Friction Reduction Research Articles

Influence of Electrical Stimulation on the Friction Performance of LiPF6-Based Ionic Liquids

This work studied the influence of the voltage parameters on the friction and superlubricity performances of LiPF6-based ionic liquids (ILs). The results show that the voltage direction and magnitude greatly affected the friction performances of ILs and that macroscale superlubricity can be achieved with a stimulation of −0.1 V. The surface analysis and experiment results indicate that the voltage magnitude influences the coefficient of friction (COF) by determining the types of substances in the tribochemical film formed on the ball, while the voltage direction influences the COF by affecting the adsorption behavior of Li(PEG)+ ions on the ball. At −0.1 V, the cation group Li(PEG)+ adsorption film and FeOOH-containing tribochemical film contribute to friction reduction. The formation of FexOy within the tribochemical film results in an increase in friction at −0.8 V. The limited adsorption of Li(PEG)+ ions and the formation of FexOy contribute to the elevated COF at +0.1 V. This work proves that the friction performances of LiPF6-based ILs could be affected by voltage parameters. A lubrication model was proposed hoping to provide a basic understanding of the lubrication mechanisms of ILs in the electric environment.

Impact of oil supply conditions on water lubrication assisted with minimal secondary lubricating medium

Abstract Previous research has revealed that introducing a secondary lubricating medium can temporarily enhance water-lubricated bearing performance, thereby reducing the risk of lubrication failure under challenging conditions. This study aims to identify the optimal injection point for the secondary lubricating medium and evaluates oil supply rate effects. Experiments are conducted using a block-on-ring test rig, complemented by CFD simulations to elucidate the underlying mechanisms. Three oil supply settings, upstream, inlet and outlet of the contact region, are compared. Results shows that upstream oil supply led to a lower critical speed at which the added oil loses any effect compared to the inlet oil supply and outlet oil supply. The effect of oil supply rates on friction reduction varies among the oil supply settings and ring rotational speeds. In conclusion, the most effective oil supply setting positions the injector at the outlet of the contact region, outperforming placement at the entrance of the contact region.

The Effect of Lubricity of Calcium Sulfonate on ZnDTP and MoDTC

Reduction of friction and wear by lubrication is necessary to improve the efficiency and prolong the lifespan of industrial machinery. However, several aspects regarding the lubrication effects in additive-combined oil are still unresolved. This study focuses on the effects of combining zinc dialkyldithiophosphate (ZnDTP), molybdenum dithiocarbamate (MoDTC), and Ca sulfonate on the frictional behavior of poly-α-olefin 4 (PAO4) lubricant oils. Ball-on-disk friction tests demonstrated that the exclusive addition of high-base Ca sulfonate solution reduced friction and wear of the lubricating oil. When combined with ZnDTP and MoDTC, the friction coefficients of PAO with high-base and low-base Ca sulfonate are affected by competitive reactions on the sliding surface. Quartz crystal microbalance with dissipation monitoring measurements suggests that high-base Ca sulfonate forms a stronger adsorption film than low-base Ca sulfonate. Atomic force microscope observations confirmed that the addition of low-base Ca sulfonate reduced friction and wear, whereas high-base Ca sulfonate induced competitive reactions with ZnDTP and MoDTC. This study provides valuable insights into the effects of the combination of additives on the lubricity of PAO and their impact on friction and wear characteristics, which are valuable for the design of suitable lubricants for industrial machinery.

Preparation and self-lubricity investigation of CNTs/Ni composite coatings under severe conditions

Carbon nanotubes (CNTs) demonstrate the potential to improve the tribological properties of nanocomposite coatings. Herein, CNTs/Ni composite coatings were quickly fabricated by the direct current (DC) electrodeposition. The adhesion strength was estimated by the scratch test incorporation with an acoustic emissive signal. Much attention was paid on the self-lubricity of the CNTs/Ni composite coating under severe conditions. Results indicated that presence of CNTs enhanced the adhesion strength of the pure Ni coating. Notably, CNTs contributed towards 54.5 % of friction reduction in comparison to the pure Ni coating at dry friction. The improvement of tribological properties was attributed to that under high contact stress the embedded CNTs were crushed to tiny lubricating particles and produced protective film on rubbing surfaces.

