Superior Friction Research Articles

Influence of slag weight fraction on mechanical, thermal and tribological properties of polymer based friction materials

This paper aimed to study the influence of blast furnace slags on mechanical, thermal and tribological properties of friction materials elaborated by the dry heat-press molding method. Physical, mechanical and thermal properties were analyzed and tribological behavior was studied for varying the extent of doping (13–43wt.%). The results indicate that the hardness decreases from 63.6 HRL to 57.0 HRL with increasing slag content from 0 to 43wt.%. But density is opposite for the doped samples. The impact strength gradually increases from 3.59kJ/m2 to 3.70kJ/m2 when the content of slag increases from 0 to 43wt.%. Doping was also found to increase the friction coefficients but decrease wear rates, mass-loss and heat release. The sample S4 has a more superior and stable friction coefficient than others because of the transfer layers formed on the surface of friction materials.

An Oil-Based Lubrication System Based on Nanoparticular TiO2 with Superior Friction and Wear Properties

We evaluated the performance of five different commercially available nanoparticle classes as additives for an oil-based lubrication system. While the silicon dioxide particles Aerosil® 300, RY300, and R972V tended to increase wear and friction in our 100Cr6 versus cast iron disc–disc contact, Aeroxide® P 25 and especially T 805 TiO2 nanoparticles showed superior anti-wear and anti-friction properties. The underlying tribological mechanism was investigated with optical microscopy, helium ion microscopy, and X-ray photoelectron spectroscopy. Subsequently, we formulated a stable lubrication system based on the best performing T 805 particles. Here, the base oil is a highly purified paraffin oil which was supplemented with 1 wt% T 805 TiO2 particles, 1 wt% Estisol® 242 or 1 wt% oleic acid, 0.15 wt% oleylamine, and 0.15 wt% Pluronic® RPE 2520. Superior lubrication and anti-wear properties of this formulation were demonstrated in 4-h test runs with a normal force of F N = 2.5 kN and a sliding velocity of 0.15 m/s in our disc–disc contact. Wear was significantly reduced along with a nearly 12-fold reduction in the friction coefficient, compared to the base oil $$(\mu_{\text{base}}^{\text{fto}} = 0.155\;\;{\text{vs}} .\;\;\mu_{\text{T805}}^{\text{fto}} \approx 0.01)$$ . Using 100Cr6 disc–ball contacts, we additionally analyzed the properties of our lubrication system in the border friction regime under higher loads (F N = 0.5 kN) in 2-h runs. In particular, on the discs with lower engagement ratio, chemo-tribological protective layers were built, which protected the parts very well against wear.

Evaluation of a superior lubrication mechanism with biphasic hydrogels for artificial cartilage

To extend the durability of artificial joints, biomimetic artificial hydrogel cartilage is proposed as a way of improving the lubrication mechanism in artificial joints. The application of hydrogels with properties similar to those of articular cartilage can be expected to duplicate the superior load-carrying capacity and lubricating ability of natural synovial joints. Frictional behaviors with three kinds of poly(vinyl alcohol) (PVA) hydrogels with high water content were examined in reciprocating tests. Interstitial fluid pressure, von Mises stress and fluid flow were compared in biphasic finite element analysis, and frictional behavior was evaluated in terms of biphasic lubrication and surface lubricity. Hybrid gel prepared by a combination of cast-drying and freeze-thawing methods showed superior low friction.

