Low Friction Properties Research Articles

209 気相合成ダイヤモンド膜と金属間の低摩擦特性における摺動速度依存性評価(学生賞IV,一般講演)

209 気相合成ダイヤモンド膜と金属間の低摩擦特性における摺動速度依存性評価(学生賞IV,一般講演)

Ultra Low Friction of DLC Coating with Lubricant

The objective of this study was to find a trigger to make clear a mechanism of the ultra low friction by evaluating the friction property of DLC-DLC combination under lubrication with the simple fluid. The Pin-on-disc reciprocating and rotating sliding tests were conducted to evaluate the friction property. The super low friction property of pure sliding with the ta-C(T) pair coated by the filtered arc deposition process under oleic acid lubrication was found at the mixed lubrication condition. It was thought that the low share strength tribofilm composed of water and acid seemed to be formed on ta-C sliding interface. Additionally, the smooth sliding surface formed on ta-C(T) was seemed to be required to keep this tribofilm. Then, the super low friction was thought to be obtained by this superlubrication condition. Although the accurate and direct experimental data must be required to make clear this super low friction mechanism, the advanced effect obtained by the simple material combination is expected to be applied on the large industrial fields in near future.

A low-friction high-load thrust bearing and the human hip joint

A hydrostatic thrust bearing operating at a pressure of 130 MPa and with a coefficient of friction rising to 0.004 in 6 days is described. It consists of interleaved oil-coated Mylar and brass sheets, each 0.1 mm thick. At this pressure, the Mylar deforms to reveal a pool of lubricant bounded by contacting layers at its edges where the pressure tapers off to zero. Thus, most of the load is borne by the oil so its effective Coulomb (slip–stick) friction is very low. Expressions for the effective coefficient of friction, the area of the solid-to-solid contact and the torque needed to rotate the bearing are given in terms of its geometry, the viscosity of the lubricant and elapsed time. The mechanism of a bearing with similar geometry and properties, the human hip joint, is compared with this plastic bearing. While their low friction properties arise from the same basic cause, the different natures of their soft deformable materials lead to the hip joint having a much wider range of action. This work is an example of new engineering leading to a fresh insight into an action of Nature, which in turn suggests an improvement in engineering.

Effect of Amide Molecular Structure on Tribological Properties of Thermoreversible Gel Lubricant

Thermoreversible gel lubricant (TR gel lube) has been developed as a unique new lubricant. TR gel lube contains a high percentage of aliphatic amide as a gel agent in the base fluid. It is able to repeatedly change from a gel state to a liquid state at the melting point. Therefore, the new lubricant is expected to be useful as an impregnant for porous tribomaterial. In previous research, the lubricants exhibited good lubricity and low friction properties. These tribological properties were depended on the molecular structure and content of amide gel agents. In this study, physicochemical properties of the TR gel lube were examined to discuss in detail the lubrication mechanism. It was revealed that TR gel lube indicated a soft gel compared with general grease by measuring dynamic viscoelasticity. Entropy changes of TR gel lubes were depended on the amide molecular structure by analyzing the thermo dynamical data. Lubricating mechanisms by oiliness effect of adsorbed gel agent and introducing to contact area were proposed.

Tribological Properties of Polymeric Composites Including Ionic Liquid and Its Application to Self-lubricating Coating

Polymeric composites, i.e. epoxy resin and polystyrene including an ionic liquid of BMImBF4 have been prepared and characterized in terms of their tribological properties. The addition of BMImBF4 up to 20 wt% has achieved to improve lubricity of the polymeric matrices in both air and vacuum without detrimentally degrading mechanical strength. BMImBF4 has been stored in pores distributing inside the polymeric matrices. As little chemical reaction between epoxy resin and BMImBF4 has revealed by Fourier transform infrared spectroscopy, BMImBF4 would work as a lubricant after seeping from the pores due to the transformation and/or the slight wear of the surface of the polymeric composites. Furthermore, coatings of the epoxy resin including BMImBF4 on silicon plates have shown low frictional properties regarding thickness raging from several to 600 μm. The coating has also performed self-lubrication on acrylic resin as well as steel previously coated with epoxy resin to avoid chemical reaction with BMImBF4.

