Lubrication Ability Research Articles

Ti3C2Tx solid lubricant coatings in rolling bearings with remarkable performance beyond state-of-the-art materials

Two-dimensional (2D) transition metal carbides, nitrides, and carbonitrides, known as MXenes, are a growing class of 2D materials, which offer great solid lubrication ability for low friction applications due to their weakly bonded multi-layer structure and tribo-layer formation with self-lubricating characteristics. To date, most studies have assessed their tribological response in basic laboratory tests. However, these tests do not adequately reflect the complex geometries, kinematics, and stresses present in machine components. Here, we aim at bridging this gap through assessment of the friction and wear performance of multi-layer Ti3C2Tx MXene solid lubricant coatings used in rolling bearings. MXenes’ tribological response is compared with state-of-the art solid lubricant coatings, which include molybdenum disulfide (MoS2), tungsten-doped hydrogenated amorphous carbon (a-C:H:W), and hydrogen-free, more graphite-like amorphous carbon (a–C). Multi-layer Ti3C2Tx MXene coatings reduce wear on the bearing washers by up to 94%, which can be attributed to the transfer of the lubricious MXene nano-sheets to secondary tribo-contacts of the bearing. While the frictional torque of all solid lubricant coatings is similar during steady-operation, the MXene-coated bearings extend the service life by 30% and 55% compared to MoS2 and DLC, respectively. This contribution demonstrates the ability of MXene solid lubricant coatings to outperform state-of-the-art solid lubricants in dry-running machine components such as rolling bearings.

Investigation of a new water-based cutting fluid for machining of titanium alloys

Titanium alloys are difficult-to-cut materials and difficult to be lubricated. In this paper, a new synthetic water-based cutting fluid for titanium alloys is developed. The main ingredients which contain polar groups are easy to adsorb on titanium alloy and form a stable boundary lubricant film. The lubricating and anti-wear properties of the developed cutting fluid were tested and the results show that the use of the developed cutting fluid leads to a low friction coefficient. Moreover, the machining performance of the developed cutting fluid was further tested through tapping, milling, and drilling. The tapping torque, machining force, tool wear, and machined surface roughness were used to evaluate the cutting fluid. It was found that the developed cutting fluid could decrease both the machining force and tool wear and get good surface quality owing to its good lubricating ability for titanium alloys.

A novel method for the evaluation of the contamination dispersing ability of lubricants (CONTA-DISP)

Water and solid particulate contamination are the two most common contaminants of lubricated systems and may be highly problematic for these systems. To reduce downtime and prevent failure, lubricant formulations contain detergent and dispersant additives that play an important role in terms of contamination tolerance. In lack of a practical procedure for the determination of the relevant properties, a novel method for the evaluation of the dispersing ability of lubricating oils is introduced. Following and combining established lubricant analysis methods, a procedure with optimum parameters was found. An assessment of the method using fresh and artificially altered lubricating oils allowed a differentiation concerning their dispersing ability.

Influence of ecofriendly protic ionic liquids on the corrosion and lubricating properties of water-glycol

Three ecofriendly protic ionic liquids (PILs) from sebacic acid, caprylic acid and ricinoleic acid were investigated their anticorrosion and lubrication performances in water-glycol. Based on the analyses of wear scar and QCM-D, the adsorption capacities of the PILs are positively related to their lubrication abilities. Compared with other two PILs, RPR with the stronger adsorption affinity can promote the more significant improvement in the lubricity of water-glycol owing to compact adsorption layer and carbon film. In addition, the results of OCM-D and electrochemical corrosion test are not completely consistent. DSD with weaker adsorption capacity show higher corrosion inhibition property contrasted with CPC, although RPR still outperform DSD and CPC. The abnormal phenomenon is properly explained by quantum chemical calculation.

Oxidational wear in lubricated contacts – Or is it?

This study examines the influence of inert gas atmosphere on the wear behaviour of rubbing steel-on-steel contacts lubricated by two hydrocarbon base fluids, isooctane and hexadecane. It is found that for both fluids, wear and mean friction in nitrogen and argon atmospheres are considerably lower than in dry air. As the oxygen content in nitrogen is increased, mean friction and wear both increase, to level out above about 10% oxygen (an O2 partial pressure of 10 kPa). Raman analysis of rubbed surfaces shows the presence of a carbon film on surfaces rubbed in inert gas and at low O2 levels. This film is not observed at high O2 levels.These findings indicate that the prevailing model of oxidational wear in lubricated contacts, that states that wear is greater in air than in inert gas because of corrosion by oxygen, is largely incorrect. Instead, the deleterious effect of oxygen on lubricated wear is primarily due to it preventing the formation of a lubricious, carbon-based boundary film that is generated from hydrocarbon base fluids on rubbing steel surfaces in inert gas conditions.The ability of organic fuels and lubricants to form carbon-based films on rubbing steel surfaces in inert atmospheres may provide a mechanism for reducing friction and wear of fuel- and oil-lubricated machine components. The study also provides a platform from which to design lubricant formulations for use in inert atmospheres.

