Lubricants

28 pages, 22903 KiB

Open AccessArticle

Cold Spray Deposition of MoS₂- and WS₂-Based Solid Lubricant Coatings

by Jeffrey R. Lince, Peter Woods, Eric Woods, Wai H. Mak, Scott D. Sitzman and Andrew J. Clough

Lubricants 2024, 12(7), 237; https://doi.org/10.3390/lubricants12070237 - 28 Jun 2024

The cold spray deposition technique has been used to produce a new class of solid lubricant coatings using powder feedstocks of the metal disulfides WS₂ or MoS₂, either pure or mixed with Cu and Ni metal powders. Friction and cycle [...] Read more.

The cold spray deposition technique has been used to produce a new class of solid lubricant coatings using powder feedstocks of the metal disulfides WS₂ or MoS₂, either pure or mixed with Cu and Ni metal powders. Friction and cycle lives were obtained using ball-on-flat reciprocating tribometry of coated 304 SS flats in dry nitrogen and vacuum at higher Hertzian contact stresses (S_max = 1386 MPa (201 ksi)). The measured friction and thickness of the coatings were much lower than for previous studies (COF = 0.03 ± 0.01 and ≤1 µm, respectively), which is due to their high metal disulfide:metal ratios. Cu-containing metal sulfide coatings exhibited somewhat higher cycle lifetimes than the pure metal sulfide coatings, even though the Cu content was only ~1 wt%. Profiling of wear tracks for coatings tested to 3000 cycles (i.e., pre-failure) yielded specific wear rates in the range 3–7 × 10⁻⁶ mm³N⁻¹m⁻¹, similar to other solid lubricant coatings. When compared to other coating techniques, the cold spray method represents a niche that has heretofore been vacant. In particular, it will be useful in many precision ball-bearing applications that require higher throughput and lower costs than sputter-deposited MoS₂-based coatings. Full article

(This article belongs to the Special Issue New Challenges in Tribology of Space Mechanisms)

► Show Figures

Figure 1

26 pages, 1185 KiB

Open AccessReview

A Review of the Rheological Consistency of Materials

by Alan Gurt and Michael Khonsari

Lubricants 2024, 12(7), 236; https://doi.org/10.3390/lubricants12070236 - 28 Jun 2024

Abstract

Despite the ubiquity and prevalence of rheological consistency across a wide range of industries, there is no clear consensus on its meaning or on one particular technique for quantifying it. Instead, there exist various definitions of “consistency” that are each specific to a [...] Read more.

Despite the ubiquity and prevalence of rheological consistency across a wide range of industries, there is no clear consensus on its meaning or on one particular technique for quantifying it. Instead, there exist various definitions of “consistency” that are each specific to a given context, and each industry has its own procedure for measuring it. This paper organizes the many subjects and terminologies associated with consistency, providing a comprehensive guide of fundamental mechanics, fundamental properties, modeling techniques, and standardized tests that describe consistency. This includes outlining the rheological models that describe the behavior of viscoelastic and non-Newtonian materials as well as the identification of numerous parameters that can be individually evaluated to comprehensively understand and quantify consistency. Such an understanding of consistency and its underlying mechanical properties encourages the refinement of current consistency test methods and development of new ones. Full article

► Show Figures

Figure 1

17 pages, 853 KiB

Open AccessArticle

Holistic Measurement of the Friction Behavior of Wet Clutches

by Patrick Strobl, Georg Johann Meingassner, Hermann Pflaum, Katharina Voelkel, Thomas Schneider and Karsten Stahl

Lubricants 2024, 12(7), 235; https://doi.org/10.3390/lubricants12070235 - 25 Jun 2024

Abstract

The safe and efficient torque transmission of wet disk clutch systems requires high coefficients of friction. To achieve good controllability and high comfort, a positive slope of the coefficient of friction over sliding velocity is ensured by a reasonable formulation of the lubricant [...] Read more.

