Lubricants

10 pages, 2782 KiB

Open AccessArticle

Corrosion Resistance and Nano-Mechanical Properties of a Superhydrophobic Surface

by Chun-Wei Yao, Ian Lian, Jiang Zhou, Paul Bernazzani, Mien Jao and Md Ashraful Hoque

Lubricants 2025, 13(1), 16; https://doi.org/10.3390/lubricants13010016 - 3 Jan 2025

Nanoindentation has been used to characterize the mechanical and creep properties of various materials. However, research on the viscoelastic and creep properties of superhydrophobic surfaces remains limited. In this study, a superhydrophobic coating was developed and its corrosion resistance was evaluated initially. Electrochemical [...] Read more.

Nanoindentation has been used to characterize the mechanical and creep properties of various materials. However, research on the viscoelastic and creep properties of superhydrophobic surfaces remains limited. In this study, a superhydrophobic coating was developed and its corrosion resistance was evaluated initially. Electrochemical impedance spectroscopy (EIS) results quantitatively confirm the enhanced anti-corrosion performance of the superhydrophobic coating. Subsequently, this study investigates the creep, hardness, strain rate sensitivity, and viscoelastic behavior of the superhydrophobic surface at the nanoscale before and after accelerated corrosion exposure. Our findings reveal that during the creep tests, the logarithmic values of creep strain rate and stress exhibited a good linear relationship. Additionally, the surface retains its key viscoelastic properties (hardness, storage modulus, loss modulus, and tan δ) even after exposure to corrosion. These results highlight the surface’s robustness under corrosive conditions, a crucial factor for applications requiring both mechanical integrity and environmental resilience. Full article

(This article belongs to the Special Issue Mechanical Tribology and Surface Technology)

► Show Figures

Figure 1

17 pages, 842 KiB

Open AccessArticle

Dynamic Response and Lubrication Performance of Spur Gear Pair Under Time-Varying Rotation Speeds

by Jiaxing Pei, Yuanyuan Tian, Hongjuan Hou, Yourui Tao, Miaojie Wu and Zhigang Guan

Lubricants 2025, 13(1), 15; https://doi.org/10.3390/lubricants13010015 - 3 Jan 2025

Abstract

The rotation speed directly influences the vibration and lubrication behaviors of gear pairs, but studying the effects of time-varying rotation speeds during their operation poses substantial challenges. The present work proposed an approach to analyzing the dynamic response and lubrication performance of spur [...] Read more.

The rotation speed directly influences the vibration and lubrication behaviors of gear pairs, but studying the effects of time-varying rotation speeds during their operation poses substantial challenges. The present work proposed an approach to analyzing the dynamic response and lubrication performance of spur gear pairs under time-varying rotation speeds. A single-degree-of-freedom torsional dynamics model was established to capture the vibration responses and meshing forces of a gear pair, with the meshing stiffness modulated by the time-varying rotation speed. Additionally, a transient elastohydrodynamic lubrication model of the gear system was proposed to obtain the pressure pro-file and film shape, incorporating the effects of time-varying rotation speeds. Three types of time-varying rotation speeds were investigated: acceleration, deceleration, and oscillation. The results reveal that the time-varying rotation speed induces chaotic motion of the gear system, resulting in significant changes in the dynamic meshing force, entrainment velocity, and curvature radius of the gear pair compared to those in constant-speed scenarios. The lubrication performance under time-varying rotation speeds also shows diverse dynamic characteristics, highlighting significant differences from that observed under a constant rotation speed. These insights contribute to a more comprehensive understanding of gear dynamics under realistic operating conditions, enhancing gears’ performance and reliability in practical applications. Full article

(This article belongs to the Special Issue Surface Machining and Tribology)

20 pages, 16997 KiB

Open AccessArticle

Contact Load and Elastohydrodynamic Lubrication Analysis of Eccentric Bearings in RV Reducer Considering the Effects of Roller Profile Modification

by Xinyue Zhang, Gang Wang, Daqi Wu, Jian Guan and Wenjie Chen

Lubricants 2025, 13(1), 14; https://doi.org/10.3390/lubricants13010014 - 3 Jan 2025

Abstract

The mechanical and tribological behavior of eccentric bearings is crucial for the performance of a RV reducer. By combining the finite element model (FEM) and the elastohydrodynamic lubrication (EHL) method, a comprehensive model for the cylindrical roller bearings applied in the RV reducer [...] Read more.