Friction Studies over Idlers Sprayed with Al2O3 Powder Using Athmosferic Plasma Spraying Method

In military and mining industry are many machine elements – in our case idlers (for tanks, conveyors, and any others machineries which are using transmissions system which are subjected of coverage with low friction proprieties powder. These machine elements (idlers) must have low friction coeficient, because the functionality of the entire transmissions systems depends on them. Also the maintenance costs are very high, that is why we proposed to studies how to improve the performances of this machine elements. Researches in surface engineering allow the obtaining of new systems of materials by coating the basic material surface with other material having superior friction properties. In order to improve the machine elements durability, wear resistance, friction, we proposed to obtain a new system of materials using Atmospheric Plasma Spraying – with Sulzer 9MCE equipment. We have chosen the steel type 34CrNiMo6, MOCN class, STAS 691 - 880 as basic material and we coated it with Al2O3 powder. We made the samples and we tested them. The analysis has been made with Tribometre, which produces some data which link us to a low friction coeficient. The Al2O3 coating deposited on steel substrate is uniformaly deposited on the based steel, and need to be polished to decrease the friction coeficient. The results showed that the new material has a better microstructure than the basic material and its physical and mechanical properties have been improved.

Exploring Cr/CrNx/CryCz/Cr-DLC film for geophysical prospecting

Cr(chromium)/CrNx/CryCz/Cr-DLC (diamond-like carbon) film in a mid-frequency dual magnetron sputtering was explored for its application in geophysical prospecting. The influences of pulsed substrate bias voltage on the surface morphology, microstructure, hardness, adhesion and friction property of the film were investigated. The proposed film provides a coating solution for executive components of geophysical instruments. Cr-DLC film at −140 V exhibited good combined properties: high hardness up to 32·5 GPa; good adhesion [Lc (critical loads) up to 63·7 N]; superior wear resistance and friction coefficient low to 0·126 at ambient atmosphere and 0·052 in a seawater environment.

Comparative study on structure and properties of titanium/silicon mono‐ and co‐doped amorphous carbon films deposited by mid‐frequency magnetron sputtering

The titanium/silicon mono‐ and co‐doped amorphous carbon films were deposited by mid‐frequency magnetron sputtering Ti target, Si target, and Ti80S20 alloy target, respectively. The effects of doped elements on the composition, surface morphology, microstructure, and mechanical and tribological properties of the films were investigated. The results reveal that the ratio of sp3 and sp2 carbon bonds of the films is regulated between 0.28 and 0.62 by a combination of Ti and Si dopant. The addition of small amounts of silicon leads to an increase in sp3 bonds and disorder degree of the sp2 carbon. The co‐doped film exhibits significantly superior friction performance than the mono‐doped films. The ultra‐low friction (μ < 0.01) was achieved under a load of 2 N in ambient air with 40% RH. By comparing to the mono‐and co‐doped films, it is thought that the sp3/sp2 ratio of the films may play a key role for the superlow friction. Copyright © 2013 John Wiley & Sons, Ltd.

Potential of thick a-C:H:Si films as substitute for chromium plating

Chromium plating is a well-established technique for corrosion and wear protection. One essential problem inherent with this process is the use of toxic and carcinogenic hexavalent chromium. A potential substitution of hard chromium with thick a-C:H:Si coatings (amorphous Si-doped hydrogenated carbon) has been studied. a-C:H:Si films represent chemical and electrochemical inert hard coatings with very favorable tribological and corrosion properties. Up to now it was only possible to deposit thin DLC-films because of the high intrinsic stress in the films.A series of laboratory tests including scratch, pin-on-disk and electrochemical corrosion measurements were performed in order to compare the performance of hard chromium and a-C:H:Si. By depositing a-C:H:Si films without using hazard chemicals in a dc-pulsed hot wall plasma system coatings with thicknesses up to 58μm were produced. These coatings exhibit elastic properties during scratching at the beginning and get a self-sustaining behavior with increased coating thickness resulting in a high load carrying capability. For hard chromium coating cracking was already observed at the very first stage of testing.Sliding tests under unlubricated conditions of a-C:H:Si films showed superior friction performance (friction coefficient μ=0.02 versus μ=1.1) and excellent wear resistance of the coating and the counterpart (wear rate 7∗10−8mm3/N−1m−1 versus 6∗10−5mm3/N−1m−1) compared to hard chromium. Further potentiometric observations demonstrated a much better corrosion resistance for thick a-C:H:Si coatings than hard chromium (Ecorr −0.28V vs. Ecorr −0.52V).

