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Lubricants
Volume 13
Issue 7
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Lubricants, Volume 13, Issue 7 (July 2025) – 39 articles

Cover Story (view full-size image): Wheel–rail friction behaviour is of critical importance for railway operations and maintenance, and is generally characterised by creep curves. This study employs the V-Track test rig to measure wheel–rail creep curves under dry contact with pressures of operational conditions and various speeds. The novelties are threefold: 1. With proper representations of train/track components, the tests revealed the effects of structural dynamics on measuring wheel–rail creep curves in real life; 2. pure lateral and longitudinal (traction/braking) friction conditions were produced with distinct experimental principles—displacement and force controlled—on the same platform, and the obtained coefficients of friction were crosschecked; 3. uncertainties in the measured creep curves were analysed, which has been rarely addressed in previous studies. View this paper
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26 pages, 10072 KiB  
Article
Mechanisms of Adhesion Increase in Wet Sanded Wheel–Rail Contacts—A DEM-Based Analysis
by Bettina Suhr, William A. Skipper, Roger Lewis and Klaus Six
Lubricants 2025, 13(7), 314; https://doi.org/10.3390/lubricants13070314 - 18 Jul 2025
Abstract
In railways, problems in braking and traction can be caused by so-called low-adhesion conditions. Adhesion is increased by sanding, where sand grains are blasted towards the wheel–rail contact. Despite the successful use of sanding in practice and extensive experimental studies, the physical mechanisms [...] Read more.
In railways, problems in braking and traction can be caused by so-called low-adhesion conditions. Adhesion is increased by sanding, where sand grains are blasted towards the wheel–rail contact. Despite the successful use of sanding in practice and extensive experimental studies, the physical mechanisms of adhesion increase are poorly understood. This study combines experimental work with a DEM model to aim at a deeper understanding of adhesion increase during sanding. The experimentally observed processes during sanding involve repeated grain breakage, varying sand fragment spread, formation of clusters of crushed sand powders, plastic deformation of the steel surfaces due to the high load applied and shearing of the compressed sand fragments. The developed DEM model includes all these processes. Two types of rail sand are analysed, which differ in adhesion increase in High-Pressure Torsion tests under wet contact conditions. This study shows that higher adhesion is achieved when a larger proportion of the normal load is transferred through sand–steel contacts. This is strongly influenced by the coefficient of friction between sand and steel. Adhesion is higher for larger sand grains, higher sand fragment spread, and higher steel hardness, resulting in less indentation, all leading to larger areas covered by sand. Full article
16 pages, 6100 KiB  
Article
Investigation of the Friction and Wear Behavior of Cr-Mo-V Steel with Different Surface Treatment Processes
by Wei Zhang, Jian Zhang, Shizhong Wei, Liuliang Chen, Wei Zhang, Zhenhuan Sun, Chong Chen, Feng Mao, Xiaodong Wang, Caihong Dou and Cheng Zhang
Lubricants 2025, 13(7), 313; https://doi.org/10.3390/lubricants13070313 - 18 Jul 2025
Abstract
Hot work die steel is an alloy steel with good high-temperature performance, which is widely used in mechanical manufacturing, aerospace, and other fields. During the working process of hot working mold steel, it is subjected to high temperature, wear, and other effects, which [...] Read more.
Hot work die steel is an alloy steel with good high-temperature performance, which is widely used in mechanical manufacturing, aerospace, and other fields. During the working process of hot working mold steel, it is subjected to high temperature, wear, and other effects, which can lead to a decrease in the surface hardness of the mold, accelerate surface damage, shorten the service life, and reduce the quality of the workpiece. In order to improve the wear resistance of the mold, this paper conducts two surface treatments, chrome plating and nitriding, on the surface of hot work mold steel, and compares the high-temperature wear behavior of the materials after the two surface treatments. The results indicate that the hot work die steel obtained higher surface hardness and wear resistance after nitriding surface modification. After nitriding treatment, the surface of hot work die steel contains ε phase (Fe2–3N), which improves its surface hardness and wear resistance, thus exhibiting better surface hardness and wear resistance than the chrome-plated sample. In this study, the high-temperature wear behavior of hot work die steel after two kinds of surface strengthening treatments was deeply discussed, and the high-temperature wear mechanism of steel after surface strengthening was revealed. It provides a theoretical basis and experimental basis for the surface modification of hot working die steel, and also provides new ideas and methods for improving the service life and workpiece quality of hot working die steel in industrial production. In this study, the advantages and disadvantages of high-temperature wear resistance of hot working die steel after chromium plating and nitriding were systematically compared for the first time, which provided a scientific basis for the selection of surface strengthening technology of hot working die steel and had important academic value and practical application significance. Full article
(This article belongs to the Special Issue Wear-Resistant Coatings and Film Materials)
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18 pages, 4348 KiB  
Article
Maskless Electrochemical Texturing (MECT) Applied to Skin-Pass Cold Rolling
by Paulo L. Monteiro, Jr., Wilian Labiapari, Washington M. Da Silva, Jr., Cristiano de Azevedo Celente and Henara Lillian Costa
Lubricants 2025, 13(7), 312; https://doi.org/10.3390/lubricants13070312 - 18 Jul 2025
Abstract
The surface topography of the rolls used in skin-pass cold rolling determines the surface finish of rolled sheets. In this sense, work rolls can be intentionally textured to produce certain topographical features on the final sheet surface. The maskless electrochemical texturing method (MECT) [...] Read more.
The surface topography of the rolls used in skin-pass cold rolling determines the surface finish of rolled sheets. In this sense, work rolls can be intentionally textured to produce certain topographical features on the final sheet surface. The maskless electrochemical texturing method (MECT) is a potential candidate for industrial-scale application due to its reduced texturing cost and time when compared to traditional texturing methods. However, there are few studies in the literature that address the MECT method applied to the topography control of cold rolling work rolls. The present work aims to analyze the viability of surface texturing via MECT of work rolls used in skin-pass cold rolling. In this study, we first investigated how texturing occurs for tool steel using flat textured samples to facilitate the understanding of the dissolution mechanisms involved. In this case, a specially designed texturing chamber was built to texture flat samples extracted from an actual work roll. The results indicated that the anodic dissolution involved in tool steel texturing occurs preferentially in the metallic matrix around the primary carbides. Then, we textured a work roll used in pilot-scale rolling tests, which required the development of a special prototype to texture cylindrical surfaces. After texturing, the texture transfer from the work roll to the sheets was investigated. Rolling tests showed that the work roll surface textured with a dimple pattern generated a pillar-shaped texture pattern on the sheet surface, possibly due to a reverse extrusion mechanism. Full article
(This article belongs to the Special Issue Recent Achievements and Future Developments in Surface Texture Control of Tribological Properties)
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17 pages, 3902 KiB  
Article
Electrical Potential-Induced Lubricity Changes in an Ionic Liquid-Lubricated Friction Pair
by Raimondas Kreivaitis, Audrius Žunda and Albinas Andriušis
Lubricants 2025, 13(7), 311; https://doi.org/10.3390/lubricants13070311 - 17 Jul 2025
Abstract
The control of lubricity induced by electric potential is appealing for numerous applications. On the other hand, the high polarity of ionic liquids facilitates the adsorption of equally charged molecules onto polar surfaces. This phenomenon and its consequences are well understood at the [...] Read more.