Dual effect of roughness during earthquake rupture sequences on faults with strongly rate-weakening friction

We numerically model earthquake rupture cycles on non-planar faults governed by rate and state friction with an enhanced dynamic weakening in the form of flash heating, investigating quantitatively the relationship between the fault geometry, stresses from the preceding earthquakes, and the rupture characteristics. On planar faults, earthquakes with similar magnitudes and stress drops periodically rupture the entire fault, propagating under a low background shear-to-normal stress ratio as self-healing slip pulses due to the large friction reduction, with a sub-Rayleigh rupture speed. Faults with low roughness levels generally show a similar pattern. Prior to some events, the stress ratio along the fault slightly increases, leading to ruptures with secondary slip pulses. As roughness increases, the stresses become more heterogeneous, leading to a more complex cycle with part of the ruptures arresting at restraining bends with a low stress ratio. Sequences of several partial ruptures lead to a significant stress accumulation on the locked fault segments. These are eventually released by crack-like earthquake ruptures with supershear propagation speed and significantly larger magnitudes, stress drops, and radiated energy than typical planar fault events. Therefore, while fault roughness provides a mechanism for rupture arrest, consistent with previous studies, it can also result in a substantial increase in earthquake magnitudes, which should be considered in hazard assessments.

Numerical and Experimental Study of a Sector-Shaped Surface Texture in Friction Reduction

Numerical and Experimental Study of a Sector-Shaped Surface Texture in Friction Reduction

A Comparative Analysis of Mechanical Properties of Polyetheretherketone (PEEK) vs. Standard Materials Used in Orthodontic Fixed Appliances: A Systematic Review.

Polyetheretherketone (PEEK), an organic thermoplastic polymer, has gained interest in dentistry due to its excellent mechanical strength, flexibility, and biocompatibility. Furthermore, the ability to utilize CAD/CAM in the fabrication of PEEK enhances accuracy, reliability, and efficiency while also saving time. Hence, several orthodontic studies have explored the utilization of PEEK in various applications, such as archwires, brackets, fixed lingual retainers, palatal expansion devices, transpalatal arches, Tübingen palatal plates, different types of space maintainers, mini-implant insertion guides, and more. However, a complete systematic review of the available data comparing the performance of PEEK with traditional orthodontic materials has not yet been conducted. Therefore, this systematic review seeks to assess if PEEK material meets the required mechanical criteria to serve as an alternative to conventional orthodontic appliances. To ensure clarity and precision, this review will specifically concentrate on fixed appliances. This systemic review followed the PRISMA guidelines and utilized databases including PubMed/MEDLINE, Embase, Springer, Web of Science, and Wiley. Searches were restricted to English language articles from January 2013 to February 2024. Keywords such as "Polyetheretherketone" or "PEEK" and "Orthodontic" or "Orthodontic device" or "Orthodontic materials" were employed across all databases. Nine studies were incorporated, covering orthodontic archwires, brackets, and fixed lingual retainers. Based on the reviewed literature, PEEK demonstrates promising potential in orthodontic fixed appliances, offering advantages in force delivery, friction reduction, and aesthetic appeal. Further research is needed to fully explore its capabilities and optimize its application in clinical practice.

Toward the Improvement of the Mechanical and Tribological Properties of Braided Ligament for ACL Reconstruction: A "Carrot and Stick" Strategy.