The mechanical and tribological behavior of eccentric bearings is crucial for the performance of a RV reducer. By combining the finite element model (FEM) and the elastohydrodynamic lubrication (EHL) method, a comprehensive model for the cylindrical roller bearings applied in the RV reducer is developed in this study. During the modeling phase, FEM is utilized to determine the bearing load, taking into account the structural flexibility. The FEM result demonstrates that a 15% increase in the maximum bearing’s load is detected by the FEM compared to the analytical model. After the simulations, the effects of the roller profile modification, the bearing load and the rolling speed on the bearing performance are revealed. The numerical results indicate that the combined generatrix shape roller results in weaker edge effects and stress concentration compared with that of the straight generatrix shape roller and the arc generatrix shape roller. The optimal values of modification length and modification quantity under various load and rolling speed conditions are provided. Furthermore, durability tests on RV reducers equipped with the three types of rollers were conducted. Experimental outcomes demonstrate that the combined generatrix shape roller significantly improves the reliability and fatigue life of the RV reducer, corroborating the numerical analyses. Full article

► Show Figures

Figure 1

19 pages, 12209 KiB

Open AccessArticle

The Effect of Geometrical Shape of Surface Texture on the Rheology and Tribology of Confined Lubricants

by Fankai Peng and Ahmad Jabbarzadeh

Lubricants 2025, 13(1), 13; https://doi.org/10.3390/lubricants13010013 - 3 Jan 2025

Abstract

Understanding lubrication at the nanoscale is essential for reducing friction. While alkanes, the primary component in most lubricants, have been studied for their molecular structure’s impact on rheology and behavior when confined by solid surfaces, the influence of confining surface texture remains underexplored. [...] Read more.

Understanding lubrication at the nanoscale is essential for reducing friction. While alkanes, the primary component in most lubricants, have been studied for their molecular structure’s impact on rheology and behavior when confined by solid surfaces, the influence of confining surface texture remains underexplored. This research uses molecular dynamics simulations to investigate the rheological behavior of thin film lubrication between various patterned rough surfaces. The study focuses on sinusoidal, sawtooth, and squaretooth wave-patterned surfaces, using hexadecane as the lubricant. The simulations examine the effects under different normal loads and shear rates. Surface patterns significantly influence the formation and structure of crystalline bridges, depending on shear rates and normal loads. The sawtooth wave-patterned surface exhibits the highest viscosity under low normal load and shear rate conditions, forming crystalline bridges with a molecular orientation perpendicular to the shear direction. The squaretooth patterns exhibit the lowest viscosities due to the nematic order in crystalline bridges with molecules aligned in the shearing direction. The sinusoidal wave-patterned surface shows intermediary viscosity with disordered crystalline bridge groups formed with random molecular orientation. The lowest viscosity provided by the squaretooth pattern surface persists across various conditions, including both transitory and steady states, under high and low loads, and over a wide range of shear rates. However, the difference in shear viscosity is reduced at higher normal loads. This research provides valuable insights for designing nanoelectromechanical systems (NEMS) and other applications where boundary conditions are critical to lubrication. Full article

(This article belongs to the Special Issue Advances in Molecular Rheology and Tribology)

► Show Figures

Figure 1

14 pages, 3219 KiB

Open AccessArticle

Friction Torque in Miniature Ball Bearings

by Denis Cojocaru, Gelu Ianuș, Vlad Cârlescu, Bogdan Chiriac and Dumitru Olaru

Lubricants 2025, 13(1), 12; https://doi.org/10.3390/lubricants13010012 - 2 Jan 2025

Abstract

The problem of estimation the friction torque in operating miniature ball bearings lubricated with oil or grease is a complex one. Generally, in an angular contact ball bearing (ACBB), various types of losses can appear including losses caused by kinematics in ball-race contacts [...] Read more.

The problem of estimation the friction torque in operating miniature ball bearings lubricated with oil or grease is a complex one. Generally, in an angular contact ball bearing (ACBB), various types of losses can appear including losses caused by kinematics in ball-race contacts (rolling, sliding and pivoting), losses between the cage and the balls and between the cage and the guiding race and losses generated by lubricant, especially at high speeds. In the miniature ACBB, the applied loads have generally low values, and some losses can be ignored. In these circumstances, the most important contribution to the increase in the losses in miniature ACBB is the presence of the lubricant. In normal rolling bearings, the lubricant has an important contribution to decrease the losses and increase the reliability in miniature ball bearing; the lubricant (oil or grease) leads to the increase in the losses compared to the dry or limit lubrication conditions. The catalogues of various rolling bearing companies have not provided more details referring to the friction losses in miniature ball bearings. In order to evaluate the total friction torque in the rolling bearings, some empirical complex relations are presented via the SKF methodology, which can be applied only to moderate and high loads applied to the rolling bearings. Other empirical relations are presented by the Schaeffler catalogue. Based on previous experiments, the authors determined the friction torque in a 7000C ACBB with the spin-down method. The experimental results were correlated with the results obtained via the theoretical model developed by Houpert for IVR lubrication conditions. The theoretical results evidenced that the hydrodynamic rolling resistance generated by the lubricant is the most important component of the friction torque for 7000C ACBB. The experimental and theoretical results were compared to the results obtained according to the SKF and Schaeffler relations. The experimental results and the results obtained with the Houpert model generally had higher values compared to the results obtained with the SKF and Schaeffler relations. Full article