The control of lubricity induced by electric potential is appealing for numerous applications. On the other hand, the high polarity of ionic liquids facilitates the adsorption of equally charged molecules onto polar surfaces. This phenomenon and its consequences are well understood at the nanoscale; however, they have recently garnered significant attention at the macroscale. This study investigates the lubricity of trihexyltetradecylphosphonium dicyanamide, a phosphonium ionic liquid, when used as a neat lubricant in reciprocating sliding under electrically charged conditions. Two different polarities with the same potential were applied to the friction pair of bearing steel against bearing steel while monitoring electrical contact resistance. The lubricity was evaluated through measurements of friction, wear, surface morphology, and composition. It was found that the application of electric potential significantly alters the lubricity of the investigated ionic liquid where a positive potential applied to the ball resulted in the least damaging situation. The recorded electrical contact resistance enabled the monitoring of tribofilm formation during reciprocation. It was found that there was minimal to no separation between interacting surfaces when the ball was changing direction. Full article
(This article belongs to the Special Issue Recent Advances in Eco-Friendly Ionic Liquids as Lubricants and Additives)
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17 pages, 4068 KiB  
Article
Mechanical Properties and Tribological Behavior of Al2O3–ZrO2 Ceramic Composites Reinforced with Carbides
by Jana Andrejovská, Dávid Medveď, Marek Vojtko, Richard Sedlák, Piotr Klimczyk and Ján Dusza
Lubricants 2025, 13(7), 310; https://doi.org/10.3390/lubricants13070310 - 17 Jul 2025
Abstract
To elucidate the key material parameters governing the tribological performance of ceramic composites under dry sliding against steel, this study presents a comprehensive comparative assessment of the microstructural characteristics, mechanical performance, and tribological behavior of two alumina–zirconia (Al2O3–ZrO2 [...] Read more.
To elucidate the key material parameters governing the tribological performance of ceramic composites under dry sliding against steel, this study presents a comprehensive comparative assessment of the microstructural characteristics, mechanical performance, and tribological behavior of two alumina–zirconia (Al2O3–ZrO2) ceramic composites, each reinforced with a 42 vol.% carbide phase: zirconium carbide (ZrC) and tungsten carbide (WC). Specifically, tungsten carbide (WC) was selected for its exceptional bulk mechanical properties, while zirconium carbide (ZrC) was chosen to contrast its potentially different interfacial reactivity against a steel counterface. ZrC and WC were selected as reinforcing phases due to their high hardness and distinct chemical and interfacial properties, which were expected to critically affect the wear and friction behavior of the composites under demanding conditions. Specimens were consolidated via spark plasma sintering (SPS). The investigation encompassed macro- and nanoscale hardness measurements (Vickers hardness HV1, HV10; nanoindentation hardness H), elastic modulus (E), fracture toughness (KIC), coefficient of friction (COF), and specific wear rate (Ws) under unlubricated reciprocating sliding against 100Cr6 steel at normal loads of 10 N and 25 N. The Al2O3–ZrO2–WC composite exhibited an ultrafine-grained microstructure and markedly enhanced mechanical properties (HV10 ≈ 20.9 GPa; H ≈ 33.6 GPa; KIC ≈ 4.7 MPa·m½) relative to the coarse-grained Al2O3–ZrO2–ZrC counterpart (HV10 ≈ 16.6 GPa; H ≈ 27.0 GPa; KIC ≈ 3.2 MPa·m½). Paradoxically, the ZrC-reinforced composite demonstrated superior tribological performance, with a low and load-independent specific wear rate (Ws ≈ 1.2 × 10−9 mm3/Nm) and a stable steady-state COF of approximately 0.46. Conversely, the WC-reinforced system exhibited significantly elevated wear volumes—particularly under the 25 N regime—and a higher, more fluctuating COF. Scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM–EDX) of the wear tracks revealed the formation of a continuous, iron-enriched tribofilm on the ZrC composite, derived from counterface material transfer, whereas the WC composite surface displayed only sparse tribofilm development. These findings underscore that, in steel-paired tribological applications of Al2O3–ZrO2–based composites, the efficacy of interfacial tribolayer generation can supersede intrinsic bulk mechanical attributes as the dominant factor governing wear resistance. Full article
(This article belongs to the Special Issue Tribological and Mechanical Characteristics of Aluminum Metal Matrix Composites and Their Applications)
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18 pages, 10294 KiB  
Article
High-Precision Normal Stress Measurement Methods for Tire–Road Contact and Its Spatial and Frequency Domain Distribution Characteristics
by Liang Song, Xixian Wu, Zijie Xie, Jie Gao, Di Yun and Zongjian Lei
Lubricants 2025, 13(7), 309; https://doi.org/10.3390/lubricants13070309 - 16 Jul 2025
Viewed by 76
Abstract
This study investigates measurement methods for and the distribution characteristics of normal stress within tire–road contact areas. A novel measurement method, integrating 3D scanning technology with bearing area curve (BAC) analysis, is proposed. This method quantifies the rubber penetration depth and calculates contact [...] Read more.
This study investigates measurement methods for and the distribution characteristics of normal stress within tire–road contact areas. A novel measurement method, integrating 3D scanning technology with bearing area curve (BAC) analysis, is proposed. This method quantifies the rubber penetration depth and calculates contact stress based on rubber deformation. The key innovation of this method lies in this integrated methodology for high-precision stress mapping. In the spatial domain, stress distribution is characterized by the percentage of area occupied by different stress intervals, while in the frequency domain, stress levels are analyzed at various frequencies. The results demonstrate that as the Mean Profile Depth (MPD) of the road texture increases, the areas under stress greater than 1.0 MPa increase, while the areas under stress less than 0.8 MPa decrease. However, when the MPD exceeds 0.7 mm, this effect becomes less pronounced. Higher loads and harder rubber reduce the proportion of areas under lower stress and increase the proportion under higher stress. Low-frequency (<800 1/m) stress components increase with an MPD up to 0.7 mm, beyond which they exhibit diminished sensitivity. Stress at the same frequency is not significantly affected by load variation but increases markedly with increasing rubber hardness. This research provides crucial insights into contact stress distribution, establishing a foundation for analyzing road friction and optimizing surface texture design oriented towards high-friction pavements. Full article
(This article belongs to the Special Issue Tire/Road Interface and Road Surface Textures)
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23 pages, 11965 KiB  
Article
Research on the Impact of Labyrinth Seal Ring Tooth Profile on the Pressure Pulsation of Leakage Chambers in High-Speed Centrifugal Pumps
by Guodong Zhao, Jiahao Xu, Jie Lian, Yanpi Lin and Zuchao Zhu
Lubricants 2025, 13(7), 308; https://doi.org/10.3390/lubricants13070308 - 16 Jul 2025
Viewed by 47
Abstract
The gap seal ring is a critical component in high-speed centrifugal pumps. The leakage rate and performance of the pump are sensitive to variation in seal ring parameters. This study investigates the influence of seal ring tooth profile on the leakage flow of [...] Read more.
