Lubricants

19 pages, 34499 KB

Open AccessArticle

Mechanism of Grinding Surface Integrity Effects on Wear Resistance of Gray Cast Iron Materials

by Jinggang Zhou, Xun Li, Han Zhang, Changrui Yu and Liangbao Liu

Lubricants 2026, 14(5), 212; https://doi.org/10.3390/lubricants14050212 - 21 May 2026

Viewed by 592

HT250 grey cast iron is a material of significance in the manufacture of precision machine tool guideways. The performance of guideways is significantly affected by the wear resistance of the machined surface. The present paper studies comparative grinding experiments conducted on HT250 using [...] Read more.

HT250 grey cast iron is a material of significance in the manufacture of precision machine tool guideways. The performance of guideways is significantly affected by the wear resistance of the machined surface. The present paper studies comparative grinding experiments conducted on HT250 using CBN and SiC wheels. The aim was to investigate the potential benefits of CBN grinding in enhancing surface wear resistance and to illuminate the underlying mechanisms. The results of these experiments demonstrate that, compared with SiC grinding, CBN grinding produces guideway specimens’ subsurface layer with finer grains (refined by approximately 15%) and notably higher microhardness (peak value of 382 HV). These microstructural improvements directly enhance the wear resistance of the ground surface. Within the tested parameter range, the optimal wear-resistant surfaces were obtained at a grinding speed of v_s = 30 m/s, a feed rate of v_f = 2000 mm/min, and a depth of cut of a_p = 6 μm. Under these conditions, surface roughness is better than R_a 0.4 μm, and surface microhardness achieves its maximum value. The wear tests were conducted using a ball-on-disk configuration under room temperature, oil lubrication, and applied loads ranging from 20 N to 80 N. The results show that, under the same loading and wear testing conditions, the wear depth of specimens machined with CBN wheels is reduced to 80–50% of that of specimens processed with conventional SiC wheels. Full article

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14 pages, 4592 KB

Open AccessArticle

Investigation on Tribological Performance of Laser Surface Texturing on Silicon Nitride Ceramic Under Hyaluronic Acid Lubrication

by Hong-Jian Wang, Jin Wang, Yan-Xian Guo, Bo Wang, Dong-Lin Wu and Huan-Xun Guo

Lubricants 2026, 14(5), 211; https://doi.org/10.3390/lubricants14050211 - 20 May 2026

Viewed by 395

Abstract

Laser surface texturing (LST) was used to process circular patterns on silicon nitride (Si₃N₄) ceramic. The surface wettability of un-textured and textured Si₃N₄ ceramic was studied. It was found that all samples were hydrophilic. The hydrophilicity [...] Read more.

Laser surface texturing (LST) was used to process circular patterns on silicon nitride (Si₃N₄) ceramic. The surface wettability of un-textured and textured Si₃N₄ ceramic was studied. It was found that all samples were hydrophilic. The hydrophilicity of the textured Si₃N₄ ceramic with a smaller interval was weaker. Effect of the interval on the tribological performance of Si₃N₄ ceramic was investigated under different reciprocating frequencies. As the reciprocating frequency increased, the coefficient of friction (COF) of Si₃N₄ ceramic showed an overall upward trend. And the COFs of textured Si₃N₄ ceramic were higher. At the reciprocating frequency of 0.5 Hz, the COFs of textured samples with different intervals were relatively close. At higher reciprocating frequency, the difference in COF gradually increased. This can be attributed to the change in lubrication state that occurs during the frictional process. Debris and plough were found at surface of all samples, and the original surface was cleaner. The surface damage of textured samples was more severe than that of un-textured samples. EDS analysis on the wear area was performed. The wear rate of the frictional pair at the interval of 250 μm was higher. It was consistent with the more significant wear marks on the surface of the Si₃N₄ ceramic at this interval. There were significant differences in the frictional process between un-textured and textured samples. For the un-textured surface, the debris was mainly concentrated at the edges of the friction trajectory. In contrast, textured patterns had the function of storing lubricant, while also generating micro-shear effects on debris and improving the status of lubrication, resulting in more complex frictional process. Full article

(This article belongs to the Special Issue Surface Engineering and Micro-Texturing for Tribological Applications)

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32 pages, 2537 KB

Open AccessArticle

Automated Detection of Tribologically Relevant Brake Torque Plateaus: A Two-Stage Approach for Flywheel Dynamometer Testing

by Stefan Altstetter, Arne Bischofberger, Sascha Ott and Tobias Düser

Lubricants 2026, 14(5), 210; https://doi.org/10.3390/lubricants14050210 - 20 May 2026

Viewed by 657

Abstract

Reliable identification of the tribologically relevant braking phase in torque signals recorded on flywheel dynamometers is a prerequisite for quantitative friction analysis and data-driven modeling of dry-running friction brakes. We define brake torque plateaus as intervals with quasi-constant surface pressure and appreciable sliding [...] Read more.

Reliable identification of the tribologically relevant braking phase in torque signals recorded on flywheel dynamometers is a prerequisite for quantitative friction analysis and data-driven modeling of dry-running friction brakes. We define brake torque plateaus as intervals with quasi-constant surface pressure and appreciable sliding velocity in which fading or drift of the coefficient of friction is explicitly admissible, while rise and decay ramps dominated by actuator dynamics are excluded. To automate this extraction across large industrial data sets, we propose a two-stage detection algorithm that sequentially narrows the search space using physics-based amplitude, gradient, and stability criteria, complemented by a Pruned Exact Linear Time (PELT)-based fallback for difficult cycles. Evaluation on 10,386 brake cycles, including 275 expert-annotated ground-truth cycles validated by a second independent expert, shows that the proposed method reaches 95% of the inter-annotator agreement ceiling on 75 held-out cycles, achieves a median Intersection-over-Union of 0.893 (11 percentage points above the strongest baseline), and a mean quality score of 9.18/10 across all cycles at under 1 ms per cycle (signals averaging 951 samples), outperforming six baseline configurations in both detection quality and runtime. Full article

(This article belongs to the Special Issue Tribology of Friction Brakes)

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15 pages, 1793 KB

Open AccessArticle

Cross Scale Tribological Behavior of Textured High-Entropy Alloy Coatings

by Yazhou Mao, Linlin Guo, Aoya Wang, Ruiyi Ma and Zixuan Wangan

Lubricants 2026, 14(5), 209; https://doi.org/10.3390/lubricants14050209 - 19 May 2026

Viewed by 581

Abstract

This paper presents a cross-scale model for predicting the tribological behavior of textured coatings made of high-entropy alloys. The research methodology includes molecular dynamic modeling, a modified fractal surface model, and the Green’s method with fast Fourier transform. The main results demonstrate the [...] Read more.

This paper presents a cross-scale model for predicting the tribological behavior of textured coatings made of high-entropy alloys. The research methodology includes molecular dynamic modeling, a modified fractal surface model, and the Green’s method with fast Fourier transform. The main results demonstrate the existence of an optimal range of parameters: a fractal dimension of 2.45–2.55 and a texturing density of 15–20%, which reduces the coefficient of friction to 40% compared with untextured surfaces. The practical significance of the work lies in the creation of a theoretical basis for the integrated design and forecasting of the tribological properties of high-entropy coatings. Full article

(This article belongs to the Special Issue Aluminum Alloy Interface Strengthening and Friction and Wear Characteristics)

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20 pages, 3822 KB

Open AccessArticle

Wear Prediction Algorithm for Feedback Ball Head of Servo Valve

by Xiaonan Pan, Jianrui Zhang and Jian Kang

Lubricants 2026, 14(5), 208; https://doi.org/10.3390/lubricants14050208 - 19 May 2026

Viewed by 431

Abstract

Wear of the feedback ball head–ball seat interface changes the contact state and reduces the feedback force in electro-hydraulic servo valves, resulting in output nonlinearity and performance degradation. Existing wear models usually assume fixed surface morphology parameters, which their ability to describe time-varying [...] Read more.