(This article belongs to the Special Issue Tribological Study in Rolling Bearing)

► Show Figures

Figure 1

21 pages, 5633 KiB

Open AccessReview

Development Status of Dynamic Sealing Technology and Discussion on Advanced Sealing Technologies

by Yan Wang, Shuoshuo Niu, Jiahao Zhang, Cong Feng, Yutong Wang, Doudou Shen, Decai Li, Tong Li, Pengcheng Cao and Yufan Zhang

Lubricants 2025, 13(1), 11; https://doi.org/10.3390/lubricants13010011 - 1 Jan 2025

Abstract

This paper reviews the current state of dynamic sealing technologies, examining the challenges faced by conventional sealing methods under complex working conditions, such as high temperature, high pressure, and corrosive environments. It also provides a concise overview of the status and developmental trends [...] Read more.

This paper reviews the current state of dynamic sealing technologies, examining the challenges faced by conventional sealing methods under complex working conditions, such as high temperature, high pressure, and corrosive environments. It also provides a concise overview of the status and developmental trends in sealing inspection technologies. From the perspective of obstruction mechanisms, this study reinterprets the concept of sealing science by redefining the classification of sealing types based on solid-phase medium obstruction, fluid hydrostatic and hydrodynamic obstruction, fluid pumping obstruction, fluid energy dissipation obstruction, and fluid impact obstruction. Comparative analyses of sealing structures across these obstruction mechanisms are presented. The sealing technology based on fluid impact medium obstruction, newly proposed by this paper, represents an innovative sealing approach. It offers distinct advantages such as zero wear, structural simplicity, and high stability, addressing longstanding issues in high-speed, large-clearance non-contact seals, including low leakage suppression efficiency, system complexity, and poor stability. Since its introduction, this novel sealing structure has garnered significant attention and recognition from both the academic and industrial sealing communities. With the potential to revolutionize the field, this groundbreaking sealing design is poised to lead the next wave of technological advancements in sealing science. Full article

(This article belongs to the Special Issue Recent Advances in Sealing Technologies)

► Show Figures

Figure 1

13 pages, 51039 KiB

Open AccessArticle

Effects of Sliding Speed on Wear Behavior of High-Velocity Oxygen Fuel-Sprayed FeCrMoNiCuBSiC Metallic Glass Coatings

by Lei Qiao, Botao Zhou, Ruifeng Li, Taotao Li, Yue Zhao, Xiaoqiang Zhang and Chul-Hee Lee

Lubricants 2025, 13(1), 10; https://doi.org/10.3390/lubricants13010010 - 30 Dec 2024

Abstract

A FeCrMoNiCuBSiC metallic glass coating was designed and then deposited by the high-velocity oxygen fuel (HVOF) spraying technique. X-ray diffraction, a scanning electron microscope, and a microhardness tester were applied to characterize the phase, microstructure, and mechanical properties of the coating. The amorphous [...] Read more.

A FeCrMoNiCuBSiC metallic glass coating was designed and then deposited by the high-velocity oxygen fuel (HVOF) spraying technique. X-ray diffraction, a scanning electron microscope, and a microhardness tester were applied to characterize the phase, microstructure, and mechanical properties of the coating. The amorphous phase was the main phase in the coating, and crystal phases were almost undetectable in the XRD results. The coating had a dense structure (the porosity was 1.47 ± 0.32%) and high Vickers microhardness (848 ± 22 HV_0.3). The wear behavior of the coatings sliding against WC-Co was studied with a pin-on-disc wear test system and was compared with that of 316L stainless steel. The coating improved the wear resistance of the steel by around 7–9 times at different sliding speeds. As the sliding speed was increased, the wear loss rate of the steel obviously increased, yet the loss rate of the coating decreased first and then increased. This happened because the contact flash temperature induced by friction increases with the sliding speed, which results in oxidative behavior and crystallization events in the coating. The dominating wear mechanism of the coating is fatigue wear combined with oxidative wear. Full article

(This article belongs to the Special Issue Wear-Resistant Coatings and Film Materials)

► Show Figures

Figure 1

18 pages, 12905 KiB

Open AccessArticle

Flow Characteristics and Experimental Verification of T-Groove Dry Gas Seal Under Different Flow States

by Lanxia Zhang, Xuexing Ding, Shipeng Wang and Shuai Zhang

Lubricants 2025, 13(1), 9; https://doi.org/10.3390/lubricants13010009 - 30 Dec 2024

Abstract

With the improvement of dry gas seal efficiency in high-parameter fields, the flow pattern of gas film lubrication is complicated. Based on gas lubrication theory, the Reynolds equation of compressible gas was established with a bidirectional T-groove dry gas seal as the research [...] Read more.

