Lubricants

22 pages, 5743 KiB

Open AccessArticle

Influence of N₂ Flow Rate on Mechanical and Tribological Properties of TAlN Coatings Deposited on 300M Substrate and Nitrocarburized Layer

by Shiwei Zuo, Qinghua Li, Zhehang Fan, Xiaoyong Tao, Xiangjie Wang, Hui Xie, Qianqian Shen, Tianshi Jia and Hongyan Wu

Lubricants 2025, 13(6), 254; https://doi.org/10.3390/lubricants13060254 - 6 Jun 2025

Abstract

This study systematically investigates the influence of nitrogen (N₂) flow rates and nitrocarburized (PNC) interlayers on the mechanical and tribological properties of TiAlN coatings deposited on 300M steel substrates via magnetron sputtering. The coatings were fabricated under three N₂ flow [...] Read more.

This study systematically investigates the influence of nitrogen (N₂) flow rates and nitrocarburized (PNC) interlayers on the mechanical and tribological properties of TiAlN coatings deposited on 300M steel substrates via magnetron sputtering. The coatings were fabricated under three N₂ flow rates (30, 90, and 150 sccm), with microstructure evolution, elemental composition, and phase transitions analyzed using SEM, EDS, AFM, and XRD. The results indicate that the PNC/TiAlN composite coatings exhibited superior interfacial adhesion and load-bearing capacity compared to standalone TiAlN coatings, attributed to the graded hardness transition and stress distribution optimization at the coating–substrate interface. Nanoindentation tests revealed enhanced hardness and elastic modulus in PNC/TiAlN systems under high N₂ flow conditions. Tribological evaluations demonstrated that the composite coatings achieved lower specific wear rates (25.23 × 10⁻⁸ mm³·N⁻¹·m⁻¹) under 7.3 N, outperforming monolithic TiAlN coatings by mitigating abrasive wear and delamination. The synergy between N₂ flow modulation and nitrocarburizing pretreatment effectively optimized coating–substrate compatibility, establishing a robust framework for designing wear-resistant TiAlN coatings in extreme service environments. This work provides critical insights into tailoring PVD coating architectures for aerospace and heavy-load applications. Full article

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26 pages, 3344 KiB

Open AccessReview

A Holistic Review of Surface Texturing in Sheet Metal Forming: From Sheet Rolling to Final Forming

by Paulo L. Monteiro, Jr. and Henara L. Costa

Lubricants 2025, 13(6), 253; https://doi.org/10.3390/lubricants13060253 - 5 Jun 2025

Abstract

Skin-pass cold rolling is a crucial step in sheet metal production, modifying the sheet surface topography, ensuring thickness uniformity, and enhancing tribological performance. A key factor in this process is the surface texturing of work rolls, which, when transferred to the rolled sheet, [...] Read more.

Skin-pass cold rolling is a crucial step in sheet metal production, modifying the sheet surface topography, ensuring thickness uniformity, and enhancing tribological performance. A key factor in this process is the surface texturing of work rolls, which, when transferred to the rolled sheet, directly affects lubrication distribution and formability in subsequent stamping operations. Properly textured sheets promote lubricant retention, reducing friction and wear, while roll wear can compromise texture transfer, leading to defects in the final product. This review presents a holistic view of surface texturing from the roll topography to the final product. First, it explores different texturing methods for work rolls, analyzing their efficiency, durability, and impact on texture transfer. Then, alternative texturing techniques and coatings are discussed as strategies to mitigate roll wear. By assessing the relationship between roll texturing and sheet drawability, this study provides insights to improve industrial processes, enhance product quality, and promote more sustainable manufacturing solutions. Full article

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16 pages, 5250 KiB

Open AccessArticle

Hybrid Additives of 1,3-Diketone Fluid and Nanocopper Particles Applied in Marine Engine Oil

by Yuwen Xu, Yan Yang, Li Zhong, Xingyuan Jing, Xiaoyu Yin, Tao Xia, Jingsi Wang, Tobias Amann and Ke Li