Fabrication and Characterization of a Multilayer Hydrogel as a Candidate for Artificial Cartilage

Bone and cartilage are highly organized tissues with gradient layered, which makes cartilage have good lubrication and bearing capacity. Inspired by the gradient structure of natural articular cartilage, the PVA–HA and PVA–HA–PAA composite hydrogels were selected to prepare a hierarchical bionic cartilage material by physical bonding. The lower PVA–HA composite hydrogel and the upper PVA–HA–PAA composite hydrogel provide excellent lubrication and loading-bearing ability to bionic cartilage materials, respectively. Furthermore, the cartilage–bone material was constructed by grafting the multilayer bionic cartilage hydrogel onto the UHMWPE after oxidation esterification to simulate the bone–cartilage hierarchical structure. The multilayer cartilage material has excellent tensile fracture properties (tensile strength 38.90 ± 1.5 MPa, 545 ± 32%, tensile modulus 1.73 ± 0.06 MPa), compression properties (compressive strength 3.1 ± 0.15 MPa, compressive modulus 4.47 ± 0.2 MPa), thermostability, friction properties (friction coefficient 0.035 ± 0.0028), and biocompatibility. Thus, the bionic cartilage material has a gradient-layered structure with high strength and low friction, which significantly improves the stability and life of artificial joints.

Tribological properties of Mo-S-C coating deposited by pulsed d.c. magnetron sputtering

Transition metal dichalcogenides such as MoS2 are widely used as solid lubricants for vacuum applications. On the other hand, diamond-like carbon coatings exhibit excellent sliding properties in the ambient environment. Our Mo-S-C coatings deposited by pulsed d.c. sputtering combine both structures to obtain stable properties regardless of the testing conditions. The coatings were studied using HR-TEM and Raman spectroscopy, revealing amorphous nature of the coating. The tribological properties were evaluated by pin-on-disc method. The results showed high lubrication ability in all the testing conditions. HR-TEM and Raman spectroscopy were employed to show the structural characteristics of the wear traces. Our results indicate that the low-friction effect should be attributed to carbon structure re-arrangement since expected wear-induced MoS2 formation was not observed.

On grinding force ratio, specific energy, G-ratio and residual stress in SQCL assisted grinding using aerosol of MWCNT nanofluid

In the present investigation, water based multi-walled carbon nanotube (MWCNT) dispersed nanofluid was produced and used as a cutting fluid in small quantity cooling lubrication (SQCL) assisted grinding of hardened AISI52100 steel. The work material was ground by an alumina wheel. The SQCL technology utilizes atomized aerosol of liquid grinding fluid. Use of MWCNT nanofluid aerosol in place of soluble oil was found to be substantially beneficial in reduction of specific energy and development of compressive residual stress on ground surface. The steady and lower value of the force ratio (tangential to normal grinding force, Ft/Fn) was suggestive of the superior lubrication and grit sharpness retention ability of the aerosol of MWCNT nanofluid. Higher compressive residual stress on the ground surface under MWCNT nanofluid environment suggests lesser grinding zone temperature, which can be attributed to its superior wettability, lubricity and heat dissipation ability of the MWCNT nanofluid. The consumption rate of grinding fluid in SQCL was varied. It could be reduced to 200 ml/h for MWCNT nanofluid to obtain an almost similar or better effect to that of 500 ml/h for soluble oil. Lesser surface tension of MWCNT nanofluid, compared to its counterpart, seemed to facilitate wetting, thus improving lubrication and heat transfer capability further.

Sonication-assisted solvothermal synthesis of noncovalent fluorographene/ceria nanocomposite with excellent extreme-pressure and anti-wear properties

This work aims to improve the dispersion and lubrication properties of fully fluorinated graphene (FG) with little influence on its fluorine content. A simple sonication-assisted solvothermal method was used to improve FG's wear-resistance property and relatively low oil dispersion stability by preparing hierarchical-structured FG/ceria (FG/CeO2) nanocomposite. With the coaction of sonication and solvothermal treatment, the CeO2 nanoparticles are decently distributed over the FG nanosheets, and no noticeable decrease of relative fluorine content is observed after the treatment. The nanocomposite shows excellent synergistic effects in dispersibility and oil lubrication ability. Without influencing FG's original extreme pressure performance, the addition of CeO2 nanoparticles improves FG's oil dispersion stability and significantly enhances FG's anti-wear performance under the extreme working loads.