The safe and efficient torque transmission of wet disk clutch systems requires high coefficients of friction. To achieve good controllability and high comfort, a positive slope of the coefficient of friction over sliding velocity is ensured by a reasonable formulation of the lubricant and choice of the friction pairing. This results in low transmittable torque at low sliding velocities. Thus, the occurrence of unwanted micro-slip in dynamic operation modes must be considered for the design of safety-relevant clutch systems. This work presents a methodology for the holistic measurement of the friction behavior of wet disk clutches. It is suitable for numerous applications and supports a sound understanding of frictional properties in the range of sliding velocities occurring in brake shifts through forced slip operation down to static torque transmission. The experimental determination of the holistic friction behavior is crucial for develo** optimized design guidelines for modern clutch systems. Full article

16 pages, 15735 KiB

Open AccessArticle

Study on the Friction Characteristics and Fatigue Life of Carbonitriding-Treated Needle Bearings

by Yong Chen, **angrun Pu, Lijie Hao, Guangxin Li and Li Luo

Lubricants 2024, 12(7), 234; https://doi.org/10.3390/lubricants12070234 - 24 Jun 2024

Abstract

Being a key component of the transmission system, the needle bearing’s performance and service life affects the overall service life of mechanical equipment. This study takes needle bearings composed of AISI 52100 steel as the research object and studies the effect of carbonitriding [...] Read more.

Being a key component of the transmission system, the needle bearing’s performance and service life affects the overall service life of mechanical equipment. This study takes needle bearings composed of AISI 52100 steel as the research object and studies the effect of carbonitriding surface strengthening treatment on the bearing friction, wear, and fatigue life. The carbon and nitrogen co-infiltration surface-strengthening method was employed to prepare cylindrical and disc samples. The surface hardness, residual austenite content, microscopic morphology and organization composition, coefficient of friction, and wear scar were studied to analyze the effect on the wear performance of the material. The bearing fatigue wear comparison test was conducted on a test bench to compare the actual fatigue life and surface damage of the needle bearing through conventional martensitic quenching heat treatment and carbonitriding treatment. The results demonstrate that the carbonitriding strengthening method enhances the toughness of the material while improving its surface hardness. It also improves the wear resistance of the needle roller bearings, and the fatigue life of the bearings is significantly improved. In conclusion, carbon and nitrogen co-infiltration treatment is a strengthening method that effectively extends the service life of needle roller bearings, indicating its high practical value. Full article

(This article belongs to the Special Issue Tribological Characteristics of Bearing System, 2nd Edition)

► Show Figures

Figure 1

17 pages, 7505 KiB

Open AccessArticle

Effect of Hydrogen Pressure on the Fretting Behavior of Rubber Materials

by Géraldine Theiler, Natalia Cano Murillo and Andreas Hausberger

Lubricants 2024, 12(7), 233; https://doi.org/10.3390/lubricants12070233 - 23 Jun 2024

Abstract

Safety and reliability are the major challenges to face for the development and acceptance of hydrogen technology. It is therefore crucial to deeply study material compatibility, in particular for tribological components that are directly in contact with hydrogen. Some of the most critical [...] Read more.

Safety and reliability are the major challenges to face for the development and acceptance of hydrogen technology. It is therefore crucial to deeply study material compatibility, in particular for tribological components that are directly in contact with hydrogen. Some of the most critical parts are sealing materials that need increased safety requirements. In this study, the fretting behavior of several elastomer materials were evaluated against 316L stainless steel in an air and hydrogen environment up to 10 MPa. Several grades of cross-linked hydrogenated acrylonitrile butadiene (HNBR), acrylonitrile butadiene (NBR) and ethylene propylene diene monomer rubbers (EPDM) were investigated. Furthermore, aging experiments were conducted for 7 days under static conditions in 100 MPa of hydrogen followed by rapid gas decompression. Fretting tests revealed that the wear of these compounds is significantly affected by the hydrogen environment compared to air, especially with NBR grades. After the aging experiment, the friction response of the HNBR grades is characterized by increased adhesion due to elastic deformation, leading to partial slip. Full article

(This article belongs to the Special Issue Tribology in Germany: Latest Research and Development)

► Show Figures

Figure 1

16 pages, 6145 KiB

Open AccessArticle

Properties of Laser-Alloyed Stainless Steel Coatings on the Surface of Gray Cast Iron Discs

by Shuwen Wang, Jiale Hao, Yu Zhou, Chunxing Gu and John Williams

Lubricants 2024, 12(7), 232; https://doi.org/10.3390/lubricants12070232 - 22 Jun 2024

Abstract

The influence of laser-alloyed stainless steel coatings on the properties of the surfaces of cast iron discs, such as friction-induced vibration and noise, friction coefficient, residual stress, hardness, and corrosion resistance, was investigated in this study. The experimental results show that after laser [...] Read more.