Chondroprotective effects of high-molecular-weight cross-linked hyaluronic acid in a rabbit knee osteoarthritis model

We hypothesized that high-molecular-weight (MW) cross-linked (CL) hyaluronic acid (HA) improves joint lubrication and has an enhanced chondroprotective effect. We examined the histopathological changes and friction coefficients in osteoarthritic knee joints after injecting high-MW CL HA. A bilateral anterior cruciate ligament transection (ACLT) model in 20 Japanese white rabbits was used. From week 5 after transection, low-MW HA (0.8×10(6)Da; HA80) or high-MW CL HA (6×10(6)Da; HA600) was injected weekly into 10 right knee for 3 weeks; normal saline (NS) was injected into the 10 left knee. A sham operation was undertaken to exclude spontaneous osteoarthritis (OA) in five knees. Results were evaluated with macroscopy, histopathology (Kikuchi's score), biomechanical testing, and rheological assessment of the joint fluid viscoelasticity. Statistical analysis was performed using one-way analysis of variance with a 95% confidence interval (CI) (P<0.05). The macroscopic findings showed severely damaged cartilage in 30% of the NS group and 20% of the HA80 and HA600 groups and intact cartilage in 100% of the sham group. The histological scores and friction coefficients of the HA600 group were significantly lower than those of the NS group (P=0.007 and P=0.002, respectively). Viscoelasticity measurements of the joint fluid showed no significant differences between the three treatment groups. High-MW CL HA exerts potential chondroprotective effects and produces superior friction coefficients. Our results suggest that HA600 delays the progression of OA effectively and improves joint lubrication significantly.

The preparation and tribological properties of thermoplastic self-assembled composite film filled with carbon nanotubes

Rare earth solution (RES) surface modification and acid treatment methods were used to functionalize carbon nanotubes (CNTs). CNT composite thin films were prepared on hydroxylated glass substrates by a self-assembling process from specially formulated solution. Atomic force microscopy, x-ray photoelectron spectrometry, and scanning electron microscopy were used to characterize the thin films. Tribological properties of the CNT thin films sliding against a steel ball were evaluated on a friction and wear tester. The experimental results showed that the friction coefficient of the glass substrate was reduced from 0.85 to 0.1 after the formation of CNT composite self-assembled film on its surface, and the film exhibited good wear resistant property. The superior friction reduction and wear resistance of CNT composite films were attributed to the improvement of load-bearing capacity afforded by the chemical bond between CNTs and the films as well as good adhesion of the films to the substrate.

Experimental Research on the Friction and Wear Properties of Ni-Based Composite Coating Prepared by Laser Cladding

In this study, the dry sliding wear behavior of Ni-based self-lubricating wear-resistant coating was characterized under various loads at 300 . Morphologies and compositions of the worn surface were analyzed by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The experimental results showed that with the increase of load, both the frictional coefficient and wear rate decreased firstly, then slightly increased. A small amount of debris dispersed on the worn surface of the coating under low load (2 N). Since the effects of oxide layer and lubricant particles spreading onto the worn surface, the coating exhibited superior friction, and improved the wear properties under moderate load (5 N). As the load further increased, till up to 10N, the worn surface started to appear some shallow grooves and craters. This was contributed to the dispersion of carbides and lubricant particles.

Application of ultra-smooth composite diamond film coated WC–Co drawing dies under water-lubricating conditions

A specific revised HFCVD apparatus and a novel process combining HFCVD and polishing technique were presented to deposit the micro- and nano-crystalline multilayered ultra-smooth diamond (USCD) film on the interior-hole surface of WC–Co drawing dies with aperture ranging from d1.0 mm to 60 mm. Characterization results indicate that the surface roughness values (Ra) in the entry zone, drawing zone and bearing zone of as-fabricated USCD coated drawing die were measured as low as 25.7, 23.3 and 25.5 nm, respectively. Furthermore, the friction properties of USCD films were examined in both dry sliding and water-lubricating conditions, and the results show that the USCD film presents much superior friction properties. Its friction coefficients against ball-bearing steel, copper and silicon nitride balls (d4 mm), is always lower than that of microcrystalline diamond (MCD) or WC–Co sample, regardless of the lubricating condition. Meanwhile, it still presents competitive wear resistance with the MCD films. Finally, the working lifetime and performance of as-fabricated USCD coated drawing dies were examined under producing low-carbon steel pipes in dry-sliding and water-lubricating conditions. Under the water-lubricating drawing condition, its production significantly increases by about 20 times compared with the conventional WC–Co drawing dies.