The role of synovial fluid constituents in the lubrication of collagen-glycosaminoglycan scaffolds for cartilage repair

Extracellular matrix (ECM)-derived scaffolds have shown promise as tissue-engineered grafts for promoting cartilage repair. However, there has been a lack of focus on fine-tuning the frictional properties of scaffolds for cartilage tissue engineering as well as understanding their interactions with synovial fluid constituents. Proteoglycan-4 (PRG4) and hyaluronan (HA) are macromolecules within synovial fluid that play key roles as boundary mode lubricants during cartilage surface interactions. The overall objective of this study was to characterize the role PRG4 and HA play in the lubricating function of collagen-glycosaminoglycan (GAG) scaffolds for cartilage repair. As a first step towards this goal, we aimed to develop a suitable in vitro friction test to establish the boundary mode lubrication parameters for collagen-GAG scaffolds articulated against glass in a phosphate buffered saline (PBS) bath. Subsequently, we sought to leverage this system to determine the effect of physiological synovial fluid lubricants, PRG4 and HA, on the frictional properties of collagen-GAG scaffolds, with scaffolds hydrated in PBS and bovine synovial fluid (bSF) serving as negative and positive controls, respectively. At all compressive strains examined (ε = 0.1–0.5), fluid depressurization within hydrated collagen-GAG scaffolds was >99% complete at ½ minute. The coefficient of friction was stable at all compressive strains (ranging from a low 0.103 ± 0.010 at ε = 0.3 up to 0.121 ± 0.015 at ε = 0.4) and indicative of boundary-mode conditions. Immunohistochemistry demonstrated that PRG4 from recombinant human (rh) and bovine sources adsorbed to collagen-GAG scaffolds and the coefficient of friction for scaffolds immersed in rhPRG4 (0.067 ± 0.027) and normal bSF (0.056 ± 0.020) solution decreased compared to PBS (0.118 ± 0.21, both p < 0.05, at ε = 0.2). The ability of the adsorbed rhPRG4 to reduce friction on the scaffolds indicates that its incorporation within collagen-GAG biomaterials may enhance their lubricating ability as potential tissue-engineered cartilage replacements. To conclude, this study reports the development of an in vitro friction test capable of characterizing the coefficient of friction of ECM-derived scaffolds tested in a range of synovial fluid lubricants and demonstrates frictional properties as a potential design parameter for implants and materials for soft tissue replacement.

Auto-Ignition of Gas Turbine Lubricating Oils in a Shock Tube Using Spray Injection

Abstract In choosing the lubricating oil for a gas turbine system, properties such as viscosity, viscosity index, corrosion prevention, and thermal stability are chosen to optimize turbine longevity and efficiency. Another property that needs to be considered is the lubricant's reactivity, as the lubricant's ability to resist combustion during turbine operation is highly desirable. In evaluating a method to define reactivity, the extremely low vapor pressure of these lubricants makes conventional vaporization by heating impractical. To this end, a new experiment was designed and tested to evaluate the reactivity of lubricating oils using an existing shock-tube facility at Texas A&amp;M University equipped with an automotive fuel injector. This experiment disperses a premeasured amount of lubricant into a region of high-temperature air to study auto-ignition. To ensure proper dispersal, a laser extinction diagnostic was used to detect the lubricant particles behind the reflected shock as they are dispersed and vaporized. An OH* chemiluminescence diagnostic was used to determine ignition delay time. Using this method, various 32-, 36-, and 46-weight lubricants identified as widely used in the gas turbine industry were tested. Experiments were conducted in postreflected shock conditions around 1370 K (2006 °F) and 1.2 atm, where ignition delay time, peak OH* emission, and time-to-peak values were recorded and compared. Ignition was observed for all but one of the lubricants at these conditions, and mild to strong ignition was observed for the other lubricants with varying ignition delay times.

