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This study investigates the tribological performance of GO/modified SiO 2 (GMS) as a composite additive and elucidates their synergistic mechanism. A four-ball friction testing machine and a Timken friction testing machine were used to evaluate the tribological performance of the GMS lubricating oil. The results show that the addition of 0.03 wt% GO and 0.12 wt% modified SiO 2 (Mod-SiO 2) in the oil resulted in a 48.70 % reduction in average friction coefficient, a 60.56 % decrease in wear, and a 1.43 % increase in P B , compared to pure GO oil. Compared to pure Mod-SiO 2 oil, the average friction coefficient decreased by 46.09 %, wear decreased by 51.40 %, and P B increased by 1.38 %. Furthermore, under different loads, the GMS lubricating oil exhibited outstanding capability in reducing frictional noise between the bearing rollers and outer ring, as well as mitigating the trend of temperature variation. The worn surfaces of the test rollers were analyzed using EDS, SEM, CLSM, TEM and Raman spectrum. The spherical Mod-SiO 2 particles adhere to the flake-like GO, preventing agglomeration and facilitating better dispersion in the lubricating oil. Therefore, GMS exhibits its significant advantages and potential as a lubricant additive. • This study investigates GO/ modified SiO 2 (GMS) as a composite additive to improve lubrication performance. • The friction behavior of GMS lubricating oil was analyzed and their synergistic effect was discussed. • GMS exhibits its significant advantages and potential as a lubricant additive. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulation is utilized to reveal the interaction and lubricating property of polyisobutylsuccinimide-polyamine (PIB-PAM) dispersant and phosphorus compound (PAE3) antioxidant in two traction systems (JP1E, JP1EC). The content ratio of PIB-PAM to PAE3 is changed. The static self-assembly of additives is observed, while PIB-PAM molecules with strongly intermolecular entanglement displays a suppressive effect on the molecular diffusion. In the shear process, the adsorption of base oil on surfaces shows a non-wall-slip friction state, and the increasing shear rate causes the adsorption film thinning and the friction coefficient rise. The strong intermolecular interaction in lubricating system induces high friction resistance. The fundamental insights into the interaction mechanism of different additives are helpful for improving lubricant research and development. • MD simulation is performed to reveal the interaction mechanisms of dispersant and antioxidant in traction systems. • The static self-assembly of additives is observed, and PIB-PAM molecules displays a suppressive effect on the molecular diffusion. • Under the shear condition, the adsorption films show a non-wall-slip friction state. • The increase in shear velocity makes the adsorption film thinning to induce the rise of friction coefficient. • Strong intermolecular interaction in lubricating system induces high friction resistance. [ABSTRACT FROM AUTHOR]

Analytical ferrography plays a crucial role in predictive maintenance, which is a proactive approach to asset and equipment management. This technique provides valuable information about the internal condition of machines and components, allowing early identification of potential problems and the scheduling of maintenance interventions before catastrophic failures occur. Ferrography allows you to identify worn particles, non-metallic inclusions and other indicators of wear on components. By analyzing samples of lubricating oil or hydraulic fluid, analytical ferrography can offer insights into the health of internal components such as gears, bearings and other critical elements. Changes in particle concentration and composition may indicate abnormal wear. This work involves the use of analytical ferrography to interpret wear results carried out with two vegetable lubricants with additives, compared to a mineral lubricant, also with additives. To assist in the interpretation of the results, the open source software Image J and a small program developed in Python were used. It was found that it is possible to use these two tools to aid the interpretation of ferrograms. [ABSTRACT FROM AUTHOR]

In this study, it is aimed to examine the effects of surface textures on the friction and wear performance of materials under different sliding conditions (dry, aqueous and oil). AISI 316 L samples with hexagonal, circle, square and rhombus geometries were produced using Laser Powder Bed Fusion (L-PBF) and non-textured samples were produced using casting and L-PBF. L-PBF samples showed high peak intensity due to rapid heating-cooling and small shifts in Bragg angles occurred. L-PBF samples had higher hardness than casting samples since they had a finer microstructure. Textured samples exhibited better tribological performance because they trapped wear debris. A higher friction was observed in samples with sharp corners due to stress concentrations. The highest tribological performance occurred in oil-lubricated conditions. • Four different (hexagon, circle, square, rhombus) surface textured models were produced with AISI 316 L powder using L-PBF. • The samples were subjected to wear tests in three different environments (dry, aqueous, oil). • The lowest friction coefficient for all sample groups was obtained in the oil-lubricated environment. • Textured samples exhibited better tribological performance than non-textured samples. [ABSTRACT FROM AUTHOR]

Better understanding of frictional behaviour of powdered soaps used in dry wire drawing can lead to improvements in wire quality and large savings in energy consumption. The latter is particularly significant given the colossal amounts of energy expended in wire drawing processes. However, there is currently a very limited understanding of the subject, including a lack of quantitative data on soap friction. This is at least in part likely to be due to complex tribological behaviour of the powdered soaps, which is very different from that of lubricating oils. This paper studies frictional behaviour of sodium and calcium powdered soaps, using a ball-on-disc tribometer (ETM rig) incorporating a powder 'scoop', and under contact conditions pertinent to die-wire contact in wire drawing. Tests employed a WC ball and C15E steel disc to mimic die and wire materials respectively. Results show that under high sliding conditions, friction coefficient with powered soaps is remarkably low, at 0.03 and 0.04 for sodium and calcium soaps respectively. Friction generally decreased with increasing contact pressure and sliding speed. Post-test analysis of ETM specimens showed the presence of thick soap layers on the rubbed surfaces. However, in ETM tests friction was observed to sharply increase leading to the onset of scuffing, soon after the supply of soap to the contact was interrupted, suggesting that any solid deposited layers are easily removed and cannot exclusively explain the low friction. The observed trends suggest that low soap friction may be due to the ability of the soaps to form low shear stress lubricating films at high contact temperatures which are associated with the harsh conditions of high-speed and high-pressure. The results provide new insights into the frictional behaviour of powdered soaps which can be used to optimise the wire drawing processes as well as a direct input to wire deformation models. • Friction in wire drawing has major impact on wire quality and energy consumption. • Ball-on-disc ETM machine is used to study friction of typical wire drawing soaps. • Soaps have remarkably low friction (0.03-0.04) at high sliding speeds and pressures. • Continuous supply of soap is needed to ensure low friction and avoid rapid scuffing. • It is likely that soaps can form low shear stress lubricating films at high contact temperature. [ABSTRACT FROM AUTHOR]

The main idea of this study was to utilize the pressure and heat produced in the friction process to make Mo nanoparticles mixed in lubrication oil into the multi-layered tribo-film. An in-house developed reciprocating wear rig was used for the tribo-film deposition and associated tribological tests. By design of experiment, the optimal deposition parameter was obtained. Results indicate that the multi-layered film consists of a Mo-based concrete structure layer and a carbon-based film. The carbon-based film was produced by the dehydrogenation and carbonization of the lubricating oil catalyzed with Mo nanoparticles. The consumption and deposition of the carbon-based film was dynamically balanced during the wear process, resulting in the outstanding tribological performance. [Display omitted] • A great amount of Mo nanoparticles were ultrasonically mixed in the base oil. • Film fabricated by utilizing the heat and pressure produced in friction process. • The film consists of Mo-based film mixed with amorphous carbide. • Realize carbon film formation and restoration in lubrication. [ABSTRACT FROM AUTHOR]

