Lubricants

20 pages, 653 KiB

Open AccessArticle

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

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

Open AccessArticle

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

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

Open AccessArticle

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

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, 3540 KiB

Open AccessArticle

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

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)

12 pages, 3473 KiB

Open AccessArticle

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

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 HV_0.5, 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

Open AccessArticle

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

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

Open AccessArticle

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

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

Open AccessArticle

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

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

Open AccessArticle

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

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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14 pages, 7219 KiB

Open AccessArticle

The Influence of Atomic Metal Conditioner Additive with Surface Revitalizer on the Lubricating Properties of Engine Oil

by Ruslans Smigins, Audrius Žunda, Albinas Andriušis, Çağla Gizem Acar and Simona Tučkutė

Lubricants 2025, 13(7), 284; https://doi.org/10.3390/lubricants13070284 - 25 Jun 2025

Abstract

The development of multifunctional lubricant additives is critical for enhancing the performance and longevity of internal combustion engines. This study investigates the influence of oil additive, containing an atomic metal conditioner (AMC), a two-dimensional sliding agent, and a patented revitalizer on lubricating properties [...] Read more.

The development of multifunctional lubricant additives is critical for enhancing the performance and longevity of internal combustion engines. This study investigates the influence of oil additive, containing an atomic metal conditioner (AMC), a two-dimensional sliding agent, and a patented revitalizer on lubricating properties of engine oil 5W-30 and on surface wear characteristics. The experimental testing involved comparative tribological evaluation using the 4-ball test. Pure commercial engine oil (PEO) 5W-30 and oil mixed with the revitalizer additive (OMA) were used. The changes in friction torque (FTq), temperature, and wear scars were analyzed. FTq evolution showed a distinct behavior across the different test cases: PEO exhibited fluctuating FTq in the initial minute and thereafter, but its value was lower, and the wear scars were smaller compared to OMA. Long-duration tests revealed that OMA resulted in significantly larger wear scars, large FTq values, and less variations emerging later in the test. When switching from PEO (1 h) to OMA (1 h) mid-test, the wear increased compared to 2 h PEO. Across all conditions, oil temperature had a strong relationship with FTq. Although some frictional improvements were observed, no definitive evidence of revitalizer-induced surface regeneration was detected, suggesting adhesive wear remained predominant under the studied conditions. Full article

(This article belongs to the Special Issue Novel Lubricant Additives in 2025)

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12 pages, 4266 KiB

Open AccessArticle

Influence of 3D-Printed PEEK on the Tribo-Corrosion Performance of Ti6Al4V Biomedical Alloy

by Dominik Jonas Federl and Abbas Al-Rjoub

Lubricants 2025, 13(7), 283; https://doi.org/10.3390/lubricants13070283 - 25 Jun 2025

Abstract

This study investigates the tribo-corrosion behavior of Ti6Al4V biomedical alloy, when sliding against fused filament fabrication (FFF) 3D-printed polyether ether ketone (PEEK) pins in a phosphate-buffered saline (PBS) solution. This research aims to evaluate wear mechanisms and electrochemical responses under simulated physiological conditions, [...] Read more.

This study investigates the tribo-corrosion behavior of Ti6Al4V biomedical alloy, when sliding against fused filament fabrication (FFF) 3D-printed polyether ether ketone (PEEK) pins in a phosphate-buffered saline (PBS) solution. This research aims to evaluate wear mechanisms and electrochemical responses under simulated physiological conditions, providing critical insights for enhancing the durability and performance of biomedical implants. Potentiodynamic polarization tests demonstrate that the Ti6Al4V alloy possesses excellent corrosion resistance, which is further enhanced under sliding conditions compared to the test without sliding. When tested against 3D-printed PEEK, the alloy exhibits a mixed wear mechanism characterized by both abrasive and adhesive wear. Open-circuit potential (OCP) measurement of Ti6Al4V demonstrates the alloy’s superior electrochemical stability, indicating high corrosion resistance and a favorable coefficient of friction. These findings highlight the potential of 3D-printed PEEK as a viable alternative for biomedical applications, offering rapid patient-specific prototyping, tunable mechanical properties, and improved surface adaptability compared to conventional materials. Full article

