest in areas including plasma processing and combustion. Cross sections of electron-impact ionization of these compounds have been measured and the kinetics of the reactions between the ions and their parent molecules examined.

Slip-ring assemblies for spacecraft, and other sliding electrical contacts, require low friction and wear, as well as low electrical resistance and noise. Most current slip-ring technologies (both solid- and liquid-lubricated) are over forty years old, and their robustness is often less than satisfactory. Newer technologies have been developed, but have also shown limitations in spacecraft applications. We are investigating alternate material technologies to address these issues, concentrating on sputter-deposition of metals (e.g., gold) containing solid lubricants (e.g., MoS2) to form electrically conductive, lubricious nanocomposite films. In the present study, we investigated the friction and endurance of co-sputtered Au/MoS2 films in sliding contact in N2 gas at different contact stresses. Seven different film compositions were studied. Films with higher metal contents were found to perform especially well at low contact stresses, which is the regime where sliding electrical contacts operate (i.e., <1 MPa). Auger Nanoprobe analysis was used to reveal how low friction is produced, even at contact stresses well below that usually used in MoS2-lubricated systems., The material reproduced in this report originally appeared in Tribology Letters. The TR is published to document the work for the corporate record.

A series of tests was performed to determine the internal temperature profile in a compliant bump-type foil journal air bearing operating at room temperature under various speeds and load conditions. The temperature profile was collected by instrumenting a foil bearing with nine, type K thermocouples arranged in the center and along the bearing's edges in order to measure local temperatures and estimate thermal gradients in the axial and circumferential directions. To facilitate the measurement of maximum temperatures from viscous shearing in the air film, the thermocouples were tack welded to the backside of the bumps that were in direct contact with the top foil. The mating journal was coated with a high temperature solid lubricant that, together with the bearing, underwent high temperature start-stop cycles to produce a smooth, steady-state mn-in surface. Tests were conducted at speeds from 20 to 50 krpm and loads ranging from 9 to 222 N. The results indicate that, over the conditions tested, both journal rotational speed and radial load are responsible for heat generation with speed playing a more significant role in the magnitude of the temperatures. The temperature distribution was nearly symmetric about the bearing center at 20 and 30 krpm but became slightly skewed toward one side at 40 and 50 krpm. Surprisingly, the maximum temperatures did not occur at the bearing edge where the minimum film thickness is expected but rather in the middle of the bearing where analytical investigations have predicted the air film to be much thicker. Thermal gradients were common during testing and were strongest in the axial direction from the middle of the bearing to its edges, reaching 3.78 degrees C/mm. The temperature profile indicated the circumferential thermal gradients were negligible., The original document contains color images. All DTIC reproductions will be in black and white. Prepared in collaboration with Purdue Univ., West Lafayette, IN. NASA grant no. WBS-22-714-09-17.

The objective of this program was to design and develop a novel hybrid coating technology and related infrastructure for the synthesis of soft phase and hard phase nano particle composite coatings. The project successfully completed design, development and testing of the following two major technologies: (1) Electrostatic coating (ESC) set up for the deposition of solid lubricant as well as hard phase nano particles; (2) Chemical vapor infiltration (CVI) for depositing binder in the porous matrix. The investigators have successfully developed and tested the ESC system for coating lubricant as well as hard nano particles on large areas and complex shapes, and have completed fabrication and testing of the CVI set up. To demonstrate the success of completion of the project, the team has deposited ZnO (0-20 nm) as well as MoS2 (0-700 nm) nano particles as soft lubricant materials and cBN as hard phase material using ESC on complex geometries (carbide insert samples) and has demonstrated TiN infiltration. The research opened many new opportunities to realize practical combinatorial coatings for the next generation of Air Force, Department of Defense (DoD) devices and systems.