Wear of the feedback ball head–ball seat interface changes the contact state and reduces the feedback force in electro-hydraulic servo valves, resulting in output nonlinearity and performance degradation. Existing wear models usually assume fixed surface morphology parameters, which their ability to describe time-varying wear evolution during repeated sliding. To address this issue, this study proposes a hybrid wear-prediction framework integrating fractal contact theory, Archard wear law, Gaussian process regression, and a servo-valve mechanical model. The real contact area and wear coefficient are expressed as functions of fractal parameters, while Gaussian process regression is used to predict their evolution under different loading cycles and displacement loads. Repeated loading tests and white-light interferometry measurements were performed to validate the proposed method. The results show that the fractal dimension of the ball seat increased by approximately 4.01%, whereas that of the ball head decreased by approximately 1.71%. After about 12,000 cycles, the fractal parameters tended to stabilize. The prediction error of the Gaussian process regression model was below 3%, and the wear-depth prediction error remained within approximately 1%. These results indicate that the proposed method can effectively capture the time-varying sliding wear behavior of the feedback ball head–ball seat interface. Full article

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21 pages, 8850 KB

Open AccessArticle

Integrated Multi-Physics Design of a GGG40 Agricultural Trailer Wheel Hub: Concurrent Topology Optimisation and CFD-Based Lubrication Enhancement

by Onur Gök

Lubricants 2026, 14(5), 207; https://doi.org/10.3390/lubricants14050207 - 19 May 2026

Viewed by 561

Abstract

Wheel hubs in heavy-duty agricultural trailers operate under demanding conditions comprising rough terrain, impact loads, and highly variable load spectra. Current design practice relies predominantly on experience-based sizing rather than systematic multi-physics analysis. This study presents an integrated design methodology combining finite element [...] Read more.

Wheel hubs in heavy-duty agricultural trailers operate under demanding conditions comprising rough terrain, impact loads, and highly variable load spectra. Current design practice relies predominantly on experience-based sizing rather than systematic multi-physics analysis. This study presents an integrated design methodology combining finite element analysis (FEA), density-based topology optimisation, and computational fluid dynamics (CFD) to concurrently improve the structural and tribological performance of a GGG40 spheroidal graphite cast iron agricultural trailer wheel hub. A reference commercial hub geometry was modelled and analysed under multiple load conditions with a safety factor of 5. Critical stress regions were identified, and the free design volume was optimised while preserving all functional surfaces. The optimised design achieved 35% mass reduction (14.9 to 9.6 kg), 30% lower maximum von Mises stress (235 to 165 MPa), and up to 40% stress reduction in the bearing seat region. Oil-circulation channels integrated into the bearing housing raised mean lubrication flow velocity by 28% and eliminated stagnation zones, yielding a more homogeneous oil-film distribution and directly benefiting bearing tribological performance. The proposed framework provides a manufacturable engineering methodology that concurrently addresses structural integrity and lubrication performance in agricultural wheel hub design. Full article

(This article belongs to the Special Issue Machine Design and Tribology)

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23 pages, 20105 KB

Open AccessArticle

Prediction Method and CFD Analysis of Windage Power Loss for Aerospace High-Speed Herringbone Gear Pair

by Linlin Li, Yuzhong Zhang and Yuanjun Ye

Lubricants 2026, 14(5), 206; https://doi.org/10.3390/lubricants14050206 - 18 May 2026

Viewed by 488

Abstract

Herringbone gear pairs are critical in high-speed aerospace transmissions, where windage power loss significantly impacts efficiency and thermal management. This study proposes a prediction method that decomposes the total windage loss into five components based on structural features: the tooth, end, circumferential, and [...] Read more.

Herringbone gear pairs are critical in high-speed aerospace transmissions, where windage power loss significantly impacts efficiency and thermal management. This study proposes a prediction method that decomposes the total windage loss into five components based on structural features: the tooth, end, circumferential, and relief groove surface losses for both gears, and the meshing extrusion loss. Theoretical models for each component are established to form a complete prediction method using fluid–structure interaction principles. CFD simulations analyze the velocity, pressure, and energy fields around the gear pair, with windage loss integrated via fluid torque on gear surfaces. Results indicate that windage loss escalates rapidly and becomes non-negligible when the driving gear speed exceeds 7000 rpm. The prediction model demonstrates strong agreement with CFD simulations, with a maximum relative error of 13.6%. Analysis reveals that the driving gear contributes the largest share of the total gear pair loss, with meshing extrusion accounting for 20.1–23.6%. For a single herringbone gear, the tooth surface is the primary source of loss (~83%), followed by the end surface (~8%), while relief groove and circumferential losses remain below 10%. This research provides a validated theoretical foundation for optimizing efficiency and thermal control in high-speed aerospace gear systems. Full article

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24 pages, 53670 KB

Open AccessArticle

Improving theThermal and Tribological Properties of Dimethyl Silicone Oil Using Ag/CNTs Composite as Multifunctional Additive

by Longhai Li, Bo Yang, Wenbin Hu, Hongping Qiu, Xiaotong Wang, Sheng Han and Jincan Yan

Lubricants 2026, 14(5), 205; https://doi.org/10.3390/lubricants14050205 - 18 May 2026

Viewed by 461

Abstract

In this study, carboxyl groups were introduced onto CNT surfaces via acid oxidation, and Ag nanoparticles were successfully deposited onto the CNTs through an in situ chemical reduction method. At an Ag-to-CNTs100 mass ratio of 3:1, the as-prepared composite achieved a thermal conductivity [...] Read more.

In this study, carboxyl groups were introduced onto CNT surfaces via acid oxidation, and Ag nanoparticles were successfully deposited onto the CNTs through an in situ chemical reduction method. At an Ag-to-CNTs100 mass ratio of 3:1, the as-prepared composite achieved a thermal conductivity of 1.45 W/(m·K) in dimethyl silicone oil, representing enhancements of 187.5% and 76.9% relative to pure Ag nanoparticles and pristine CNTs100, respectively, at equivalent loadings. Concurrently, tribological tests revealed that the AgHTs-3 at a 3:1 mass ratio and 25 wt% loading exhibited a steady-state friction coefficient of 0.08–0.12, reflecting an approximately 72% reduction compared with pure dimethyl silicone oil. Electrical conductivity measurements demonstrated that CO-CNTs100 attained saturation at 30 wt% with a resistivity of 36.5 Ω·m, whereas the AgHTs-3 nanocomposite achieved a resistivity of 4.7 Ω·m at 35 wt%. The incorporation of Ag nanoparticles effectively enhanced the overall performance of the nanocomposites. Through the formation of a synergistic heterostructure with carboxyl-functionalized carbon nanotubes, the composite not only significantly improved the thermal conductivity of dimethyl silicone oil but also effectively optimized the interfacial lubricating film while substantially reducing the friction coefficient and wear volume. Moreover, the introduction of silver promoted the dispersion stability of the composites in dimethyl silicone oil, enabling higher filler loadings and thereby effectively boosting electrical conductivity. Full article

(This article belongs to the Special Issue Preparation, Tribological Behavior, and Applications of Lubricant Additives)

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25 pages, 23722 KB

Open AccessArticle

Modeling and Experimental Investigation of Dynamic Stiffness and Damping Coefficients of Aerostatic Spindles Considering Rotor Cylindricity Errors

by Wenjing Wu, Longhang Hou, Wenbo Wang, Guangzhou Wang, Guozhen Fan, Guoqing Zhang and Hechun Yu

Lubricants 2026, 14(5), 204; https://doi.org/10.3390/lubricants14050204 - 15 May 2026

Viewed by 525

Abstract

Aerostatic spindles are indispensable in the ultra-precision manufacturing field due to their high accuracy and low friction. However, rotor manufacturing errors will affect the thickness and uniformity of the air film, thereby limiting the improvement and application of the aerostatic spindle. To explore [...] Read more.