The gap seal ring is a critical component in high-speed centrifugal pumps. The leakage rate and performance of the pump are sensitive to variation in seal ring parameters. This study investigates the influence of seal ring tooth profile on the leakage flow of pump chambers. Numerical simulation and experimental tests are used to analyze the impact of four different tooth-height labyrinth seal ring structures on the pressure pulsation characteristics of pump leakage chambers. It can be concluded that the use of labyrinth seal rings can significantly reduce the pressure pulsation and leakage rate of pump chambers. For the Case 2 structure with a tooth height of 0.18 mm, the pressure pulsation in the pump chamber can be reduced by a maximum of 22.5%, and the leakage rate can be reduced by 41.1%. For the Case 3 structure with a tooth height of 0.23 mm, the pressure pulsation in the pump chamber can be reduced by a maximum of 30.3%, and the leakage rate can be reduced by 40.6%. The use of labyrinth seal rings significantly reduces the pressure pulsation intensity of the impeller surfaces, which improves the force stability of the high-speed centrifugal pump impeller. This study is helpful in providing theoretical support for the design of labyrinth seal rings in high-speed centrifugal pumps. Full article
(This article belongs to the Special Issue Recent Advances in Sealing Technologies)
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24 pages, 10860 KiB  
Article
Dynamic Characteristics of ‘Floating’ Valve Plate for Internal Curve Hydraulic Motor
by Wei Ma, Guolai Yang, Wenbin Cao, Shaohui Yao, Guixiang Bai, Chuanchuan Cao and Shoupeng Song
Lubricants 2025, 13(7), 307; https://doi.org/10.3390/lubricants13070307 - 15 Jul 2025
Viewed by 91
Abstract
The internal curve hydraulic motor valve plate has a clearance self-compensation performance that can effectively improve the working efficiency of the valve plate. However, the dynamic characteristics of the valve plates require further investigation. This study considers the self-compensating ‘floating’ valve plate as [...] Read more.
The internal curve hydraulic motor valve plate has a clearance self-compensation performance that can effectively improve the working efficiency of the valve plate. However, the dynamic characteristics of the valve plates require further investigation. This study considers the self-compensating ‘floating’ valve plate as the research object, proposes a dynamic characteristic analysis method for the internal curve hydraulic motor valve plate, and explores the changing rule of oil film thickness and surplus pressing force of the valve plate. The results showed that an increase in the inlet pressure and oil temperature led to an increase in the thickness of the oil film, and the amplitude of the oil film thickness was larger, whereas the rotational speed of the oil film thickness of the valve plate pair was not obvious. When the inlet pressure is lower than 8 MPa, and the oil temperature is in the range of 20–30 °C, the oil film is mainly subjected to the squeezing effect of the valve plate, and the displacement of the valve plate decreased with increasing rotational speed. The inlet pressure is the main factor affecting the displacement of the ‘floating’ valve plate, and when the inlet pressure reaches 8.7 MPa, the valve plate is in hydrostatic balance support. In addition, the surplus pressing force coefficient of the valve plate decreased with increasing inlet pressures. This study provides theoretical support for the design of variable pressing force valve plates for internal curve hydraulic motors by investigating the dynamic characteristics of “floating” valve plates. Full article
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22 pages, 11458 KiB  
Article
Convolutional Neural Networks—Long Short-Term Memory—Attention: A Novel Model for Wear State Prediction Based on Oil Monitoring Data
by Ying Du, Hui Wei, Tao Shao, Shishuai Chen, Jianlei Wang, Chunguo Zhou and Yanchao Zhang
Lubricants 2025, 13(7), 306; https://doi.org/10.3390/lubricants13070306 - 15 Jul 2025
Viewed by 171
Abstract
Wear state prediction based on oil monitoring technology enables the early identification of potential wear and failure risks of friction pairs, facilitating optimized equipment maintenance and extended service life. However, the complexity of lubricating oil monitoring data often poses challenges in extracting discriminative [...] Read more.
Wear state prediction based on oil monitoring technology enables the early identification of potential wear and failure risks of friction pairs, facilitating optimized equipment maintenance and extended service life. However, the complexity of lubricating oil monitoring data often poses challenges in extracting discriminative features, limiting the accuracy of wear state prediction. To address this, a CNN–LSTM–Attention network is specially constructed for predicting wear state, which hierarchically integrates convolutional neural networks (CNNs) for spatial feature extraction, long short-term memory (LSTM) networks for temporal dynamics modeling, and self-attention mechanisms for adaptive feature refinement. The proposed architecture implements a three-stage computational pipeline. Initially, the CNN performs hierarchical extraction of localized patterns from multi-sensor tribological signals. Subsequently, the self-attention mechanism conducts adaptive recalibration of feature saliency, prioritizing diagnostically critical feature channels. Ultimately, bidirectional LSTM establishes cross-cyclic temporal dependencies, enabling cascaded fully connected layers with Gaussian activation to generate probabilistic wear state estimations. Experimental results demonstrate that the proposed model not only achieves superior predictive accuracy but also exhibits robust stability, offering a reliable solution for condition monitoring and predictive maintenance in industrial applications. Full article
(This article belongs to the Special Issue Future of Digital Tribology: Prediction of Tribological Performance Using Sensors, Signal Processing and Machine Learning)
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22 pages, 9751 KiB  
Article
Investigation on the Coupling Effect of Bionic Micro-Texture Shape and Distribution on the Tribological Performance of Water-Lubricated Sliding Bearings
by Xiansheng Tang, Yunfei Lan, Sergei Bosiakov, Michael Zhuravkov, Tao He, Yang Xia and Yongtao Lyu
Lubricants 2025, 13(7), 305; https://doi.org/10.3390/lubricants13070305 - 14 Jul 2025
Viewed by 164
Abstract
Water-lubricated bearings (WLB), due to their pollution-free nature and low noise, are increasingly becoming critical components in aerospace, marine applications, high-speed railway transportation, precision machine tools, etc. However, in practice, water-lubricated bearings suffer severe friction and wear due to low-viscosity water, harsh conditions, [...] Read more.
Water-lubricated bearings (WLB), due to their pollution-free nature and low noise, are increasingly becoming critical components in aerospace, marine applications, high-speed railway transportation, precision machine tools, etc. However, in practice, water-lubricated bearings suffer severe friction and wear due to low-viscosity water, harsh conditions, and contaminants like sediment, which can compromise the lubricating film and shorten their lifespan. The implementation of micro-textures has been demonstrated to improve the tribological performance of water-lubricated bearings to a certain extent, leading to their widespread adoption for enhancing the frictional dynamics of sliding bearings. The shape, dimensions (including length, width, and depth), and distribution of these micro-textures have a significant influence on the frictional performance. Therefore, this study aims to explore the coupling effect of different micro-texture shapes and distributions on the frictional performance of water-lubricated sliding, using the computational fluid dynamics (CFD) analysis. The results indicate that strategically arranging textures across multiple regions can enhance the performance of the bearing. Specifically, placing linear groove textures in the outlet of the divergent zone and triangular textures in the divergent zone body maximize improvements in the load-carrying capacity and frictional performance. This specific configuration increases the load-carrying capacity by 7.3% and reduces the friction coefficient by 8.6%. Overall, this study provided critical theoretical and technical insights for the optimization of WLB, contributing to the advancement of clean energy technologies and the extension of critical bearing service life. Full article
(This article belongs to the Special Issue Water Lubricated Bearings)
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20 pages, 5652 KiB  
Article
Capacitive Sensing of Solid Debris in Used Lubricant of Transmission System: Multivariate Statistics Classification Approach
by Surapol Raadnui and Sontinan Intasonti
Lubricants 2025, 13(7), 304; https://doi.org/10.3390/lubricants13070304 - 14 Jul 2025
Viewed by 181
Abstract
The quantification of solid debris in used lubricating oil is essential for assessing transmission system wear and optimizing maintenance strategies. This study introduces a low-cost capacitive proximity sensor for monitoring total solid particle contamination in lubricants, with a focus on ferrous (Fe), non-ferrous [...] Read more.