Low friction properties of nano-structured C-Ni films prepared by thermionic vacuum arc method

Nano-structured C-Ni coatings were prepared using the thermionic vacuum arc method and tribological properties were evaluated in order to obtain carbon-metal layers to act as solid lubricants. The C-Ni films prepared by TVA method were characterised as a metallic complex of nano-crystals (5 nm average diameter) surrounded by carbon amorphous structures with a strong graphitisation tendency. The coefficients of friction of the coatings, measured using a CSM ball-on-disc tribometer, were in the range of 0.19-0.27 3-5 times lower than the uncoated substrates.

Texturing of UHMWPE surface via NIL for low friction and wear properties

Wear is a major obstacle limiting the useful life of implanted ultra-high molecular weight polyethylene (UHMWPE) components in total joint arthroplasty. It has been a continuous effort in the implant industry to reduce the frictional wear problem of UHMWPE by improving the structure, morphology and mechanical properties of the polymer. In this paper, a new paradigm that utilizes nanoimprint lithography (NIL) in producing textures on the surface of UHMWPE is proposed to efficiently improve the tribological properties of the polymer. Friction and wear experiments were conducted on patterned and controlled (non-patterned) UHMWPE surfaces using a commercial tribometer, mounted with a silicon nitride ball, under a dry-sliding condition with normal loads ranging from 60 to 200 mN. It has been shown that the patterned UHMWPE surface showed a reduction in the coefficient of friction between 8% and 35% as compared with the controlled (non-patterned) surface, depending on the magnitude of the normal load. Reciprocating wear experiments also showed that the presence of surface textures on the polymer resulted in lower wear depth and width, with minimal material transfer to the sliding surface.

Assessment of polymer composites for hydrodynamic journal‐bearing applications

AbstractPolymer composites are used as facing materials in hydrodynamic bearings for their low friction and ‘compliant’ properties, which play an important role during machinery operation. In journal bearings, this low friction property can be of significant importance during start and stop cycles when insufficient oil is available to fully separate the surfaces in relative motion. Current work is aimed at determining a suitable material for use in hydrodynamic journal bearings for applications in hydroelectric power plants. This study investigates friction and wear encountered during the transition from the stationary state to operational speed (acceleration) during initial start‐up. This is examined for virgin poly‐tetra‐fluoro‐ethylene (PTFE) together with a series of commercially available PTFE‐based composites and a babbitt material in boundary/mixed lubrication conditions. Tests are performed using standard laboratory block‐on‐ring test apparatus with a VG32 mineral oil. Copyright © 2009 John Wiley & Sons, Ltd.

Or0404—Effect of a Tribochemical Reacted Film on Friction and Wear Properties of DLC Coatings

AbstractDiamond‐like carbon (DLC) coatings provide low friction properties without lubricants and, with lubricants, should provide super low friction. In this study, the friction and wear properties of DLC coatings with lubrication in the sliding contact area were evaluated to find an environmentally friendly material combination that can provide super low friction (i.e., a coefficient of friction lower than 0.01). The friction and wear properties of a steel pin on a DLC coated disk with lubrication were evaluated by using environmentally friendly fluids (organic acid or alcohol) as lubricants. In a sliding test of tetrahedral amorphous carbon (ta‐C) lubricated with DL (a mixture of dextrorotatory and levorotatory molecules)‐lactic acid, a super low coefficient of friction (0.01) was obtained at the end of the test and was much lower than that of an uncoated disk and an amorphous hydrogenated carbon (a‐C:H) disk. The coefficient of friction obtained with DL‐lactic acid was lower than that seen for acetic acid or glycerol. The ta‐C disk lubricated with DL‐lactic acid showed a small wear scar width. The main reason for the reduced friction and wear is probably attributable to the formation of a tribochemical reacted film in a tribochemical reaction with the acid. An oxidation film (white colored layer) of FeO also formed on the mating pin under DL‐lactic acid lubrication in the sliding contact area. These results showed not only the difference in the adsorbed lubricants due to the chemical structure of DLC, but also that the oxidized condition of the steel pin influenced the coefficient of friction.