A sulfur-containing carbon nanosphere (SCN) with the corrosion inhibitor M16 (M16 @SCN) was successfully prepared through post-carbonization and then electrostatic adsorption. The as-prepared SCN have rich pore and high specific surface area of 578.9 m2g−1 due to high-temperature carbonization of polythiophene (PT), which as a nanocontainer could upload corrosion inhibitor M16 to obtain M16 @SCN. The M16 @SCN exhibits anti-corrosion performance via controlled release of M16 and improved tribological performance, with friction coefficient of 0.1, extreme pressure of 850 N, and reduction in wear volume of 88.6%. The M16 adsorbed on the nanosphere improves the dispersion of SCN in the lubricating oil, and the SCN acts as a nanocontainer to ensure the performance of M16 under harsh conditions. The good tribological properties are attributed to the synergistic effect between SCN and M16 in the friction process, resulting in a rigid protective oil film was produced on friction pair via tribochemical reactions and physical adsorption. [Display omitted] • Sulfur-containing carbon nanosphere with corrosion inhibitor (M16 @SCN) was prepared by electrostatic adsorption. • The as-prepared M16 @SCNs exhibit excellent tribological performance when used as oil additive. • The superior lubrication performance was attributed the oil film formed by the synergistic interaction during friction. [ABSTRACT FROM AUTHOR]

Ti 3 C 2 T x MXene nanosheets are employed to graft ionic liquids via Michael addition or Schiff base reactions, with polydopamine acting as a bridging agent. This process creates a robust and synergistic tribological interface when the hybrids are used as lubricating additives in oil. The structural hybridization harnesses the high surface area and weak interlayer forces of MXenes, along with the thermal stability and film-forming capabilities of ionic liquids. The study reveals that lubricants fortified with these functionalized nanosheets exhibit a notable reduction in the average coefficient of friction from 0.188 to 0.112 and an 81.7% decrease in wear volume. These results highlight the untapped potential of structurally optimized, ionic liquid-functionalized MXenes as a transformative advancement in the field of tribology. [Display omitted] • Ionic liquid functionalized MXene (MX@IL) is synthesized by polydopamine bridging the [NH 2 C 2 MIm][Br] and the MXene. • As a lubricant additive of oil, MX@IL shows low COF of 0.112 and 81.7% reduction in wear volume as compared with SN500. • The improved tribological performance arises from the formation of a tribofilm and the presence of interface slippage. [ABSTRACT FROM AUTHOR]

Slippery liquid infused surfaces (SLISs) provide excellent dynamic lubrication properties by storing the lubricant internally to form a homogeneous liquid layer to insulate external ambient fluids. However, the kinetic instability caused by lubricant depletion gradually degrades the surface slippery performance. Herein, inspired by skin gland secretion system, silicon gels with sustainable self-replenishment were prepared using polydimethylsiloxane (PDMS) and commercially available dimethyl silicone oils. By carefully tuning the kinematic viscosity and content of infused oil, the surfaces of corresponding silicon gels demonstrated significant syneresis behavior, and the lubricating oils released from the surface were still detected after continuous wiping for more than 120 days. More importantly, when the ratio of working fluid to infused oil was 6.8, the maximum drag reduction of silicon gel in Couette flow could reach up to about 16%, while the surfaces remained long-lasting water repellency under the continuous shear action of encapsulated water. Self-replenishable silicon gels exhibiting strong kinetic stability were expected to provide valuable design insights for robust slippery interfaces. [Display omitted] • The kinematic viscosity and content of infused oil were tuned to obtain the syneresis behavior. • At specific viscosity ratios, significant drag reduction is achieved as the oil layer relieves wall friction. • Silicone gels with sustainable self-replenishment exhibit long-lasting syneresis and robust dynamic slippery properties. [ABSTRACT FROM AUTHOR]

Lubricants are indispensable ingredients for alleviating friction and wear in mechanical components especially in automobile. However, due to its poor heat transfer capabilities, traditional lubricants are denatured under extreme working conditions, leading to lubrication failure during the friction process. Therefore, this study elaborately put forward to a novel MoS 2 /h-BN hybrid nanoparticle as efficient nano-additive for engine oil. The results of experiments and molecular dynamics simulation jointly show that compared with mono nanoparticles, hybrid nano-lubricants (NL) thermal conductivity was significantly improved than that of base oil owing to the synergistic effect. The corresponding mechanism for the improving heat transfer performance was suitably proposed based on the Mean Square Displacement (MSD) and Radial Distribution Function (RDF) results at the microscopic atomic level. [Display omitted] [ABSTRACT FROM AUTHOR]

Recent interest in carbon dioxide-based refrigeration has increased. Despite the positive environmental impacts, carbon dioxide makes a complex refrigerant due to elevated pressures and temperatures inside the compressor and the reactivity of CO 2 with the lubricant. Tribological experiments were performed using synthetic oils paired with ductile iron tribo-pairs under high pressure CO 2. The three lubricants investigated were PAG (Polyalkylene Glycol) and two POE (Polyolester) oils of different viscosities. Elevated temperatures resulted in higher unstable COF for POE and quicker corrosion and degradation of the tribolayer on the surface. In the case of POE, corrosion is significant in causing unstable COF performance at higher temperatures as the ester groups in POE result in more reactivity with the iron surface. [ABSTRACT FROM AUTHOR]

As a nanoscale carbon material, carbon spheres (CS) are expected to achieve ideal lubrication performance by reducing direct contact between friction pairs and bearing loads. In this work, 2D Cu-MOFs surface modified (CS@Cu(BDC)) CS was added to the base oil, which exhibited a remarkable reduction in friction coefficient and wear rate (62.2%, 33.9%), the width of the friction pair wear marks was decreased by 30.8% relative to the base oil. The improvement in performance can be attributed to the polishing, repairing, filling and tribo-film forming effects of CS@Cu(BDC). This work provided an effective strategy for diversifying the surface structure of CS and opened new avenues for the development of a new generation of green and efficient lubricant additives. • Introducing 2D Cu-MOFs on the surface of carbon spheres as a nanoadditive for heavy-duty lubricants. • Composite nanoparticles present excellent dispersion stability in the base oil. • Form a stable tribofilm on the surface of the Fe substrate. • The synergistic effect of carbon spheres and MOFs shows significant anti-wear properties. [ABSTRACT FROM AUTHOR]

This study investigates lubricating performances of oils through altering the working conditions in accelerated aging tests, observing the degradations on the lubricants' performances and incorporating in-time detections for verification. To meet the aims, a new measuring system has been developed to observe alterations of the recorded viscosity index, color difference, thermal coefficient and torque transmission in the oil film under electrical discharges. To resolve the quality of lubricating oil in real time, the discharging waveforms and the acoustic indexes were applied to the marginal Hilbert spectrum for characterizing the time-frequency domain features. The Fisher score of the selected features successfully differentiated the new and used lubricants. The physical effects in association with the degradations of oil films are reported in detail. [ABSTRACT FROM AUTHOR]