The quantification of solid debris in used lubricating oil is essential for assessing transmission system wear and optimizing maintenance strategies. This study introduces a low-cost capacitive proximity sensor for monitoring total solid particle contamination in lubricants, with a focus on ferrous (Fe), non-ferrous (Al), and non-metallic (SiO2) debris. Controlled tests were performed using five mixing ratios of large-to-small particles (100:0, 75:25, 50:50, 25:75, and 0:100) at a fixed debris mass of 0.5 g per 25 mL of SAE 85W-140 automotive gear oil. Cubic regression analysis yielded high predictive accuracy, with average R2 values of 0.994 for Fe, 0.943 for Al, and 0.992 for SiO2. Further dimensionality reduction using Principal Component Analysis (PCA), along with Linear Discriminant Analysis (LDA) of multivariate statistical analysis, effectively classifies debris types and enhances interpretability. These results demonstrate the potential of capacitive sensing as an offline, non-invasive alternative to traditional techniques for wear debris monitoring in transmission systems. These results confirm the potential of capacitive sensing, supported by statistical modeling, as a non-invasive, cost-effective technique for offline classification and monitoring of wear debris in transmission systems. Full article
(This article belongs to the Special Issue Tribological Research on Transmission Systems)
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15 pages, 2184 KiB  
Article
First-Principles Study on Interfacial Triboelectrification Between Water and Halogen-Functionalized Polymer Surfaces
by Taili Tian, Bo Zhao, Yimin Wang, Shifan Huang, Xiangcheng Ju and Yuyan Fan
Lubricants 2025, 13(7), 303; https://doi.org/10.3390/lubricants13070303 - 11 Jul 2025
Viewed by 239
Abstract
Contact electrification (CE), or triboelectrification, is an electron transfer phenomenon occurring at the interface between dissimilar materials due to differences in polarity, holding significant research value in tribology. The microscopic mechanisms of CE remain unclear due to the complex coupling of multiple physical [...] Read more.
Contact electrification (CE), or triboelectrification, is an electron transfer phenomenon occurring at the interface between dissimilar materials due to differences in polarity, holding significant research value in tribology. The microscopic mechanisms of CE remain unclear due to the complex coupling of multiple physical processes. Recently, with the rise of triboelectric nanogenerator (TENG) technology, solid–liquid contact electrification has demonstrated vast application potential, sparking considerable interest in its underlying mechanisms. Emerging experimental evidence indicates that at water–polymer CE interfaces, the process involves not only traditional ion adsorption but also electron transfer. Halogen-containing functional groups in the solid material significantly enhance the CE effect. To elucidate the microscopic mechanism of water–polymer CE, this study employed first-principles density functional theory (DFT) calculations, simulating the interfacial electrification process using unit cell models of water contacting polymers. We systematically and quantitatively investigated the charge transfer characteristics at interfaces between water and three representative polymers with similar backbones but different halogen-functionalized (F, Cl) side chains: fluorinated ethylene propylene (FEP), polyvinyl chloride (PVC), and polytetrafluoroethylene (PTFE), focusing on evaluating halogen’s influence and mechanism on interfacial electron transfer. The results reveal that electron transfer is primarily governed by the energy levels of the polymer’s lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO). Halogen functional groups modulate the material’s electron-donating/accepting capabilities by altering these frontier orbital energy levels. Consequently, we propose that the critical strategy for polymer chemical modification resides in lowering the LUMO energy level of electron-accepting materials. This study provides a novel theoretical insight into the charge transfer mechanism at solid–liquid interfaces, offers guidance for designing high-performance TENG interfacial materials, and holds significant importance for both the fundamental theory and the development of advanced energy devices. Full article
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19 pages, 4518 KiB  
Article
The Impact of Curcumin, Gingerol, Piperine, and Proanthocyanidin on the Oxidative Stability of Sunflower and Soybean Oils for Developing Bio-Lubricants
by Diana-Luciana Cursaru and Dănuța Matei
Lubricants 2025, 13(7), 302; https://doi.org/10.3390/lubricants13070302 - 10 Jul 2025
Viewed by 298
Abstract
Vegetable oils can serve as a fundamental raw material for formulating lubricants due to their exceptional lubricating properties, which are indicated by viscosity indexes greater than 100. Vegetable oils, due to their unsaturated fatty acids with one or more double bonds, have two [...] Read more.
Vegetable oils can serve as a fundamental raw material for formulating lubricants due to their exceptional lubricating properties, which are indicated by viscosity indexes greater than 100. Vegetable oils, due to their unsaturated fatty acids with one or more double bonds, have two significant drawbacks: low oxidation stability and poor performance in low temperatures. The oxidative stability of sunflower and soybean oils was evaluated and correlated with the unsaturation degree calculated based on fatty acid profiles. Different percentages of piperine, curcumin, gingerol, and proanthocyanidin (0.5, 1, 2, and 3 wt.%) have been tested as potential bio-additives for sunflower and soybean oils. All four bio-additives have been observed to enhance oxidation resistance, with gingerol being the most effective, followed by curcumin, piperine, and proanthocyanidin. Bio-additives’ effectiveness increases when applied to bio-oils with lower degrees of unsaturation, such as soybean oil. Adding gingerol significantly enhances the induction period, increasing it by about 10 times for soybean oil and 6 times for sunflower oil. This suggests that gingerol can effectively prolong the induction period of both oils. Full article
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37 pages, 4353 KiB  
Article
Tribo-Electrochemical Characterization of Brush-Scrubbed Post-CMP Cleaning: Results for Tartrate-Supported Removal of Residual Oxides from Copper Films
by Collin M. Reff, Kassapa U. Gamagedara, David R. Santefort and Dipankar Roy
Lubricants 2025, 13(7), 301; https://doi.org/10.3390/lubricants13070301 - 8 Jul 2025
Viewed by 357
Abstract
Wafer cleaning after chemical mechanical planarization (CMP) is a critical processing step for copper metallization in integrated circuits. Post-CMP cleaning (PCMPC) commonly combines surface (electro)chemistry with the tribology of brush scrubbing to remove CMP residues from wafer surfaces. While the complex mechanisms of [...] Read more.
Wafer cleaning after chemical mechanical planarization (CMP) is a critical processing step for copper metallization in integrated circuits. Post-CMP cleaning (PCMPC) commonly combines surface (electro)chemistry with the tribology of brush scrubbing to remove CMP residues from wafer surfaces. While the complex mechanisms of brush-operated PCMPC are supported by this combination, the conventional electroanalytical methods of assessing PCMPC efficiency are typically operated in the absence of surface brushing. Using a model experimental system with tartaric acid (TA) as a cost-effective cleaner of Cu-oxides, we illustrate here how post-CMP Cu samples can be electrochemically examined using brush cleaning to design/assess PCMPC test solutions. A pH-neutral cleaning solution is employed, where TA also serves as a partial dissolution suppressor of Cu, and CMP-treated wafer samples are scrubbed with a commercial PCMPC brush as sample surfaces are simultaneously probed with electrochemical measurements. The results show the active roles of tribology/lubrication and surface chemistry in the removal of CMP residues. The electrochemically determined residue removal efficiencies of PCMPC are found to be ~97% and ~56% in the presence and in the absence of surface brushing, respectively. The implications of these findings are explored in the general context of evaluating PCMPC formulations. Full article
(This article belongs to the Special Issue Advances in Tribochemistry)
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13 pages, 4246 KiB  
Article
Study on the Characteristics of CO2 Displacing Non-Newtonian Fluids
by Yu-Ting Wu, Sung-Ki Lyu, Zhen Qin, Yanjun Qin, Hua Qiao and Bing Li
Lubricants 2025, 13(7), 300; https://doi.org/10.3390/lubricants13070300 - 8 Jul 2025
Viewed by 218
Abstract
CO2 displacement is a key technique that was examined through numerical methods in a 3D Hele–Shaw cell, with CO2 as the displacing phase and shear-thinning fluids as the displaced phase. Without interfacial tension effects, the displacement shows branching patterns forming two [...] Read more.