The influence of laser-alloyed stainless steel coatings on the properties of the surfaces of cast iron discs, such as friction-induced vibration and noise, friction coefficient, residual stress, hardness, and corrosion resistance, was investigated in this study. The experimental results show that after laser alloying, the surface hardness of the cast iron discs increased significantly. The residual stresses on the surfaces of the laser-alloyed discs changed from tensile to compressive residual stresses, while any compressive residual stresses increased by more than six times. Most of the laser-alloyed discs demonstrated better performance in friction-induced vibration and noise dam** and friction reduction. Metallographic observation and XRD (X-ray diffraction) analysis results show that the laser-alloyed layer is mainly a mixture of acicular martensite and dendritic material, while the phase composition of laser-treated discs is mainly martensitic, [Fe, Ni], Fe₃Si, Cr₂₃C₆, and austenite, which plays a significant role in the improvement of the properties of the laser-alloyed cast iron in physics, tribology and corrosion resistance. This research has significance for the laser surface treatment of various cast irons and steels, which is an increasingly important manufacturing technology in the vehicle friction brake industry. Full article

► Show Figures

Figure 1

20 pages, 14942 KiB

Open AccessArticle

Microstructural, Mechanical and Tribological Behaviors of Cu/LLDPE-Based Composite Coatings for Lightweight Applications

by Basma Ben Difallah, Ayda Bouaziz, Ana Horovistiz, Mohamed Kharrat, Maher Dammak, César Cardoso and António Pereira

Lubricants 2024, 12(7), 231; https://doi.org/10.3390/lubricants12070231 - 21 Jun 2024

Abstract

This research work focuses on the development and analysis of copper-filled linear low-density polyethylene (LLDPE) coatings deposited on LLDPE substrate via a thermocompression process. A dry mechanical mixing technique is employed to mix the copper–LLDPE powders. This relevant technology aims to develop new [...] Read more.

This research work focuses on the development and analysis of copper-filled linear low-density polyethylene (LLDPE) coatings deposited on LLDPE substrate via a thermocompression process. A dry mechanical mixing technique is employed to mix the copper–LLDPE powders. This relevant technology aims to develop new solid lubricating layered composite coatings without a negative environmental impact. Four different materials of the coatings are considered, i.e., LLDPE + 2 wt.% Cu, LLDPE + 6 wt.% Cu, LLDPE + 10 wt.% Cu and LLDPE + 20 wt.% Cu. The microstructural characterizations indicate a good degree of dispersion and adhesion between the continuous and dispersed phases at 20 wt.% Cu coatings. The mechanical properties of the pure polymer and the fully filled composite materials are investigated experimentally using tensile tests and Micro-Vickers hardness. The stiffness, hardness and mechanical strength of the composites are enhanced. Friction tests are also carried out via a linear reciprocating sliding tribometer. The incorporation of copper powder has a significant improvement on the friction and wear properties of the developed coatings. Higher copper powder loading provides a lower friction coefficient and wear volume loss. The best tribological performances are obtained with the LLDPE + 20 wt.% Cu coating. The wear mechanism of the LLDPE substrate is severe adhesive wear, and it becomes mild abrasive wear in case of the 20 wt.% Cu coating. Full article

► Show Figures

Figure 1

15 pages, 13938 KiB

Open AccessArticle

Effect of Harmful Bearing Currents on the Service Life of Rolling Bearings: From Experimental Investigations to a Predictive Model

by Volker Schneider, Marius Krewer, Gerhard Poll and Max Marian

Lubricants 2024, 12(7), 230; https://doi.org/10.3390/lubricants12070230 - 21 Jun 2024

Abstract

This study investigates the effects of harmful bearing currents on the service life of rolling bearings and introduces a model to predict service life as a function of surface roughness. Harmful bearing currents, resulting from electrical discharges, can cause significant surface damage, reducing [...] Read more.