Dynamic behavior of rolling elements determines the performance including the extent of skidding and wear in ball bearings, which are influenced by many factors. A comprehensive investigation of dynamic behaviors of high speed ball bearings has been conducted both numerically and experimentally. The dynamic model of high speed ball bearings applicable to a wide range of shaft speeds has been developed, taking into account rheological behavior of lubricating oil, curvature effect, collision between balls and cage and thermal effect. Analyses of ball speeds and interaction forces, as well as sliding speed within ball-raceway contact ellipse have been carried out. The ball-to-race ratio (BRR) of speed has been studied specifically under various operating conditions to reflect the cage speed with high precision. A set of experiments have accordingly been performed on a test rig where optic fiber transducer was employed to obtain the orbital speed of ball. The increase of orbital speed of ball with shaft speed was observed in experiments under different axial load. Numerical results from dynamic simulations also agree with the experimental results based on the investigated ball bearing. The present model is versatile over a wide range of operating conditions. [Display omitted] • Dynamic model considering oil rheology and thermal effect for high speed ball bearings has been developed. • Ball motions including orbital speed and rotational speed are analyzed. • The ball-to-race ratios of speed under different axial loads and shaft speeds are measured on a customized test rig. [ABSTRACT FROM AUTHOR]

Herein, the real-time structural composition, physicochemical properties and oxidation behavior of ester aviation lubricating oil (ALO) in a complete oil change cycle is investigated deeply based on a certain in-service aeroengine. Theoretical calculations and gas chromatograph-mass spectrometer results reveal that the ester group (109.54 kcal mol−1), C–O bond (109.55 kcal mol−1) and C–C bond (123.38 kcal mol−1) between α-C and β-C in 1-decanoyl-3-nonanoyl-propyl-2-dodecanoate (base oil of ester ALO) breaks orderly at high temperature due to their lower bond energy. The further oxidation, cyclization, esterification and polymerization occurs among the formed intermediates and forms coking precursor via unsaturated double ester, unsaturated single ester and ternary ester. Based on these results, a possible oxidation and coking mechanism of ester ALO is proposed. • The physicochemical properties of ester ALO in a complete oil change cycle is investigated. • Oxidation and coking mechanism of ester ALO are proposed based on a certain in-service aeroengine. • Tribological performance of ester ALO with different service time is evaluated. • Composition and property of coking particles are discussed. [ABSTRACT FROM AUTHOR]

Bubble evolution and shear thinning effect are main factors affecting lubrication behavior of bubbly oil. In this study, a thermohydrodynamic lubrication model for the bubbly oil considering the bubble evolution and the shear thinning effect was established based on the multiphase mixtures theory. The influence of bubble evolution and shear thinning effect on the static behavior of bubbly oil lubricated bearing was analyzed, and an experimental study was conducted to verify the model. The result shows that the bubble radius is mainly dependent on the liquid pressure; the bearing static behavior is affected by the bubble evolution through the interface effect; the shear thinning effect of the pure oil can be enhanced with regarding the bubble evolution effect. • A thermohydrodynamic lubrication model for the bubbly oil was established based on the multiphase mixtures theory. • Bubble evolution and shear thinning effect on the lubrication performance of bubbly oil is discovered. • The bubble evolution process can be calculated with using the thermohydrodynamic lubrication model established. • An in-depth physical research on the bubbly oil lubrication is conducted through a case study with using journal bearing. [ABSTRACT FROM AUTHOR]

The lubricating layer of Slippery Liquid-Infused Porous Surfaces (SLIPS) has certain fluidity and low friction coefficient so that it can serve as a good barrier and protection effect. However, common SLIPS suffer from poor oil-holding capacity that lubricating oil is easy to be washed away and irreparable in practical application. Inspired from self-lubricating earthworm skin, we demonstrate a nanochannels surface covered by silicone-oil-infused polydimethylsiloxane (PDMS), which could form continuous self-complement lubricating layer. The strong capillarity of the confined nanochannels showed self-repairing properties of injected liquid film, which can recover lubricating performance quickly after physical damage for many times, exhibiting high stability. This study provides a simple and reliable way for the preparation of long-term effective antifouling functional interface materials. [ABSTRACT FROM AUTHOR]

The interlayer coupling interaction of bentonite (BT) material behave superior performance and unique functionality by introducing guest functional molecules. As intercalation agents, ionic liquids (ILs) with high polarity and molecular structure regulation can provide excellent lubricity and multifunctionality. Herein, the novel IL-modified intercalation bentonite (IL-BT) were designed and prepared by functionalization of the imidazolium-based and phosphorus-based ILs. And ultra-thin lamellar structure morphology is obtained, which contributes to the enhanced dispersion and stability in base oils. For IL -BT, their strong interlayer slip can significantly improve lubrication properties. Besides, FIB-TEM results show that unique tribofilm is detected at the sliding asperity. The excellent tribological properties are attributed to the synergistic lubricity of interlayer slip, tribo-chemical reaction and repair effect during friction. [Display omitted] • Novel IL functionalized bentonite composite (IL-BT) was designed and prepared. • Ultra-thin lamellar morphology for IL-BT was obtained, as well as excellent dispersion stability. • Superior tribological properties can be noticed even at 2.74 GPa. • The synergistic lubricity and unique triboflim induced by IL-BT is explored on the metal surface. [ABSTRACT FROM AUTHOR]

Graphene oxide (GO) is a layered lubricant with high performance, but its application is limited by complex synthesis and relatively low resistance to environmental moisture. In this study, a simple and versatile self-assembly method was developed to prepare GO coatings with thicknesses ranging from the nanometer to micrometer scale. The results indicate that tribological performance is significantly influenced by ambient humidity. During friction, water molecules tend to form hydrogen bonds with oxygen functional groups and defects on GO nanosheets, destroying the ordered layer structure and thus degrading tribological performance. In addition, the further incorporation of lubricating oil is beneficial for achieving lower friction attributed to the synergistic effect of GO coating and oil film that serves as a moisture repellent. [ABSTRACT FROM AUTHOR]

Compared with lubricating oil, grease can firmly adhere to the lubricated surface without loss even on the vertical surface, which is more conducive to improving the durability of triboelectric nanogenerators (TENGs) in practical engineering applications by reducing material wear. However, the correlation between property parameters of grease and triboelectrification is still unclear. In this paper, rotary freestanding TENG with the most severe wear among the working modes of TENGs is taken as the research subject. First, the tribological properties and electrification performance of TENGs lubricated by different greases are studied, and then the effects of the dielectric constant, shear-thinning behavior and cone penetration on the electrical output as well as durability of TENG are explored to reveal the triboelectrification mechanism of the grease-lubricated interface. The results show that, the electrical output of TENG lubricated by the grease with a low dielectric constant can increase by more than 3.5 times compared to dry friction, where the thickener in the grease participates in triboelectrification at the grease-lubricated interface. With increasing sliding distance, the electrical output increases first and then decreases, and the durability is related to the shear-thinning behavior of grease. For greases with similar relative dielectric constant, with increasing cone penetration, the maximum electrical output of TENG decreases, but its durability is improved. This study provides a new approach to improve the electrical output and durability of TENG simultaneously, which further promotes the practical applications of TENGs. [Display omitted] • The thickener in the grease will participate in triboelectrification at the grease-lubricated interface. • The grease with a low dielectric constant is beneficial to improve the electrical output. • The durability of grease-lubricated triboelectric nanogenerator is related to the shear-thinning behavior of grease. • With increasing cone penetration, the maximum electrical output decreases, but the durability is improved. [ABSTRACT FROM AUTHOR]