Lubricants 2025, 13(6), 252; https://doi.org/10.3390/lubricants13060252 - 4 Jun 2025

Abstract

The lubrication performance of the cylinder liner–piston ring (CLPR) is crucial for the energy efficiency and operating reliability of marine diesel engines. To enhance the boundary lubrication of marine engine oil, a 1,3-diketone fluid HPTD (1-(4-hexylphenyl) tridecane-1,3-dione, HPTD) was introduced as an ash-free [...] Read more.

The lubrication performance of the cylinder liner–piston ring (CLPR) is crucial for the energy efficiency and operating reliability of marine diesel engines. To enhance the boundary lubrication of marine engine oil, a 1,3-diketone fluid HPTD (1-(4-hexylphenyl) tridecane-1,3-dione, HPTD) was introduced as an ash-free friction modifier. Besides that, octadecylamine-functionalized nanocopper particles (ODA-Cu) were also added to the marine oil to improve its anti-wear behavior. Through cylinder-on-disk friction tests, the appropriate contents of HPTD and ODA-Cu were determined, which then formed hybrid additives and modified the engine oil. The tribological performance of the modified oil was analyzed under various normal loads, reciprocating frequencies, and testing temperatures. Based on the synergy of the tribochemical reaction of HPTD and the mending effect of ODA-Cu on the sliding surface, the modified oil not only had lower sulfated ash content but also exhibited superior lubrication performance (i.e., reduced coefficient of friction by 15%, smaller wear track by 43%, and higher maximum non-seizure load by 11%) than the pristine engine oil. The results of this study would be helpful for the design of novel hybrid eco-friendly additives for marine engine oil. Full article

(This article belongs to the Special Issue Marine Tribology)

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16 pages, 9251 KiB

Open AccessArticle

Topology Optimization of Textured Journal Bearings

by Hanqian Kong, Chunxing Gu, Di Zhang and Lanfei Wu

Lubricants 2025, 13(6), 251; https://doi.org/10.3390/lubricants13060251 - 4 Jun 2025

Abstract

The journal bearing, a critical component of the rotating shaft, is influenced by various factors including friction, wear, and heat effects under actual working conditions. This study developed an advanced approach for optimizing the performance of journal bearings with surface texture. This approach [...] Read more.

The journal bearing, a critical component of the rotating shaft, is influenced by various factors including friction, wear, and heat effects under actual working conditions. This study developed an advanced approach for optimizing the performance of journal bearings with surface texture. This approach allows for finding the influences of bearing parameters such as journal clearance, rotational speed, and shaft eccentricity ratio on the optimization results. The results show that whether under smaller journal clearances, higher rotational speeds, or larger shaft eccentricity ratios, the formation of intricate bifurcation patterns and enhanced branching in surface textures is consistently promoted. The optimized texture’s shape leads to a reduction in texture depth while significantly improving both the load-carrying capacity (LCC) and oil film thickness. This approach precisely determines the spatial and depth characteristics of texture elements, ensuring their optimal placement and geometry, and offers valuable insights and directions for future research. Full article

(This article belongs to the Special Issue Tribological Characteristics of Bearing System, 3rd Edition)

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24 pages, 4367 KiB

Open AccessArticle

Thermoplastic Labyrinth Seals Under Rub Impact: Deformation Leakage Mechanisms and High Efficiency Optimization

by Fei Ma, Zhengze Yang, Yue Liu, Shuangfu Suo and Peng Su

Lubricants 2025, 13(6), 250; https://doi.org/10.3390/lubricants13060250 - 4 Jun 2025

Abstract

Labyrinth seals, extensively used in aerospace and turbomachinery as non-contact sealing devices, undergo accelerated wear and enhanced leakage due to repeated rub-impact between rotating shafts and sealing rings. To address the problem of increased leakage under rub-impact conditions, this research integrates experimental and [...] Read more.