Aerostatic spindles are indispensable in the ultra-precision manufacturing field due to their high accuracy and low friction. However, rotor manufacturing errors will affect the thickness and uniformity of the air film, thereby limiting the improvement and application of the aerostatic spindle. To explore this issue, this paper presents theoretical modelling and experimental work. Rotor cylindricity errors were first evaluated based on manufacturing errors, and a calculation model of the film thickness considering rotor cylindricity errors was established. By solving the dynamic Reynolds equation considering cylindricity errors, the dynamic stiffness and damping of aerostatic spindles were obtained. The influence mechanism of rotor cylindricity errors on the dynamic stiffness and damping coefficients of the rotor–bearing system was revealed. The stiffness coefficients K_xx, K_yy, and K_xy are more sensitive to the saddle-shaped errors, and the stiffness coefficient K_yx and both damping coefficients are more closely related to bucket-shaped errors. Regarding the influence of the cylindricity errors’ extremal position, the main and cross stiffness coefficients are sensitive to saddle-shaped errors and bucket-shaped errors, respectively; the main and cross-damping coefficients are sensitive to bucket-shaped errors. Under the effect of three kinds of error shapes, when the rotor cylindricity errors value is less than 1 μm, the dynamic stiffness and damping coefficients are conducive to improving the dynamic characteristics of the rotor–bearing system. Multiple rotors were manufactured, and their cylindricity errors were measured, and then the dynamic characteristics of the assembled aerostatic spindles with these rotors were tested. It was found that the dynamic stiffness of spindles with saddle-shaped errors is larger than that of spindles with conical-shaped errors, and the greater the error values are, the worse the rotation accuracy. The experimental results are consistent with the theoretical findings, thus verifying the feasibility and validity of the established theoretical model. This study improves the error tolerance design accuracy of rotors and thereby enhances the dynamic performance of aerostatic spindles. Full article

(This article belongs to the Special Issue Hydrostatic and Hydrodynamic Bearings)

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24 pages, 3892 KB

Open AccessArticle

Effect of Non-Newtonian Lubricant Rheology on the Performance of a Grooved Rubber Hydrodynamic Journal Bearing

by Mahdi Zare Mehrjardi, Ahmad Golzar Shahri, Asghar Dashti Rahmatabadi and Mehrdad Rabani

Lubricants 2026, 14(5), 203; https://doi.org/10.3390/lubricants14050203 - 15 May 2026

Cited by 1 | Viewed by 930

Abstract

The present study provides a comprehensive investigation into the hydrodynamic performance of grooved rubber journal bearings (GRJBs) employed as shaft supports in various rotating systems, with particular emphasis on marine applications. These bearings are lubricated with non-Newtonian fluids such as modern oil containing [...] Read more.

The present study provides a comprehensive investigation into the hydrodynamic performance of grooved rubber journal bearings (GRJBs) employed as shaft supports in various rotating systems, with particular emphasis on marine applications. These bearings are lubricated with non-Newtonian fluids such as modern oil containing additives and viscoelastic water-based lubricant, which—owing to its complex composition including hydrocarbon chains, metal oxides, and impurity particles and contaminants such as salts, organic substances, microalgae, biopolymers, and microorganisms—deviates from the ideal Newtonian fluid model and demonstrates non-Newtonian rheological behavior. By examining various theories used in the analysis of non-Newtonian fluid behavior, the power-law model, which has a high degree of generality, has been employed in the present study. Also, to improve modeling accuracy, the elastic deformation of the rubber bush in this study is characterized using the Winkler foundation approach and analyzed via the finite element method (FEM). This advanced mechanical formulation, integrated with non-Newtonian lubrication modeling of lubricant using the power-law fluid model, and the parametric assessment of groove number and dimensions on steady-state bearing performance parameters, constitutes the core of this research. The investigation focuses on groove configurations of 4, 6, 8, and 10 channels. The findings indicate that increasing the groove count partitions the convergent pressure film zone into discrete segments, thereby reducing the maximum hydrodynamic pressure while intensifying the overall energy dissipation within the bearing. Additionally, the influences of rheological properties of the fluid—namely the power-law index (n) and the consistency index (m)—on key performance characteristics are thoroughly examined. An increase in both parameters enhances the effective viscosity and load carrying capacity; however, the exponential amplification due to the power-law index exhibits a more pronounced effect on load capacity and peak pressure compared to the consistency index. Full article

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18 pages, 8612 KB

Open AccessArticle

Unsupervised Segmentation of Wear Surface Defects in Hydroturbine Bearing Pads Guided by Local Anomaly Scores

by Xiaolong Yang, Jingxuan Han, Gang Wan, Fengdi Zhu, Chuangji Qin, Ning Xu and Shuo Wang

Lubricants 2026, 14(5), 202; https://doi.org/10.3390/lubricants14050202 - 14 May 2026

Viewed by 323

Abstract

Vision-based defect detection on bearing-pad wear surfaces is essential for quantifying damage geometry and assessing condition in hydroturbine units. Compared with 2D color images, depth images can suppress disturbances caused by complex textures, surface color variations, and specular reflections, thereby providing a more [...] Read more.

Vision-based defect detection on bearing-pad wear surfaces is essential for quantifying damage geometry and assessing condition in hydroturbine units. Compared with 2D color images, depth images can suppress disturbances caused by complex textures, surface color variations, and specular reflections, thereby providing a more reliable basis for precise damage localization. Nevertheless, depth-based damage segmentation under a large field of view remains challenging, mainly due to fine-scale texture noise and weak defect saliency; moreover, robust defect probability estimation is often hindered by limited labeled data. To address these challenges, this paper proposes an unsupervised defect segmentation framework for hydroturbine friction components guided by local anomaly score distributions. First, a salient damage detection module is developed based on topography–texture separation, which mitigates the interference of local micro-texture noise on defect segmentation. Then, a normal reference dataset is constructed using defect-free bearing-pad depth images, and an unsupervised network is employed as the core to generate anomaly score representations of potential damage regions for coarse localization. Finally, the obtained anomaly score distribution is used as adaptive weights to fuse depth-based defect cues with morphological processing, enabling self-adaptive refinement of the damage regions. Experiments on real depth images acquired from hydroturbine bearing pads demonstrate that the proposed method achieves accurate defect extraction and reliable geometric quantification. Quantitative evaluations on the testing set yield a mean surface area error of 9.39% ± 4.25% and a volume error of 4.91% ± 2.85%, with best-case errors dropping as low as 3.67% and 1.03%, respectively. Crucially, these results demonstrate that our framework goes beyond mere visual detection; by operating entirely without pixel-level annotations, it offers a highly practical tool for diagnosing specific lubrication failure modes and driving predictive maintenance in actual hydroturbine engineering. Full article

(This article belongs to the Special Issue Advanced Methods for Wear Monitoring)

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29 pages, 30317 KB

Open AccessReview

Water-Lubricated Photothermal Surfaces for Anti-Icing and Deicing

by Chunlei Gao, Yongzhi Liu and Yongyi Du

Lubricants 2026, 14(5), 201; https://doi.org/10.3390/lubricants14050201 - 14 May 2026

Cited by 1 | Viewed by 602

Abstract

Ice accumulation on critical infrastructure surfaces threatens operational safety in aviation, power transmission, and transportation systems. Conventional anti-icing and deicing strategies, such as chemical deicers and energy-intensive active heating, have inherent drawbacks. These include environmental pollution, high energy consumption, and low efficiency. In [...] Read more.