This study investigates the effects of harmful bearing currents on the service life of rolling bearings and introduces a model to predict service life as a function of surface roughness. Harmful bearing currents, resulting from electrical discharges, can cause significant surface damage, reducing the operational lifespan of bearings. This study involves comprehensive experiments to quantify the extent of electrical stress caused by these currents. For this purpose, four series of tests with different electrical stress levels were carried out and the results of their service lives were compared with each other. Additionally, a novel model to correlate the service life of rolling bearings with varying degrees of surface roughness caused by electrical discharges was developed. The basis is the internationally recognized method of DIN ISO 281, which was extended in the context of this study. The findings show that the surface roughness continues to increase as the electrical load increases. In theory, this in turn leads to a deterioration in lubrication conditions and a reduction in service life. Full article

(This article belongs to the Special Issue Tribology in Germany: Latest Research and Development)

► Show Figures

Figure 1

18 pages, 7904 KiB

Open AccessArticle

A Graph-Data-Based Monitoring Method of Bearing Lubrication Using Multi-Sensor

by **nzhuo Zhang, Xuhua Zhang, Linbo Zhu, Chuang Gao, Bo Ning and Yongsheng Zhu

Lubricants 2024, 12(6), 229; https://doi.org/10.3390/lubricants12060229 - 20 Jun 2024

Abstract

Super-precision bearing lubrication condition is essential for equipment’s overall performance. This paper investigates a monitoring method of bearing lubrication using multi-sensors based on graph data. An experiment was designed and carried out, establishing a dataset including vibration, temperature, and acoustic emission signals. Graph [...] Read more.

Super-precision bearing lubrication condition is essential for equipment’s overall performance. This paper investigates a monitoring method of bearing lubrication using multi-sensors based on graph data. An experiment was designed and carried out, establishing a dataset including vibration, temperature, and acoustic emission signals. Graph data were constructed based on a priori knowledge and a graph attention network was employed to conduct a study on monitoring bearing lubrication abnormalities and discuss the influence of a missing sensor on the monitoring. The results show that the designed experiments can effectively respond to the degradation process of bearing lubrication, and the graph data constructed based on a priori knowledge show a good effect in the anomaly monitoring process. In addition, the multi-sensor plays a significant role in monitoring bearing lubrication. This work will be highly beneficial for future monitoring methods of bearing lubrication status. Full article

(This article belongs to the Special Issue New Conceptions in Bearing Lubrication and Temperature Monitoring)

► Show Figures

Figure 1

15 pages, 8783 KiB

Open AccessArticle

A Phenomenological Model for Estimating the Wear of Horizontally Straight Slurry Discharge Pipes: A Case Study

by **nggao Li, Yidong Guo, **ngchun Li, Hongzhi Liu, Yi Yang and Yingran Fang

Lubricants 2024, 12(6), 228; https://doi.org/10.3390/lubricants12060228 - 19 Jun 2024

Abstract

When a slurry TBM advances in pebble and rock strata, large rock particles are carried in pipelines out of a tunnel by moving slurry. To estimate the wear of horizontally straight slurry discharge pipes, a phenomenological model was proposed that was mainly based [...] Read more.

When a slurry TBM advances in pebble and rock strata, large rock particles are carried in pipelines out of a tunnel by moving slurry. To estimate the wear of horizontally straight slurry discharge pipes, a phenomenological model was proposed that was mainly based on knowledge gained by means of direct and indirect in situ observations. The proposed model applies an equation composed of three variables, namely, the wear rate (λ), the central angle (2α), and the excavated tunnel length (L), to estimate the wear distribution along a pipe’s internal surface. The results indicated that wear mainly occurred on the bottoms of pipes. In addition, linear relationships between the maximum pipe wear amount (δ_max) and the excavated tunnel length (L) were found for specific pipes and specified types of ground. The observed wear rates of different pipes in different types of ground had varied constants. The wear rates were higher for pipes in rock ground than for those in a pebble layer. For horizontally straight pipes, the observed wear rates were 0.0045 mm/m in a pebble layer and 0.0212 mm/m in rock ground. Lastly, to improve the proposed model, more field monitoring will be necessary to determine the pipe wear rates in different types of ground in the future. Full article

(This article belongs to the Special Issue Modeling and Characterization of Wear)

► Show Figures

Figure 1

12 pages, 7547 KiB

Open AccessArticle

Effect of CeO₂ Content on Microstructure and Wear Resistance of Laser-Cladded Ni-Based Composite Coating

by Bingqing Zhang, Wenqing Shi, Yiming Lin, Longwei Jiang, Lijun Wang and Kuanfang He

Lubricants 2024, 12(6), 227; https://doi.org/10.3390/lubricants12060227 - 19 Jun 2024

Abstract

In order to improve the wear resistance of 45 steel, in this study, WC/Ni60 composite coatings with different CeO₂ additions (0, 1, 2, and 3 wt%) were prepared on 45 steel by the laser cladding technique; the experimental analysis was carried out [...] Read more.