Labyrinth seals, extensively used in aerospace and turbomachinery as non-contact sealing devices, undergo accelerated wear and enhanced leakage due to repeated rub-impact between rotating shafts and sealing rings. To address the problem of increased leakage under rub-impact conditions, this research integrates experimental and numerical methods to investigate the deformation mechanisms and leakage characteristics of thermoplastic labyrinth seals. A custom designed rub-impact test rig was constructed to measure dynamic forces and validate finite element analysis (FEA) models with an error of 5.1% in predicting tooth height under mild interference (0.25 mm). Computational fluid dynamics (CFD) simulations further demonstrated that thermoplastic materials, such as PAI and PEEK, displayed superior resilience (with rebound ratios of 57% and 70.3%, respectively). Their post-impact clearances were 4.8–18.3% smaller than those of PTFE and F500. Leakage rates were predominantly correlated with interference, causing a substantial increase compared to the original state; at 0.25 mm interference (reverse flow), increases ranged from 151% (PAI) to 217% (PTFE), highlighting material-dependent performance degradation. Meanwhile, tooth orientation modulated leakage by 0.5–3% through the vena contracta effect. Based on these insights, two optimized inclined-tooth geometries were designed, reducing leakage by 28.2% (Opt1) and 28.1% (Opt2) under rub-impact. These findings contribute to the development of high-performance labyrinth seals suitable for extreme operational environments. Full article

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

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42 pages, 13512 KiB

Open AccessArticle

Dynamic Characteristic Analysis of Angular Contact Ball Bearings with Two-Piece Inner Rings in Aero-Engine Main Shafts Under Unsteady-State Conditions

by Haisheng Yang, Qiang Liu and Si’er Deng

Lubricants 2025, 13(6), 249; https://doi.org/10.3390/lubricants13060249 - 30 May 2025

Abstract

The dynamic interactions among the internal components of aero-engine main shaft bearings under unsteady-state conditions are intricate, involving clearance collisions, contact, friction, and lubrication. The dynamic characteristics of bearings significantly influence the performance and stability of mechanical systems. This study establishes a rigid–flexible [...] Read more.

The dynamic interactions among the internal components of aero-engine main shaft bearings under unsteady-state conditions are intricate, involving clearance collisions, contact, friction, and lubrication. The dynamic characteristics of bearings significantly influence the performance and stability of mechanical systems. This study establishes a rigid–flexible coupling dynamic model for angular contact ball bearings with two-piece inner rings based on Hertz contact theory and lubrication theory. It systematically analyzes the dynamic characteristics of bearings under the coupling effects of acceleration, deceleration, and impact load. This study explores the influence of various loads, bearing speeds, and groove curvature radius coefficients on the dynamic characteristics of bearings. The findings indicate that the uniform speed phase of a bearing is highly responsive to impact load, followed by the deceleration phase, while the acceleration phase shows lower sensitivity to impact load. The groove curvature radius coefficient significantly affects the contact stress between the ball and its corresponding raceway, with contact stress increasing as the groove curvature radius coefficient rises. As the axial load decreases and the radial load, bearing speed, and groove curvature radius coefficient increase, there is a rise in pocket force, guiding force, and maximum equivalent stress of the flexible cage. Impact load leads to short-term intense fluctuations in the thickness of the bearing oil film, which can be alleviated by an increase in axial load. The oil film thickness firstly increases and then decreases with respect to the groove curvature radius coefficient. Furthermore, variations in bearing speed notably influence the thickness of the bearing oil film. This study analyzes the dynamic characteristics of bearings under the coupling effects of acceleration, deceleration, and impact load, offering insights for the design and optimization of angular contact ball bearings with two-piece inner rings. Full article

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21 pages, 669 KiB

Open AccessArticle

On the Non-Dimensional Modelling of Friction Hysteresis of Conformal Rough Contacts

by Kristof Driesen, Sylvie Castagne, Bert Lauwers and Dieter Fauconnier

Lubricants 2025, 13(6), 248; https://doi.org/10.3390/lubricants13060248 - 30 May 2025

Abstract

Friction hysteresis, ingaphenomenon observed when a sliding contact is subjected to an oscillatory motion has significant implications in fields such as tribology and robotics. Understanding and quantifying friction hysteresis is essential for improving the performance and efficiency of many sliding contacts. In this [...] Read more.