Synthesis and properties of W–Se–C coatings deposited by PVD in reactive and non-reactive processes

Transition metal dichalcogenides (TMD) are well known for their self lubricant properties, due to unique crystal structure, with low hardness which makes them inappropriate in applications requiring high load bearing capacity. Nevertheless, there is still a considerable potential for further improvements since other TMDs such as diselenides remain almost unknown. The WSeC coatings were deposited by either co-sputtering from WSe 2 and C targets or by working in reactive mode in an Ar + CH 4 atmosphere. Carbon content varied from 25 at.% up to 70 at.%, Se/W ratio of co-sputtered coatings was between 0.9 and 1.0, with no significant influence of the carbon content on their variations, while in the reactive process it reached values higher than 1.7. The hardness of the coatings was evaluated by nanoindentation, with values between 1.6 and 5.6 GPa. The structure of the coatings was analysed by X-ray diffraction in glancing mode, showing that the coatings have a quasi-amorphous structure. Finally, the selected samples were tested on pin-on-disc showing low friction properties of WSeC co-sputtered coatings.

Development of a nickel–polymer composite by using friendly environmental polymeric surfactant

A nickel–fluoro polymer composite was produced by electro deposition. The composite offers many attractive properties that make it ideal for a wide range of industrial applications. It offers very low friction and wear properties on a sliding surface. The composite was improved by adding the synthesized polymeric surfactant from the waste coke industry. The adsorption isotherms of this polymer at different interfaces were determined. The relation between the zeta potential and co-deposition of these solid particles was investigated by studying the effect of polymer on mobility or dispersion with respect to zeta potential of solid. The effect of different size particles on degree of dispersion was investigated. The relationship between the adsorption of polymer and the mechanism of efficiency was discussed according to its structures and thermodynamics. Morphology structure of coated surface and its corrosion resistance were determined and compared with free composite.

Probing biolubrication with a nanoscale flow

The fluidity of lipid membranes is an essential property for their biological function. Here we use a dynamic surface forces apparatus to probe flow at the nanoscale on supported phospholipid bilayers and we present direct mechanical measurements of their fluidity. We show that gel-phase DPPC bilayers deposited on glass behave as a rigid surface for the flow, whereas fluid DOPC bilayers are mobile and slide with a very low friction coefficient. These findings provide new perspectives for the investigation of the lubricant properties of phospholipid bilayers and for the design of biomaterial and biomedical devices of low frictional properties.

Influence of surface topography of arc-deposited TiN and sputter-deposited WC/C coatings on the initial material transfer tendency and friction characteristics under dry sliding contact conditions

The influence of surface topography of PVD coatings on the initial material transfer tendency and friction characteristics in dry sliding contact conditions has been investigated. A modified scratch test was used to evaluate the material transfer tendency between ball bearing steel and two different PVD coatings, TiN and WC/C, under dry sliding contact conditions. Post test characterisation of the contact surfaces was performed using SEM/EDS and AES in order to map the initiation points and mechanisms for material transfer. The results show that the resulting topography of the PVD coated surfaces is strongly dependent on both the substrate material topography and the topography induced by the coating deposition process used. In sliding contact with a softer surface the coating topography results in a significant material pick-up tendency of the PVD coated surfaces. The material pick-up is mainly controlled by the abrasive action of hard coating asperities and as a result a polishing post treatment of the as-deposited PVD coatings significantly reduces the material pick-up tendency. For the WC/C coating, showing intrinsic low friction properties, the post treatment inhibits the material pick-up and results in a low and stable friction coefficient ( μ ~ 0.1). For the TiN coating, that lacks intrinsic low friction properties, the post treatment reduces the material pick-up tendency but has no significant influence on the friction characteristics. This is mainly due to the presence of metallic Ti originating from the macroparticles on the TiN coating which results in a reactive surface that promotes a strong adhesion between the mating surfaces.