Surface Morphology and Characteristics of Electroplated Au/Ni Films for Connector Contact Materials

The surfaces of the connector terminals used for electrical connection of components are electroplated with Sn, Au, or Ag in order to improve reliability. For electronic devices that require particularly high reliability, hard gold is used. The characteristics of gold deposits of various surface morphologies were examined. Gold films with increased surface roughness exhibited superior friction and wear properties without a large increase in contact electrical resistance after friction testing. Increasing the surface roughness also resulted in higher solder adhesion strength and improved corrosion resistance to sulfur dioxide gas.

Reinforcement of poly ether sulphones (PES) with exfoliated graphene oxide for aerospace applications

Composite materials have been used for aerospace for some time now and have gained virtually 100% acceptance as the materials of choice. Speciality polymers like poly ether sulphones (PES), poly ether ether ketones(PEEK), poly ether imides (PEI) are highly preferred materials as plastic matrix due to their superior temperature performance, excellent wear & friction resistance, excellent dimensional accuracy, high tensile strength, high modulus, precise machinability and chemical resistance. In recent years nanoadditives like single and multiwall carbon nanotubes, graphenes and graphene oxides(GO) are finding huge market potential in aerospace and automobile industries. But manufacture related factors such as particle/ matrix interphases, surface activation, mixing process, particle agglomeration, particle size and shape may lead to different property effects. In this research GO/PES composites were prepared by high shear melt blending technique. GO monolayers were exfoliated from natural graphite flake and dispersed homogeneously in PES matrix for the GO content ranging between 0.5 to 2.0 volume percentage with a high shear twin screw batch mixer. These melt blended nanocomposites were injection moulded for mechanical property validation of tensile strength, flexural modulus and impact resistance. Addition of 0.5 volume percentage of GO enhanced the tensile strength and flexural modulus by 40% and 90% respectively. The results show that addition of GO to PES increase mechanical properties due to the formation of continuous network, good dispersion and strong interfacial interactions. The strong interfacial interactions were accounted for the increase in glass transition temperature. Also there was a significant improvement in the impact resistance of the PES/ GO nanocomposite. The injection moulded samples were tested for stealth performance by measuring the electromagnetic shielding property.

An electron microscopy study of the effect of Ce on plasma sprayed bronze coatings

The Cu-Al eutectoid alloy is an excellent material for mould due to its superior low friction. The conventional sand casting technique, however, is not feasible to fabricate high Al bronze because of high hardness and brittleness. Plasma arc spray has been used to produce high Al/Fe bronze coatings for mould. The inherent impurities such as H, O, N, S during the spray, however, may affect the coating's mechanical strength. One approach is to utilise the active rare earth Ce to clean up these impurities. The study is to investigate the effect of Ce on the microstructure, which has few reported in the literature.

Influence of bias voltage on microstructure and properties of Al-containing diamond-like carbon films deposited by a hybrid ion beam system

Al-containing diamond-like carbon films were deposited using a hybrid ion beam system composed of an anode-layer ion source and a magnetron sputtering with various bias voltages. XPS, TEM and Raman spectroscopy were applied to characterize the film composition, microstructure, and carbon atom bond. Nano-indentation and ball-on-disk tribo-tester were also used to study the mechanical properties and tribological behavior, respectively. The results showed that the bias voltage played a significant role on the microstructure of the films, and nano-stripe structures were observed in the DLC films, which resulted in the relatively high hardness of the films. The friction tests revealed that the films possessed a superior friction performance with a friction coefficient of about 0.02. Specially, the film with the nano-stripe clusters exhibited a good wear resistance, though those nano-clusters seemed to increase the friction coefficient.