Friction hysteresis, ingaphenomenon observed when a sliding contact is subjected to an oscillatory motion has significant implications in fields such as tribology and robotics. Understanding and quantifying friction hysteresis is essential for improving the performance and efficiency of many sliding contacts. In this paper, we introduce six non-dimensional groups to characterize and study friction hysteresis behaviour for rough conformal sliding contacts. The proposed non-dimensional groups are specifically designed to capture the essential features of friction hysteresis loops encountered based upon previous work of present authors. The non-dimensional groups are derived from a mixed friction model composed of the transient Reynolds equation, a statistical mixed friction contact model, and the load balance. The non-dimensional groups capture physical parameters that influence friction behaviour, including normal load, sliding speed, viscosity, density, and surface roughness. By expressing these parameters in non-dimensional form, the proposed groups provide a concise and generalizable framework for analysing friction hysteresis across different systems and scales. To demonstrate the effectiveness of the non-dimensional groups, we establish a comprehensive relationship between the proposed groups and typical friction hysteresis loops encountered. Through numerical simulations, we find relationships that govern the transition between different hysteresis loop shapes and sizes. This knowledge can inform the design and optimization of systems where friction hysteresis plays a crucial role. Full article

(This article belongs to the Special Issue Advanced Computational Studies in Frictional Contact)

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25 pages, 6613 KiB

Open AccessArticle

Microstructure, Mechanical Strength, and Tribological Behavior of B₄C/WS₂-Hybrid-Reinforced B319 Aluminum Matrix Composites

by Ufuk Tasci

Lubricants 2025, 13(6), 247; https://doi.org/10.3390/lubricants13060247 - 29 May 2025

Abstract

Hybrid B319 aluminum matrix composites reinforced with 10 wt% B₄C and varying WS₂ contents were fabricated to improve mechanical and tribological performance. The composite containing 2 wt% WS₂ showed the best overall results, with a 29% increase in microhardness [...] Read more.

Hybrid B319 aluminum matrix composites reinforced with 10 wt% B₄C and varying WS₂ contents were fabricated to improve mechanical and tribological performance. The composite containing 2 wt% WS₂ showed the best overall results, with a 29% increase in microhardness (104.3 HV) and a 20% improvement in transverse rupture strength (196.3 MPa) compared to unreinforced B319. Additionally, the friction coefficient dropped by 64% (from 0.497 to 0.178), and the specific wear rate was reduced to 4.34 × 10⁻⁶ mm³/N·m. Microstructural analyses confirmed homogeneous reinforcement distribution and adequate interfacial bonding. These enhancements are attributed to the dual action of B4C-induced strengthening and WS₂-mediated tribo-film formation, offering a promising solution for lightweight, wear-resistant components in engineering applications. 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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Graphical abstract

26 pages, 7153 KiB

Open AccessArticle

Dynamic Precision and Reliability of Multi-Link Linkages with Translational Pair Clearance

by Quanzhi Zuo, Mingyang Cai, Yuyang Lian, Jianuo Zhu and Shuai Jiang

Lubricants 2025, 13(6), 246; https://doi.org/10.3390/lubricants13060246 - 29 May 2025

Abstract

This study investigates the dynamic behavior and reliability of planar multi-link linkages with clearance in translational pairs. Using the Lagrange multiplier method, a dynamic model that accounts for clearance effects is developed. Furthermore, a reliability model is established by combining the first-order second-moment [...] Read more.