Ice accumulation on critical infrastructure surfaces threatens operational safety in aviation, power transmission, and transportation systems. Conventional anti-icing and deicing strategies, such as chemical deicers and energy-intensive active heating, have inherent drawbacks. These include environmental pollution, high energy consumption, and low efficiency. In recent years, photothermal-responsive extremely water-repellent surfaces have attracted widespread attention. They can harvest renewable solar energy and achieve efficient anti-icing and deicing through tailored interfacial wetting properties. This review summarizes photothermal extremely water-repellent surfaces based on the “water as a lubricating layer” strategy. This strategy reduces ice adhesion strength and enables low-energy deicing. It works by forming a continuous lubricating film via photothermally induced interfacial meltwater. We discuss photothermal conversion mechanisms and strategies to enhance performance for stable lubricating film formation. We also analyze the stagewise physics of anti-icing and deicing, focusing on the interfacial tribological behavior of the water film. Key engineering challenges are addressed, including mechanical durability and all-weather applicability. Finally, we clarify future research directions for industrial translation. This review aims to provide theoretical insights and technical pathways for developing next-generation anti-icing and deicing surfaces that are efficient, eco-friendly, and sustainable. Full article

(This article belongs to the Special Issue Advances in Frictional Interfaces)

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25 pages, 11424 KB

Open AccessArticle

Friction and Wear Behavior of Graphite Inlay Lubrication Structures for Localized Rings with Spherical Friction Pairs

by Xiang Xu, Xingyu Ma, Chang Sun, Haihua Wu, Xinze Zhao, Biao Liu and Meiyun Zhao

Lubricants 2026, 14(5), 200; https://doi.org/10.3390/lubricants14050200 - 13 May 2026

Viewed by 433

Abstract

Conventional solid-inlay lubrication research has focused on the overall inlay layout and generalized lubrication effects; localized inlay lubrication enables precise release of the lubricant and rapid formation of a uniform and dense lubricant film. The aim of this study is to use a [...] Read more.

Conventional solid-inlay lubrication research has focused on the overall inlay layout and generalized lubrication effects; localized inlay lubrication enables precise release of the lubricant and rapid formation of a uniform and dense lubricant film. The aim of this study is to use a combination of simulations and experimentation to establish a localized spherical friction pair containing a filled-hole structure, so that optimal lubrication can be predicted accurately. We designed seven different kinds of localized annular band inlay axial tiles, with ratios of 10, 12, 15, 18, 20, 22, and 25; carried out a transient mechanical analysis through finite element software, comparing the equivalent stress and friction coefficient of the inlay tiles with different ratios; and conducted friction wear tests through a self-developed spherical wear test bench. The friction surfaces of the tested specimens were analyzed for sliding friction coefficients and wear, as well as by SEM surface and EDS analyses. The results show that the best mechanical properties and the smallest theoretical friction coefficients are obtained when the relative ratio of the ring diameter to inlay hole diameter is 25. This study provides a theoretical basis for the design of spherical solid-inlay lubrication structures in the region of the split-belt ring design. Full article

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20 pages, 3846 KB

Open AccessArticle

Study on Tribological Properties and Cutting Performance of Ce Element-Doped TiAlN Tool Coating

by Mingyi Chang, Weidong Zhang, Dongzhou Jia, Xiaoqiang Wu, Yongqiang Fu and Qi Gao

Lubricants 2026, 14(5), 199; https://doi.org/10.3390/lubricants14050199 - 12 May 2026

Viewed by 513

Abstract

Titanium alloy is difficult to cut, with tools prone to adhesion and diffusion wear that reduces life and surface quality. Traditional coatings fail to meet precision machining demands. Based on TiAlN, Ce-doped coatings were prepared via magnetron sputtering at varying powers to investigate [...] Read more.

Titanium alloy is difficult to cut, with tools prone to adhesion and diffusion wear that reduces life and surface quality. Traditional coatings fail to meet precision machining demands. Based on TiAlN, Ce-doped coatings were prepared via magnetron sputtering at varying powers to investigate mechanical and tribological properties. The results show that with the increase in Ce doping amount, the hardness, elastic modulus, H/E, and H³/E² ratios of the coating increase first and then decrease, and the friction coefficient decreases first and then increases. The performance is optimal at 50 W, the friction coefficient is 0.676, and the film-based adhesion is 113.8 N. Compared with the TiAlN coating, the hardness increased by 12%, the wear loss decreased by 24%, and the H/E and H³/E² increased by 31% and 95%, respectively. The mechanism analysis shows that the appropriate amount of Ce doping can improve the toughness of the coating by grain refinement and solid solution strengthening and significantly inhibit adhesive wear and oxidative wear. Ce-modified tools were further prepared for titanium alloy turning experiments. Compared with uncoated and traditional TiAlN-coated tools, Ce doping can effectively reduce tool wear and improve the surface quality of the workpiece and has significant advantages under high-speed and large cutting depth conditions. This study systematically reveals the adaptive lubrication mechanism of Ce-doped TiAlN coating in the cutting process of titanium alloy and provides theoretical support and engineering guidance for the preparation of special tool coatings for difficult-to-machine materials. Full article

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20 pages, 5464 KB

Open AccessArticle

Novel Alternative Particle Systems for Managing Friction in the Wheel/Rail Interface

by William Skipper, Anup Chalisey and Roger Lewis

Lubricants 2026, 14(5), 198; https://doi.org/10.3390/lubricants14050198 - 12 May 2026

Viewed by 414

Abstract

At present, silica sand particles are used on GB railways for traction enhancement. In this study, novel particle systems with a range of properties were assessed to see if there was potential for particles to be more widely used in friction management. The [...] Read more.

At present, silica sand particles are used on GB railways for traction enhancement. In this study, novel particle systems with a range of properties were assessed to see if there was potential for particles to be more widely used in friction management. The tests were carried out at representative contact pressures, using the High Pressure Torsion (HPT) approach. Particles were applied to dry, wet and leaf-contaminated interfaces. A strong relationship was found between particle hardness and traction. Particle systems were identified that could be used to lubricate the interface (friction < 0.1) or provide intermediate levels of friction (0.2–0.3), and one that could be used for traction enhancement as an alternative to silica sand (increasing friction to above 0.1 with a leaf layer present). Full article

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17 pages, 3046 KB

Open AccessArticle

Design, Synthesis and Multifunctional Additive Performance of Novel Hindered Phenolic Amide–Esters

by Zenghui Li, Chaofan Xu, Xisheng Fu, Fengbin Liao, Yunqi Huang, Jing Hu, Xiaomei Xu, Hongmei Yang, Yanan Zhao, Xiuli Sun and Yong Tang

Lubricants 2026, 14(5), 197; https://doi.org/10.3390/lubricants14050197 - 9 May 2026

Viewed by 1156

Abstract

Harsh modern industrial working conditions require high-performance lubricants, but traditional additives are limited by single functionality and poor compatibility, driving the development of multifunctional alternatives. Two novel hindered phenolic amide–esters (MADE, DAME) were synthesized and characterized. Their thermal/storage stability, antioxidant and tribological properties [...] Read more.