In order to improve the wear resistance of 45 steel, in this study, WC/Ni60 composite coatings with different CeO₂ additions (0, 1, 2, and 3 wt%) were prepared on 45 steel by the laser cladding technique; the experimental analysis was carried out by means of scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), a Vickers hardness tester, and a friction and wear tester. The results show that CeO₂ had little effect on the phase composition of the coatings; however, with the increase in CeO₂ content, the CeO₂ played a key role in refining the grains of the coating, thus reducing the generation of cracks. In addition, CeO₂ could effectively strengthen the internal structure of the coating and improve its microhardness and wear resistance. Particularly noteworthy is the observed reduction in both the friction coefficient and mass loss of the coating when the CeO₂ addition reached 2%. This suggests an enhancement in the tribological performance of the coating at this concentration. Full article

(This article belongs to the Topic Advanced Manufacturing and Surface Technology)

► Show Figures

Figure 1

17 pages, 3484 KiB

Open AccessArticle

Prediction of Lubrication Performances of Vegetable Oils by Genetic Functional Approximation Algorithm

by Jianfang Liu, Yaoyun Zhang, Sicheng Yang, Chenglingzi Yi, Ting Liu, Rongrong Zhang, Dan Jia, Shuai Peng and Qing Yang

Lubricants 2024, 12(6), 226; https://doi.org/10.3390/lubricants12060226 - 18 Jun 2024

Abstract

Vegetable oils, which are considered potential lubricants, are composed of different types and proportions of fatty acids. Because of their diverse types and varying compositions, they exhibit different lubrication performances. The genetic function approximation algorithm was used to model the quantitative structure–property relationship [...] Read more.

Vegetable oils, which are considered potential lubricants, are composed of different types and proportions of fatty acids. Because of their diverse types and varying compositions, they exhibit different lubrication performances. The genetic function approximation algorithm was used to model the quantitative structure–property relationship between fatty acid structure and the wear scar diameter and friction coefficients measured by four-ball friction and wear tests. Based on the models with adjusted R² greater than 0.9 and fatty acid compositions of vegetable oils, the wear scar diameter and friction coefficients of Xanthoceras sorbifolia bunge oil and Soybean oil as validation oil samples were predicted. The difference between the predicted and experimental values was small, indicating that the models could accurately predict the lubrication performances of vegetable oils. The lubrication performances of 14 kinds of vegetable oils were predicted by GFA-QSPR models, and the primary factors influencing their lubrication properties were studied by cluster analysis. The results show that the content of C18:1 has a positive effect on the lubrication performances of vegetable oils, while the content of C18:3 has a negative effect, and the length of the carbon chain of fatty acids significantly affects their lubrication properties. Full article

► Show Figures

Figure 1

30 pages, 11350 KiB

Open AccessReview

Fundamental Mechanisms Underlying the Effectiveness of Nanoparticle Additives to Lubricants: 25 Examples Linking Nano- to Macroscale Friction

by Jacqueline Krim and Alex I. Smirnov

Lubricants 2024, 12(6), 225; https://doi.org/10.3390/lubricants12060225 - 18 Jun 2024

Abstract

Studies of the fundamental origins of friction have undergone rapid acceleration in recent years by providing valuable information on the nanoscale mechanisms responsible for friction at the macroscopic level. Significant efforts have been directed at develo** composite nanofluids and nanoparticle additives to unlock [...] Read more.

Studies of the fundamental origins of friction have undergone rapid acceleration in recent years by providing valuable information on the nanoscale mechanisms responsible for friction at the macroscopic level. Significant efforts have been directed at develo** composite nanofluids and nanoparticle additives to unlock new tribological properties unattainable by traditional lubricants. The studies are now further evolving by develo** methods to achieve active control over nano- and/or mesoscale friction through the application of magnetic and electric fields external to the contact. These methods constitute an area of rapidly growing interest, and they also illuminate how the performance of conventional lubricants could be enhanced through the synergistic addition of nanoparticles (NPs). This mini review highlights 25 publications that collectively reveal significant progress, as well as important outstanding challenges, to the fundamental understanding of how the addition of NPs impacts lubricant performance. The first two topics focus on how Quartz Crystal Microbalance (QCM) nanotribological response to solid contacts can be linked to macroscale friction coefficients in the boundary lubrication regime and how QCM response upon immersion into a liquid is linked to macroscale lubricity in the mixed and hydrodynamic regimes. The third and fourth topics highlight the pivotal role of nanoparticle charge and surface treatments, while also indicating that the rolling of nanoparticles is ineffective and/or detrimental. The fifth topic focuses on applications that demonstrate the tuning of friction by varying nanoparticle electric charge and/or an external electric potential. The highlighted literature was selected to demonstrate a range of experimental and theoretical research, to provide direct connections between the nanoscale and macroscale tribological attributes, and to emphasize environmentally friendly lubricating materials such as water-based nanofluids. Full article