Bone tunnel enlargement has been troubling the clinical adoption of braided artificial ligaments for decades, to which mechanical and tribological performance promotion shall be an effective and promising approach. Herein, a "carrot and stick" strategy has been introduced with two types of polyethylene terephthalate (PET) fibers to fabricate hybrid textures, which is expected to advance fatigue and tribological performance without yielding essential mechanical strength and biocompatibility. Owing to advancements in such a "carrot and stick" strategy, the obtained grafts present three promising properties: i) enhancement of mechanical strength; ii) coefficient of friction (COF) reduction of 25% at the greatest extent, thus lowering the risk of bone tunnel enlargement; iii) final displacement shrinkage of graft length after cyclic loadings, favored in the clinic for isometric reconstruction. The results obtained in this study show that the "carrot and stick" strategy can be a creative and convenient method to optimize the service life, saving the complication rate of artificial ligaments for clinical applications.

A new approach to contact angle measurement and effects of evaporation on the contact angle

The solid material's wettability behavior is determined by the contact angle value. The wettability of materials is critical in the coating, lubricating, and insulating industries. In high-tech industries including corrosion resistance, water-oil separation, medical material production, implant technology, and friction reduction, the contact angle is very important. A new method called the full angle method was used to measure the contact angle and compared with current methods. The wettability behavior of plexiglass, which is employed in a variety of applications ranging from lighting to decorating, and industrial designs to accessory production, was explored in this study. The measurement of the contact angle was done by dropping 1.8 M (molar) of saltwater over the plexiglass materials. In order to examine the effect of evaporation on the contact angle, changes in contact angle, height and baseline were investigated depending on the waiting time. 

Influence of Few-Layer Graphene on Frictional Properties of Lithium Compound Grease

The frictional properties of lithium compound grease (LCG) with different percentage compositions of few-layer graphene (FLG) were investigated, and the mechanisms of temperature and loading effects on LCG containing FLG are also considered. The concluding effect shows that 1 wt% FLG is more appropriate for friction and wear modifiers for lithium compound grease at elevated temperatures and less suitable at ordinary temperatures. Thickener chemisorption film, FLG layering film, and tribo-reaction film consisting of FeO(OH), Fe2O3, Fe3O4, Li2O, and other oxides assist in the establishment of a lubricating boundary film on the friction interfaces lubricated with LCG containing FLG. The poor fluidity of lithium compound grease at low temperatures leads to poor dispersion of FLG, decreasing friction reduction capability. Under elevated temperature and low load condition, adding 1wt% FLG to LCG can only improve its wear-resistant property, the abrasion volume of steel plate reduced by 24.49%. Under elevated temperature and high load condition, adding 1wt% FLG to LCG can only enhance its anti-friction characteristics.. Conversely, FLG is unsuitable as an anti-friction and wear-resistant additive for LCG at low-temperature conditions.

Current carrying tribological properties of multi arc ion plated titanium nitride doped silver coating

Sliding electrical contact materials play a crucial role in the transmission and conversion of electrical energy, but due to various factors such as force, electricity, and heat, the interface exhibits complex wear behavior. A single solid or liquid lubrication system can no longer meet the growing performance requirements of current carrying tribology. In this study, a TiN-Ag coating was prepared using multi arc ion plating technology, and a solid–liquid composite lubrication system was formed with ionic liquid and polyurea grease, respectively. Through current carrying friction and wear tests, their tribological properties, electrical contact resistance(ECR) values, and stability were tested, and compared with the results obtained during dry friction. The coating and worn surfaces were analyzed using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The results indicated that compared with dry friction, TiN-Ag coatings lubricated with ionic liquids and polyurea grease showed higher friction reduction, wear resistance, and conductivity, especially the synergistic effect between ionic liquids and coatings is prominent. The behavior of ionic liquids under voltage was analyzed, and it was found that ionic liquids formed a physical adsorption film composed of a mixture of anions and cations on the worn surface. The ordered layered structure improved the tribological performance of the system.

