Presented in this study is a new class of “greener” lubricants, room temperature ionic liquids, that represent a promising potential solution to many of the problems associated with both conventional lubricants and those based on natural oils. In this study, friction and wear tests were carried out using a pin-on-disk tribometer under ambient conditions to characterize the performance of the ionic liquids as lubricants. Specifically, ionic liquids consisting of salicylate, benzoate (common food additives) and saccharinate (an artificial sweetener) anions with conventional phosponium cations were evaluated as lubricants and compared to petroleum-based lubricants and natural oils in regards to structure and performance. The ionic liquids generally demonstrated better tribological performance than either the petroleum-based lubricants or natural oils. The mechanisms governing the chemical composition and improved tribological performance are discussed while highlighting possible industrial applications of this new class of lubricants.

A new additive was produced from a natural oil and boron. The synthesis involves the use of the epoxidized form of soybean oil which then undergoes a catalytic ring opening to produce the additive material. Due to their remaining triacylglycerol structure, the products are highly compatible with bio-based lubricants and due to their covalent boron attachments, show effective properties for the reduction of wear. Some performance examples: Using a traditional Falex 4-ball wear test, the scar diameter observed in a soybean oil lubricant could be reduced from 0.61 mm to 0.41 mm by the inclusion of 1% or the additive. A second generation additive, while not as effective at reducing wear, was able to increase the oxidation onset temperature of soybean oil under pressurized oxygen by 14 °C. Next, these additives were tested in a formulation of biobased gear oil composed of heat treated soybean oil and synthetic esters. In the best formulation, these additives were able to surpass the oxidation onset of a gear oil that was formulated with commercially available additives, while giving nearly as good of performance by wear scar analysis. This oxidation onset value, of 258 °C, approaches that of off-the-shelf gear oils. Overall, these new additives are strong performers which can be made using simple chemistry. Their properties combined with their high biobased content are valuable assets in the search for biobased lubricants and gear oils.

Polycrystalline diamond (PCD) bearings are designed for use in extreme environments; this includes process-fluid-lubricated applications such as those in oil and gas drilling turbines and marine hydrokinetic (MHK) energy machines. Past uses of PCD bearings in oil and gas down-hole tool applications have proven them to be robust, long lived, and rugged [1]. To be effective in MHK machines, PCD bearings must demonstrate adequate bearing efficiency and life in a submerged marine environment not nearly as severe as an oil well bore or a gas well bore. This paper discusses the advantages PCD bearings could provide when used in underwater MHK energy machines. Laboratory test results are presented that can help predict the performance of PCD in these MHK applications. Results from three types of tests are presented including tests that measure bearing capacity, those that observe and qualify hydrodynamic properties during testing, and those that evaluate diamond wear rates through a test representing the life time of a bearing in a MHK energy application. Failure tests conducted to measure bearing capacity revealed the PCD bearing could well endure conditions found in MHK machines, and coefficient of friction (COF) tests demonstrated the PCD ability to move from a boundary lubrication regime, to mixed mode lubrication, and then become hydrodynamic. The PCD wear test was designed to simulate years in the life of a tidal stream power generator, an MHK energy machine, and showed the PCD life is more than adequate for the MHK application. Bearing capacity, COF, and wear observed during laboratory testing illustrate that PCD thrust bearings can provide a robust, long lasting, and low maintenance bearing in MHK applications.

Several kinds of Polytetrafluoroethylene (PTFE) composites are currently being used in reciprocating hydrogen gas compressors as seal material which should articulate against metal counterfaces in pressurized hydrogen gas. Although their friction and wear behavior has large impact on the efficiency and reliability of gas compressors, available information about tribological characteristics of PTFE composites in high pressure hydrogen gas is quite limited. In this study, friction and wear of graphite filled PTFE and bronze filled PTFE were evaluated in the 40 MPa hydrogen gas environment by using a pin-on-disk type apparatus enclosed in a high pressure vessel to supply experimental data for the design of gas compressors in hydrogen fuelling stations. AISI316L austenitic stainless steel disk was used as a sliding counterface. All experiments were conducted under dry condition with the average contact pressure of 1.8 MPa, the sliding speed of 100 mm/s and the gas temperature of 327 K. The friction force exerted between PTFE composites and stainless steel was evaluated by a load cell during the experiment and the wear rate of composites was evaluated from the weight loss of pin specimens. In addition, chemical analysis of the polymer transfer film formed on the disk surface were conducted by using X-ray photoelectron spectrometer. Friction and wear tests were also conducted in 40 MPa helium gas for comparison. Results indicated that bronze filled PTFE was more sensitive to the gas pressure and gas species; it showed good friction and wear behavior in high pressure hydrogen, although friction in high pressure helium became very high. On the other hand, the effects of high pressure gas environment were relatively small for the friction and wear of graphite filled PTFE.