This study investigates the dynamic behavior and reliability of planar multi-link linkages with clearance in translational pairs. Using the Lagrange multiplier method, a dynamic model that accounts for clearance effects is developed. Furthermore, a reliability model is established by combining the first-order second-moment method with the stress-strength interference theory. Numerical simulations were performed to evaluate the impact of varying clearance sizes and driving speeds on motion errors and system reliability. This study also explores the nonlinear dynamics of the end-effector. The results indicate that increased clearance and higher driving speeds lead to certain changes in motion errors and operational reliability. Phase diagrams and Poincaré maps reveal directional differences in dynamic stability: chaotic motion along the X-direction and periodic oscillations along the Y-direction. These findings provide valuable insights for optimizing mechanism design and enhancing operational reliability. Full article

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14 pages, 4846 KiB

Open AccessArticle

Study of Corrosion, Power Consumption, and Wear Characteristics of Herringbone-Grooved Fan Bearings in High-Temperature and High-Humidity Environments

by Jim-Chwen Yeh, Yu-Chang Lee, Chun-Hsiang Huang, Ming-Yuan Li and Chin-Chung Wei

Lubricants 2025, 13(6), 245; https://doi.org/10.3390/lubricants13060245 - 28 May 2025

Abstract

Fans are essential electronic components for heat dissipation in electronic systems, with fan bearings being critical parts that determine fan performance and lifespan. This paper investigates the corrosion, wear, power consumption, temperature, and vibration characteristics of a newly designed and manufactured powder metallurgy [...] Read more.

Fans are essential electronic components for heat dissipation in electronic systems, with fan bearings being critical parts that determine fan performance and lifespan. This paper investigates the corrosion, wear, power consumption, temperature, and vibration characteristics of a newly designed and manufactured powder metallurgy bearing with herringbone oil grooves for fans under high-humidity and high-temperature conditions. Corrosion experiments on iron–copper powder metallurgy bearings show that a higher environmental temperature and humidity result in greater corrosion current and reduced corrosion resistance. Bearings operated under high humidity (85% RH) and a high temperature (80 °C) for 0, 3, and 8 days, respectively, revealed that wear and corrosion occur simultaneously. The longer the operating time, the more significant the wear and corrosion. After 3 and 8 days, the lubricating oil flow in the oil grooves decreased by 9.8% and 51.5%, respectively. When bearings subjected to varying degrees of corrosion were tested under the same standard operating conditions, it was found that the bearings corroded for 3 and 8 days, resulting in a significant increase in the number of wear debris particles, higher RMS vibration values, and a power consumption increase of 6.9% and 7.8%, respectively. The percentage of iron elements on the surface gradually decreased, with the copper elements being the primary wear particles during the wear process. However, due to the increased clearance between the rotating shaft and the bearing caused by wear, the fan temperature slightly decreased with increased surface wear. Full article

(This article belongs to the Special Issue Recent Advances in Tribological Properties of Machine Tools)

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18 pages, 7950 KiB

Open AccessArticle

Combined Effects of DLC Coating and Surface Texturing on Seizure and Friction in Reciprocating Sliding

by Slawomir Wos, Waldemar Koszela, Andrzej Dzierwa and Pawel Pawlus

Lubricants 2025, 13(6), 244; https://doi.org/10.3390/lubricants13060244 - 28 May 2025

Abstract

Surface texturing is designed to improve the functional properties of machine elements by generating dimples on the surface contacted. Friction and wear resistance can also be improved by creating diamond-like carbon (DLC) coatings. These two techniques were combined to extend the lifetime of [...] Read more.