Droplet Motion on Designed Microtextured Superhydrophobic Surfaces with Tunable Wettability

Superhydrophobic surfaces have shown promising applications in microfluidic systems as a result of their water-repellent and low-friction properties over the past decade. Recently, designed microstructures have been experimentally applied to construct wettability gradients and direct the droplet motion. However, thermodynamic mechanisms responsible for the droplet motion on such regular rough surfaces have not been well understood such that at present specific guidelines for the design of tunable superhydrophobic surfaces are not available. In this study, we propose a simple but robust thermodynamic methodology to gain thorough insight into the physical nature for the controllable motion of droplets. On the basis of the thermodynamic calculations of free energy (FE) and the free-energy barrier (FEB), the effects of surface geometry of a pillar microtexture are systematically investigated. It is found that decreasing the pillar width and spacing simultaneously is required to lower the advancing and receding FEBs to effectively direct droplets on the roughness gradient surface. Furthermore, the external energy plays a role in the actuation of spontaneous droplet motion with the cooperation of the roughness gradient. In addition, it is suggested that the so-called "virtual wall" used to confine the liquid flow along the undesired directions could be achieved by constructing highly advancing FEB areas around the microchannels, which is promising for the design of microfluidic systems.

Gas adsorption on quasicrystalline surfaces

The low-friction properties of quasicrystal surfaces suggest their use as coatingson moving machine parts, including those in internal combustion engines. Insuch applications, additional lubricants are typically used. Since the low-frictionproperties of quasicrystals are thought to depend on their aperiodic structures, theinteractions of lubricants on quasicrystalline surfaces may have an impact on theirfrictional properties. In this paper, we address the fundamental issues that affect thegrowth and structural properties of gases on a quasicrystal surface. Studies of theadsorption and growth of rare gases on quasicrystal surfaces are reviewed, andnew results are presented for the modeling and simulation of hydrocarbons onquasicrystal surfaces. The calculated interaction parameters are presented for methaneadsorption on ten-fold Al–Ni–Co. Methane is found to form aperiodically orderedstructures, consistent with the rules established earlier for rare gases on Al–Ni–Co.

Hard Coating 응용을 위한 DC 마그네트론 스퍼터링 방법을 이용하여 증착한 TiN 박막의 특성에 대한 연구

Titanium nitride (TiN) thin films are widely used for hard coatings due to their superior hardness, chemical stability, low friction and good adhesion properties. In this study, we investigated the effect of DC power on the characteristics of TiN thin films deposited on Si and glass substrates by DC magnetron sputtering using TiN target. We made TiN films of 300 nm thickness with various DC powers. The structural properties of films are investigated by x-ray diffractions (XRD) and tribological properties are measured by nano-indentation, nano-scratch tester. The rms roughness was measured by atomic forced microscopy (AFM). In the result, TiN films had the smooth surface and exhibited (111) directions with the increase of DC Power. Also, especially in case of 175 W DC power, TiN film exhibited the maximum hardness about 8 GPa, and the critical load near 25.

Innovative polymer‐based shaft instruments for minimally invasive surgery

Minimally invasive surgery (MIS) has become an important field in the health care sector over the last decade. Still, there is the need for improving existing instruments and developing new tools providing increased functionality. This work presents innovative solutions and experimental results for a new generation of innovative polymer‐based shaft instruments for minimally invasive surgery. The investigated components comprise a new kind of end‐effector mechanism and an improved force transmission for actuating the effector.The new end‐effectors consist of few discrete parts. They combine the advantages of compliant joints with those of conventional hinges (“hybrid effector”). The simple configuration will be advantageous during sterilization and, furthermore, is suitable for large‐scale production by polymer technology. The effectors show low friction and low backlash properties and therefore high functionality.In addition to that we have developed a new kind of sensitive hydraulic force transmission which may replace the force transmission by push rods of conventional shaft instruments. The hydraulic force transmission is based on leakage‐free embedding of the hydraulic fluid in modified polymer tubing. This specific hydraulic transmission component provides high efficiency force transmission and can be entirely fabricated by polymers.Both newly developed solutions reveal an increased functionality and due to their simple configuration can be manufactured by polymer technology, e.g. injection moulding. They show the potential for large‐scale production of a new class of polymer‐based shaft instruments for minimally invasive surgery.