Harsh modern industrial working conditions require high-performance lubricants, but traditional additives are limited by single functionality and poor compatibility, driving the development of multifunctional alternatives. Two novel hindered phenolic amide–esters (MADE, DAME) were synthesized and characterized. Their thermal/storage stability, antioxidant and tribological properties in synthetic oil were evaluated, with commercial 1010 and T203 as references. DFT calculations and worn surface analysis were also employed to clarify the lubrication mechanism. The results indicate that MADE exhibits better thermal/storage stability, comprehensive antioxidation and lubricating performance than DAME, with residual mass of 85.3% and 73.2% at 300 °C, respectively. A total of 1 wt.% MADE shortens the running-in period to 200 s (vs. 300 s for base oil), reduces the average. WSD by 12.1% and wear volume by 60.2%. Mechanistically, MADE adsorbs strongly on metal surfaces and forms a protective tribofilm via tribochemical reaction, exhibiting synergistic antioxidant and anti-wear effects. This work establishes a novel and sustainable paradigm for developing next-generation, multifunctional lubricant additives with high performance. Full article

(This article belongs to the Special Issue Preparation, Tribological Behavior, and Applications of Lubricant Additives)

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19 pages, 6151 KB

Open AccessArticle

Study on the Tribocorrosion Behaviors of DLC-Si Films in a Seawater Environment

by Xiaoxue Li, Xiaoqiang Wu, Zhiyong Zhang and Yongqiang Fu

Lubricants 2026, 14(5), 196; https://doi.org/10.3390/lubricants14050196 - 7 May 2026

Viewed by 584

Abstract

The performance requirements of wear-resistant and anti-corrosion coatings for marine equipment continue to increase. Diamond-like carbon (DLC) film has become a preferred protective material due to its high hardness, low friction and chemical inertia. To reveal the tribocorrosion mechanism of Si-doped DLC films [...] Read more.

The performance requirements of wear-resistant and anti-corrosion coatings for marine equipment continue to increase. Diamond-like carbon (DLC) film has become a preferred protective material due to its high hardness, low friction and chemical inertia. To reveal the tribocorrosion mechanism of Si-doped DLC films in a seawater environment, a Cr-WC-WC/C transition layer and DLC-Si films with different Si contents were prepared by high-power pulsed magnetron sputtering (HiPIMS) technology on 304 stainless steel. The tribocorrosion tests were carried out under open-circuit potential and dynamic polarization conditions in seawater. The results show that Si doping improved the tribocorrosion resistance of the films. The sample with Si content of 9.26 at.% has the lowest self-corrosion current density, the smallest volume loss, complete wear scar morphology and no obvious substrate exposure. The strengthening mechanism is attributed to Si doping, which induces the formation of a SiO_x passivation film and a hydrated silica gel lubrication layer. This establishes a synergistic solid-chemical lubrication system, inhibits sp² cluster growth, prolongs the diffusion path of corrosive media, and mitigates the damaging wear–corrosion synergy. This study confirms that moderate Si doping can significantly improve the wear resistance and corrosion resistance of DLC films in a seawater environment, and provides a theoretical basis for the design and application of carbon-based protective coatings for marine equipment. Full article

(This article belongs to the Special Issue Interfacial Friction and Lubrication)

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22 pages, 2903 KB

Open AccessArticle

Tribological and Sealing Performance of Squamous Textured Mechanical Sealing Faces: Experimental and Theoretical Analysis

by Xianghua Zhan, Na Zhang, Zhentao Li, Xiaoying Li, Dengke Chen and Yancong Liu

Lubricants 2026, 14(5), 195; https://doi.org/10.3390/lubricants14050195 - 7 May 2026

Viewed by 903

Abstract

Mechanical seal faces frequently operate under harsh and dynamic conditions, where maintaining stable and efficient lubrication remains a critical challenge. Surface texturing has emerged as an effective approach to improve the lubrication and tribological performance of sealing end faces. This study investigates the [...] Read more.

Mechanical seal faces frequently operate under harsh and dynamic conditions, where maintaining stable and efficient lubrication remains a critical challenge. Surface texturing has emerged as an effective approach to improve the lubrication and tribological performance of sealing end faces. This study investigates the lubrication behavior and sealing characteristics of squamous textured mechanical sealing faces through a combination of sealing experiments and mixed lubrication modeling. The results indicate that during start-up, increasing rotational speed enhances the load-carrying capacity and reduces contact force, resulting in thicker lubricant films and lower friction coefficients. Consequently, the sealing interface gradually transitions from mixed to hydrodynamic lubrication. Moreover, with increasing medium pressure, both the critical rotational speed and duration required for this lubrication regime transition increase. Under various steady periods, smooth seal faces predominantly operate in the mixed lubrication regime, whereas textured faces maintain hydrodynamic lubrication, reducing the average friction coefficient and temperature rise by 69.5% and 51.8%, respectively. These findings provide crucial insights into the performance improvement and practical applications of squamous textures for high-efficiency, long-lifespan mechanical seals. Full article

(This article belongs to the Special Issue Laser Surface Engineering for Advanced Tribological Performance)

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27 pages, 34553 KB

Open AccessArticle

Effective Suppression of Friction-Induced Stick-Slip Vibration at Brake Interfaces of High-Speed Trains via Rational Selection of Disc Spring Materials

by Jin Peng, Zaiyu Xiang, Shaohao Deng, Jiakun Zhang and Xiaoqin Liu

Lubricants 2026, 14(5), 194; https://doi.org/10.3390/lubricants14050194 - 6 May 2026

Viewed by 679

Abstract

The friction-induced stick-slip vibration (FISSV) generated by intense friction between the brake disc and brake pads of high-speed trains is a critical issue affecting braking stability, the service life of foundational braking components, and ride comfort. The floating friction block structure, which effectively [...] Read more.

The friction-induced stick-slip vibration (FISSV) generated by intense friction between the brake disc and brake pads of high-speed trains is a critical issue affecting braking stability, the service life of foundational braking components, and ride comfort. The floating friction block structure, which effectively regulates interfacial contact characteristics through the elastic deformation of disc springs, thereby improving tribological behavior, represents an effective approach for mitigating FISSV. However, the topic of how to design the floating structure of the friction block to produce the best suppression impact on FISSV emerges, using the choice of disc spring material as an example. Thus, the purpose of this study is to look at how disc spring material affects stick-slip vibration (SSV) at the high-speed train floating brake interface. Four typical disc spring materials—304 stainless steel, Mubea-specific spring steel, 50CrVA high-alloy spring steel, and 60Si₂MnA silicon-manganese spring steel—were selected. Through braking tribological tests and explicit dynamics-wear coupling simulations, the effects of material differences on interfacial friction-wear characteristics and SSV behavior were systematically studied. The findings show that the stiffness of the disc spring material greatly influences the dynamic responsiveness of the system and the contact pressure distribution at the braking interface, elasticity, and damping characteristics. 60Si₂MnA spring steel, owing to its excellent elastic recovery and load equalization capability, promoted the formation of uniformly dispersed medium-to-small contact platforms on the interface, resulting in the mildest wear. Concurrently, its system vibration energy exhibited a more dispersed distribution in the frequency domain, with low SSV intensity and weak nonlinear behavior, demonstrating the best comprehensive performance. Materials with poorer compatibility, such as 304 stainless steel, tended to cause localized stress concentration, exacerbating wear and intensifying severe high-frequency SSV. The influence mechanism of disc spring material at the interface is shown by this work, providing an important basis for material optimization and vibration suppression design in floating brake pad structures. Full article

(This article belongs to the Special Issue Friction-Induced Noise and Vibration)

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22 pages, 71164 KB

Open AccessArticle

Molecular Interactions at Asperity Contacts Under Boundary Lubrication

by Dong Sun, Liqin Wang, Deng Pan, Tingjian Wang, Le Gu and Chuanwei Zhang

Lubricants 2026, 14(5), 193; https://doi.org/10.3390/lubricants14050193 - 6 May 2026

Viewed by 767

Abstract

Boundary lubrication plays a crucial role in determining the service performance and operational lifespan of mechanical components. However, continuum mechanics models and experimental studies are unable to elucidate the dynamic evolution of intermolecular interactions at the interface under boundary lubrication from a microscopic [...] Read more.