Enhanced Lubrication Ability of Polyalphaolefin and Polypropylene Glycol by COOH-Functionalized Multiwalled Carbon Nanotubes as an Additive

In the current study, the tribological performance of two different synthetic lubricants, i.e., polyalphaolefin (PAO 100) and polypropylene glycol (PPG 2000), were analyzed. The COOH-functionalized multiwalled carbon nanotubes (MWCNTs) were used as an additive in varying fractions (0.025-0.15 wt.%). The friction and wear studies were carried out as per ASTM D6425 by using SRV 5 tribometer with a ‘ball on disk’ configuration. The results showed that tribological performance gets enhanced remarkably with the inclusion of MWCNTs in both lubricants as compared to the pure lubricants. PAO 100 demonstrated the lowest coefficient of friction and wear volume at a concentration of 0.025 and 0.05 wt.% of MWCNTs, respectively. However, 0.025 wt.% of additive in PPG 2000 exhibited the maximum reduction in the coefficient of friction (~6%) and wear volume (~86%). The results confirmed that PAO 100 showed better tribological performance as compared to PPG 2000. The lubrication mechanism of MWCNTs has been demonstrated through the investigation of worn steel ball surfaces by using various characterization techniques such as scanning electron microscope, energy-dispersive x-ray spectroscopy (EDS) and scan probe microscope.

Investigation of role of cartilage surface polymer brush border in lubrication of biological joints

Although experimental evidence has suggested that the polymer brush border (PBB) on the cartilage surface is important in regulating fluid permeability in the contact gap, the current theoretical understanding of joint lubrication is still limited. To address this research gap, a multiscale cartilage contact model that includes PBB, in particular its effect on the fluid permeability of the contact gap, is developed in this study. Microscale modeling is employed to estimate the permeability of the contact gap. This permeability is classified into two categories: For a gap size > 1 µm, the flow resistance is assumed to be dominated by the cartilage roughness; for gap size < 1 µm, flow resistance is assumed to be dominated by the surface polymers extending beyond the collagen network of the articular cartilage. For gap sizes of less than 1 µm, the gap permeability decreases exponentially with increasing aggrecan concentration, whereas the aggrecan concentration varies inversely with the gap size. Subsequently, the gap permeability is employed in a macroscale cartilage contact model, in which both the contact gap space and articular cartilage are modeled as two interacting poroelastic systems. The fluid exchange between these two media is achieved by imposing pressure and normal flux continuity boundary conditions. The model results suggest that PBB can substantially enhance cartilage lubrication by increasing the gap fluid load support (e.g., by 26 times after a 20-min indentation compared with the test model without a PBB). Additionally, the fluid flow resistance of PBB sustains the cartilage interstitial fluid pressure for a relatively long period, and hence reduces the vertical deformation of the tissue. Furthermore, it can be inferred that a reduction in the PBB thickness impairs cartilage lubrication ability.

Adsorption and Lubrication of α-Gel (α-Form Hydrated Crystal) Dispersion at Solid/Liquid Interfaces.

We characterized the adsorption and desorption of α-gel (α-form hydrated crystal) dispersions in aqueous media using a quartz crystal microbalance with dissipation monitoring (QCM-D) technique. The α-gel was formed from a mixture of N-[3-(dimethylamino)propyl]docosanamide (APA-22) L-lactic acid salt, 1-octadecanol (C18OH), and water. The solid substrate employed in this study as a model for hair was silica. The QCM-D measurements revealed that the α-gel dispersions yielded a rigid adsorption film on the negatively charged silica surface. The adsorption mass decreased with decreasing domain size (on the micrometer scale) of the α-gel dispersions. The adsorption film highly restricted the desorption of the α-gel from the silica surface even after rinsing with water. The adsorption film also exhibited excellent lubrication ability in aqueous media both before and after rinsing with water. We expect that the α-gel formed by APA-22 L-lactic acid is a potential ingredient for formulating an environment-friendly hair conditioner owing to its high adsorption, limited desorption, and excellent lubrication abilities on the solid surface.

Оценка стабильности смазывающей способности дизельных топлив при их искусственном окислении и опытном хранении

The paper is given to investigation and definition of optimal parameters of oxidation of diesel fuels for the purpose of estimation its lubrication stability under the storage conditions. On the foundation of critical analyze of previous method’s parameters it were corrected the volume of oxidating fuel, the type of catalyze-active metal, which is contacting the fuel and also the fuel-metal and fuel-air contact-square. These corrections are allowed to increase the adequacy of chemical composition changes of diesel fuel at the oxidation to the same changes at the storage conditions. It was found that using the cuprum as the catalyze-active material of storage tanks increases the appearance of carbonyl and carboxyl oxidation products and decreases the appearance of hydroxyl oxidation products that is not adequately the chemical changes of diesel fuels while its storage in steel tare. On the foundation of three samples of diesel fuel investigation was found that decreasing of lubrication ability of diesel fuel at its storage for the 10 months could be forecasted by its oxidation via the developed method at least of 2, 4 and 6 hours with the following estimation lubrication ability of oxidated samples.