Although ionic liquids (ILs) have proven to be multifunctional and universal lubricant additives, their solubility in different polar lubricating oils varies greatly. This variability restrains their widespread use as general-purpose lubricating additives. To address this issue, three protic ionic liquids (PILs) with high solubility in lubricating oils with differing polarities were selected as additives, and their tribological performances in polyethylene glycol (PEG) and synthetic pentaerythritol carboxylic ester oil (5750) were systematically investigated. These findings were interesting, as PILs effectively improved the lubrication properties of PEG but impaired those of 5750. Additionally, a variety of surface analysis techniques and MD simulation were employed to further explore the lubrication mechanisms of PILs, and results indicated that they exhibited distinct tribological performance. [Display omitted] • PILs can be used as additives both in polar and non-polar oils. • PILs could enhance the lubrication performance of PAO and PEG. • MD simulation confirms that polar oils and anions of PILs can adsorb on the interface. • Anions of PILs with long alkyl chains perform better lubricating properties in PEG. • PILs would deteriorate the lubricity of ester oils by destroying the original oil film. [ABSTRACT FROM AUTHOR]

The poor dispersion stability of nanoparticles in oils limited their application. To address this problem, diverse of nanoparticles were introduced to supramolecular gels to fabricate a new lubricant (Nano-Gel). The results of molecular dynamics simulation show that gelators adsorbed onto the surface of nanoparticles at the non-covalent interaction. Besides, the intricate networks of supramolecular gels show spatial confinement to nanoparticles, which improved the dispersion stability of nanoparticles. Compared with supramolecular gels lubricant, Nano-Gel shows good anti-friction and anti-wear properties. The excellent tribological properties would be contributed to the self-repairing and tribo-film formed by nanoparticles and gelators. The Nano-Gels provide effective solution to the application of nanoparticles in lubricating oil, which have great values to prolong the life of mechanisms. [Display omitted] • The manuscript reported a new lubricant that diverse of nanoparticles were introduced to supramolecular gels. • The supramolecular gels realized the long-term dispersion stability of different nanoparticles in lubricants. • Dispersion stability mechanism of nanoparticles in supramolecular gels were penetrated by molecular dynamic simulations. • Nanoparticles as lubricant additives improved the anti-friction and anti-wear performances of supramolecular gels. [ABSTRACT FROM AUTHOR]

Power output is an important property of steam turbines and more accurate trend prediction is essential for understanding the operation of power plants and anomaly detection in equipment. Equipment power is strongly influenced by human factors and achieving accurate trend prediction is often impossible. In the current research, a continuous prediction model was developed on the basis of deep learning to establish the relationships among oil online monitoring parameters and equipment power. The model used long short term memory (LSTM) method to develop a trend prediction model for oil wear state parameters. Trend prediction results were applied as a test set to establish a deep belief networks (DBN) prediction model for predicting device power. In modeling process, continuous prediction model was optimized via feature selection method on the basis of ridge regression with L2 regularization, recursive feature elimination (RFE) and differential evolution (DE) algorithms for the elimination of subjective factor to decrease cumulative error of forecasting. Comparative experimental results showed that LSTM-RFE-DE-DBN continuous prediction model outperformed LSTM-RFE-DE-BPNN and LSTM-DBN. The developed model realized continuous prediction and applied lubricating oil wear status with objective factors to perform the power prediction of power plant turbines with subjective factors. [ABSTRACT FROM AUTHOR]

The ongoing trend for using ever lower viscosities of lubricating oils, with the aim of improving the efficiency of mechanical systems, means that machine components are required to operate for longer periods under thin film, mixed lubrication conditions where the risk of surface damage is increased. For this reason, the role of zinc dialkyldithiophosphate (ZDDP) antiwear lubricant additive has become increasingly important in order to provide adequate surface protection. It is known that due to its exceptional effectiveness in reducing surface wear, ZDDP may promote micropitting by preventing adequate running-in of the contacting surfaces. However, the relationship between ZDDP tribofilm growth rate and the evolution of micropitting has not been directly demonstrated. To address this, we report the development of a novel technique using MTM-SLIM to obtain micropitting and observe ZDDP tribofilm growth in parallel throughout a test. This is then applied to investigate the effect of ZDDP concentration and type on micropitting. It is found that oils with higher ZDDP concentrations produce more micropitting but less surface wear and that, at a given concentration, a mixed primary-secondary ZDDP results in more severe micropitting than a primary ZDDP. Too rapid formation of a thick antiwear tribofilm early in the test serves to prevent adequate running-in of sliding parts, which subsequently leads to higher asperity stresses and more asperity stress cycles and consequently more micropitting. Therefore, any adverse effects of ZDDP on micropitting and surface fatigue in general are mechanical in nature and can be accounted for through ZDDP's influence on running-in and resulting asperity stress history. The observed correlation between antiwear film formation rate and micropitting should help in the design of oil formulations that extend component lifetime by controlling both wear and micropitting damage. • Growth of ZDDP films and evolution of micropitting are observed simultaneously. • Anti-wear formulations that result in fast tribofilm growth promote micropitting. • Inadequate anti-wear formulations suppress microptting but result in excessive wear. • Optimal formulations are able to control both wear and micropitting. • Anti-wear additives are shown to affect contact stress history and hence surface fatigue damage. [ABSTRACT FROM AUTHOR]