Boundary lubrication plays a crucial role in determining the service performance and operational lifespan of mechanical components. However, continuum mechanics models and experimental studies are unable to elucidate the dynamic evolution of intermolecular interactions at the interface under boundary lubrication from a microscopic perspective, including phenomena such as asperity contact and lubricant film rupture. In this study, a molecular dynamics simulation approach was employed to construct a boundary lubrication friction model incorporating lubricant molecules, aiming to investigate the influence of applied load and asperity height on the dynamic evolution of atomic interactions at the interface from the perspective of energy variation, under conditions both with and without asperity contact. The results indicate that van der Waals interactions dominate the frictional response, and severe asperity contact leads to a sharp increase in van der Waals energy, which in turn results in a decrease in normal force, thereby increasing the friction coefficient. When the upper and lower surfaces remain separated by the lubricant, an increase in van der Waals energy leads to higher friction force, consequently elevating the friction coefficient. In the absence of contact, the friction coefficient decreases with increasing load; however, once asperity contact occurs, higher loads accelerate lubricant film failure and intensify direct interfacial contact, leading to more pronounced stick–slip oscillations and increased wear. This study provides atomic-scale insights for the design and performance optimization of boundary lubrication interfaces. Full article

(This article belongs to the Special Issue Advances in Mechanical and Tribological Properties of Nanocomposites)

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19 pages, 3677 KB

Open AccessArticle

Influence of Infill Density on the Degradation and Tribological Performance of FDM-Printed PLA for Biomedical Applications

by Nebojša Zdravković, Živana Jovanovic Pešić, Dalibor Nikolić and Dragan S. Džunić

Lubricants 2026, 14(5), 192; https://doi.org/10.3390/lubricants14050192 - 30 Apr 2026

Cited by 2 | Viewed by 648

Abstract

This study investigates the influence of physiological body fluids on the mass stability and tribological performance of polylactic acid (PLA) samples produced by Fused Deposition Modeling (FDM) 3D printing. Body fluid exposure was simulated using Dulbecco’s Modified Eagle Medium (DMEM) under controlled conditions. [...] Read more.

This study investigates the influence of physiological body fluids on the mass stability and tribological performance of polylactic acid (PLA) samples produced by Fused Deposition Modeling (FDM) 3D printing. Body fluid exposure was simulated using Dulbecco’s Modified Eagle Medium (DMEM) under controlled conditions. Black PLA filament was printed with three infill densities (15%, 20%, and 90%) and immersed in DMEM for 7 days at 37 ± 1 °C. Mass measurements revealed that lower infill densities resulted in significantly higher mass loss, with the 15% infill samples exhibiting the greatest reduction (5.07%), while the 90% infill samples showed negligible change (0.17%). Tribological testing using a CSM nanotribometer under loads of 5 mN, 500 mN, and 1000 mN demonstrated that infill density critically affects friction and wear behavior. The 90% infill samples exhibited the lowest wear volumes and the most stable tribological response, while the 15% infill samples showed degradation-dominated contact behavior. Although the friction measurements for the 15% infill samples were consistent, their interpretation should be approached with caution due to pronounced surface deterioration and debris-mediated sliding. This behavior is attributed to structural weakening caused by immersion in DMEM, which promoted material degradation and influenced the tribological response. These findings confirm the critical role of structural density in wear resistance. To the best of our knowledge, this is the first study to systematically investigate the combined effect of hydrolytic degradation and tribological behavior of FDM-printed PLA as a function of infill density under simulated physiological conditions. These findings provide a scientific basis for optimizing infill density in the design of PLA-based surgical instrument guides, where both degradation resistance and tribological performance under body fluid exposure are essential. The findings should be interpreted within the limitations of the experimental design. Full article

(This article belongs to the Special Issue Machine Design and Tribology)

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23 pages, 5525 KB

Open AccessArticle

Analysis of Oil-Gas Two-Phase Flow Characteristics of Bearing Chamber Sealing System with Baffle Structure

by Guozhe Ren, Rui Wang, Mingzhang Wang, Huan Zhao and Wenfeng Xu

Lubricants 2026, 14(5), 191; https://doi.org/10.3390/lubricants14050191 - 30 Apr 2026

Viewed by 819

Abstract

In order to explore the influence of baffle structure on the oil–gas two-phase flow and leakage characteristics of aero-engine bearing chamber sealing systems, based on the VOF two-phase flow model, this paper systematically carried out a transient numerical simulation of the bearing chamber [...] Read more.

In order to explore the influence of baffle structure on the oil–gas two-phase flow and leakage characteristics of aero-engine bearing chamber sealing systems, based on the VOF two-phase flow model, this paper systematically carried out a transient numerical simulation of the bearing chamber sealing systems with conventional configurations and baffle configurations. The oil distribution, leakage and flow evolution of the two types of configurations under different baffle heights, sealing pressure differences and rotational speeds were compared and analyzed. The results show that the higher the height of the baffle, the more obvious the accumulation effect of the lubricating oil and the greater the leakage. The increase in sealing pressure difference helps to suppress leakage and reduce leakage fluctuation. The increase in rotational speed aggravates the centrifugal effect of the lubricating oil and makes the leakage increase significantly. This paper reveals the multi-parameter coupling mechanism of the baffle structure on the leakage control of the bearing chamber sealing system, and it provides a theoretical basis for the optimal design of the bearing chamber sealing structure of the aero-engine. Full article

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21 pages, 12568 KB

Open AccessArticle

Numerical Analysis of Load Capacity and Friction Torque of Eccentric Magnetorheological Fluid Seals

by Alexander Fetisov, Yuri Kazakov and Maksim Litovchenko

Lubricants 2026, 14(5), 190; https://doi.org/10.3390/lubricants14050190 - 29 Apr 2026

Cited by 1 | Viewed by 674

Abstract

This paper presents the results of numerical calculation of steady-state magnetorheological fluid flow in the gap of an eccentric seal subjected to an external radial magnetic field. A coupled problem combining magnetic field analysis and laminar viscoplastic flow with Bingham rheology is solved [...] Read more.