Microstructure and tribology of TiC(Ag)/a-C:H nanocomposite coatings deposited by unbalanced magnetron sputtering

TiC(Ag)/a-C:H nanocomposite coatings with various Ag concentrations were fabricated on Si p(100) substrates. The composition and structure of as-deposited nanocomposite coatings were systemically investigated, and the friction and wear behaviors were also evaluated under the ambient, high temperature and high vacuum, respectively. Results show that the TiC nanocrystallites were formed in the amorphous hydrogenated carbon matrix near the substrate. The co-dopant Ag possessed nanocrystalline structure in the as-fabricated coatings whilst it formed Ag clusters (10–50nm) on the surface. Furthermore, the introduction of Ag caused a significant reduction in the residual compressive stress without considerable decrease of the hardness and improved the adhesive strength of nanocomposite coatings. Tested as-deposited and after annealed at 500°C coatings, the TiC(Ag)/a-C:H coatings showed a reduction of friction coefficients and wear rates with increment of Ag concentration. Under high vacuum condition, the TiC(Ag)/a-C:H coatings presented superlow friction behavior where the friction coefficient was reduced from 0.01 to 0.005 and lifetime increased from 0 to 1500 cycles. The significant improvement in tribological properties was mainly attributed to the low shear strength of Ag clusters on the surface as well as Ag diffusion to surface and wear track of coatings. The superior friction and wear behaviors of TiC(Ag)/a-C:H coatings make them good candidates as solid lubrication materials in space and aircraft applications.

Si添加およびTi添加DLC/DLC摺動のトライボロジー特性

Diamond-like carbon (DLC) films have been widely applied to machine components of many types. DLC has excellent tribological properties, but it must be improved to reduce friction further. Deposition with a different element-doped DLC on both sides of a sliding surface is expected to produce a superior friction coefficient. Therefore, we investigated the tribological properties of different element-doped DLC/DLC sliding to achieve sliding with lower friction. For our study, we used Plasma-Based Ion Implantation and Deposition (PBIID) to prepare three DLC films of pure-DLC, Si-DLC, and Ti-DLC. Each DLC film bond structure was analyzed using Raman spectroscopy. Hardness and roughness were measured by nano-indentation and atomic force microscopy. Regarding their tribological properties, friction coefficients were measured using ball-on-disk friction tests. Subsequently the chemical elements in wear tracks were analyzed using energy dispersive x-ray spectroscopy. Results obtained through the study revealed the following. (1) Different kinds of DLC/DLC sliding achieved a much lower friction coefficient than a single kind of DLC/DLC sliding. (2) Occurrence of mild wear particles functioned as a solid lubricant. The particles effectively reduced the friction coefficient. (3) Adhesion of wear particles was observed in wear tracks after Si-DLC/Ti-DLC sliding. (4) Friction coefficients of the Si-DLC/Ti-DLC sliding were the lowest, about 0.021, by appropriate adhesion of the wear particles.

Effects of Mesh Density on Static Load Performance of Metal Mesh Gas Foil Bearings