With the improvement of dry gas seal efficiency in high-parameter fields, the flow pattern of gas film lubrication is complicated. Based on gas lubrication theory, the Reynolds equation of compressible gas was established with a bidirectional T-groove dry gas seal as the research object. The Reynolds equation was solved to obtain a modified turbulent film pressure distribution law that affects gas lubrication. The effectiveness of the calculation program was verified by experimental tests. The results show that with an increase in operating parameters, the turbulence effect caused the gas film pressure fluctuation in the T-groove region to intensify, resulting in gas film flow instability. In addition, the inertia effect improved, which slowed down the leakage and affected the change law of stiffness and the rigid leakage ratio. When the fluid speed and gas pressure were low, the inertia effect could be ignored. When the groove depth was increased to 8 μm, the height difference between the trough and non-T-groove region became larger due to the combination of the turbulence and inertia effects. Further, when the gas film thickness was 3 μm, the opening force and gas film stiffness were high due to the dynamic pressure effect in the small film thickness groove. An increase in the gas film thickness weakened the turbulence effect and reduced the gas film pressure fluctuation. Full article

(This article belongs to the Special Issue High Performance Machining and Surface Tribology)

► Show Figures

Figure 1

13 pages, 9820 KiB

Open AccessArticle

Enhanced Tribological Properties of Ethylene Glycol-Based Lubricants by Nitrogen–Phosphorus Co-Doped Carbon Dots

by Haiyang Wang, Zhongyi He, Kai Qiu, Liping Xiong, Lili Li and Jian Liu

Lubricants 2025, 13(1), 8; https://doi.org/10.3390/lubricants13010008 - 29 Dec 2024

Abstract

In this study, we successfully synthesized two types of nitrogen–phosphorus co-doped carbon dots (CDs), namely 6NP-CDs and eNP-CDs, and incorporated them as additives into ethylene glycol-based lubricants. We systematically evaluated the effects of these CD additives on the tribological properties of the lubricants [...] Read more.

In this study, we successfully synthesized two types of nitrogen–phosphorus co-doped carbon dots (CDs), namely 6NP-CDs and eNP-CDs, and incorporated them as additives into ethylene glycol-based lubricants. We systematically evaluated the effects of these CD additives on the tribological properties of the lubricants through four-ball friction experiments. The experimental results demonstrate that lubricants enhanced with the CDs exhibit significantly improved tribological properties compared to the base lubricant, particularly in terms of anti-wear performance. Notably, 6NP-CDs exhibited superior wear resistance and friction reduction at concentrations of 0.1 wt.% and 0.2 wt.%. Furthermore, increasing the concentration of eNP-CDs further reduced the friction coefficient of the base lubricant, and at its optimal concentration, it outperformed 6NP-CDs in terms of wear resistance and friction reduction. Molecular structure analysis indicates that the concentration of nitrogen and phosphorus atoms, as well as the chain length of functional groups, significantly influence friction characteristics. Specifically, a greater content of heteroatoms and longer chain lengths correlate with improved friction performance. The results suggest that incorporating 6NP-CDs and eNP-CDs into ethylene glycol-based lubricants can lead to significant enhancements in tribological performance under heavy loads. Full article

► Show Figures

Figure 1

22 pages, 3247 KiB

Open AccessArticle

Experimental Identification of the Void Fraction in a Large Hydrodynamic Offset Halves Bearing

by Alexander Engels, Sören Wettmarshausen, Michael Stottrop, Thomas Hagemann, Christoph Weißbacher, Hubert Schwarze and Beate Bender

Lubricants 2025, 13(1), 7; https://doi.org/10.3390/lubricants13010007 - 29 Dec 2024

Abstract

A common approach to optimising hydrodynamic journal bearings for power loss is to reduce the lubricant supply and direct the oil to specific bearing areas where it is needed to guarantee safe operation. This requires information on the processes in the gap and [...] Read more.