CO2 displacement is a key technique that was examined through numerical methods in a 3D Hele–Shaw cell, with CO2 as the displacing phase and shear-thinning fluids as the displaced phase. Without interfacial tension effects, the displacement shows branching patterns forming two vertically symmetric fingers, regardless of whether the displacing fluid is air or CO2. Under CO2 displacement, viscous fingering propagates farther and achieves higher displacement efficiency than air. Compared with air displacement, the finger advancing distance increases by 0.0035 m, and the displacement efficiency is 15.2% higher than that of air displacement. Shear-thinning behavior significantly influences the process; stronger shear thinning enhances interfacial stability and suppresses fingering. As the power-law index n increases (reducing shear thinning), the fingering length extends. Variations in interfacial tension reveal it notably affects fingering initiation and velocity in CO2 displacement of non-Newtonian fluids, but has a weaker impact on fingering formation. Interfacial tension suppresses short-wavelength perturbations, critical to interface stability, jet breakup, and flows, informing applications like foam-assisted oil recovery and microfluidics. Full article
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18 pages, 2215 KiB  
Article
Research on Sealing Performance of Supercritical Hydrogen Cylindrical Seals Based on Multi-Objective Optimization of Spiral Grooves
by Xueliang Wang, Zegan Gao, Wei Zhang, Junjie Lu, Min Jiang, Leibo Wu and Xuejing Wu
Lubricants 2025, 13(7), 299; https://doi.org/10.3390/lubricants13070299 - 7 Jul 2025
Viewed by 213
Abstract
Aimed at hydrogen turbines, this research employs advanced noncontact cylindrical sealing and optimizes its sealing structure to enhance efficiency. Therefore, this paper considers the variable density and viscosity cylindrical sealing model with actual gas effects and explores the impact of groove parameters on [...] Read more.
Aimed at hydrogen turbines, this research employs advanced noncontact cylindrical sealing and optimizes its sealing structure to enhance efficiency. Therefore, this paper considers the variable density and viscosity cylindrical sealing model with actual gas effects and explores the impact of groove parameters on load capacity, leakage, and friction force under two different temperature and pressure conditions. A multivariate linear regression analysis model is established. Subsequently, the NSGAII algorithm is used to perform multi-objective optimization design under operational conditions. The TOPSIS methods are applied to select the optimal parameters. This study shows that the groove depth of the spiral groove has the most significant impact on sealing performance when the groove depth is 2 μm. Full article
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45 pages, 1648 KiB  
Review
Tribological Performance Enhancement in FDM and SLA Additive Manufacturing: Materials, Mechanisms, Surface Engineering, and Hybrid Strategies—A Holistic Review
by Raja Subramani, Ronit Rosario Leon, Rajeswari Nageswaren, Maher Ali Rusho and Karthik Venkitaraman Shankar
Lubricants 2025, 13(7), 298; https://doi.org/10.3390/lubricants13070298 - 7 Jul 2025
Viewed by 541
Abstract
Additive Manufacturing (AM) techniques, such as Fused Deposition Modeling (FDM) and Stereolithography (SLA), are increasingly adopted in various high-demand sectors, including the aerospace, biomedical engineering, and automotive industries, due to their design flexibility and material adaptability. However, the tribological performance and surface integrity [...] Read more.
Additive Manufacturing (AM) techniques, such as Fused Deposition Modeling (FDM) and Stereolithography (SLA), are increasingly adopted in various high-demand sectors, including the aerospace, biomedical engineering, and automotive industries, due to their design flexibility and material adaptability. However, the tribological performance and surface integrity of parts manufactured by AM are the biggest functional deployment challenges, especially in wear susceptibility or load-carrying applications. The current review provides a comprehensive overview of the tribological challenges and surface engineering solutions inherent in FDM and SLA processes. The overview begins with a comparative overview of material systems, process mechanics, and failure modes, highlighting prevalent wear mechanisms, such as abrasion, adhesion, fatigue, and delamination. The effect of influential factors (layer thickness, raster direction, infill density, resin curing) on wear behavior and surface integrity is critically evaluated. Novel post-processing techniques, such as vapor smoothing, thermal annealing, laser polishing, and thin-film coating, are discussed for their potential to endow surface durability and reduce friction coefficients. Hybrid manufacturing potential, where subtractive operations (e.g., rolling, peening) are integrated with AM, is highlighted as a path to functionally graded, high-performance surfaces. Further, the review highlights the growing use of finite element modeling, digital twins, and machine learning algorithms for predictive control of tribological performance at AM parts. Through material-level innovations, process optimization, and surface treatment techniques integration, the article provides actionable guidelines for researchers and engineers aiming at performance improvement of FDM and SLA-manufactured parts. Future directions, such as smart tribological, sustainable materials, and AI-based process design, are highlighted to drive the transition of AM from prototyping to end-use applications in high-demand industries. Full article
(This article belongs to the Special Issue Wear and Friction in Hybrid and Additive Manufacturing Processes)
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18 pages, 7681 KiB  
Article
Microstructure, Phase Components, and Tribological Properties of Al65Cu20Fe15 Quasicrystal Coatings Deposited by HVOF
by Sherzod Kurbanbekov, Tulkinzhon Gaipov, Pulat Saidakhmetov, Alibek Tazhibayev, Sherzod Ramankulov, Sattarbek Bekbayev, Arai Abdimutalip and Dilnoza Baltabayeva
Lubricants 2025, 13(7), 297; https://doi.org/10.3390/lubricants13070297 - 6 Jul 2025
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Abstract
Quasicrystalline coatings based on Al65Cu20Fe15 are of increasing interest as potential alternatives to conventional wear-resistant materials due to their unique structural and tribological properties. This study explores the influence of air pressure during high-velocity oxy-fuel (HVOF) spraying on [...] Read more.
Quasicrystalline coatings based on Al65Cu20Fe15 are of increasing interest as potential alternatives to conventional wear-resistant materials due to their unique structural and tribological properties. This study explores the influence of air pressure during high-velocity oxy-fuel (HVOF) spraying on the phase composition, morphology, and wear behavior of Al65Cu20Fe15 coatings deposited on U8G tool steel. Coatings were applied at a fixed spraying distance of 350 mm using three air pressures (1.9, 2.1, and 2.3 bar), with constant propane (2.0 bar) and oxygen (2.1 bar) supply. X-ray diffraction analysis identified the formation of Al78Cu48Fe14 and Al0.5Fe1.5 phases, while scanning electron microscopy revealed a dense, uniform microstructure with low porosity and homogeneous element distribution across all samples. Tribological testing using the ball-on-disk method showed wear track widths ranging from 853.47 to 952.50 µm, depending on the air pressure applied. These findings demonstrate that fine-tuning the air pressure during HVOF spraying significantly influences the structural characteristics and wear resistance of the resulting quasicrystalline coatings, highlighting their promise for advanced surface engineering applications. Full article
(This article belongs to the Special Issue Wear and Friction of High-Performance Coatings and Hardened Surfaces)
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28 pages, 6299 KiB  
Article
A Study on an Experimental System of Wiper–Windshield Friction Vibration and Noise
by Ningning Liu, Yansong Wang, Hui Guo, Zhian Mao, Shuai Zhang, Shuang Huang and Tao Yuan
Lubricants 2025, 13(7), 296; https://doi.org/10.3390/lubricants13070296 - 5 Jul 2025
Viewed by 255
Abstract
With the rapid development of electric vehicles, the issue of wiper–windshield friction noise has become more prominent. However, limitations in the hardware and software configurations of existing experimental systems restrict in-depth studies of frictional vibration and noise mechanisms. This study develops an experimental [...] Read more.