This paper presents the results of numerical calculation of steady-state magnetorheological fluid flow in the gap of an eccentric seal subjected to an external radial magnetic field. A coupled problem combining magnetic field analysis and laminar viscoplastic flow with Bingham rheology is solved to obtain pressure and velocity distributions within the seal gap, from which the hydrodynamic reaction forces of the fluid film and the rotor friction torque are determined. A parametric study was conducted in the ranges of rotor angular velocity ω = 100–400 rad/s, relative eccentricity ε = 0–0.9, and magnetic flux density B₀ = 0–0.5 T at the pressure differential Δp = 2 atm. Analysis of the results shows that increasing the magnetic flux density from 0 to 0.5 T leads to an increase in the seal reaction force from 12 N to 642 N and the friction torque from 0.35 N·m to 11.23 N·m. The most intensive growth of both characteristics is observed in the range B₀ = 0–0.3 T, beyond which saturation occurs as the MRF yield stress reaches its plateau value. An optimal control range of B₀ = 0.1–0.2 T was determined, ensuring maximum seal energetic efficiency as quantified by the load capacity-to-friction torque ratio, which is maximized at 70 N/(N·m). Based on the obtained results, the consequences of using magnetorheological seals on the performance of the rotor system are discussed, including the analysis of the sealing effect on rotor-dynamic stability. Within the proposed optimal range, it is shown that an increase in magnetic flux density leads to a sign reversal of the horizontal reaction F₂, while the monotonic growth of the ratio |F₂|/F₁ indicates an intensification of cross-coupling and a corresponding reduction in the rotordynamic stability margin at higher values of B₀. Full article

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17 pages, 5778 KB

Open AccessArticle

Lubrication Mechanisms of Core–Shell Ag@Cu Microparticles as Lubricant Additives in EHC-50 Base Oil

by Jianbin Zhang, Ming Yi, Leilei Li, Ting Lv, Yanling Wang, Libang Feng, Chaoyang Zhang and Mohamed Kamal Ahmed Ali

Lubricants 2026, 14(5), 189; https://doi.org/10.3390/lubricants14050189 - 28 Apr 2026

Cited by 1 | Viewed by 783

Abstract

Lubricant additives play a crucial role in improving the tribological performance of lubricating oils to reduce frictional energy losses and improve the durability and reliability of mechanical systems. In this study, soft metallic-based core–shell Ag@Cu microparticles were synthesized via an in-situ galvanic displacement [...] Read more.

Lubricant additives play a crucial role in improving the tribological performance of lubricating oils to reduce frictional energy losses and improve the durability and reliability of mechanical systems. In this study, soft metallic-based core–shell Ag@Cu microparticles were synthesized via an in-situ galvanic displacement method and incorporated into EHC-50 base oil with various concentrations. The tribological performance evaluations indicated that 0.3 wt% Ag@Cu significantly enhanced friction-reducing and anti-wear properties, achieving a stable friction coefficient of 0.12, a 45% reduction, and a wear volume reduction of 75% compared to the pristine oil. Additionally, the surface characterization techniques (SEM/EDS, XPS, XRD, and TOF-SIMS) were employed to explore the wear patterns and related lubrication mechanisms. The results indicated that the synergistic interaction between the micro-bearing effect, physical mending, and tribochemical reactions facilitated the formation of a robust tribofilm composed of metallic Ag, ternary CuFe₃O₂, and sulfides, which achieved higher lubrication performance. Ultimately, this research provides novel metallic micro-additives, offering a facile approach to formulating wear-resistant lubricants with significant potential for saving energy for mechanical tribosystems in industrial applications. Full article

(This article belongs to the Special Issue Lubrication Challenges in Electric Vehicle Transmissions)

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29 pages, 10697 KB

Open AccessArticle

Multi-Source Data Fusion-Driven Performance Prediction and Method Evaluation for Spiral Groove Dry Gas Seal

by Jiashu Yu, Xuexing Ding and Jianping Yu

Lubricants 2026, 14(5), 188; https://doi.org/10.3390/lubricants14050188 - 28 Apr 2026

Viewed by 475

Abstract

Spiral-groove dry gas seals are widely used in various rotating machinery, and their performance prediction is of great significance for structural design and operational optimization. Existing studies still face several limitations, including the limited fidelity of numerical simulations, the insufficient number of experimental [...] Read more.

Spiral-groove dry gas seals are widely used in various rotating machinery, and their performance prediction is of great significance for structural design and operational optimization. Existing studies still face several limitations, including the limited fidelity of numerical simulations, the insufficient number of experimental samples, and the restricted generalization capability of models based on a single data source. To address these issues, this study constructed a multi-source data system integrating numerical simulation data and experimental data, and systematically compared four representative data fusion methods, namely the uncertainty-weighted fusion algorithm, TrAdaBoost, MFDNN, and CoKriging, with analysis of their applicability and predictive performance. The results show that multi-source data fusion can effectively exploit the complementary advantages of different data sources and improve the prediction accuracy of dry gas seal performance. In terms of the comparison of data fusion methods, all four methods achieved good results for the groove-depth problem; however, for the spiral-angle and groove-number problems, which exhibit stronger nonlinear characteristics, clear differences were observed among the methods. Among them, TrAdaBoost showed the best overall performance, followed by MFDNN, then CoKriging, while the uncertainty-weighted method was relatively weaker. In terms of seal performance, the influence of groove depth on seal performance was relatively direct; the spiral angle is recommended to be controlled within 10–14°, and the groove number within 12–16, so as to balance opening force and leakage rate. This study can provide a reference for the rapid performance prediction and parameter optimization of spiral-groove dry gas seals. Full article

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18 pages, 5339 KB

Open AccessArticle

Study on the Lubrication Performance and Mechanism of Silver/Modified Graphene Oxide Composite Additives

by Jia Sun, Zhe Jiang, Songhua Li, Lixiu Zhang, Zhenyu Yin and Shiqi Li

Lubricants 2026, 14(5), 187; https://doi.org/10.3390/lubricants14050187 - 28 Apr 2026

Viewed by 489

Abstract

Under complex friction conditions, base oils usually exhibit insufficient friction-reducing and anti-wear performance, poor shear resistance of the lubricating film, and weak interfacial adsorption stability. Herein, graphene oxide (GO) was surface-modified with the silane coupling agent KH550 and compounded with Ag nanoparticles to [...] Read more.

Under complex friction conditions, base oils usually exhibit insufficient friction-reducing and anti-wear performance, poor shear resistance of the lubricating film, and weak interfacial adsorption stability. Herein, graphene oxide (GO) was surface-modified with the silane coupling agent KH550 and compounded with Ag nanoparticles to fabricate a silver/modified graphene oxide (Ag/KGO) composite lubricant additive. The microstructure and chemical characteristics of the Ag/KGO composite were characterized by SEM, XRD, FTIR, and Raman spectroscopy. Tribological tests performed on a Si₃N₄/GCr15 friction pair demonstrated that the lubricant containing 0.15 wt% Ag/KGO achieved the optimal tribological performance, with the average friction coefficient decreasing to 0.053, 51.8% lower than that of the base oil, and the wear scar width and depth decreasing by 34.5% and 75.7%, respectively. Molecular dynamics simulations revealed that Ag/KGO enhanced the interfacial adsorption strength and improved the shear stability of the lubricating film. Mechanism analysis indicated that KGO facilitated the formation of a stable lubricating film at the friction interface, while Ag nanoparticles acted as nano-bearings. Their synergistic effect reduced interfacial shear resistance and alleviated wear. These findings provide theoretical support for the design and development of high-performance composite lubricant additives. Full article

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19 pages, 7998 KB

Open AccessArticle

Influence of TiO₂ Additive on the Tribological Performance of Bonded MoS₂ Solid Lubricants

by Parastoo Fallah, Cara Hensley, Charles J. Beall, Rolf Wuthrich and Pantcho Stoyanov

Lubricants 2026, 14(5), 186; https://doi.org/10.3390/lubricants14050186 - 28 Apr 2026

Cited by 1 | Viewed by 1015

Abstract

To elucidate the role of environmentally friendly oxide additives in a molybdenum disulfide (MoS₂)-based solid lubricant, this study investigates the tribological behavior of a MoS₂–TiO₂ coating deposited via a spray-bonding process and compares it with a commercial Sb [...] Read more.