A common approach to optimising hydrodynamic journal bearings for power loss is to reduce the lubricant supply and direct the oil to specific bearing areas where it is needed to guarantee safe operation. This requires information on the processes in the gap and the surrounding pocket areas for both pre-design and simulation. In this paper, a system consisting of a total of eight cameras is used to determine the void fraction in deep grooves outside the lubricant film. The void fraction in the lubrication gap is determined using a novel method for the evaluation of two proximity measurements. While the variation of the deep groove void fraction is realised by a special oil supply and radially adjustable deep groove elements, the gap void fraction is adjusted by the oil supply in the lube oil pockets at the pad leading edges. On the one hand, the experimental investigations show that the void fraction of the deep groove areas has hardly any influence on the general operating behaviour. On the other hand, the void fraction in the lubrication gap can be measured quantitatively for the first time, and the operating point-dependent gas fractions can be visualised. It is also shown that gaseous cavitation is the main mechanism in partially filled regions of the lubrication gap. Full article

(This article belongs to the Special Issue Advances in Lubricated Bearings, 2nd Edition)

► Show Figures

Figure 1

18 pages, 6190 KiB

Open AccessArticle

Wear Behavior Analysis and Gated Recurrent Unit Neural Network Prediction of Coefficient of Friction in Al10Cu-B₄C Composites

by Mihail Kolev, Ludmil Drenchev, Veselin Petkov, Rositza Dimitrova, Krasimir Kolev and Boris Yanachkov

Lubricants 2025, 13(1), 6; https://doi.org/10.3390/lubricants13010006 - 28 Dec 2024

Abstract

Aluminum-based metal matrix composites reinforced with B₄C are advanced materials recognized for their exceptional combination of lightweight properties, high hardness, and superior wear resistance. These characteristics make them perfectly suited for applications demanding exceptional performance in extreme mechanical and tribological environments. [...] Read more.

Aluminum-based metal matrix composites reinforced with B₄C are advanced materials recognized for their exceptional combination of lightweight properties, high hardness, and superior wear resistance. These characteristics make them perfectly suited for applications demanding exceptional performance in extreme mechanical and tribological environments. This study investigates the wear behavior, microstructural characteristics, and predictive modeling of Al10Cu-B₄C composites fabricated via powder metallurgy with varying B₄C contents (0, 2.5, 5, and 7.5 wt.%). The addition of B₄C microparticles to Al10Cu composites significantly influenced their tribological properties with 2.5 wt.% B₄C achieving a 21.74% reduction in the coefficient of friction (COF) and 7.5 wt.% B₄C providing a remarkable 65.00% improvement in wear resistance. Microstructural analysis using SEM and EDS was conducted on the unreinforced materials and the reinforced composites both before and after the wear tests. To further analyze and predict the tribological performance, a Gated Recurrent Unit neural network was developed to predict COF values. The need for this model arises from its potential to cost-effectively facilitate the prediction of COF, diminishing the need for extensive experimental testing while being noted for its simplicity and ease of implementation in practical applications. The model achieved excellent accuracy with an R² of 0.9965 for the test set and 0.9917 for the validation set. Additionally, feature importance analysis using Random Forest models identified reinforcement-related features as the dominant predictors for both COF and mass wear. These findings demonstrate the potential of Al10Cu-B₄C composites for emerging industrial applications, where enhanced wear resistance and controlled friction are critical for improving efficiency and durability under rigorous operating conditions. Furthermore, this study highlights the efficacy of neural network models in accurately predicting COF, providing a powerful tool for optimizing the performance of advanced composite materials. Full article

(This article belongs to the Special Issue Tribology for Lightweighting)

► Show Figures

Figure 1

20 pages, 5307 KiB

Open AccessArticle

Influence of Sulfur-Phosphorus Additive Interaction Effects on the Performance of Roller Bearing Greases

by Han Peng, Yike Chen, Linjian Shangguan, Yanchi Li and Qi Wang

Lubricants 2025, 13(1), 5; https://doi.org/10.3390/lubricants13010005 - 28 Dec 2024

Abstract

Friction wear is inevitable in roller bearings at high speeds, under heavy loads and vibration, and in other operating conditions. The use of grease can significantly reduce frictional wear. Sulfur–phosphorus additives have excellent anti-wear properties, oxidation resistance, and stability under high load and [...] Read more.