In-situ tribo-induced formation of superb lubricious carbon-based tribofilms on the catalytical active MoN-Ag film surfaces

The establishment of environmentally friendly lubrication systems is of significant importance to the sustainable development. Here, we demonstrated an environmentally friendly approach, where superb lubricious carbon-based tribofilms formed in situ originating from base oil through tribochemical reactions, on the surfaces of catalytically active MoN-Ag film. We focused on the study of the tribological behavior of the MoN-Ag/oil solid-liquid system under varying loads. Through detailed characterization analysis of the carbon-based tribofilms, we elucidated the mechanism of friction reduction and wear resistance of the MoN-Ag film in the base oil, as well as the formation mechanism of carbon-based tribofilms. Furthermore, we provided a thermodynamic perspective to clarify the influence of load on the tribo-induced tribochemical reactions within the MoN-Ag/oil solid-liquid system.

Rheological and tribological properties of ZrP intercalation compounds as lubricating grease thickener

ABSTRACT Here, we study layered zirconium phosphate intercalated with octadecyltrimethylammonium bromide (STAB-ZrP) as a thickener by thickening five types of base oils. The thickening ability and fluidity behavior of STAB-ZrP gel were evaluated using rheological measurements. The tribological properties of STAB-ZrP gel were investigated using a reciprocating tribometer under temperatures of 25 °C and -15 °C. The rheological results showed that STAB-ZrP gel had grease-like characteristics. Naphthenic and alkyl naphthalene as the base oil can lead to the higher thickening ability. Naphthenic oil maintained the most colloidal stability at 25 °C and -15 °C. STAB-ZrP gel exhibited superior anti-wear and friction reduction, owing to the formation of a solid protective film on the contact interface. The layered structure and morphology of STAB-ZrP after thickening were confirmed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). This research established the relationship of STAB-ZrP with base oils in terms of their performance. STAB-ZrP acts as both a thickener and a solid additive in the STAB-ZrP gel system. This study can serve a beneficial trial for future preparations of lubricating grease.

Ionic liquid lubricity enhancement with bio-oil derived from microwave pyrolysis of bamboo

In response to the growing demand for environmentally friendly lubrication, this study explores the potential of bio-oil-infused lubricants. The investigation focuses on the interaction between bio-oil, derived from raw bamboo (Phyllostachys edulis) through microwave pyrolysis at power levels between 500 and 800 W at 700 ∘C, and the protic ionic liquid, [Oley][Oleic]. The bio-oil, predominantly composed of diethyl phthalate (DEP) and fatty acid methyl ester (FAME), is blended with [Oley][Oleic] at concentrations of 1.0, 2.0, and 5.0 wt%. Friction measurements using a ball-on-disk setup reveal a substantial 58.9% reduction in friction and a 30.6% reduction in wear when [Oley][Oleic] is combined with bio-oil pyrolysed with a microwave power of 800 W. To maintain a low coefficient of friction (CoF) and wear for [Oley][Oleic], it is imperative to aim for an optimal DEP:FAME ratio in the bio-oil of approximately 2.0, within concentrations ranging from 0.2 to 1.0 wt%. The study highlights the complex tribological balance among viscosity, load-bearing capacity, and the chemical nature of bio-oil components, contributing to enhanced lubricity. As industries increasingly seek eco-friendly lubrication, this study offers a valuable knowledge base for developing sustainable and high-performance lubricants derived from renewable biomass sources.

Dual in-situ observation of tribochemical and morphological evolution of single-layer WS2 and multi-layer WS2/C coatings