Molecular dynamics simulation and experimental investigation of tribological behavior of nanodiamonds in aqueous suspensions

The tribological performance of nanodiamonds (ND) in aqueous suspensions was investigated via experiments and molecular dynamics (MD) simulations. The results indicated that the introduction of ND significantly improved the naturally poor lubrication ability of water. The best performance was characterized by reductions of 70% and 88% in friction and wear, respectively. The enhancement of the tribological performance was mainly attributed to the ball-bearing effect of the ND. The rolling motion of the nanodiamond particles was verified by MD simulation. Moreover, results indicated that the lubrication quality of the ND was affected by the sonication process in the nano lubricant preparation.

Semi-convertible Hydrogel Enabled Photoresponsive Lubrication

Summary A semi-convertible hydrogel with reversible photoresponsive supramolecular lubricating ability is demonstrated by integrating a responsive supramolecular system of α-cyclodextrins/polyethylene glycol (α-CD/PEG) and competitive guest 1-[p-(phenylazo)benzyl]pyridinium bromide (AzoPB) within a poly(vinyl alcohol) (PVA) and polyacrylamide (PAAm) framework. The competitive host-guest interaction between α-CD/PEG supramolecular network and AzoPB after UV and visible-light irradiation enables the appearance and disappearance of the sol-state layer on the hydrogel surface while the PVA and PAAm consistently keeps the framework. This semi-convertible process realizes the reversible photoresponsive lubricating ability and variable toughness. We envision that this finding will offer a possible way for fabricating novel smart devices far beyond lubrication, leading to an emerging branch of interdisciplinary materials science that integrates supramolecular chemistry, hydrogel, and surface science.

Tribological performance of ionic liquid‐lubricated carbon brush/collector ring current‐carrying friction system

The lubricity and anti-wear ability of ionic liquids (ILs) were studied by a current-carrying friction test on IL-lubricated carbon brushes. The results indicated that the conductivity and wear resistance of different ILs are different, and may vary for different carbon brushes. The E468e carbon brush was found to be more sensitive to IL lubrication than D172 carbon brush. Importantly, an analysis of the wear surfaces of the D172 and E468e carbon brushes revealed that, due to the different materials of the two carbon brushes and the composition of the IL, the lubrication effect on the carbon brushes was different. The viscosity of the IL will affect its wettability on the carbon brush surface. The better the wettability, the easier the movement of ions on the surface, which makes it easier to form a conductive physical adsorption film. Therefore, in practice, a better IL must be selected by considering the wettability of IL and carbon brushes.

Simple method for preparing nanometer thick Ti3C2TX sheets towards highly efficient lubrication and wear resistance

MXene, as a two-dimensional material with excellent properties, has been applied in many fields. However, there is little attention paid to the preparation methods of MXene nanosheets. Herein, we report a novel and simple method for preparing Ti3C2TX nanosheets by using alternate pressure (AP)assisted, where the yield can achieve 42.4% and the thickness of nanosheet is about 2 nm. Moreover, the presence of hydrophilic functional groups on the surface made Ti3C2TX suitable to be used as water lubricating additives, which displays highly efficient lubrication (~34.74%) and wear resistance (~45.58%) ability compared with pure water. Our work provides not only a new strategy to yield Ti3C2TX nanosheets, but also an exploration of their tribological behaviors as water lubrication nanoadditive.

Superlubricity of Zwitterionic Bottlebrush Polymers in the Presence of Multivalent Ions.

In this study, we report lubrication properties of physisorbed zwitterionic bottlebrush polymers in the presence of multivalent ions using the surface force apparatus. Unlike polyelectrolyte brushes, the lubrication properties of which diminish drastically in the presence of multivalent ions at concentrations as low as 0.1 mM, zwitterionic bottlebrush polymers exhibit friction coefficients as low as ∼10-3 at such concentrations of multivalent ions up to intermediate normal loads. This lubrication ability persists until surface wear occurs at high normal loads. The surface wear is demonstrated to be triggered by the multivalent ions bridging the polymer chains and dehydrating the zwitterionic moieties. Finally, the analysis of the polymer film stability suggests that the partial desorption of polymers in the presence of the ions does not affect the lubrication performance. Therefore, even in the physisorbed state, zwitterionic brushes perform significantly better than covalently grafted polyelectrolyte brushes in the presence of multivalent ions.