大気中無潤滑下におけるＤＬＣ‐Ｓｉ膜の低摩擦特性

The aim of this study is to examine the effect of silicon in DLC-Si films on friction properties, and to clarify the mechanism of low friction under dry sliding conditions. The friction coefficient of DLC-Si films was measured using a ball-on-disk type tester at a load of 10N and a sliding velocity of 0.2m/s with no lubricant in an ambient air atmosphere. Compared to DLC films without Si, DLC-Si films exhibited an extremely low friction coefficient (about 0.05) ranging from 4 to 17at. % in silicon. On the wear surface of DLC-Si coated disks, the formation of Si-OH was eventually detected using derivatization-XPS. In order to explain the relation between Si-OH formation and low friction behavior, model samples with Si-OH, Si-H and their mixture on the silicon wafer were prepared, and the friction coefficient of the samples was measured with a ball-on-plate type tester. Compared to Si-H, Si-OH had a lower friction coefficient. Furthermore, Si-OH surface analyzed by ATR-IR showed spectra with broad band at around 3400cm−1, indicating the existence of adsorbed water on the Si-OH surface. From the results obtained, it was suggested that DLC-Si films exhibited a low friction property caused by the formation of Si-OH and adsorbed water in it under the dry sliding condition.

Advanced low-friction tool steel for metal processing: properties and industrial experiences

Owing to an increased competitive situation in many metalworking segments, a more intense focus is directed on lead time reduction and general cost savings. An adequate tooling performance in relation to the production length is of vital importance here. Cold-work tool steels can be designed to resist various types of failure modes in metalworking applications. An advanced tool steel with low-friction properties designed to counteract galling has proven to be a complement or even an alternative to surface-coated tool steels. The properties are fundamentally different to tool steel grades used today owing to a specific hard phase introduced in the martensitic matrix. Application tests from various metalworking applications such as deep drawing, cutting, cold extrusion and powder pressing have shown significant performance increases for the new low-friction tool steel. This paper describes the new alloy and results from different application tests.

Lubrication mode analysis of articular cartilage using Stribeck surfaces

Lubrication of articular cartilage occurs in distinct modes with various structural and biomolecular mechanisms contributing to the low-friction properties of natural joints. In order to elucidate relative contributions of these factors in normal and diseased tissues, determination and control of lubrication mode must occur. The objectives of these studies were (1) to develop an in vitro cartilage on glass test system to measure friction coefficient, μ; (2) to implement and extend a framework for the determination of cartilage lubrication modes; and (3) to determine the effects of synovial fluid on μ and lubrication mode transitions. Patellofemoral groove cartilage was linearly oscillated against glass under varying magnitudes of compressive strain utilizing phosphate buffered saline (PBS) and equine and bovine synovial fluid as lubricants. The time-dependent frictional properties were measured to determine the lubricant type and strain magnitude dependence for the initial friction coefficient ( μ 0= μ( t→0)) and equilibrium friction coefficient ( μ eq= μ( t→∞)). Parameters including tissue-glass co-planarity, normal strain, and surface speed were altered to determine the effect of the parameters on lubrication mode via a ‘Stribeck surface’. Using this testing apparatus, cartilage exhibited biphasic lubrication with significant influence of strain magnitude on μ 0 and minimal influence on μ eq, consistent with hydrostatic pressurization as reported by others. Lubrication analysis using ‘Stribeck surfaces’ demonstrated clear regions of boundary and mixed modes, but hydrodynamic or full film lubrication was not observed even at the highest speed (50 mm/s) and lowest strain (5%).