AbstractThe outstanding tribological performance of transition metal dichalcogenides (TMDs) is attributed to their unique sandwich microstructure and low interlayer shear stress. This advantageous structure allows TMDs to demonstrate exceptional friction reduction properties. Furthermore, the incorporation of TMDs and amorphous carbon (a-C) in multi-layer structures shows excellent potential for further enhancing tribological and anti-oxidation properties. Amorphous carbon, known for its high ductility, chemical inertness, and excellent wear resistance, significantly contributes to the overall performance of these multi-layer coatings. To gain an in-depth understanding of the tribological mechanism and evolution of TMDs’ multi-layer coatings, a dual in-situ analysis was carried out using a tribometer equipped with a 3D laser microscope and a Raman spectrometer. This innovative approach allowed for a comprehensive evolution of the tribological, topographical, and tribochemical characteristics of both single-layer WS2 and multi-layer WS2/C coatings in real time. The findings from the dual in-situ tribotest revealed distinct failure characteristics between the single-layer WS2 coating and the multi-layer WS2/C coating. The single-layer WS2 coating predominantly experienced failure due to mechanical removal, whereas a combination of mechanical removal and tribochemistry primarily influenced the failure of the multi-layer WS2/C coating. The tribological evolution process of these two coatings can be classified into four stages on the basis of their tribological behavior: the running-in stage, stable friction stage, re-deposition stage, and lubrication failure stage. Each stage represents a distinct phase in the tribological behavior of the coatings and contributes to our understanding of their behavior during sliding.

Solid lubrication performance of multi-layered V2CTx coatings

MXenes induce excellent wear resistance under solid lubrication due to their distinctive surface chemistry, easy-to-shear ability, and capability to form low-friction and wear-resistant tribofilms. However, beyond the extensively studied Ti3C2Tx, other promising members of the MXene family remain largely underexplored. Therefore, we spray-coated multi-layer vanadium carbide (V2CTx) coatings (thickness ∼10.8 μm) on steel substrates and studied their tribological performance for prolonged times (10,000 cycles) using a reciprocating ball-on-disk tribometer with acting contact pressure of 445 MPa in ambient conditions. Results show that V2CTx-coated substrates demonstrate an 8-fold reduction in friction (COF of 0.11) and a 10-fold wear rate reduction (1.405 × 10−6 mm3 N−1 m−1). High-resolution materials characterization confirmed that the remarkable tribological performance of these coatings can be traced back to the formation of protective films on the substrate (tribofilm) and counterbody (transferfilm) consisting of contact pressure and frictional heat-induced degraded, deformed, exfoliated V2CTx nanosheets, nanocrystalline oxides, and amorphous carbon debris. This work fully elucidates the tribological potential of V2CTx, which is of utmost relevance for designing high-performance lubricating materials. Our work has assessed the performance of multi-layer V2CTx (M2XTx) due to its remarkable thermal stability, low molecular weight, good mechanical properties, and high interlayer spacing, thus serving as an entry point into diverse MXene compositions, including M4X3Tx (V4C3Tx).

Micropitting performance and friction behaviour of DLC coated bearing steel surfaces : On the influence of Glycerol-based lubricants

A better understanding about the rolling contact fatigue and micropitting performance of machine component surfaces lubricated with environmentally friendly lubricants is critical to designing and further formulating new lubricants intended to be used in rolling–sliding contacts such as those found in gear and bearing applications. In this work, the frictional behaviour and rolling contact fatigue (RCF) performance of DLC, Cr/a-WC:H/a-C:H and a-C:Cr coatings under glycerol-based lubrication in rolling sliding contact conditions have been investigated. Traction maps, Stribeck curves, and fatigue plots have been generated by using a micropitting test rig (MPR). The initiation and progression of micropitting was monitored by means of white light optical interferometry and scanning electron microscopy (SEM). Results indicated that glycerol-based lubricants exhibited a significant friction reduction as the hydrodynamic effect is enhanced at higher rolling-speeds. Under boundary lubrication the friction coefficient was significantly higher compared to the values obtained with a commercial mineral-based transmission oil. Compared to uncoated steel surfaces, DLC coatings effectively reduced the volume loss and micropitting progression. Irrespective of the coating thickness, DLC showed an excellent tribological behaviour when the base lubricant favours the onset of mild-wear, over micropitting. When the lubricant formulation favoured the onset of micropitting, the coatings tended to prematurely fail due to debonding from the substrate, and local micro-spallation. The experiments demonstrated that friction reduction does not necessarily correspond with a reduction of micropitting.