(This article belongs to the Special Issue Eco-Friendly Lubricating Additives)

► Show Figures

Figure 1

20 pages, 6217 KiB

Open AccessArticle

Research on Design and Optimization of Micro-Hole Aerostatic Bearing in Vacuum Environment

by Guozhen Fan, Youhua Li, Yuehua Li, Libin Zang, Ming Zhao, Zhanxin Li, Hechun Yu, Jialiang Xu, Hongfei Liang, Guoqing Zhang and Weijie Hou

Lubricants 2024, 12(6), 224; https://doi.org/10.3390/lubricants12060224 - 17 Jun 2024

Abstract

Micro-hole aerostatic bearings are important components in micro-low-gravity simulation of aerospace equipment, and the accuracy of micro-low-gravity simulation tests is affected by them. In order to eliminate the influence of air resistance on the attitude control accuracy of remote sensing satellites and achieve [...] Read more.

Micro-hole aerostatic bearings are important components in micro-low-gravity simulation of aerospace equipment, and the accuracy of micro-low-gravity simulation tests is affected by them. In order to eliminate the influence of air resistance on the attitude control accuracy of remote sensing satellites and achieve high fidelity of micro-low-gravity simulation tests, in this study, a design and parameter optimization method was proposed for micro-hole aerostatic bearings for a vacuum environment. Firstly, the theoretical analysis was conducted to investigate the impact of various bearing parameters and external conditions on the bearing load capacity and mass flow. Subsequently, a function model describing the variation in bearing load capacity and mass flow with bearing parameters was obtained utilizing a BP neural network. The parameters of aerostatic bearings in a vacuum environment were optimized using the non-dominated sorting genetic algorithm (NSGA-II) with the objectives of maximizing the load capacity and minimizing the mass flow. Subsequently, experimental tests were conducted on the optimized bearings in both atmospheric and vacuum conditions to evaluate their load capacity and mass flow. The results show that in a vacuum environment, the load capacity and mass flow of aerostatic bearings are increased compared to those in standard atmospheric conditions. Furthermore, it has been determined that the optimal solution for the bearing’s load capacity and mass flow occurs when the bearing has an orifice aperture of 0.1 mm, 36 holes, and an orifice distribution diameter of 38.83 mm. The corresponding load capacity and mass flow are 460.644 N and 11.816 L/min, respectively. The experimental and simulated errors are within 10%; thus, the accuracy of the simulation is verified. Full article

(This article belongs to the Special Issue Tribological Characteristics of Bearing System, 2nd Edition)

► Show Figures

Figure 1

14 pages, 5569 KiB

Open AccessArticle

Thermal Stability and High-Temperature Super Low Friction of γ-Fe₂O₃@SiO₂ Nanocomposite Coatings on Steel

by Qunfeng Zeng

Lubricants 2024, 12(6), 223; https://doi.org/10.3390/lubricants12060223 - 17 Jun 2024

Abstract

The thermal stability of the γ-Fe₂O₃@SiO₂ nanocomposites and super low friction of the γ-Fe₂O₃@SiO₂ nanocomposite coatings in ambient air at high temperature are investigated in this paper. X-ray diffraction, scanning electron microcopy, transmission [...] Read more.

The thermal stability of the γ-Fe₂O₃@SiO₂ nanocomposites and super low friction of the γ-Fe₂O₃@SiO₂ nanocomposite coatings in ambient air at high temperature are investigated in this paper. X-ray diffraction, scanning electron microcopy, transmission scanning electron microcopy, high-temperature tribometer, thermogravimetric analysis and differential scanning calorimetry were used to investigate the microstructure, surface morphology and high-temperature tribological properties of the γ-Fe₂O₃@SiO₂ nanocomposite coatings, respectively. The results show that the γ-Fe₂O₃@SiO₂ nanocomposite with the core–shell structure has excellent thermal stability because the SiO₂ shell inhibits the phase transition of the γ-Fe₂O₃ phase to the α-Fe₂O₃ phase in the nanocomposites. The temperature of the phase transition in γ-Fe₂O₃ can be increased from 460 to 829 °C. The γ-Fe₂O₃@SiO₂ nanocomposite coatings exhibit super low friction (0.05) at 500 °C. A high-temperature super low friction mechanism is attributed to γ-Fe₂O₃ and the tribochemical reactions during sliding. Full article