Friction wear is inevitable in roller bearings at high speeds, under heavy loads and vibration, and in other operating conditions. The use of grease can significantly reduce frictional wear. Sulfur–phosphorus additives have excellent anti-wear properties, oxidation resistance, and stability under high load and high-speed conditions. Their application in roller bearings enhances the performance of the grease, thus ensuring the normal operation of roller bearings. This study focuses on the effect of interaction between sulfur–phosphorus additives. Using a friction and wear tester and a rotational rheometer, the original roller bearing grease Fuchs 585k plus was used as the original grease, and the original grease was blended with MoS₂, MoS₂+TBP, and MoS₂+T321, respectively, to comparatively analyze the effect of sulfur–phosphorus additives and their interaction effect on the tribological and rheological properties of the roller bearing grease. The results show that the addition of all the above three additives can improve the anti-wear performance and anti-shear performance of roller bearing grease. Among them, the most significant optimization effect is MoS₂+T321, followed by MoS₂, and finally MoS₂+TBP. This result provides a new idea for the performance enhancement and formulation optimization of roller bearing grease. Full article

► Show Figures

Figure 1

17 pages, 19581 KiB

Open AccessArticle

Investigation of Anti-Friction Properties of MoS₂ and SiO₂ Nanolubricants Based on the Friction Pairs of Inconel 718 Superalloy and YG6 Carbide

by Lijie Ma, Fengnan Li, Shijie Ba, Zunyan Ma, Xinhui Mao, Qigao Feng and Kang Yang

Lubricants 2025, 13(1), 4; https://doi.org/10.3390/lubricants13010004 - 27 Dec 2024

Abstract

In order to improve the anti-friction property of common mineral oil and develop a high-performance lubricant, MoS₂ and SiO₂ nano-additives were individually dispersed into the 350SN mineral oil at various weight percentages to prepare nanolubricants. Then, the viscosity, wettability, and tribological [...] Read more.

In order to improve the anti-friction property of common mineral oil and develop a high-performance lubricant, MoS₂ and SiO₂ nano-additives were individually dispersed into the 350SN mineral oil at various weight percentages to prepare nanolubricants. Then, the viscosity, wettability, and tribological properties of the nanolubricants were measured and analyzed with a rotary viscometer, a contact angle measuring instrument, and a friction tester. Finally, the action mechanism of two nano-additives was explained based on the energy spectrum test results of the abrasion surface. The results show that MoS₂ and SiO₂ nano-additives could improve the viscosity of the base fluid and change its wettability, giving nanolubricants better anti-friction performance than the base fluid. Due to the difference in physical properties, SiO₂ and MoS₂ nanolubricants presented different friction reduction rules with the increase in nano-additive percentage. Under experimental conditions, SiO₂ nanolubricants showed better anti-friction effects than MoS₂ nanolubricants. When the SiO₂ percentage was 10 wt% and 15 wt%, the maximum friction coefficient was reduced to 0.06, which was about 1/3 of that with the base fluid. In this case, the abrasion surface quality was significantly improved, and the abrasion trace size was about half that of the base fluid. The energy spectrum test results show that the action mechanism of the MoS₂ nano-additive is the adsorption film effect and mending effect of nanoparticles, while the main action mechanism of the SiO₂ nano-additive should be the polishing effect and rolling effect of nanoparticles. Full article

(This article belongs to the Special Issue Mechanical Tribology and Surface Technology)

► Show Figures

Figure 1

12 pages, 5585 KiB

Open AccessArticle

Friction Properties of Alumina–Silicon Carbide–Silver–Graphene Nanoplatelet Self-Lubricating Composite Prepared by SPS Technique

by Viktor Puchý, Jana Andrejovská, Richard Sedlák, Róbert Džunda, František Kromka, Ivan Petryshynets, Mária Podobová and Ladislav Falat

Lubricants 2025, 13(1), 3; https://doi.org/10.3390/lubricants13010003 - 27 Dec 2024

Abstract

Al₂O₃ with SiC, silver, and graphene nanoplatelets (GNPs) powder mixture was produced by ball milling using ethanol as dispersion media. The GNP-reinforced Al₂O₃-SiC-Ag ceramic–metal composites were densified by spark plasma sintering technology (SPS). A homogeneous dispersion [...] Read more.

Al₂O₃ with SiC, silver, and graphene nanoplatelets (GNPs) powder mixture was produced by ball milling using ethanol as dispersion media. The GNP-reinforced Al₂O₃-SiC-Ag ceramic–metal composites were densified by spark plasma sintering technology (SPS). A homogeneous dispersion of GNPs in Al₂O₃-SiC-Ag was observed from the sintered samples, and the GNPs were embedded between the grains, which resulted in increasing the contact area. The trans-granular mechanism of crack propagation becomes increasingly dominant by adding GNPs. The hardness reaches 27 GPa, as tested by the Vickers microhardness method, which reflects an increase of 11% compared to Ag-GNPs-free Al₂O₃-SiC. On the other hand, by adding Ag-GNP content, the improvement in density is limited. Wear mechanisms, as determined through ball-on-flat testing, including adhesion, abrasion, and microcracks, are observed and discussed. The composite demonstrated remarkable self-lubricating properties, exhibiting a lower coefficient of friction (COF) and wear rate in an air environment compared to monolithic Al₂O₃-SiC. This improvement is attributed to the formation of a self-lubricating film, enabled by the uniform distribution of Ag and GNPs within the Al₂O₃-SiC matrix. The findings of this study propose a novel material design approach for developing self-lubricating ceramic composites with hybrid solid lubricants. Full article