(This article belongs to the Special Issue Tribology of Polymeric Composites)

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15 pages, 6776 KiB

Open AccessArticle

Evolution of Frictional Wear Behavior of C/C-CuNi Composites by Arc Discharge

by Xizong Liu, Yulei Zhang, Heng Wu, Dongsheng Zhang, Jiaqi Liu and Haibo Ouyang

Lubricants 2025, 13(7), 282; https://doi.org/10.3390/lubricants13070282 - 23 Jun 2025

Abstract

This study fabricated a C/C-CuNi composite using the hydrothermal co-deposition method and investigated its friction and wear behavior as well as the underlying mechanisms after being subjected to arc discharge ablation. The results indicate that the graphitization degree of the material matrix was [...] Read more.

This study fabricated a C/C-CuNi composite using the hydrothermal co-deposition method and investigated its friction and wear behavior as well as the underlying mechanisms after being subjected to arc discharge ablation. The results indicate that the graphitization degree of the material matrix was significantly enhanced after arc discharge ablation, accompanied by a transformation in the carbon microstructure. Carbon nanotubes and graphene structures were generated in the arc ablation zone. Under low arc discharge density, limited pits and open pores are formed on the material surface, with the generated graphene structures effectively reducing friction. Specifically, CN-5 exhibited a stable friction coefficient, a wear rate of 5.2 mg/km, and partial self-repair capability. In contrast, CN-10, under high arc discharge density, suffered from structural collapse, matrix-fiber debonding, and extensive open pores, leading to increased surface roughness. The combined effects of frictional heat and Joule heating elevated the wear surface temperature, triggering matrix oxidation and a sharp rise in wear rate to 14.7 mg/km. The wear mechanisms of C/C-CuNi composites under continuous arc conditions involve arc erosion wear, oxidative wear, abrasive wear, and adhesive wear. Full article

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17 pages, 13043 KiB

Open AccessArticle

Lubrication Performance Promotion of GTL Base Oil by BN Nanosheets via Cascade Centrifugation-Assisted Liquid-Phase Exfoliation

by Jiashun Liu, Shuo Xiang, Xiaoyu Zhou, Shigang Lin, Kehong Dong, Yiwei Liu, Donghai He, Yunhong Fan, Yuehao Liu, Bingxue Xiong, Kai Ma, Kaiyang Xiao, Genmao Luo, Qinhui Zhang and Xin Yang

Lubricants 2025, 13(7), 281; https://doi.org/10.3390/lubricants13070281 - 23 Jun 2025

Abstract

Broad lateral size and thickness distributions impede the application of hexagonal boron nitride nanosheets (BNNSs) as friction modifiers in base oil, although they possess remarkable potential for lubrication performance promotion. In this work, a cascade centrifugation-assisted liquid-phase exfoliation approach was presented to prepare [...] Read more.

Broad lateral size and thickness distributions impede the application of hexagonal boron nitride nanosheets (BNNSs) as friction modifiers in base oil, although they possess remarkable potential for lubrication performance promotion. In this work, a cascade centrifugation-assisted liquid-phase exfoliation approach was presented to prepare BNNSs from hexagonal boron nitride (h-BN) efficiently and scalably. Subsequently, they were ultrasonically dispersed into gas-to-liquid (GTL) base oil, and their lubrication performance promotion was evaluated by a four-ball tribotester. Tribological tests demonstrated that BNNS possesses excellent friction-reducing and anti-wear properties in GTL. Furthermore, the findings indicate that at a BNNS content of 0.8 wt.%, the system displayed the lowest COF and WSD. Particularly, with an addition of 0.8 wt.% BNNS into GTL, the AFC and WSD are reduced significantly by 40.1% and 35.4% compared to pure base oil, respectively, and the surface roughness, wear depth, and wear volume were effectively reduced by 91.0%, 68.5%, and 76.8% compared to GTL base oil, respectively. Raman, SEM-EDS, and XPS results proved that the outstanding friction-reducing and anti-wear properties of BNNS can mainly be ascribed to the presence of physical adsorption film and tribo-chemical film, which were composed of FeOOH, FeO, Fe₃O₄, and B₂O₃. Full article