In order to overcome the mismatching between traditional additives and DLC coatings in solid-liquid lubricating system. Cu nanoparticles modified with diisooctyl dithiophosphoric acid (NPCuDDP) were prepared and used as nano-additives in DLC/PAO solid-liquid lubricating systems. Four kinds of DLC coatings including amorphous carbon (a-C) and amorphous carbon doped with Si (a-C(Si)), Al (a-C(Al)) and H (a-C(H)) respectively, with a hardness range from 22 GPa to 7 GPa were used to study the tribological mechanism and adaptability of NPCuDDP to the hardness and composition of DLC coatings. It was found that NPCuDDP reduced the COF of DLC coatings/PAO systems by 19%–22% regardless of their hardness and composition and made the wear rate of all DLC coatings decrease by 2–3 orders of magnitude. While the composite of tribofilm was decided by the doped elements in DLC coatings. The doped element H inhibited the oxidation of copper in tribofilm, and led to the lowest wear rate of a-C(H) coating. The doped element Al in a-C(Al) facilitated the enrichment of phosphates on friction surface. The hardness rather than composition of DLC coatings determines whether traditional additive ZDDP can form tribofilm. ZDDP can only form Zinc polyphosphate tribofilm on the steel balls rubbed with a-C, a-C(Si) and a-C(Al) coatings whose hardness was over 12 GPa. The friction coefficient of the system increases greatly because of the high strength of ZDDP tribofilm. The high activity of soft metal nano-particle in NPCuDDP urged the formation of tribofilm on friction surface easily and produced a significant antifriction and antiwear effect, and is expected to replace traditional small molecule additives as the high-efficiency special lubricating oil additives for DLC coatings solid-liquid lubrication system. Image 1 • Copper nano-additives exhibit extensive adaptability to four kinds of DLC coatings with a hardness range of 7–22 GPa. • The wear rate of all DLC coatings decreased by 2–3 orders of magnitude due to copper nano-additives. • The doped element H inhibited the oxidation of copper in tribofilm, and led to the lowest wear rate of a-C(H) coating. • The doped element Al in a-C(Al) facilitated the enrichment of phosphates on friction surface. • The hardness rather than composition of DLC coatings determines whether traditional additive ZDDP can form tribofilms. [ABSTRACT FROM AUTHOR]

In this paper, we present the synthesis and tribological properties of two naphthatate-based lubricating oils. The structure and purity of the oils were analyzed using nuclear magnetic resonance spectra and high resolution mass spectra. Their thermal and oxidation stability, flash point and pour point, viscosity and viscosity index, and friction reduction and anti-wear properties were also tested. In the results, the two isooctyl naphthatate-based oils (INA) displayed better lubricating properties than a reference sample of isooctyl sebacate (ISE) on three different friction pairs. The new oils also offered higher oxidation stability than the reference sample. It was found that the stability and lubrication properties of ester-based lubricating oils can be significantly improved by introducing a naphthalene ring into the molecular structure. This is because there is a large π-electron conjugate system on the naphthalene ring, which not only reduces the likelihood of an oxidation chain reaction, but also enables the oil to form an orderly and stable lubricating film on metal surfaces. One of the oils, 2,3-INA, was found have better oxidation stability than the other one, 1,4-INA, because its oxidized groups are positively affected by the steric and conjugation effects of the two ester groups. Two new types of ester lubricating oil isooctyl naphthatate (INA) were synthesized. Due to the presence of multiple ester groups and naphthalene rings in the molecular structure, it shows better friction reducing and anti-wear properties than the reference sample isooctyl sebacate (ISE). More importantly, it exhibits remarkably higher oxidation stability than the reference sample. Image 1 • Isooctyl naphthatate (INA) were synthesized from Naphthalene dicarboxylic acid and isooctanol through esterification. • 2,3-INA and 1,4-INA showed good friction reducing and anti-wear properties on three different friction pairs. • 2,3-INA and 1,4-INA have excellent oxidation stability due to the presence of a naphthalene ring in the molecule. [ABSTRACT FROM AUTHOR]

The chemical degradation/oxidation of lubricating grease is investigated experimentally from an energy point of view. A Pressure Differential Scanning Calorimeter (PDSC) is used to measure the activation energies of two lithium-complex greases and to monitor their chemical degradation through induction time. For this purpose, an experimental setup consisting of a heating chamber, a temperature controller and an energy meter is designed, built, and calibrated to heat up grease samples and measure pure energy absorption during the chemical degradation at different test temperatures. A relationship between the energy absorption of the grease and its chemical degradation is established that is independent of the testing time and temperature. It is shown that the energy absorption of the grease approaches to an identical maximum value in a shorter time in high temperatures and a longer time in low temperatures. The maximum energy absorption depends on the grease type and experimental results reveal that it can be used to estimate the grease chemical life. A roller tester rig is used to measure and compare the lubrication ability of two chemically degraded grease samples and to validate the results of the research. To gain further insight, experimental results are presented to examine the flow characteristics of a chemically degraded grease in an elastohydrodynamic (EHL) line contact with a comparison to that of the fresh grease. • State of chemical degradation can be determined regardless of temperature and time. • A relationship between energy absorption of a grease and chemical degradation is established. • Maximum energy absorption values are calculated and compared to measured activation energy. • Predictions of the theory are verified using a roller tester rig. [ABSTRACT FROM AUTHOR]

This study attempts to use ionic liquids (ILs) as oil additives to lubricate oxygen-diffusion (OD) case-hardened titanium for improved friction and wear behavior. Four oil-soluble ILs were used as additives in a base oil for boundary lubrication of an OD-treated Ti-6Al-4V surface sliding against a bearing steel ball. The ILs improved the friction behavior to various extents and the two phosphate ILs clearly outperformed the conventional ZDDP. Unlike ZDDP that adversely caused a higher material loss, ILs exhibited excellent wear protection suggesting good material-chemical compatibility. Particularly, the carboxylate IL protected the OD-Ti surface from any measurable wear. The morphology and chemical composition of the worn surfaces and tribofilms were examined to gain insights of the anti-wear mechanism. • Ionic liquids (ILs) as oil additives showed superior performance in lubricating oxygen-diffused titanium alloy (OD-Ti). • Phosphate ILs outperformed phosphinate and carboxylate ILs as well as the traditional ZDDP in friction behavior. • While phosphate and phosphinate ILs protected both OD-Ti and steel to some extent, carboxylate IL minimized the titanium wear. • The protective tribofilm on the OD-Ti surface was found to be deposit of reacted wear debris from the steel counterface. [ABSTRACT FROM AUTHOR]

The paper describes series of four-ball tribological and dichromatic interference test results obtained under different contact pressures and performed for polyalphaolefin (PAO) suspended synthetic magnesium silicate hydroxide (MSH) nanoparticles. Results show that MSH as additives in oil exhibits excellent anti-wear performance, and even results in 'zero wear' under a maximum Hertzian pressure of 2.71 GPa. Their anti-wear mechanisms are various depending on the contact pressure. Under a relative mild pressure, MSH can effectively increase the oil film thickness, thus to achieve a substantial reduction in wear. As the test pressure becomes severer, a tribofilm containing Mg, Si and O would form on the worn surface to provide a secondary anti-wear guarantee. • Synthetic MSH nanoparticles' anti-wear mechanisms depend on the contact pressure. • The slid surfaces lubricated with MSH-containing oil have almost 'no wear' under a pressure of 2.71 GPa. • Dichromatic interference tests confirm MSH aggregates penetrate into the contact and increase the oil film thickness. • MSH nanoparticles' cleavage promote a distribution of anti-wear tribofilm. [ABSTRACT FROM AUTHOR]