Low friction polytetrafluoroethylene (PTFE) has been studied extensively and is widely used in tribological applications in bulk form. Tribological properties of thin film PTFE are less reported due to its poor wear resistance. Here, we show that by incorporating Au nanoparticles in PTFE thin film, it is possible to significantly increase the wear resistance of the film. PTFE/Au nanoparticle composite thin films were fabricated on stainless steel substrates by dipping the substrate into a mixture of Au nanoparticle solution and PTFE aqueous dispersion. The friction and wear test results show that Au nanoparticles significantly reduced the wear of the PTFE thin film while preserving its low coefficient of friction (COF). Furthermore, substrate surface topography was found to have a significant effect on the friction and wear performances.

The properties of metallic alloys can be substantial modified by the addition of a second phase particles. This is especially noticeable when hard particles are incorporated in a relatively soft matrix, often resulting in improved mechanical and tribological performance. This paper presents the results of our study on mechanical and tribological performance enhancement of 6061 Aluminum alloys by incorporation of B 4 C particle via Friction stir processing (FSP). Unidirectional ball on flat friction and wear tests were conducted with a base material, friction stir processed 6061-Al and 6061-Al doped with B 4 C particles via FSP against 52100 bearing steel balls under dry sliding conditions. The incorporation of particles not only reduced friction by 30% but also reduced wear by 2 orders of magnitude compared to unprocessed base and FSP material without particles incorporation. FSP alone without particles addition did not have a significant effect on the tribological behavior of the tested aluminum alloy.

In this study, friction and wear tests were performed in order to investigate the effect of sliding velocity and normal load on the friction and wear characteristics of multi-layered diamond-like carbon (DLC) coating used for machine elements (automotive engine tappet, etc). Friction and wear tests against AISI 52100 bearing steel ball were performed under various sliding velocities (0.25, 0.5, 1 and 2 m/s) and normal loads (6.13, 20.7 and 49.0 N). As a result of test, kinetic friction coefficients and wear rates of multi-layered DLC coating and AISI 52100 bearing steel were obtained under each test condition. The result showed that the kinetic friction coefficients and wear rates generally decreased with the increase in sliding velocity and normal load.

Particulate contaminated lubricants can be detrimental to any tribosystem. Debris can originate from the external environment, be unintentionally introduced during fabrication, or be generated internally during operation. These particles, if not carefully filtered out, can have serious implications on the integrity of a tribosystem. This study focused on the abrasive wear observed from four-ball wear tests in the presence of lubricant with particulate contaminants. The contaminants studied were silicon dioxide sand particles and self generated AISI E-52100 steel particles. The particles were submerged in an industrial EP gear oil. The effects of particle size, composition, and concentration on abrasive wear of sliding interfaces was analyzed.

A new multidirectional motion pin-on-disk (MPOD) apparatus was designed, built and validated. Multidirectional motion was proven to have influence on the wear behaviour due to the difference in shear stress, especially in biotribology experiments for prosthetic joint materials. This MPOD was designed to realize the ‘adhesive polishing’ effect observed in multidirectional sliding wear test. Following axiomatic design principle, several modules, such as loading unit, motion generation and pin guiding modules were developed according to the uncoupled design matrix. Force transducers were assembled separately in X and Y direction for precisely measuring, and a frequency control system was assembled to provide a wide range of rotation speed. Preliminary tests were performed by using ultra high molecular weight polyethylene pins against zirconium oxide disks, and the experimental results were analyzed and compared with those observed in unidirectional wear tester.