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13 pages, 2467 KiB

Open AccessArticle

Thermal-Tribological Synergy in PTFE-Based Self-Lubricating Retainers for Ball Bearings Under Oil-Depleted Conditions

by Zhining Jia and Caizhe Hao

Lubricants 2025, 13(7), 280; https://doi.org/10.3390/lubricants13070280 - 23 Jun 2025

Abstract

To investigate the temperature rise characteristics and tribological performance of angular contact ball bearings equipped with polymer-based self-lubricating retainers under oil-depleted conditions. PTFE-based composite retainers were fabricated using cold-press sintering technology. Comparative experiments on 7206C were conducted on three bearing configurations (domestic, imported [...] Read more.

To investigate the temperature rise characteristics and tribological performance of angular contact ball bearings equipped with polymer-based self-lubricating retainers under oil-depleted conditions. PTFE-based composite retainers were fabricated using cold-press sintering technology. Comparative experiments on 7206C were conducted on three bearing configurations (domestic, imported NSK, and YSU-S1/S2 self-lubricating retainer bearing) using a dedicated fatigue tester under oil-depleted lubrication. This study demonstrates that angular contact ball bearings equipped with PTFE-based self-lubricating retainers exhibit superior thermal behavior under oil-depleted conditions. Compared to domestic and imported NSK bearings, the retainer-equipped bearing reduced equilibrium temperatures by 2~3 °C versus NSK/domestic bearings, with 60% lower peak temperatures. The high speed further facilitates the formation of transfer films, resulting in a smoother raceway and notably enhancing the bearing’s temperature rise characteristics. This study establishes a material–process–performance framework, bridging polymer composites and industrial bearing design. Full article

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25 pages, 4187 KiB

Open AccessArticle

The Development and Performance Assessment of Palm Kernel Nut Oil as a Cutting Fluid for the Turning of AA6061

by Omolayo M. Ikumapayi, Opeyeolu T. Laseinde, Rasaq A. Kazeem, Peter Onu and Tin T. Ting

Lubricants 2025, 13(7), 279; https://doi.org/10.3390/lubricants13070279 - 21 Jun 2025

Abstract

This study focuses on investigating the manufacturing, characterization, and assessment of palm kernel nut oil as a cutting fluid (CF) in the machining of aluminium 6061 alloy. Cutting fluids are vital in machining operations as they reduce friction, dissipate heat, and prolong the [...] Read more.

This study focuses on investigating the manufacturing, characterization, and assessment of palm kernel nut oil as a cutting fluid (CF) in the machining of aluminium 6061 alloy. Cutting fluids are vital in machining operations as they reduce friction, dissipate heat, and prolong the lifespan of tools. Palm kernel nut oil, derived from the fruit of a palm kernel, has attracted attention due to its environmentally friendly and readily biodegradable characteristics. This study involved the extraction, refinement, and characterization of palm kernel nut oil for its potential application as a cutting fluid. An experimental investigation was conducted to evaluate the performance of palm kernel nut oil (PKNO) as a CF through turning operations on aluminium 6061 alloy. The experimental parameters included the cutting speed, feed rate, and depth of cut, while the effectiveness of the CF was assessed based on key performance indicators such as surface roughness and cutting temperature. The findings demonstrated that the PKNO-CF exhibited favourable physical properties, including optimal viscosity, density, and pH levels. Furthermore, a detailed chemical analysis confirmed the absence of hazardous components, establishing palm kernel nut oil as a safer and more environmentally friendly alternative to conventional cutting fluids. This study aligns with United Nations Sustainable Development Goal (SDG) 12: Responsible Consumption and Production as it promotes the use of an environmentally friendly and biodegradable cutting fluid, reducing reliance on conventional, potentially hazardous cutting fluids and reducing environmental pollution. By utilizing palm kernel nut oil as a sustainable alternative, this research supports eco-friendly manufacturing practices and minimizes environmental impact in machining operations Full article