► Show Figures

Figure 1

22 pages, 1673 KiB

Open AccessReview

Recent Studies on Nanomaterials as Additives to Lubricants Under Electrified Conditions for Tribology: Review

by Khodor Nasser, María J. G. Guimarey and Neuma das Mercês Pereira

Lubricants 2025, 13(1), 2; https://doi.org/10.3390/lubricants13010002 - 24 Dec 2024

Abstract

The tribological performance of nanolubricants in electric drivetrains has gained attention due to the rapid growth of electric vehicles. Nanomaterials, especially those with high thermal conductivity and low electrical conductivity, are favored as lubricant additives for use in electrical conditions. Low-viscosity lubricants, known [...] Read more.

The tribological performance of nanolubricants in electric drivetrains has gained attention due to the rapid growth of electric vehicles. Nanomaterials, especially those with high thermal conductivity and low electrical conductivity, are favored as lubricant additives for use in electrical conditions. Low-viscosity lubricants, known for their good thermal conductivity, are increasingly being considered for electric powertrains. Combining appropriate nanomaterials with lubricants can optimize nanolubricants for electric drivetrains, with stability, tribocorrosion, and electro-viscosity being key factors. Traditional tribometers, when modified to apply external electrical power, allow testing of nanolubricants under electrical conditions, providing insights into their behavior with positive and/or negative electrical charges. To achieve accurate and stable results, tribological test systems must be adapted, requiring well-isolated rigs for controlled data collection. This adaptation enables a better understanding of the interaction between nanomaterials and surfaces under lubrication. This paper reviews studies that use modified tribometers to analyze nanolubricant performance under mechanical and electrical conditions and explores the effects of electrical and thermal factors on lubricant properties, nanomaterials, and their mechanisms under triboelectric conditions. Full article

(This article belongs to the Special Issue Thermophysical and Tribological Characterization of Additivated Lubricants with Nanoparticles)

► Show Figures

Figure 1

20 pages, 10404 KiB

Open AccessArticle

Effect of Nanodiamonds on Friction Reduction Performance in Presence of Organic and Inorganic Friction Modifiers

by A. K. Piya, L. Yang, N. Emami and A. Morina

Lubricants 2025, 13(1), 1; https://doi.org/10.3390/lubricants13010001 - 24 Dec 2024

Abstract

The strive to reduce harmful emissions from transport has resulted in an increased emphasis on minimising friction in lubricated contacting components to improve the energy efficiency of automotive engines. In this sense, it is of particular interest to investigate whether a synergistic tribological [...] Read more.

The strive to reduce harmful emissions from transport has resulted in an increased emphasis on minimising friction in lubricated contacting components to improve the energy efficiency of automotive engines. In this sense, it is of particular interest to investigate whether a synergistic tribological performance could be achieved by combining two or more friction modifier additives with nanoparticles. This study conducts a comprehensive investigation into the tribological characteristics of lubricant formulations enriched with nanodiamonds (NDs), combined with organic (Glycerol Monooleate, GMO) and inorganic (molybdenum dithiocarbamate, MoDTC) friction modifiers and a low-concentration anti-wear additive (Zinc dialkyl dithio-phosphate, ZDDP). The interaction between NDs and MoDTC has been evaluated using reciprocal sliding tests at two different temperatures. The outcomes of the tribological experiments revealed that the interaction of NDs and MoDTC can enhance the friction and wear performance of steel pairs. However, this enhanced performance is shown to highly depend on other additives present in the lubricant mixture. Analysis of wear scars using High-Resolution Transmission Electron Microscopy (HRTEM), Atomic Force Microscopy (AFM) and Raman spectroscopy reveals that when NDs are fully entrapped into the formed tribofilm that contains the MoDTC-derived MoS₂ layer, the lowest friction coefficient can be achieved. Full article

(This article belongs to the Special Issue Recent Advances in Green Lubricants)

► Show Figures

Graphical abstract

9 pages, 7000 KiB

Open AccessArticle

Inhomogeneous Nanoscale Conductivity and Friction on Graphite Terraces Explored via Atomic Force Microscopy

by A. Kutay Ozyurt and Mehmet Z. Baykara

Lubricants 2024, 12(12), 462; https://doi.org/10.3390/lubricants12120462 - 21 Dec 2024

Abstract

The interplay of conductivity and friction in layered materials such as graphite is an open area of investigation. Here, we measure local conductivity and friction on terraces of freshly cleaved highly oriented pyrolytic graphite via atomic force microscopy under ambient conditions. The graphite [...] Read more.