Bearings and seals used in fuel cell vehicles and related hydrogen infrastructures are operating in pressurized gaseous hydrogen. However, there is a paucity of available data about the friction and wear behavior of materials in high pressure hydrogen gas. In this study, authors developed a pin-on-disk type apparatus enclosed in a high pressure vessel and characterized tribological behavior of polymeric sealing materials, such as polytetrafluoroethylene (PTFE) based composites, in gaseous hydrogen pressurized up to 40 MPa. As a result, the friction coefficient between graphite filled PTFE and austenitic stainless steel in 40 MPa hydrogen gas became lower compared with the friction in helium gas at the same pressure. The chemical composition of worn surfaces was analyzed by using X-ray photoelectron spectrometer (XPS) after the wear test. Results of the chemical analysis indicated that there were several differences in chemical compositions of polymer transfer film formed on the stainless disk surface between high pressure hydrogen environment and high pressure helium environment. In addition, the reduction of surface oxide layer of stainless steel was more significant in high pressure hydrogen gas. These particular effects of the pressurized hydrogen gas on the chemical condition of sliding surfaces might be responsible for the tribological characteristics in the high pressure hydrogen environment.

Laboratory abrasive wear tests have been reported on permanent moulded toughened austempered ductile iron. The influence of austempering temperature on the abrasive wear behavior have been studied and discussed. The results indicate that with increase in austempering temperature from 300°C to 350°C, the abrasive wear resistance increased, and as the austempering temperature increased to 400°C, there was reduction in the abrasive wear resistance. These results have been interpreted based on the structural features and graphite morphology.

Machine components in the fuel cell vehicle and related hydrogen infrastructures are operating within high pressure hydrogen gas. Especially, polymer seals used in gas compressors and regulator valves should be articulating against their metal counter face in pressurized hydrogen gas. However, the effect of high pressure hydrogen gas on tribological behavior of sliding surfaces has not been identified yet. In this study, effects of the pressurized hydrogen gas environment on wear behavior of polymeric sealing materials were examined by exposing polymer specimens and their sliding counterface to the high pressure hydrogen gas prior to the wear test. Unfilled polytetrafluoroethylene (PTFE) and 15% graphite filled PTFE were tested as representative polymer sealing materials and 316L austenitic stainless steel was used as a sliding counterface. Results of X-ray photoelectron spectrometer (XPS) analysis of the exposed stainless surface indicated that metal oxides in the surface passive layer of 316L stainless steel could be reduced to some extent by high pressure hydrogen. Increased metal contents of the stainless surface enhanced the development of polymer transfer film and consequently lower the specific wear rate of PTFE and PTFE composites.

Ring-on-ring rolling/sliding contact tests were conducted to evaluate the impact of ground, black oxided, isotropically finished (ES20), and tungsten carbide-incorporated amorphous hydrocarbon coated surfaces (ES322) on friction and wear in high slip contacts relevant to wind turbine gearbox bearings. The testing was performed in three phases, including Stribeck testing, adhesive wear testing, and cyclic acceleration testing. Results indicated that neither black oxide treatment nor ES20 had long-term adhesive wear protection benefits. However, ES20 exhibited the lowest traction coefficients in boundary lubrication during run-in as compared to the other test surfaces. Only the contacts containing the ES322 hard-coated surface consistently survived the harshest slip and boundary lubrication conditions.

Wear reduction by Carbon Nanotube (CNT) addition in composites with Ultra-High Molecular Weight Polyethylene (UHMWPE), Polyimide (PI), Polytetrafluoroethylene (PTFE), and epoxy resins have been reported separately. We studied Polypropylene (PP) and Polyamide (PA) composites and showed that with the addition of Multi-wall Carbon Nanotube (VGCF: Vapor Grown Carbon Fiber), wear decreased for PA composites but increased for PP composites. Differences in tribological characteristics of CNT composites with different resins were not well understood. In this paper, we compared tribological and mechanical characteristics of VGCF composites with PE, PP, and Polyacetal (POM) resins. Ball-on-Disk wear tests and mechanical strength measurements were performed. It was found that with the increase in VGCF content, specific wear amount (SWA) of VGCF-PE composite decreased while SWA of VGCF-POM composite stayed almost constant and SWA of VGCF-PP composite increased. On the other hand, with the increase in VGCF content, the tensile strength of VGCF-PE composite was increased but those of VGCF-PP and VGCF-POM composite were decreased. Decrease in SWA of VGCF-PE composite corresponded to the increase in tensile strength with VGCF content. We considered that the intermolecular force between side wall of VGCF and PE was strong enough to make both the SWA small and the tensile strength large.