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

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17 pages, 4414 KiB

Open AccessArticle

A New Sustainable Approach to Enhancing the Subtractive Process in the Additive–Subtractive Hybrid Manufacturing of AISI H13 Dry Machining

by Hiva Hedayati and Maryam Aramesh

Lubricants 2025, 13(7), 278; https://doi.org/10.3390/lubricants13070278 - 21 Jun 2025

Abstract

In additive–subtractive hybrid manufacturing (ASHM), machining and additive processes are combined in a single operation to merge the benefits of both. This method faces challenges, especially during the machining steps. Parts made through additive manufacturing often have low machinability due to factors like [...] Read more.

In additive–subtractive hybrid manufacturing (ASHM), machining and additive processes are combined in a single operation to merge the benefits of both. This method faces challenges, especially during the machining steps. Parts made through additive manufacturing often have low machinability due to factors like residual stresses and fine, hard microstructures. In ASHM, intermediate heat treatments are not possible, leading to the increased hardness of the printed material. Cutting fluids, typically used to reduce temperature and friction, can contaminate the build environment and impair layer adhesion; therefore, they are not recommended in ASHM. This study investigates soft metallic lubricant coatings in ASHM as substitutes for conventional fluid lubricants during dry machining. The coatings form a lubricating layer between the tool and workpiece, providing an alternative to cutting fluids. This research evaluates their effectiveness in improving the surface integrity of additively manufactured parts and supporting dry machining. The results of our research show a 65% reduction in force, a 50% reduction in tool wear, and a reduction in microstructural changes during machining while maintaining dry machining. Full article

(This article belongs to the Special Issue Coatings and Lubrication in Extreme Environments)

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23 pages, 4779 KiB

Open AccessArticle

Ti-C and CFs Work Together to Enhance the Comprehensive Tribological Properties of PTFE-Based Composites for the Manufacture of Wave Glider Power Shafts

by Angang Yan, Xingju Yao, Yuan Wei, Qianjian Guo, Yulong Wang, Wuqiang Tang and Xian Xu

Lubricants 2025, 13(7), 277; https://doi.org/10.3390/lubricants13070277 - 20 Jun 2025

Abstract

Wave gliders’ power system shafts face complex conditions. To enhance their operational stability, it is crucial to study PTFE, a polymer material that could replace traditional metals. This study added carbon fiber (CF), titanium carbide (Ti-C), and both to a PTFE matrix. The [...] Read more.

Wave gliders’ power system shafts face complex conditions. To enhance their operational stability, it is crucial to study PTFE, a polymer material that could replace traditional metals. This study added carbon fiber (CF), titanium carbide (Ti-C), and both to a PTFE matrix. The impact of seawater immersion on water absorption and the mechanical properties was examined, as well as friction and wear characteristics under constant amplitude cyclic (CAC) loading and seawater lubrication. The results indicated that while Ti-C boosts PTFE matrix hardness, its poor binding with the PTFE matrix leads to high water absorption in Ti-C/PTFE (PTFE-3), causing a significant decrease in the mechanical properties post-immersion and poor friction and wear performance. In contrast, CFs and the PTFE matrix have good interfacial bonding and greatly improve the resistance of the PTFE matrix to cyclic loading and seawater immersion. Therefore, CF/PTFE (PTFE-2) shows good mechanical and tribological properties. Moreover, incorporating a certain amount of CFs into Ti-C enhances its adhesion to the PTFE matrix, reducing the occurrence three-body wear and allowing Ti-C to fully utilize its high hardness. Thus, the combination of Ti-C and CFs markedly improves PTFE’s mechanical and tribological properties under cyclic loading and in seawater. Full article

(This article belongs to the Special Issue Tribology of Polymeric Composites)