With the rapid development of electric vehicles, the issue of wiper–windshield friction noise has become more prominent. However, limitations in the hardware and software configurations of existing experimental systems restrict in-depth studies of frictional vibration and noise mechanisms. This study develops an experimental system with functions for working condition adjustment, data acquisition, and analysis of wiper–windshield frictional vibration and noise. First, the overall design of the wiper–windshield experimental system is described. The system allows adjustment of the motion gear and friction coefficient and facilitates data collection and analysis of pressure, vibration, and noise. The design includes the mechanical structure, electronic and electrical components, and software system of the experimental setup. A PLC control program (lower computer) and human–computer interaction software (upper computer) based on LabVIEW are developed to drive and control the mechanical structure, enabling working condition adjustment, data acquisition, and analysis. Finally, an experimental scheme is implemented to verify the feasibility of the wiper–windshield experimental system. Mechanical property, vibration, and noise data from the wiper are collected by simulating the operating conditions of a real vehicle. The experimental results demonstrate that the designed wiper–windshield experimental system can adjust various working conditions and support the collection and analysis of diverse data, facilitating theoretical research on the generation mechanism, influence rules, and control methods for wiper–windshield frictional vibration and noise. Full article
(This article belongs to the Special Issue Experimental Modelling of Tribosystems)
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15 pages, 2397 KiB  
Article
Tribological Evaluation of Brake Materials with Silk and Grewia optiva Natural Fibers
by Gustavo S. Gehlen, Tej Singh, Liu Y. Barros, Jean Carlos Poletto, Germano Lasch, Alice A. Rodrigues, Régis H. S. Souza, Ney F. Ferreira, Sharafat Ali and Patric D. Neis
Lubricants 2025, 13(7), 295; https://doi.org/10.3390/lubricants13070295 - 3 Jul 2025
Viewed by 339
Abstract
The growing demand for sustainable, high-performance composite materials has increased the interest in natural fibers as reinforcements for brake friction materials (BFMs). Silk and Grewia optiva fibers, in particular, have emerged as promising candidates for BFMs due to their good mechanical properties, biodegradability, [...] Read more.
The growing demand for sustainable, high-performance composite materials has increased the interest in natural fibers as reinforcements for brake friction materials (BFMs). Silk and Grewia optiva fibers, in particular, have emerged as promising candidates for BFMs due to their good mechanical properties, biodegradability, and availability. To evaluate their potential, friction materials were formulated with 6% Grewia (GF), 6% silk (SF), and a hybrid formulation containing 3% of both fibers (SGF), alongside a reference material reinforced with 6% aramid fiber (AF). These composites were then tested on a braking tribometer using an extended SAE J2522 procedure to assess their performance. The AF formulation showed slightly better wear resistance and the GF formulation showed inferior performance during high-temperature cycles, whereas SF and SGF performed close to the reference formulation (AF) in these sections. In terms of friction stability, SF matched the AF formulation, while GF demonstrated significantly poorer stability. The first high-temperature exposure of the BFMs (Fade 1) served as a critical thermal settlement phase, after which they demonstrated both improved friction stability and repeatable performance characteristics. Finally, this study demonstrates that silk fiber represents a viable, sustainable alternative to aramid in BFMs, exhibiting comparable performance in terms of friction stability and thermal resistance. Full article
(This article belongs to the Special Issue Experimental Advances in Eco-Friendly Friction Materials)
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12 pages, 262 KiB  
Article
Temperature Gradients in Tire Rubber Can Reduce/Increase Tensile Stresses and Hence Wear and Fatigue
by Jean-Emmanuel Leroy and Michele Ciavarella
Lubricants 2025, 13(7), 294; https://doi.org/10.3390/lubricants13070294 - 30 Jun 2025
Viewed by 730
Abstract
It has been known for some time that grading of the elastic modulus (namely, softer in the surface) leads to a significant reduction in tensile stresses due to contact loadings; this has been studied mostly to suppress the cracking of brittle materials. In [...] Read more.
It has been known for some time that grading of the elastic modulus (namely, softer in the surface) leads to a significant reduction in tensile stresses due to contact loadings; this has been studied mostly to suppress the cracking of brittle materials. In particular, a recent study has demonstrated that the effect is most pronounced for a large Poisson’s ratio, as is the case for incompressible materials. Grading of the modulus occurs intrinsically in viscoelastic materials like rubber when there is a temperature gradient within the rubber, which leads to significant changes of tensile stresses, affecting fatigue and wear. Friction and wear have been analyzed experimentally in the past with respect to mean temperature, revealing an ideal range of temperature with the highest friction and lowest wear, but the effect of the temperature gradient is not as well understood. The present paper presents a simple model of a sinusoidal wave of pressure and shear traction moving on a viscoelastic half-plane (standard material) at constant velocity, finding an approximate solution for a linear variation of viscosity across the depth. We find that tensile stresses may be very significantly altered by temperature changes of a few degrees only across the depth equal to the wavelength of the loading wave. In particular, they are reduced if the temperature decreases with depth, with beneficial effects for fatigue and wear. Full article
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19 pages, 653 KiB  
Article
On the Influence of the Convective Term in the Navier–Stokes Equation on the Forces in Hydrodynamic Bearings
by Jiří Vacula and Pavel Novotný
Lubricants 2025, 13(7), 293; https://doi.org/10.3390/lubricants13070293 - 30 Jun 2025
Viewed by 281
Abstract
Many theories describing the flow of viscous fluids in thin lubrication layers during rotor motion inside a stator, including the influence of the convective term in the Navier–Stokes equation, are known and widely used. However, the results of individual studies show some inconsistencies [...] Read more.
Many theories describing the flow of viscous fluids in thin lubrication layers during rotor motion inside a stator, including the influence of the convective term in the Navier–Stokes equation, are known and widely used. However, the results of individual studies show some inconsistencies in evaluating the influence of the convective term on the force occurring in the lubrication layer. Here, the effect of the convective term on the force acting on an arbitrarily moving rotor is explained based on a theoretical analysis of the Navier–Stokes equation. It is shown that for a constant fluid density in the case of an arbitrary trajectory of the centre of a non-rotating rotor, the convective term has zero effect on the force on the rotor. A non-zero effect of the convective term may only arise as a result of the spatial distribution of the momentum density at the inlet and outlet surfaces of the lubricating layer or as a result of variable fluid density due to cavitation or the compressibility of the fluid. Thus, the theoretical discussion presented here clarifies the numerical solutions obtained by researchers in the field of hydrodynamic lubrication and allows us to understand the reasons for the numerical behaviour of some simplified models. Full article
(This article belongs to the Special Issue Tribological Research on Transmission Systems)
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21 pages, 5651 KiB  
Article
Design and Experimental Setup of an Innovative Tribometer Aiming to Evaluate Small Quantities of Lubricants
by Lenine Marques de Castro Silva, Adilson José de Oliveira, Aylla Maria Alencar Rocha, José Josemar de Oliveira Junior and Salete Martins Alves
Lubricants 2025, 13(7), 292; https://doi.org/10.3390/lubricants13070292 - 29 Jun 2025
Viewed by 316
Abstract
The proposed tribometer design evaluates lubricants’ lubricating and wear protection properties at the interface of a loaded set of gears. However, this tribometer configuration and testing procedure described in standard ISO 14645-1 does not limit the tribological studies of gear test rigs. This [...] Read more.