In this study, the graphene was prepared by liquid phase exfoliation method, and then through microfluidization technique it was uniformly dispersed into SAE 10W-30 lubricating oil. The lubricating oils without graphene and with four different graphene concentrations were tested twice respectively on a pin-on-disc tribometer under high specific pressure of 10 MPa and low linear velocity of 0.3 m/s. After testing, the scratches on discs were observed by scanning electron microscope (SEM) and three-dimensional (3D) surface metrology system. The oil with 0.05 wt% graphene exhibited the minimum friction coefficient, lowest specific wear rate and slightest scratch. The results illustrated that the graphene dispersed into SAE 10W-30 oil with optimum concentration improved the anti-friction and anti-wear performances. • Graphene was prepared by liquid phase exfoliation method. • Graphene grains contained a low number of defects and did not easily dissolved in oil. Microfluidization technique has been used to homogenize the graphene-composed lubricating oils. • Graphene reduced the surface roughness and partially prevented the direct contact of metal asperities. Moreover, graphene provided much low interlaminar shear stress. • An optimum content of liquid phase exfoliated graphene in SAE 10W-30 was found. [ABSTRACT FROM AUTHOR]

Abstract Spent bleaching clay (SBC) is one of the solid wastes in oil companies and its reuse is significant. The present work investigated the preparation and tribological properties of nano-MoS 2 /SBC in ABS plastics. Results showed that nest-like nano-MoS 2 spheres with ∼65 nm diameters were uniformly deposited on SBC. Compared with SBC and nano-MoS 2 , the nano-MoS 2 /SBC presented better tribological properties by reducing friction by ∼20% and wear by ∼67% under selected conditions. Nano-MoS 2 and ABS can both transfer to the steel ball counterpart. ABS was mainly transferred to the fringe of the wear scar via its adhesion effect. However, the nano-MoS 2 was transferred to the intact wear scar to form a transferring film, which primarily caused the lubrication of nano-MoS 2 /SBC in ABS. Highlights • A nano-MoS 2 /SBC (spent bleaching clay) composite was prepared. • Wear resistance of ABS plastic was remarkably improved by nano-MoS 2 /SBC. • A new approach was explored for the resource utilization of spent bleaching clay. [ABSTRACT FROM AUTHOR]

Abstract In this paper, the matching properties of nickel aluminum-silver solid-lubricating alloy coupled with various tribo-pairs in seawater environment were investigated. The results revealed that the Ni 3 Al Ag alloy mating with Al 2 O 3 is an appropriate tribo-pair compared with the SiC and 316L steel counterparts. The Ni 3 Al Ag alloy rubbing against Al 2 O 3 exhibits the desirable lubricating properties because mild plowing effect contributes to slightly mechanical action and Ag distributed on the worn surface brings the surface shearing stress down. When the Ni 3 Al Ag alloy is coupled with SiC, the increasing plowing effect and slight material transfer deteriorate the friction behavior. As for the 316L steel counterface, the aggravation of plowing effect and the formation of ferric oxide play adverse roles in tribological behavior. Highlights • Ni 3 Al Ag alloy coupled with Al 2 O 3 exhibits low friction coefficient in seawater. • The mild furrow and Ag improve tribological behavior of Ni 3 Al Ag/Al 2 O 3 tribo-pair. • The increasingly plowing and slight material transfer deteriorate SiC counterface. • The coarse plowing and ferric oxide exacerbate steel counterface. [ABSTRACT FROM AUTHOR]

Different types of wear particles in lubricating oil are crucial information sources for describing wear properties of rotating machinery components. Solving the problem of particle classification using artificial intelligence models depends on sufficient wear samples, though the samples are difficult to obtain, especially in lubricants with real-time online monitoring. First, a high precision particle analyzer for online acquisition of multi-particle images in the circulating oil system based on the optical direct imaging method is developed. Then, a novel hybrid convolutional neural network (CNN) model based on the visual geometry group (VGG) network feature and residual block, called VRCNN, is proposed to classify nine types of metallic and non-metallic particles, including normal, sliding, fatigue, cutting, sphere, ceramic, bubble, plastic, and fiber, using their images. Finally, a dataset produced by a pin disc friction tribometer and bearing accelerated fatigue tester is used to demonstrate the approach. The proposed VRCNN model is also compared with the typical classifiers, including AlexNet, VGG16, RestNet50, SqueezeNet, MobileNetV2, and ShuffleNetV2 models in terms of classification accuracy, standard deviation of accuracy, F1-score, and detection time. The results show that the VRCNN model has a classification accuracy of more than 95%, and its response time is superior to that of the other networks. Furthermore, the operational process of the VRCNN classifier is analyzed visually using the Grad-CAM map. This work is beneficial for improving any type of rotating machinery's wear mechanism analysis. • A particle analyzer based on direct imaging principle is designed for online monitoring and classification of particles. • An innovative convolutional neural network, called VRCNN, is developed for the automatic classification of particles. • The VRCNN provides a detailed classification of nine types of particles, including metals and nonmetals. • Online particle monitoring and classification is low cost, short time-consuming, and reduces manual monitoring errors. • The practical experiment is conducted for validation. [ABSTRACT FROM AUTHOR]

A sensitivity-improved reflection coefficient amplitude method for determining wide-range lubricating oil film thickness is proposed based on partial reflection waves, which are obtained by removing the first reflection wave. Numerical analysis and experimental testing are conducted to verify the proposed method. The results show the lubricating oil film thickness ranging from the spring model region to the resonant region can be calculated based on the proposed partial-wave reflection coefficient amplitude method. In comparison to the existing reflection coefficient amplitude method, the measurement accuracy of the lubricating oil film thickness is significantly improved for the transition region which locates between the spring model region and the resonant region, for instance, the observed maximum relative error is decreased to 9% from 60%. • A sensitivity-improved- reflection coefficient amplitude method. • The partial reflection waves are obtained by removing the first reflection wave. • An amplitude method for wide-range lubricating oil film thickness measurement. • An amplitude method for measuring oil film thickness with high accuracy. [ABSTRACT FROM AUTHOR]

The purpose of this research is to indicate the potential differences in bearing characteristics resulting from the application of different lubricant types with the same viscosity grade. The effect of different environmentally acceptable lubricants (EALs) on hydrodynamic journal bearing properties is studied experimentally and compared to the properties obtained after lubrication with a reference mineral oil. The results of the studies proved that a bearing lubricated with EALs had practically the same properties as one lubricated with mineral oil. The calculations for the tested bearing system showed that the variations of selected lubricant parameters, such as specific heat or thermal conductivity, do not significantly affect the properties of the bearing, i.e. the minimum film thickness or power losses. • Theoretical and experimental work was conducted. • Theoretical part – calculations – FSI modeling was used for calculations. • Experimental research – was conducted for real scale journal bearings on unique test rig designed and build on University. • Journal bearing lubricated by different type oils properties were studied and compared. [ABSTRACT FROM AUTHOR]

A journal bearing test bench is used to find the transition speed between the hydrodynamic and mixed lubrication regimes for a modified magnetorheological (MR) fluid. It is shown that the transition speed of the bearing can be reduced by applying a local magnetic field near minimum film when it is lubricated with the MR fluid, and that this will only marginally increase friction. The lubricating performance of the MR fluid is compared to that of a reference oil, and all experimental results are compared with a Finite Element model based on the Reynolds equation. • Low viscosity magnetorheological fluid was used to lubricate a journal bearing. • Friction at high speeds was lower than with a standard lubricating oil. • The magnetically induced load capacity increase at low speeds was retained. [ABSTRACT FROM AUTHOR]