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24 pages, 9695 KiB

Open AccessArticle

Investigation of Microstructural, Mechanical, and Tribological Properties of TiC and MWCNT Reinforced Hot-Pressed Scalmalloy^® Hybrid Composites

by Taha Alper Yilmaz

Lubricants 2025, 13(7), 276; https://doi.org/10.3390/lubricants13070276 - 20 Jun 2025

Abstract

In this study, hybrid composite materials were fabricated using a Scalmalloy^® matrix with fixed multi-walled carbon nanotube (MWCNT, 0.8%) content and varying titanium carbide (TiC; 5%, 10%, 15%) reinforcements via the hot-pressing method. Unlike conventional approaches in the literature that utilize additive [...] Read more.

In this study, hybrid composite materials were fabricated using a Scalmalloy^® matrix with fixed multi-walled carbon nanotube (MWCNT, 0.8%) content and varying titanium carbide (TiC; 5%, 10%, 15%) reinforcements via the hot-pressing method. Unlike conventional approaches in the literature that utilize additive manufacturing, this research presents the first successful production of Scalmalloy^®-based hybrid composites through a traditional powder metallurgy method. This method enabled the development of a more homogeneous and equiaxed microstructure. The composites were characterized using SEM, EDS, MAP, and XRD analyses, along with density and microhardness measurements. Mechanical performance was evaluated through Vickers hardness and transverse rupture strength (TRS) tests, while dry sliding wear behavior was examined in detail. The hardness of the 15% TiC + 0.8% MWCNT-reinforced composite increased from 87 HV to 181 HV (a 108% improvement), and TRS increased from 354 MPa to 545 MPa (a 54% improvement). Additionally, wear surface examinations showed that as the reinforcement ratio increased, the severity of surface damage decreased and abrasive wear mechanisms became more dominant. These findings demonstrate that hybrid reinforcement with TiC and MWCNT significantly enhances both mechanical and tribological performance, offering a promising alternative to additive manufacturing for Scalmalloy^®-based composite production. 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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27 pages, 4277 KiB

Open AccessArticle

Probability Density Evolution and Reliability Analysis of Gear Transmission Systems Based on the Path Integration Method

by Hongchuan Cheng, Zhaoyang Shi, Guilong Fu, Yu Cui, Zhiwu Shang and Xingbao Huang

Lubricants 2025, 13(6), 275; https://doi.org/10.3390/lubricants13060275 - 19 Jun 2025

Abstract

Aimed at dealing with the problems of high reliability solution cost and low solution accuracy under random excitation, especially Gaussian white noise excitation, this paper proposes a probability density evolution and reliability analysis method for nonlinear gear transmission systems under Gaussian white noise [...] Read more.

Aimed at dealing with the problems of high reliability solution cost and low solution accuracy under random excitation, especially Gaussian white noise excitation, this paper proposes a probability density evolution and reliability analysis method for nonlinear gear transmission systems under Gaussian white noise excitation based on the path integration method. This method constructs an efficient probability density evolution framework by combining the path integration method, the Chapman–Kolmogorov equation, and the Laplace asymptotic expansion method. Based on Rice’s theory and combined with the adaptive Gauss–Legendre integration method, the transient and cumulative reliability of the system are path integration method calculated. The research results show that in the periodic response state, Gaussian white noise leads to the diffusion of probability density and peak attenuation, and the system reliability presents a two-stage attenuation characteristic. In the chaotic response state, the intrinsic dynamic instability of the system dominates the evolution of the probability density, and the reliability decreases more sharply. Verified by Monte Carlo simulation, the method proposed in this paper significantly outperforms the traditional methods in both computational efficiency and accuracy. The research reveals the coupling effect of Gaussian white noise random excitation and nonlinear dynamics, clarifies the differences in failure mechanisms of gear systems in periodic and chaotic states, and provides a theoretical basis for the dynamic reliability design and life prediction of nonlinear gear transmission systems. Full article

(This article belongs to the Special Issue Nonlinear Dynamics of Frictional Systems)

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