(This article belongs to the Collection Rising Stars in Tribological Research)

► Show Figures

Figure 1

16 pages, 8162 KiB

Open AccessArticle

Wear Characterization of Cold-Sprayed HEA Coatings by Means of Active–Passive Thermography and Tribometer

by Raffaella Sesana, Luca Corsaro, Nazanin Sheibanian, Sedat Özbilen and Rocco Lupoi

Lubricants 2024, 12(6), 222; https://doi.org/10.3390/lubricants12060222 - 17 Jun 2024

Abstract

The aim of this work is to verify the applicability of thermography as a non-destructive technique to quantify the wear performance of several high-entropy alloy coatings. Thermal profiles obtained from passive and active thermography were analyzed and the results were correlated with the [...] Read more.

The aim of this work is to verify the applicability of thermography as a non-destructive technique to quantify the wear performance of several high-entropy alloy coatings. Thermal profiles obtained from passive and active thermography were analyzed and the results were correlated with the classical tribological approaches defined in standards. HEA coatings made of several chemical compositions (Al_xCoCrCuFeNi and MnCoCrCuFeNi) and realized by using different cold spray temperatures (650 °C, 750 °C, and 850 °C) were tested in a pin-on-disk configuration, with a dedicated pin developed for the wear tests. Then, the wear performances of each sample were analyzed with the hardness and wear parameter results. The thermal profiles of passive and active thermography allowed a complete characterization of the wear resistance and performance analysis of the coatings analyzed. The results are also compared with those presented in the literature. Full article

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

► Show Figures

Figure 1

17 pages, 3036 KiB

Open AccessArticle

Heat and Mass Transformation of Casson Hybrid Nanofluid (MoS₂ + ZnO) Based on Engine Oil over a Stretched Wall with Chemical Reaction and Thermo-Diffusion Effect

by Shreedevi Madiwal and Neminath B. Naduvinamani

Lubricants 2024, 12(6), 221; https://doi.org/10.3390/lubricants12060221 - 16 Jun 2024

Abstract

This study investigates the potential of a hybrid nanofluid composed of MoS₂ and ZnO nanoparticles dispersed in engine oil, aiming to enhance the properties of a lubricant’s chemical reaction with the Soret effect on a stretching sheet under the influence of an [...] Read more.

This study investigates the potential of a hybrid nanofluid composed of MoS₂ and ZnO nanoparticles dispersed in engine oil, aiming to enhance the properties of a lubricant’s chemical reaction with the Soret effect on a stretching sheet under the influence of an applied magnetic field. With the growing demand for efficient lubrication systems in various industrial applications, including automotive engines, the development of novel nanofluid-based lubricants presents a promising avenue for improving engine performance and longevity. However, the synergistic effects of hybrid nanoparticles in engine oil remain relatively unexplored. The present research addresses this gap by examining the thermal conductivity, viscosity, and wear resistance of the hybrid nanofluid, shedding light on its potential as an advanced lubrication solution. Overall, the objectives of studying the hybrid nanolubricant MoS₂ + ZnO with engine oil aim to advance the development of more efficient and durable lubrication solutions for automotive engines, contributing to improved reliability, fuel efficiency, and environmental sustainability. In the present study, the heat and mass transformation of a Casson hybrid nanofluid (MoS₂ + ZnO) based on engine oil over a stretched wall with chemical reaction and thermo-diffusion effect is analyzed. The governing nonlinear partial differential equations are simplified as ordinary differential equations (ODEs) by utilizing the relevant similarity variables. The MATLAB Bvp4c technique is used to solve the obtained linear ODE equations. The results are presented through graphs and tables for various parameters, namely, M, Q, β, Pr, Ec, Sc, Sr, Kp, Kr, and