To elucidate the role of environmentally friendly oxide additives in a molybdenum disulfide (MoS₂)-based solid lubricant, this study investigates the tribological behavior of a MoS₂–TiO₂ coating deposited via a spray-bonding process and compares it with a commercial Sb₂O₃-containing formulation (Everlube 620C). Interfacial characteristics and wear-related mechanisms were systematically analyzed using scanning electron microscopy (SEM), focused ion beam (FIB), Raman spectroscopy, and X-ray diffraction (XRD). The MoS₂–TiO₂ coating exhibited a higher steady-state coefficient of friction (0.35–0.45) and wear compared to the baseline. Its wear behavior was governed by fracture-induced three-body abrasion, driven by the hard and brittle nature of TiO₂, which promotes stress concentration at particle–matrix interfaces, crack initiation, particle pull-out, and debris generation. These processes suppress the formation of a desirable MoS₂-rich tribo/transfer film, leading to deformation-dominated friction. Overall, the findings indicate that the intrinsic mechanical properties and interfacial behavior of TiO₂ limit its effectiveness as an additive in MoS₂-based coatings, highlighting the importance of additive selection and compatibility in achieving optimal tribological performance. Notably, this study was performed at an additive volume fraction equivalent to that of Sb₂O₃ in Everlube 620C, serving as a foundation and indicating that further optimization of TiO₂ particle size and concentration is required to achieve comparable performance. Full article

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17 pages, 5023 KB

Open AccessArticle

Numerical Investigation of Spring-Energized Seals for a Fluid Swivel in a Single-Point Mooring System

by Xianjin Fang, Yingzi Zhang, Chen Tang, Zhiran Lu, Zehua Hu, Haiwei Chen, Hunian Shan, Shaohui Yang, Zhilin Liu, Yan Huang and Chenglong Li

Lubricants 2026, 14(5), 185; https://doi.org/10.3390/lubricants14050185 - 26 Apr 2026

Viewed by 696

Abstract

Single-point mooring systems are among the key systems for offshore oilfield development. The fluid swivel is a core component of such systems, enabling fluid transfer while allowing the vessel to follow the weather vane effect. The spring-energized seal is critical for ensuring reliable [...] Read more.

Single-point mooring systems are among the key systems for offshore oilfield development. The fluid swivel is a core component of such systems, enabling fluid transfer while allowing the vessel to follow the weather vane effect. The spring-energized seal is critical for ensuring reliable fluid transmission. Existing studies on spring-energized seals primarily focus on small-scale mechanisms, with limited research on large-scale seal design under complex operating conditions. This work investigates the dynamic sealing performance of the oil-transferring rotary joint in a 300,000 ton VLCC catenary single-point mooring system. A spring-energized seal is designed with a PTFE-based composite as the sealing jacket and Inconel 718 as the spring material. A finite element model of the spring-energized seal is developed in ANSYS 2022 R1, and the design is optimized to achieve lower equivalent strain, more uniform contact pressure distribution, larger contact width, and reduced friction. Fatigue life analysis of the optimized design verifies its reliability over a 10-year service period. The proposed study provides a reference for the design of dynamic seals in high-end offshore engineering equipment. Full article

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22 pages, 9159 KB

Open AccessArticle

Ultralow-Friction in Graphene–Nanodiamond Functionalized DLC Coatings: Transfer-Layer Evolution Under Variable Load and Humidity

by Andrea Mescola, Federico Zanni, Alberto Rota, Cristina Bernini, Andrea Gerbi, Riccardo Carzino, Luca Repetto, Michał Bartkowski, Silvia Giordani, Renato Buzio and Guido Paolicelli

Lubricants 2026, 14(5), 184; https://doi.org/10.3390/lubricants14050184 - 24 Apr 2026

Viewed by 885

Abstract

Diamond-like carbon (DLC) coatings are widely used as protective and self-lubricating surfaces in metal–metal contacts. Their frictional behavior is governed by the formation and evolution of carbon-rich transfer layers (TLs), which can be tailored through functionalization with carbon nanomaterials. Recent studies have shown [...] Read more.

Diamond-like carbon (DLC) coatings are widely used as protective and self-lubricating surfaces in metal–metal contacts. Their frictional behavior is governed by the formation and evolution of carbon-rich transfer layers (TLs), which can be tailored through functionalization with carbon nanomaterials. Recent studies have shown that graphene sheets (GSs) and nanodiamonds (NDs) act synergistically to achieve ultra-low friction in microrough (~0.2 μm) metal–DLC contacts under dry N₂ at a 1 N load. Here, we probe how this lubrication mechanism evolves with increasing load from 1 to 10 N—corresponding to local contact pressures up to ~11–16 GPa—respectively, in dry N₂ and humid air conditions. Ball-on-disk experiments are performed on an industrial hydrogenated DLC coating sliding against stainless-steel. In dry N₂, GS–ND functionalization yields a low and stable coefficient of friction across the entire load range, reaching a minimum of about 0.05. In humid air, higher friction levels are observed across all loads (CoF ~0.10–0.15), accompanied by oxidation-driven modifications of both wear debris and the counterface contact region, with oxygen content increasing by more than a factor of three compared to dry N₂. Detailed microscopy and spectroscopy analyses indicate that enhanced lubricity in dry N₂ arises from TLs incorporating GSs, NDs, and nanoscroll-like structures, whereas humid air promotes interfacial amorphization and oxidation, leading to load-insensitive friction and boundary lubrication effects through physisorbed water molecules. Full article

(This article belongs to the Special Issue Superlubricity Mechanisms and Applications)

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19 pages, 6684 KB

Open AccessArticle

Controlled Laser Sintering as a Strategy for Improved Tribological Performance of Ni-Cr-Ti₃SiC₂ Coatings

by Mohammad Ashikul Alam, Nihal Ahmed, Md Abid Hossain, Janak Paudel, Bo Shen, Maharshi Dey and Sujan Ghosh

Lubricants 2026, 14(5), 183; https://doi.org/10.3390/lubricants14050183 - 23 Apr 2026

Cited by 1 | Viewed by 1238

Abstract

The poor tribological and mechanical performance of Al alloys hinders their use in practical applications where low COF and high durability are required. This study examined and evaluated a novel laser-sintered Ni-Cr coating to improve the load-carrying capacity and tribological performance of an [...] Read more.

The poor tribological and mechanical performance of Al alloys hinders their use in practical applications where low COF and high durability are required. This study examined and evaluated a novel laser-sintered Ni-Cr coating to improve the load-carrying capacity and tribological performance of an Al alloy (Al 6061) substrate. The authors demonstrate that laser sintering cycle count is a decisive process variable governing coating dispersion, microstructural consolidation, and tribological performance in Ni-Cr coatings fabricated via Selective Laser Sintering (SLS). Increasing the laser cycle count progressively refined the surface morphology, improved coating dispersion, and strengthened interparticle bonding. As a result, the average durability after three cycles was seven times that after one laser cycle, accompanied by markedly improved COF. To further improve durability and load-carrying capacity, Ti₃SiC₂ was introduced into the Ni-Cr coating. The coating containing 10 wt% Ti₃SiC₂ exhibited a 20-fold increase in durability, extending the time to failure to approximately 70,000 s (700 m) while maintaining a low coefficient of friction (~0.48) compared with the coating containing no Ti₃SiC₂. The greater durability of the Ni-Cr-10wt%Ti₃SiC₂ coating in this novel study was attributed to improved adhesion to the substrate, better particle distribution during sintering, and greater load-carrying capacity. While further process changes do not yield feasible samples, this study showed that surface properties can be improved within the available small-process regime. Overall, laser sintering of a Ni-Cr-10wt%Ti₃SiC₂ coating shows promise as a means to improve the tribological and mechanical performance of Al 6061. This study should aid researchers and other stakeholders in fabricating well-adhering, durable, and tribotactic composite coatings on Al6061 and similar material systems. Full article

(This article belongs to the Special Issue Laser Surface Engineering for Advanced Tribological Performance)

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Lubricants, Volume 14, Issue 5 (May 2026) – 32 articles

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