Oil-containing materials depend on micropore structures to store lubricating oil. However, the micropore structure, an important component of such materials, is difficult to control. Herein, a porous iron-based oil-containing material was successfully prepared via powder metallurgy with TiH 2 and polyamide 66 short fiber as dual pore formers. Scanning electron microscopy observations and analyses indicated that the complementary effect of dual pore formers enabled the formation of an interconnected hierarchical pore structure with two pore types, which not only provided abundant oil storage spaces but also facilitated the transfer of oil within the materials. Based on ring-on-block friction and wear tests, the iron-based oil-containing composite presented a low coefficient of friction (about 0.078) under a contact pressure of 1.2 MPa. • PA 66 SF and TiH 2 have a strong complementary effect on the growth of open pores. • PA 66 SF has a tailored size that can serve as a better fiber-like pore template. • A hierarchical pore structure contributes to the oil storage–release performance. • Rapid oil-release behavior can prevent further material deterioration during sliding. [ABSTRACT FROM AUTHOR]

Magnesium (Mg) and its alloys are crucial for energy-efficient vehicles due to their strong and lightweight properties, necessitating high-temperature fabrication and lubrication to reduce oxidation, friction, and wear. This paper investigated the tribological performance of lubricating oil using different particles to a Mg alloy subjected to contact sliding in an open system at high temperatures up to 250 °C. The overall experimental results showed improved tribological performances by using the two types of nanoparticles / nanoparticle-clusters (concentration ≥ 0.5 wt%) compared with the base silicone oil. The mechanisms by which the two types of nano lubricants improved the tribological performance are different. Al 2 O 3 particles provided a more stable Al-rich anti-wear surface at higher temperatures in the range of 200–250 °C, while a tribo-chemical reaction film was formed with MoS 2 additives, generating MoO 3 and MgSO 4. It is generally concluded that Al 2 O 3 has more positive effect in terms of reduced coefficient of friction and wear rate as comparison to MoS 2. • Two types of silicone oil based nano lubricants for the sliding contact of a Mg alloy in an open system at high temperatures. • The tribological characteristics with different types of nano lubricants at elevated temperatures. • Tribofilm formation and removal during contact sliding of the contact pair due to high concentration Al 2 O 3 nano lubricants at high temperatures. • Pits on the Mg AZ31B disc surface due to the clustering of MoS 2 nanoparticles in the lubricant. [ABSTRACT FROM AUTHOR]

The connecting rod small-end bearing system is one of engine's rotating friction pairs under the most severe condition. Significant deformation, high temperature, and the coupling action of multi-bearing tribology and multi-body dynamics make the simulation challenging. This study develops a new tribo-dynamics model considering deformation and thermal effects for the small-end bearing system. A full-scale engine test is conducted, and the predicted severe wear position is consistent with the experimental one. Results show the axial uneven wear and temperature rise happens in the bearing lower surface after considering elastic deformation and thermal effects. The piston pin is decelerated to stop nearly and then accelerated by the friction torque during compression and work strokes that differs from the simplified rigid model. • A new tribo-dynamics model for engine small-end bearing considering elastic deformation and thermal effects is established. • The predicted wear position is consistent with the experimental one by a full-scale test. • The axial uneven wear and temperature distribution happen after bearing deformation and thermal effects are considered. [ABSTRACT FROM AUTHOR]

The improvement of interface compatibility of nanomaterials as nanoadditives was conductive to raise the friction performances in oil. Herein, we successfully constructed a corncob-shaped Ni-BTC MOFs@HNTs nanocomposite through the controllable growth of nanospherical Ni-BTC MOFs on the external surface of HNTs nanotubes. The composition and structure of Ni-BTC MOFs@HNTs were determined by a catalog of characterization. Due to being the better interface compatibility of MOFs in organic compound, the existence of Ni-BTC MOFs on the external surface of HNTs evidently promoted the dispersibility of HNTs nanotubes in oil. The tribological behaviors of Ni-BTC MOFs@HNTs as nanoadditives in base oils were deeply studied by ball-on-ball contact friction. The experimental results showed that the average friction coefficient and wear scar diameter of Ni-BTC MOFs@HNTs -base oil were decreased by 39.7% and 29.4% at 0.04 wt% adding content relative to base oil, respectively. Meanwhile, the carrying capacity of Ni-BTC MOFs@HNTs-base oil was increased by 16.3%. Finally, the worn surfaces lubricated by Ni-BTC MOFs@HNTs-base oil were deeply characterized by a series of spectra analysis, thus revealing the synergistic lubrication effect of Ni-BTC MOFs and HNTs. [Display omitted] [ABSTRACT FROM AUTHOR]

With the development of major equipment towards high power density, the bearing speed is getting higher and higher. In the oil-jet lubrication mode, the fluid in the bearing chamber is a two-phase flow of oil and air. Under high-speed operating conditions, the air in the bearing chamber has a significant impact on the lubricating oil flow field and bearing temperature. This article presents a functional cage with wing structures that is designed to regulate the fluid flow field inside the bearing chamber. The numerical simulation model of 2/14 bearing is established. Through computational fluid dynamics (CFD) software, the effects of wing angle, position and length on the regulation of the flow field in the bearing cavity and the axial velocity are analyzed. The results indicate that appropriately increasing the angle and length of the wings, while positioning them closer to the inlet, is an effective way to enhance the regulation of the bearing flow field. The calculation of oil-air two-phase flow and temperature rise test verify that the functional cage bearing has the function of enhancing lubrication and heat dissipation. This research offers both a theoretical basis and practical approaches for developing high-speed bearings that have better lubrication performance and improved heat dissipation. [ABSTRACT FROM AUTHOR]

Experimental research was conducted on mechanical seals with pressurized lubricated-oil, focusing on lubrication and leakage inhibition of herringbone-grooved face seals. Through the visualization experiments and axial displacement tests, this study evaluated the performance of the inner-diameter-side (IDS) and middle-diameter-side (MDS) herringbone grooved seals based on the measured cavitation region, leakage rate, friction torque, surface temperature of stator, and axial displacement of the primary ring. The experiment results show that, increasing the width of the seal dam can reduce the hydrodynamic effect and cavitation development of the liquid film but enhance the hydrostatic effect, maintain a small leakage range, the maximum leakage rate is less than 19 mL∙min−1. Zero-leakage can be achieved in MDS due to cavitation suction. The axial displacement curves indicate that the runout amplitude of IDS is smaller than that of MDS, the maximum axial displacement difference is about 25 µm, the stability of IDS is better than MDS. Comparisons of surface temperature and friction torque demonstrates that the lubrication of MDS is better than that of IDS. [ABSTRACT FROM AUTHOR]