ϕ_{2} *

(hybrid nanolubricant parameters) and various state variables. A comparative survey of all the graphs is presented for the nanofluid (MoS₂/engine oil) and the hybrid nanofluid (MoS₂ + ZnO/engine oil). The results reveal that the velocity profile diminished against the values of M, Kp, and β, and the temperature profile rises with Ec and Q, whereas Pr decreases. The concentration profile is incremented (decremented) with the value of Sr (Sc and Kr). A comparison of the nanofluid and hybrid nanofluid suggests that the velocity f′ (η) becomes slower with the augmentation of

ϕ_{2} *

whereas the temperature increases when

ϕ_{2} *

= 0.6 become slower. Full article

► Show Figures

Figure 1

11 pages, 2893 KiB

Open AccessArticle

Driving Water through Sub-2-Nanometer Carbon Nanotubes

by Jian Liu and Wei Cao

Lubricants 2024, 12(6), 220; https://doi.org/10.3390/lubricants12060220 - 16 Jun 2024

Abstract

The ultra-low friction observed between water and carbon nanotubes has been extensively reported recently. In this study, we delve into the factors influencing the liquid–solid friction, including surface properties such as surface wettability and roughness of carbon nanotubes, as well as the driving [...] Read more.

The ultra-low friction observed between water and carbon nanotubes has been extensively reported recently. In this study, we delve into the factors influencing the liquid–solid friction, including surface properties such as surface wettability and roughness of carbon nanotubes, as well as the driving forces involving temperature gradient and pressure drop. Utilizing non-equilibrium molecular dynamics simulations on carbon nanotube models with a diameter of ~1 nm, we observe a significant increase in water flux within a specific range of wettability, independent of roughness. This range is expected to shift to smaller values with increased pressure drop and temperature gradient. Both the mechanical transport coefficient and the thermo-osmosis coefficient exhibit a negative correlation with wettability, and roughness further decreases these coefficients. Through this work, we provide insights into the effects of surface properties on fluid transport through nanopores, contributing valuable information for the optimization of high-performance membrane processes. Full article

► Show Figures

Figure 1

15 pages, 18401 KiB

Open AccessArticle

Laser-Induced Graphene/h-BN Laminated Structure to Enhance the Self-Lubricating Property of Si₃N₄ Composite Ceramic

by Wei Li, **zhi Dong, Dalong Xu, Yifan Dong, Sikandar Iqbal, **gwei Li, Ting Luo and Bingqiang Cao

Lubricants 2024, 12(6), 219; https://doi.org/10.3390/lubricants12060219 - 15 Jun 2024

Abstract

Incorporating graphene as ceramic additives can significantly enhance both the toughness and self-lubricating characteristics of ceramic matrices. However, due to the difficult dispersion and easy agglomeration of graphene, the preparation process of composite ceramics still faces many problems. In this study, a laminated [...] Read more.

Incorporating graphene as ceramic additives can significantly enhance both the toughness and self-lubricating characteristics of ceramic matrices. However, due to the difficult dispersion and easy agglomeration of graphene, the preparation process of composite ceramics still faces many problems. In this study, a laminated laser-induced reduced graphene oxide/hexagonal boron nitride (L-rGO/h-BN) was introduced as an additive into a silicon nitride matrix, then a silicon nitride/reduced graphene oxide/hexagonal boron nitride (Si₃N₄/L-rGO/h-BN) ceramic composite was successfully synthesized using Spark Plasma Sintering technology. This approach led to enhancements in both the mechanical and self-lubricating properties of silicon nitride ceramics. This is due to the good monodispersity of the incorporating graphene in the silicon nitride matrix. The flexural strength and fracture toughness of the ceramic composite experienced notable increases of 30.4% and 34.4%, respectively. Tribological experiments demonstrate a significant enhancement in the self-lubricating performance of ceramic composites upon the incorporation of L-rGO/h-BN. The coefficient of friction and wear spot diameter experienced reductions of 26.6% and 21%, respectively. These improvements extend the potential industrial applications of Si₃N₄/L-rGO/h-BN ceramic composites. Throughout the friction process, the evenly exposed rGO and h-BN demonstrate an effective self-lubricating effect on the wear surface. This research paves the way for a novel approach to fabricating high-performance self-lubricating structural ceramics. Full article

(This article belongs to the Special Issue 2D Materials in Tribology)

► Show Figures

Figure 1

Journal Description

Lubricants

Latest Articles

Journal Menu

Journal Browser

Highly Accessed Articles

Latest Books

E-Mail Alert

News

Topics

Conferences

Special Issues

Topical Collections

Further Information

Guidelines

MDPI Initiatives

Follow MDPI