The proposed tribometer design evaluates lubricants’ lubricating and wear protection properties at the interface of a loaded set of gears. However, this tribometer configuration and testing procedure described in standard ISO 14645-1 does not limit the tribological studies of gear test rigs. This study aimed to design and manufacture a mechanical transmission test rig capable of investigating the tribological condition of a lubricated enclosed gears transmission. The methodology consisted of (i) a definition of the test rig’s requirements; (ii) downsizing the main subassemblies present in the ISO 14635-1 test rig; (iii) designing innovative subassemblies; (iv) an instrumentation and data acquisition system, and (v) setup testing. The proposed system is suitable for evaluating small quantities of lubricants, allowing the analysis of special lubricants such as nanolubricants and ionic liquids in development for gearbox applications. Also, the dynamic loading avoids interruption in the test, providing results closer to working conditions. The experimental test evaluated the lubrication ability of two different base oils simultaneously under various loading conditions. Also, monitoring vibration signals helped identify the appearance of damage on the gear surface. Full article
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17 pages, 2032 KiB  
Article
Intelligent Evaluation of Permeability Function of Porous Asphalt Pavement Based on 3D Laser Imaging and Deep Learning
by Rui Xiao, Jingwen Liu, Xin Li, You Zhan, Rong Chen and Wenjie Li
Lubricants 2025, 13(7), 291; https://doi.org/10.3390/lubricants13070291 - 29 Jun 2025
Viewed by 384
Abstract
The permeability of porous asphalt pavements is a critical skid resistance indicator that directly influences driving safety on wet roads. To ensure permeability (water infiltration capacity), it is necessary to assess the degree of clogging in the pavement. This study proposes a permeability [...] Read more.
The permeability of porous asphalt pavements is a critical skid resistance indicator that directly influences driving safety on wet roads. To ensure permeability (water infiltration capacity), it is necessary to assess the degree of clogging in the pavement. This study proposes a permeability evaluation model for porous asphalt pavements based on 3D laser imaging and deep learning. The model utilizes a 3D laser scanner to capture the surface texture of the pavement, a pavement infiltration tester to measure the permeability coefficient, and a deep residual network (ResNet) to train the collected data. The aim is to explore the relationship between the 3D surface texture of porous asphalt and its permeability performance. The results demonstrate that the proposed algorithm can quickly and accurately identify the permeability of the pavement without causing damage, achieving an accuracy and F1-score of up to 90.36% and 90.33%, respectively. This indicates a significant correlation between surface texture and permeability, which could promote advancements in pavement permeability technology. Full article
(This article belongs to the Special Issue Tire/Road Interface and Road Surface Textures)
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14 pages, 5229 KiB  
Article
The Effect of Kappa Phases on Tribocorrosion Behaviour of Nickel Aluminum Bronze (NAB) and Manganese Aluminum Bronze (MAB)
by Carlos Berlanga-Labari, Adrián Claver, María Victoria Biezma-Moraleda and José Fernández-Palacio
Lubricants 2025, 13(7), 290; https://doi.org/10.3390/lubricants13070290 - 29 Jun 2025
Viewed by 284
Abstract
Nickel aluminum bronze (NAB) and manganese aluminum bronze (MAB) are widely used in propulsion and seawater handling systems in naval platforms due to their attractive combination of mechanical strength, toughness, and very low susceptibility to marine corrosion. Nevertheless, it is well known that [...] Read more.
Nickel aluminum bronze (NAB) and manganese aluminum bronze (MAB) are widely used in propulsion and seawater handling systems in naval platforms due to their attractive combination of mechanical strength, toughness, and very low susceptibility to marine corrosion. Nevertheless, it is well known that they can suffer from selective phase corrosion and erosion–corrosion, primarily caused by cavitation and sand erosion. Both alloys have a multiphase microstructure that governs their mechanical and chemical behavior. The tribocorrosion behavior of cast NAB and MAB alloys was studied in artificial seawater to analyze the effect on microstructure. The microstructure and nanohardness were evaluated and correlated with tribocorrosion test results conducted under two different loads (10 and 40 N) in a unidirectional sliding mode using a 1 M NaCl solution as the electrolyte. A significant increase in the corrosion rate due to the wear effect was observed in both alloys. MAB exhibited a slightly better tribocorrosion performance than NAB, which was attributed to significant differences in the shape, distribution, and size of the intermetallic kappa phases—rich in iron, aluminum, and nickel—within the microstructure. Pitting corrosion was observed in NAB, while selective corrosion of kappa phases occurred in MAB, highlighting the role of the protective layer in the tribocorrosion behavior of both alloys. These findings were supported by post-test solution analysis using ICP-AES and corrosion product characterization by EDX. A synergistic effect between wear and corrosion was confirmed for both alloys, as erosion removes the protective layer, exposing fresh material to continuous friction and favoring a progressive material loss over time. The practical impact of this study lies in improving the control and design of highly alloyed bronze microstructures under in-service corrosion–erosion conditions. Full article
(This article belongs to the Special Issue Fundamentals and Applications of Tribocorrosion)
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12 pages, 3473 KiB  
Article
Microstructure and Mechanical Properties of Laser-Clad Inconel 718 Coatings on Continuous Casting Mold Copper Plate
by Yu Liu, Haiquan Jin, Guohui Li, Ruoyu Xu, Nan Ma, Hui Liang, Jian Lin, Wenqing Xiang and Zhanhui Zhang
Lubricants 2025, 13(7), 289; https://doi.org/10.3390/lubricants13070289 - 28 Jun 2025
Viewed by 329
Abstract
Mold copper plates (Cr–Zr–Cu alloy) frequently fail due to severe wear under high-temperature conditions during continuous casting. To solve this problem, Inconel 718 coatings were prepared on the plate surface via laser cladding to enhance its high-temperature wear resistance. The results demonstrate that [...] Read more.
Mold copper plates (Cr–Zr–Cu alloy) frequently fail due to severe wear under high-temperature conditions during continuous casting. To solve this problem, Inconel 718 coatings were prepared on the plate surface via laser cladding to enhance its high-temperature wear resistance. The results demonstrate that the coatings exhibit a defect-free structure with metallurgical bonding to the substrate. The coating primarily consists of a γ-(Fe, Ni, Cr) solid solution and carbides (M23C6 and M6C). Notably, elongated columnar Laves phases and coarse Cr–Mo compounds were distributed along grain boundaries, significantly enhancing the coating’s microhardness and high-temperature stability. The coating exhibited an average microhardness of 491.7 HV0.5, which is approximately 6.8 times higher than that of the copper plate. At 400 °C, the wear rate of the coating was 4.7 × 10−4 mm3·N−1·min−1, significantly lower than the substrate’s wear rate of 8.86 × 10−4 mm3·N−1·min−1, which represents only 53% of the substrate’s wear rate. The dominant wear mechanisms were adhesive wear, abrasive wear, and oxidative wear. The Inconel 718 coating demonstrates superior hardness and excellent high-temperature wear resistance, effectively improving both the surface properties and service life of mold copper plates. Full article
(This article belongs to the Special Issue Surface Modification: Microstructure and Tribological Characterization)
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19 pages, 3685 KiB  
Article
Extraction of Pavement Texture–Friction Surface Density Index Using High-Precision Three-Dimensional Images
by Niangzhi Mao, Shihai Ding, Xiaoping Chen, Changfa Ai, Huaping Yang and Jiayu Wang
Lubricants 2025, 13(7), 288; https://doi.org/10.3390/lubricants13070288 - 27 Jun 2025
Viewed by 355
Abstract
Pavement surface texture significantly affects its skid resistance. To characterize pavement surface texture and analyze its correlation with skid resistance, this paper proposes a novel three-dimensional (3D) texture evaluation index: mean texture surface area density (MTSAD). First, field tests were conducted on Chengdu [...] Read more.