The interplay of conductivity and friction in layered materials such as graphite is an open area of investigation. Here, we measure local conductivity and friction on terraces of freshly cleaved highly oriented pyrolytic graphite via atomic force microscopy under ambient conditions. The graphite surface is found to exhibit a rich electrical landscape, with different terraces exhibiting different levels of conductivity. A peculiar dependency of conductivity on scan direction is observed on some terraces. The terraces that exhibit this dependency are also found to show enhanced friction values. A hypothesis based on tip asymmetry and the puckering effect is proposed to explain the findings. Our results highlight the non-triviality of the electrical and tribological properties of graphite on the nanoscale, as well as their interplay. Full article

► Show Figures

Figure 1

17 pages, 8947 KiB

Open AccessArticle

Exploring the Effect of Interface Contact States on Brush/Ring Current-Carrying Friction

by Chenshi Li, Xinze Zhao, Yaru Lv, Yang Li, Wanting Li and Wei Yang

Lubricants 2024, 12(12), 461; https://doi.org/10.3390/lubricants12120461 - 20 Dec 2024

Abstract

A carbon brush/collector ring set will have phenomena such as firing and ablation during operation, which is due to the existence of various abnormal contact modes of the brush/ring during operation, thus changing the carbon brush/collector ring interface state. To analyze the effects [...] Read more.

A carbon brush/collector ring set will have phenomena such as firing and ablation during operation, which is due to the existence of various abnormal contact modes of the brush/ring during operation, thus changing the carbon brush/collector ring interface state. To analyze the effects of different contact modes on the performance of the brush/ring, in this paper, we construct the contact modes of the air gap (loss of contact leads to the existence of a small gap between the two surfaces), direct contact (contact with abrasive particulate media), and surface porosity contact (contact when there is a large pit on the surface of the collector ring due to manufacturing quality defects and abnormal abrasion), and analyze the effects of the various states on the core parameters such as current conduction, ring surface damage, and carbon brush abrasion, which provide a basis for the active suppression of the damage. Full article

► Show Figures

Figure 1

39 pages, 22737 KiB

Open AccessArticle

Comparative Research in the Field of the Parametric Effect of Lubricant Cavitation Initiation and Development on Friction and Wear in Piston Ring and Cylinder Liner Assemblies

by Polychronis Dellis

Lubricants 2024, 12(12), 460; https://doi.org/10.3390/lubricants12120460 - 20 Dec 2024

Abstract

This research follows closely previous findings in flow characteristics and phenomena that take place in the piston ring and cylinder liner interface during motoring and firing engine operation, and also compares results between different optical engine set-ups. Cavitation visualisation in a simulating lubrication [...] Read more.

This research follows closely previous findings in flow characteristics and phenomena that take place in the piston ring and cylinder liner interface during motoring and firing engine operation, and also compares results between different optical engine set-ups. Cavitation visualisation in a simulating lubrication single-ring test rig and oil transport and cavitation visualisation in custom made cylinder assemblies of optical engines are the tools used to quantify the transport process under the piston ring and cylinder liner. Simplification of the interface is an essential technique that enhances the researcher’s confidence in results interpretation. Engine complexity and severe oil starvation are impeding the analysis of the experimental results. Visualisation experiments constitute an effective way to test various lubricant types and assess their overall performance characteristics, including their properties and cavitation behaviour. The repeatability of the visualisation method establishes the parametric study effects and offers valuable experimental results. As a further step towards the lubricant composition effect, a link between the lubricant formulation and the operating conditions could be established as the oil performance is assessed with a view to its transport behaviour. Image processing is used to quantify the impact of cavitation on piston ring lubrication in conjunction with varied operating and lubricant parameters. The characteristics of the lubricant and the working environment have an impact on these types of cavities. Viscosity, cavitation, oil film thickness (OFT), lubricant shear-thinning characteristics and friction are all linked. Full article

(This article belongs to the Special Issue Tackling Emissions from the Internal Combustion Engine: Advances in Piston/Bore Tribology)

► Show Figures

Figure 1

Journal Description

Lubricants

Latest Articles

Journal Menu

Journal Browser

Highly Accessed Articles

Latest Books

E-Mail Alert

News

Topics

Conferences

Special Issues

Topical Collections

Further Information

Guidelines

MDPI Initiatives

Follow MDPI