This revision to the Joint Test Report for Validation of Alternatives to Lead-Containing Dry Film Lubricants for Antigalling/Antifretting, Antiseizing, and Assembly Aid Applications includes an additional test requirement for humidity resistance. This requirement was identified by turbine engine original equipment manufacturers based on experience in evaluating water-based dry film lubricants (DFLs) for antigalling/antifretting applications. Exposure of some DFLs to hot, humid conditions has the potential to rehydrate the binder, rendering the DFL as a "wet" coating that is susceptible to removal. This report was prepared by the NDCEE. This report was prepared on behalf of, and under guidance provided by the Propulsion Environmental Working Group (PEWG) and the Joint Group on Pollution Prevention (JG-PP). The structure, format, and depth of technical content of the report were determined by the JG-PP Working Group, PEWG, original equipment manufacturers, and other Government technical representatives in response to the specific needs of this project., Engineering and Technical Services for Joint Group on Acquisition Pollution Prevention (JG-PP). Sponsor report no. NDCEE-CR-2004-013.

The objective was primarily to utilize the newly developed Air Force super-hard coating process technologies in practical applications, such as turbine engine rotor components, precision shafts and ball bearings, and bearing races. This would give the Air Force the capability of practically coating real precision mechanical parts with solid lubricant films of the highest toughness. These films would be of the highest hardness and the most resilient to damage, extending the life of high cost precision aircraft components. This is driven by the fact that the primary cost in producing aircraft components is the precision machining required., The original document contains color images.

Solid-lubricant coatings for sliding electrical contact applications like slip-ring assemblies have very different requirements from typical applications like ball bearings and cutting tools: they have significantly lower contact stresses and sliding speeds. We are optimizing the performance of sputter-deposited nanocomposite Au-MoS2 films for such low con tact stress applications. Higher contact stress pin-on-disk tests (S(sub m) = 730 MPa) showed that low Au-MoS2 films (i.e., 22 to 38 at% Au) outperformed those with higher Au content (i.e. greater or equal to 55 at% Au). In contrast, low contact stress disk-on-disk tests (S(sub m) ^ 0.3 MPa) showed that higher Au-content films outperformed low Au-MoS2 films. These results, along with Auger Nanoprobe post-test analysis, indicate that Au provides structural integrity for the films in the high-contact-stress tests, while optimizing the MoS2 transfer rate in the low-contact-stress tests. The results are promising for sliding electrical contacts because high-Au films not only perform the best tribologically, but also exhibit the highest electrical conductivity., The original document contains color images. All DTIC reproductions will be in black and white. Briefing charts only.

Cesium oxythiomolybdate (Cs2MoOS3) is under consideration as a high temperature solid lubricant for silicon nitride bearings. However, Cs2MoOS3oxidizes below the proposed maximum use temperature of 800 ˚C, and the oxidation process is complex. In the presence of silicon nitride, the oxidation reactions change. The purpose of the present research was to determine the chemistry of Cs2MoOS3 coatings grown by pulsed laser deposition (PLD) on several substrates (Si3N4, SiC, Inconel, Al2O3 and ZrO2), and to determine the changes in chemistry and crystal structure after annealing in air to temperatures up to 800 ˚C. Many of the oxidation products identified are expected to be lubricious at elevated temperatures., The original document contains color images. Pub. in Thin Solid Films v406 p164-173, 2002.

The sliding friction and wear of silicon nitride was investigated in 600 deg C air using a ball-on-disk configuration. Two cesium-based inorganic films were studied as potential high-temperature solid lubricants for limited-life turbine engine bearing applications: a sodium silicate bonded Cs2WOS3 coating and a cesium silicate chemical reaction film. Wear surfaces were characterized using various analytical techniques. The best tribological performance was obtained with thin chemical reaction films annealed in sulfur-rich air. Friction coefficients (f) and wear factors as low as 0.04 and 4 x 10(exp -9) cu mm/N.m respectively, were obtained at 600 deg C with this system. These are comparable to boundary liquid lubricating films at much lower temperatures. The data provide conclusive evidence that neither tungsten nor molybdenum is necessary for low friction at 600 deg C. The results also suggest that sulfur and cesium play important roles in the formation of a lubricious silicate film by chemically reacting with the silicon dioxide scale that naturally forms on silicon nitride surfaces. This occurs via a complex hot-corrosion mechanism involving the inward diffusion of oxygen from the surrounding air and cesium from the coatings and the outward diffusion of nitrogen and magnesium from the silicon nitride substrate. It is believed that sulfur provides a reaction path for the hot-corrosion mechanism.