Water weakening and the compressive brittle strength of carbonates: Influence of fracture toughness and static friction

Water is ubiquitous within the pore space of rocks and has been shown to affect their physical and mechanical behaviour. Indeed, water can act on the rock strength via mechanical (i.e., reducing the effective stresses) or chemical effects (e.g., mineral dissolution, mineral alteration, subcritical crack growth, etc.). As rock macroscopic strength is controlled by both fracture toughness and friction at the grain-scale, these parameters should also be affected in presence of water. While some recent studies have measured the effect of water on both fracture toughness and frictional parameters to constrain the water weakening of porous rock compressive strength, the physical parameters, or rock characteristics, that influence this weakening are as of yet unclear. Here, we report a series of laboratory experiments in order to determine the influence of a water-saturated, as opposed to dry, environment on five limestones’ strengths. The uniaxial compressive strength, the mode-I fracture toughness and the static friction parameters are of interest. The experiments show that, for the tested limestones, water-saturated conditions provoke a reduction of the uniaxial compressive strength by up to 53 %. This reduction is accompanied by a reduction of the mode-I fracture toughness by up to 34 % and of the static friction by up to 16 %. Even though the water weakening of the uniaxial compressive strength is not influenced by the sample porosity, the mode-I fracture toughness reduction in the presence of water is accentuated for high-porosity limestones. Additionally, low porosity limestones appear to promote higher static friction reductions in water-saturated environments.

Green lubrication: Mustard oil-based bio-lubricant enhanced with waste eggshell-derived CaO nanoparticles for sustainable and eco-friendly industrial solutions

The adoption of bio-lubricants derived from vegetable oils is pivotal in advancing environmental sustainability and mitigating the ecological impact of industrial machinery. This study introduces a groundbreaking bio-lubricant formulated with mustard oil as the base, augmented by CaO nanoparticles synthesized from waste eggshells. The CaO nanoparticles were synthesized through a sol-gel method and meticulously characterized via scanning electron microscopy (SEM) and X-ray diffraction (XRD). This investigation delves into the tribological, rheological, and thermal properties of the developed bio-lubricant, highlighting its potential as a sustainable alternative. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were employed to evaluate thermal stability and cold flow properties, revealing promising results. A comparative study with commercially available engine oil (SAE20W40) underscores the superior performance of the bio-lubricant. The key innovation lies in the incorporation of CaO nanoparticles, facilitated by a surfactant, which substantially enhances wear and friction reduction, lubrication qualities, shear stability, viscosity-temperature behavior, and thermal stability. These advancements position our bio-lubricant as a high-performance, environmentally friendly substitute for conventional lubricants. The study's findings underscore its potential for widespread industrial adoption, promising a transformative shift towards sustainable and eco-conscious lubrication practices.

Tribological performances of MoS2/C60 nanocomposite as lubricating additive in dioctyl sebacate

Purpose This paper aims to solve the problems molybdenum disulfide (MoS2) nanosheets suffer from inadequate dispersion stability and form a weak lubricating film on the friction surface, which severely limits their application as lubricant additives. Design/methodology/approach MoS2/C60 nanocomposites were prepared by synthesizing molybdenum disulfide (MoS2) nanosheets on the surface of hydrochloric acid-activated fullerenes (C60) by in situ hydrothermal method. The composition, structure and morphology of MoS2/C60 nanocomposites were characterized. Through the high-frequency reciprocating tribology test, its potential as a lubricant additive was evaluated. Findings MoS2/C60 nanocomposites that were prepared showed good dispersion in dioctyl sebacate (DOS). When 0.5 Wt.% MoS2/C60 was added, the friction reduction performance and wear resistance improved by 54.5% and 62.7%, respectively. Originality/value MoS2/C60 composite nanoparticles were prepared by in-situ formation of MoS2 nanosheets on the surface of C60 activated by HCl through hydrothermal method and were used as potential lubricating oil additives. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-10-2023-0321/