Metal mesh materials have been used successfully in vibration isolators and bearing dampers due to their superior friction or hysteresis damping mechanism. These materials are formed to metal mesh (or wire mesh) structures in ring-shape by compressing a weave of metal wires, in general. Recently, oil-free rotating machinery implement metal mesh structures into hydrodynamic gas foil bearings by replacing bump strip layers with them, to increase its bearing structural damping. A metal mesh foil bearing (MMFB) consists of a top foil and support elastic metal mesh pads installed between a rotating shaft and a housing. The present research presents load capacity tests of a MMFB at rotor rest (0 rpm) and 30 krpm for three metal mesh densities of 13.1%, 23.2%, and 31.6%. The metal mesh pad of test MMFB is made using a stainless steel wire with a diameter of 0.15 mm. Test rig comprises a rigid rotor with a diameter of 60 mm supported on two ball bearings at both ends and test MMFB with an axial length of 50 mm floats on the rotor. Static loads is provided with a mechanical loading device on test MMFB and a strain gauge type load cell measures the applied static loads. A series of static load versus deflection tests were conducted for selected metal mesh densities at rest (0 rpm). Test data are compared to further test results of static load versus journal eccentricity recorded at the rotor speed of 30 krpm. Test data show a strong nonlinearity of bearing deflection (journal eccentricity) with static load, independent of rotor spinning. Observed hysteresis loops imply significant structural damping of test MMFB. Measured journal deflections at 0 rpm are in similar trend to recorded journal eccentricities at the finite rotor speed; thus implying that the MMFB performance depends mainly on the metal mesh structures. The paper also estimates linearlized stiffness coefficient and damping loss factor of test MMFB using the measured static load versus deflection test data at 0 rpm and 30 krpm. The results show that the highest mesh density of 31.6% produces highest linearlized stiffness coefficient and damping loss factor. With rotor spinning at 30 krpm, the linearlized stiffness coefficient and damping loss factor decrease slightly, independent of metal mesh densities. The present test data will serve as a database for benchmarking MMFB predictive models.

Influence of electric potentials on the tribological behaviour of silicon carbide

Abstract Thanks to their superior friction and wear properties in aqueous environments, silicon carbide (SiC) ceramics are commonly used for slide bearings and face seals in pumps. Tribochemical reactions of SiC with water have a major influence on the frictional behaviour as well as on the wear rates. It has been presumed that low friction coefficients (in the order of 0.1) are reached by smoothening of the surfaces, which favours hydrodynamic conditions even in water, and by the formation of lubricious oxide scales through tribochemical reaction of SiC with water. Silicon carbide is electrically semiconducting. Due to additives like boron or aluminium, silicon carbide ceramics can exhibit a considerable specific electrical conductivity. Therefore, electrochemical reactions with water or aqueous electrolytes and subsequent friction, wear and corrosion may be influenced electrochemically. A pin-on-disc tester was modified to study SiC under the influence of electric potentials between −1 and +1 V (vs. Ag/AgCl). It was observed that under cathodic polarisation of the SiC samples, both friction coefficient and wear rates were drastically decreased. Surprisingly, despite the formation of oxide scales under positive (anodic) polarisation the friction coefficients increased significantly, which contradicts the fundamental hypothesis of a lubricating effect of the oxide scales. After switching off the electric potentials, the friction coefficient instantly changed to adopt normal values of ca. 0.1. These results show that it is possible to influence or even control the tribological behaviour of electrically conductive ceramics in aqueous media by electric potentials. New models based on electrochemical surface effects are necessary to describe the observed effects.

Tribological characteristics of self-assembled nanometer film deposited on phosphorylated 3-aminopropyltriethoxysilane

Thin films deposited on the phosphonate 3-aminopropyltriethoxysilane (APTES) self-assembled monolayer (SAM) were prepared on the hydroxylated silicon substrate by a self-assembling process from specially formulated solution. Chemical compositions of the films and chemical state of the elements were detected by X-ray photoelectron spectrometry (XPS). The thickness of the films was determined with an ellipsometer, while the morphologies and nanotribological properties of the samples were analyzed by means of atomic force microscopy (AFM). As the results, the target film was obtained and reaction might have taken place between the thin films and the silicon substrate. It was also found that the thin films showed the lowest friction and adhesion followed by APTES-SAM and phosphorylated APTES-SAM, whereas silicon substrate showed high friction and adhesion. Microscale scratch/wear studies clearly showed that thin films were much more scratch/wear-resistant than the other samples. The superior friction reduction and scratch/wear resistance of thin films may be attributed to low work of adhesion of nonpolar terminal groups and the strong bonding strength between the films and the substrate.