Lubricant on thin-film magnetic disks is divided into two parts. One is bonded lubricant that is fixed on disk surface and remains on disk surface after solvent rinsing. The other is mobile lubricant that can move on disk surface and is removed by solvent rinsing. It has been believed that mobile lubricant is imperative to design reliable hard disk drives. However, mobile lubricant would also be a cause of high friction between heads and disks. We started our studies on disks without mobile lubricant to find the possibility of disks with only bonded lubricant. In this paper, tribological characteristics of disks with and without mobile lubricant at the same lubricant thickness were compared using our transparent pin-on-disk wear tests. The results showed that pin wear was smaller on disks without mobile lubricant than those on disks with mobile lubricant in low load or slow speed conditions. The reason of this was considered to be the contact force increase by meniscus force due to lubricant bridge.

Si 3 N 4 reinforced Al6061 composite is fabricated by liquid metallurgy technique. Si 3 N 4 particles are nickel coated prior to addition to molten metal to improve its wettability and to ensure excellent bond between matrix and the reinforcement. Metallographic studies, friction and wear tests were carried out using pin on disc type machine. Coefficient of friction and wear rate were measured at loads varying from 20–100N and sliding velocities from 0.314–1.574m/s. It is observed that Al6061-4wt%Si 3 N 4 composites exhibited lower wear rate and lower coefficient of friction when compared with matrix alloy under all the test conditions studied.

The authors investigated the viability of UHMWPE composites for use in orthopaedic bearing applications as an alternative to crosslinking. Two composite systems were used, both based on a UHMWPE matrix: PtZr quasicrystals and Zr particle fillers. Through wear testing and impact toughness measurement it was shown that these two fillers produced composites that had high wear resistance and more impact toughness than the crosslinked polymer. These results suggest that further investigation into the use of composites for implant bearing surfaces is warranted and that appropriate criteria for filler materials must be developed to spur development of longer-lasting devices.

Tribological characteristics of Al-Si alloy impregnated graphite composite (ALGR-MMC) in contact with bearing steel were investigated under insufficiently lubricated reciprocating sliding conditions. Ball (JIS SUJ2 bearing steel) on disk (ALGR-MMC) type wear tests were conducted under unlubricated conditions , i.e., in air with high (70%) and low (≤ 1%) relative humidity (RH), under drop-feed lubrication , i.e., oil-drops were deposed on the disk surface before commencing the tests, and under immersion lubrication , i.e., the ball-on-disk contact was submerged in a oil (SAE30) bath. Reciprocating sliding movement was maintained, under a contact load of 40 N at a frequency of 3.3 Hz and amplitude of 3.5 mm, for 100,000 cycles. Tribological properties were continuously monitored. Variation of the kinetic friction coefficient (KFC) versus the number of reciprocating cycles (NRC) was obtained for various amounts of oil (lubrication conditions) and two values of the air RH. For drop-feed lubrication the KFC has at beginning the same value as that under immersed lubrication, but if breakdown of the oil film has occurred after a certain NRC, it increases towards the value corresponding to unlubricated conditions. Connected to the oil film breakdown, there is a certain transition range, expressible both in terms of the oil amount and NRC. Minimum quantity of oil to avoid the film breakdown was found. Due to its self-lubricating properties, ALGR-MMC was able to endure adverse lubrication conditions such as insufficiently lubricated reciprocating sliding.

Wear at the nanoscale is a key limitation of conventional silicon and silicon nitride atomic force microscope (AFM) probe tips. Tip degradation and contamination induced by tip-sample interactions can result in decreased resolution and uncertainty in AFM measurements. Prediction and control of the wear behavior is challenging since there is no rigorous theory for the wear of a <100 nm asperity. However, ultrananocrystalline diamond (UNCD) and diamond-like carbon (DLC) are potentially ideal materials for AFM probe applications because of their high stiffness and hardness, low surface roughness, low macroscale friction coefficient and wear, and chemical inertness. The nanoscale adhesion and wear behavior of UNCD, DLC, silicon, and silicon nitride AFM probes have been characterized through systematic AFM wear tests and characterization of the corresponding nanoscale modification of the tips through transmission electron microscopy (TEM) imaging, AFM-based adhesion measurements, and AFM-based blind reconstruction of the tip shape. Our results demonstrate that significant reductions in the nanoscale wear can be achieved through the use of these carbon-based materials. We will discuss how the nanoscale wear behavior of the tips can be linked to their intrinsic materials properties through consideration of the mechanics and physics of nanoscale contacts.

The present paper describes wear tests performed using human cartilage on cartilage under various working conditions. Wear was assessed by determining the concentration of proteoglycans (PG) and hydroxyproline in the lubricating solution.