Pavement surface texture significantly affects its skid resistance. To characterize pavement surface texture and analyze its correlation with skid resistance, this paper proposes a novel three-dimensional (3D) texture evaluation index: mean texture surface area density (MTSAD). First, field tests were conducted on Chengdu Greenway pavement using a portable laser scanner to collect high-precision texture data, while a pendulum friction tester was employed to measure the British Pendulum Number (BPN). Subsequently, digital image processing technology was employed for the 3D reconstruction of pavement texture. Leveraging the high-resolution data characteristics and incorporating the concept of infinite subdivision, an innovative method for calculating the pavement texture surface area was developed, ultimately yielding the MTSAD. Finally, polynomial regression analysis was performed to examine the correlation between MTSAD and BPN, revealing a coefficient of determination (R2) of 0.8302. The results demonstrate a close relationship between MTSAD and pavement friction, while proving that texture indices that are easy to promote can be obtained through high-precision 3D point cloud images, and validating the potential of non-contact texture measurement as a viable alternative to conventional contact-based friction testing methods. Full article
(This article belongs to the Special Issue Tire/Road Interface and Road Surface Textures)
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23 pages, 8211 KiB  
Article
An Experimental Study of Wheel–Rail Creep Curves Under Dry Contact Conditions Using V-Track
by Gokul J. Krishnan, Jan Moraal, Zili Li and Zhen Yang
Lubricants 2025, 13(7), 287; https://doi.org/10.3390/lubricants13070287 - 26 Jun 2025
Viewed by 378
Abstract
Friction behaviour at the wheel–rail interface is of critical importance for railway operations and maintenance and is generally characterised by creep curves. The V-Track test rig was used in this study to measure both the lateral and longitudinal creep curves with uncontaminated dry [...] Read more.
Friction behaviour at the wheel–rail interface is of critical importance for railway operations and maintenance and is generally characterised by creep curves. The V-Track test rig was used in this study to measure both the lateral and longitudinal creep curves with uncontaminated dry interface conditions, utilising contact pressures representative of operational railway wheel–rail systems. The novelties of this study are threefold. 1. With proper representations of train/track components, the V-Track tests revealed the effects of structural dynamics on measuring wheel–rail creep curves in real life. 2. Pure lateral and longitudinal creepage conditions were produced with two distinct experimental principles—displacement- and force-controlled—on the V-Track, i.e., by carefully controlling the angle of attack and the traction/braking torque, respectively, and thus the coefficient of friction from lateral and longitudinal creep curves measured on the same platform could be cross-checked. 3. The uncertainties in the measured creep curves were analysed, which was rarely addressed in previous studies on creep curve measurements. In addition, the measured creep curves were compared against the theoretical creep curves obtained from Kalker’s CONTACT. The influence of wheel rolling speed and torque direction on the creep curve characteristics was then investigated. The measurement results and findings demonstrate the reliability of the V-Track to measure wheel–rail creep curves and study the wheel–rail frictional rolling contact. Full article
(This article belongs to the Special Issue Tribology in Railway Engineering)
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17 pages, 10204 KiB  
Article
Effect of Nanographene Water-Based Lubricant (NGWL) on Removal Behavior of Pure Copper
by Ziheng Wang, Zhenjing Duan, Shuaishuai Wang, Ji Tan, Peng Bian, Jiyu Liu, Jinlong Song and Xin Liu
Lubricants 2025, 13(7), 286; https://doi.org/10.3390/lubricants13070286 - 26 Jun 2025
Viewed by 331
Abstract
Pure copper is an important metal material in the fields of integrated circuits, mold manufacturing, and aerospace. Its excellent ductility and plasticity lead to problems such as burrs and tool wear in cutting, which poses great challenges to the improvement of machining accuracy [...] Read more.
Pure copper is an important metal material in the fields of integrated circuits, mold manufacturing, and aerospace. Its excellent ductility and plasticity lead to problems such as burrs and tool wear in cutting, which poses great challenges to the improvement of machining accuracy and surface quality. To achieve high-quality and efficient processing of pure copper, this paper proposes to use nanographene water-based lubricant (NGWL) to regulate its removal behavior. A single-grain diamond scribing test and a micro-milling test were carried out to systematically study the action mechanism of NGWL on removal behavior of pure copper. The results showed that, compared with dry scribing at normal forces of 100, 400, 700, and 1000 mN, the material removal efficiency induced by NGWL was increased by 54.1%, 80.7%, 44.8%, and 30.3%, respectively. Compared with dry micro-milling at feed speeds of 200, 600, 1000, and 1400 μm/s, for the 75°XT4E tool, the surface roughness Sa with NGWL-assisted micro-milling was reduced by 75.5%, 73.1%, 61.4%, and 44.2%, respectively. Similarly, for the 65°UDT4E tool, compared to dry micro-milling, the Sa with NGWL lubrication was also reduced by 28.9%, 52.2%, 54.4%, and 36.9%, respectively. The Sa of pure copper induced by NGWL could be as low as about 20 nm without scales. Overall, NGWL can regulate removal behavior of pure copper by alleviating plastic deformation and promoting ductile fracture, thereby providing a new approach to achieving high-quality and efficient processing of pure copper. Full article
(This article belongs to the Special Issue High Performance Machining and Surface Tribology)
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21 pages, 6027 KiB  
Article
Static Characteristic Analysis of Multi-Layer Foil Thrust Bearing: Considering Parameter Effects
by Yulong Jiang, Qianjing Zhu, Zhongwen Huang and Dongyan Gao
Lubricants 2025, 13(7), 285; https://doi.org/10.3390/lubricants13070285 - 25 Jun 2025
Viewed by 422
Abstract
A modified static characteristic model for the multi-layer foil thrust bearing (MLFTB) is established. In this model, the finite difference method and the thick plate element are implemented, the compressible Reynolds equation is linearized by the Newton–Raphson method, and the evolution law of [...] Read more.
A modified static characteristic model for the multi-layer foil thrust bearing (MLFTB) is established. In this model, the finite difference method and the thick plate element are implemented, the compressible Reynolds equation is linearized by the Newton–Raphson method, and the evolution law of the static characteristics with the geometric and operational parameters is derived by iterative solution. The results indicate that the bearing capacity could be generally decreased by around 3.15% when considering the slip boundary condition, which should not be neglected. Also, when under the rigorous wedge effect, the pressure peak near the mini clearance exhibits an obvious double peak shape. The bearing capacity can be slightly enhanced by an increase in the tilt angle of the thrust disk. In comparison to data in the literature, the current model shows satisfactory precision for the multi-layer foil thrust bearing. It aims to provide effective predictive means and theoretical reference for MLFTB. Full article
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