The feasibility of using nanoparticles (NPs) as lubricant viscosity modifiers has attracted considerable attention as they can increase/decrease the lubricant viscosity. However, due to the lack of theoretical guidance for interface design, the practical application of NP viscosity modifiers is limited. In this study, molecular dynamics simulations are performed to analyze the non-bonding interactions of four typical lubricating oil/NP solid–liquid interfaces with different interface polarities. A model of the mechanism through which the NPs regulate the shear viscosity of the lubricating oil is proposed based on the solid–liquid interface slip behavior, which is verified experimentally. It is found that the shear resistance of the interface is determined by the "liquid all-atomic Coulomb potential energy" (LACPE) and is positively correlated with the "potential well" values of the LACPE distributed in the tangent plane parallel to the wall. Adjusting the characteristics of the solid surface and the "polar units", which are inside the lubricant molecules, as well as the linking modes between the polar units, is proposed as a means to regulate the interfacial shear resistance. This work could provide guidance for interface design and the R&D of nanoscale viscosity modifiers. [ABSTRACT FROM AUTHOR]

Proper solid-liquid lubricating materials can generate synergistic effect, achieving long life under harsh operating condition for space equipment. Herein, the solid-liquid systems were constructed by WS 2 -Al film and typical space lubricating oils with different molecules (P201 and PFPE). The results indicate that the systems markedly prolong the life and firstly appear obvious tribological dissimilarities. Especially, WS 2 -Al/P201 system exhibits more longer life exceeding 6 × 105 r. It is attributed that the compact tribolayer consisting of numerous nanosheets lied flat on wear track surface and good transfer film are well formed. Differently, WS 2 -Al/PFPE system is found to happen more serious tribo-oxidation and only generate numerous floccule-like debris. Eventually, interactions between WS 2 -Al crystals and oil molecules are essentially revealed during friction process. • WS 2 -Al/oil systems generate synergistic effect, significantly prolonging the lubricating life. • Tribological dissimilarities of WS 2 -based solid-liquid systems are firstly appeared obviously. • WS 2 -Al/PFPE system occurs to more serious tribo-oxidation. • Preferential adsorption for oil molecules is confirmed to occur on WS 2 -Al crystal planes. [ABSTRACT FROM AUTHOR]

In this work, the lubricating ability and physicochemical properties of three ionic liquids (ILs) containing the same anion and three different cations are studied. Steel-steel contact, lubricated with each IL was studied using a ball-on-flat reciprocating tribometer. The three ILs presented very similar values of thermal stability, density, and surface tension. Trihexyltetradecylammonium bis(trifluoromethylsulfonyl) amide showed the best wettability at 25 °C, but the worst wettability at 100 °C. The influence of the surface finish in the lubricating properties of the ILs were also investigated. Results show higher wear values for fine-finished surfaces. No significant differences in the tribological performance of the ILs are found at low frequency; however, tribo-attack of the imidazolium-based IL on steel, resulted in higher wear at 5 Hz. [ABSTRACT FROM AUTHOR]

The Morton effect ME is a thermally induced, rotordynamic instability, which is frequently reported in overhung machines supported with oil-lubricated bearings. Synchronous journal whirling results in an uneven viscous shearing of the lubricant film and temperature variation around the journal circumference. This bends the shaft and under certain conditions causes increasing synchronous vibration. Previous research focused solely on oil-lubricated bearings. A transient, high-fidelity ME methodology is presented to expand the scope to tilting pad gas bearing (TPGB) systems. Three dimensional finite element models are established to predict the rotor and bearing temperature and dynamic responses in the time domain. Simulations indicate that the ME can occur in the TPGB systems and may be sensitive to imbalance and overhung mass. [ABSTRACT FROM AUTHOR]

In a direct acting valve train configuration, tappet rotation plays a key role in improving lubrication, reducing wear and friction. However, to the best of the authors' knowledge, no studies were found to investigate the rotation of tappet under the effect of different coatings, thicknesses of tappets and formulations with Molybdenum Dialkyl Dithiocarbamate (MoDTC) which has been recently reported to be detrimental to Diamond-Like Carbon (DLC) wear. In this work, a new technique of measuring tappet rotation has been developed. A giant magnetoresistance (GMR) sensor coupled with a split pole ferrite disk magnet was used. The sensor was installed very close to the tappet/bucket while the magnet was mounted into the underside of the tappet. Experiments were performed using standard production steel tappets coated with Mn-phosphate (MnPO 4 ) and diamond-like carbon (DLC) coatings. In general, results showed that the tappet rotation is strongly dependant on oil formulation, clearance, speed/temperature, and surface roughness of the coating. MoDTC promoted the rotation of the tappet under both coatings. In addition, DLC inserts showed an increase in tappet rotation as compared to MnPO 4 inserts. Nevertheless, regardless of the type of coating, the thickest tappets showed the highest rotation. [ABSTRACT FROM AUTHOR]

For many precision devices with limited amount of lubricants, the retention of lubricating oil between solid surfaces is of great significance for the lubrication reliability in the long-term operation. In this study, the spreading behavior of a synthetic 1,3-diketone lubricant (1-(4-ethyl phenyl) nonane-1,3-dione) 02/06 on steel surfaces was investigated. By measuring the surface tension of oil and the surface energy of steel, the spreading parameter of 02/06 was determined, which was much smaller than the reference oils with similar viscosity. Rotary friction test shows that 02/06 was positioned at the contact region in the presence of a strong centrifugal force and performed a stable ultralow friction. Moreover, the addition of 02/06 into the reference oils also improved the lubricant retention. [ABSTRACT FROM AUTHOR]

Gasoline engine oil (SAE 5W20) was contaminated with four levels (0%, 4%, 8% and 12%) of gasoline fuel and submitted to terahertz time-domain spectroscopy (THz-TDS). Three sampling methods were used to compare measurement variations. For all sampling methods, refractive index decreased with increased fuel contamination and absorption coefficient increased with increased fuel contamination. Absorption coefficients were significantly different for each fuel contamination level for each sampling method across the entire 0.5–2.5 THz range. The frequency of 0.5 THz produced the best model of absorption coefficient predicting fuel contamination with a root-mean-square error of 0.21% points. THz-TDS demonstrated high potential for estimating gasoline fuel contamination in gasoline engine oil. [ABSTRACT FROM AUTHOR]

The wear map can directly reflect the wear state and mechanism of the friction pair under different conditions and is widely used in wear prediction and fault diagnosis of steel materials. However, there are few reports on the wear map of the engine cylinder liner and its materials. In this study, the operating parameters were obtained through an engine bench test. The parameters near the cylinder liner's top dead center （TDC） were selected as wear test parameters. Thousands of hours of reciprocating lubrication wear tests were carried out on a multi-function wear tester. By analyzing the wear rate variation under different test parameters, the cylinder liner's wear state was divided into mild, medium, and severe wear. The morphology of the wear scar surface and cross-section of the cylinder liner was analyzed by scanning electron microscope (SEM) and then drawing the wear mechanism map. The results show that the primary wear mechanism under slight wear is spalling wear, accompanied by the plastic deformation phenomenon. Delamination wear is the primary mechanism in the medium wear state, accompanied by a small amount of massive spalling wear. The delamination wear is mainly caused by the crack generated by graphite in or below the deformation layer. The primary wear mechanism of the severe wear state is massive spalling. At this time, the graphite at the bottom of the deformation layer plays the role of primary cracks, which causes the plastic deformation layer to fall off. [ABSTRACT FROM AUTHOR]