Surface texturing is designed to improve the functional properties of machine elements by generating dimples on the surface contacted. Friction and wear resistance can also be improved by creating diamond-like carbon (DLC) coatings. These two techniques were combined to extend the lifetime of the elements and minimise friction in reciprocating conformal sliding contact. This work is functionally important for assemblies operating under high normal loads. Experiments were carried out in initially lubricated reciprocating sliding contact using an Optimol SRV 5 tribotester in the flat-on-flat configuration. The disc samples were untextured, laser textured, and DLC-coated untextured and textured. The combination of DLC coating and surface texturing caused an enhancement of the tribological performance of the sliding pair compared to that of untextured discs with and without DLC coating and textured discs without DLC coating. The DLC coating of the untextured disc caused a growth in the lifetime of a friction pair by a factor of 2.4. Seizure resistance also increased due to surface texturing of the steel disc for pit area ratios of 9 and 13%. Combining surface texturing with pit area ratios of 3 and 9% and DLC coating led to a decrease in the coefficients of friction of sliding pairs compared to only textured and coated discs. The DLC coating caused a decrease in the wear of the disc sample and reduction in wear levels of the counter samples in comparison to those of textured discs without DLC coatings. Full article

(This article belongs to the Special Issue Tribology of Textured Surfaces)

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28 pages, 11569 KiB

Open AccessArticle

Optimization of Micro-Texture Parameters for Machine Tool Guide Rail Combination Based on Response Surface Methodology and Research on Its Anti-Friction and Lubrication Performance

by Youzheng Cui, Bingyang Yan, Minli Zheng, Haijing Mu, Chengxin Liu, Dongyang Wang, Xinmiao Li, Qingwei Li, Hui Jiang, Fengjuan Wang and Qingming Hu

Lubricants 2025, 13(6), 243; https://doi.org/10.3390/lubricants13060243 - 27 May 2025

Abstract

In the process of heavy-duty cutting, the reciprocating motion of the sliding guide pair surface is prone to local wear, which seriously affects the overall machining accuracy and service life of the machine tool. This study proposes a biomimetic micro-texture design scheme combining [...] Read more.

In the process of heavy-duty cutting, the reciprocating motion of the sliding guide pair surface is prone to local wear, which seriously affects the overall machining accuracy and service life of the machine tool. This study proposes a biomimetic micro-texture design scheme combining elliptical grooves and shell-shaped grooves on the surface of carp as biomimetic prototypes to enhance the oil film bearing capacity, drag reduction, and wear resistance of guide rail pairs. Based on Fluent fluid simulation research, it has been shown that this texture has a better dynamic pressure lubrication effect. We used response surface methodology to optimize the texture design parameters and further verify the accuracy of the optimal parameters with the NSGA-II genetic algorithm. The results show that under lubricated conditions, the load-bearing pressure of the combined micro-textured guide rail pair increased by 53.79%, the friction coefficient decreased by 39.04%, and the temperature decreased by 15.83%. This texture can still significantly improve drag reduction and wear resistance in a low-oil state. Full article

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20 pages, 10062 KiB

Open AccessArticle

Experimental Study on Vibration Characteristics of Journal Bearing-Rotor System Under Base Roll and Pitch Motions

by Fangcheng Xu, Jiyu Wang, Kaidi Zhu, Guilong Wang, Jingwei Yi and Zhongliang Xie

Lubricants 2025, 13(6), 242; https://doi.org/10.3390/lubricants13060242 - 27 May 2025

Abstract

Currently, there is limited experimental research on the stability of journal bearing-rotor systems under base motion, and the influence of rocking motion on the stability of such systems remains unclear. This study develops an experimental test rig for a journal bearing-rotor system and [...] Read more.

Currently, there is limited experimental research on the stability of journal bearing-rotor systems under base motion, and the influence of rocking motion on the stability of such systems remains unclear. This study develops an experimental test rig for a journal bearing-rotor system and employs a six-degrees-of-freedom shaking table to apply complex alternating loads, with the aim of investigating the effects of rocking amplitude and frequency on the vibration characteristics of the shaft system. The experimental results show that, under the excitation of base roll and pitch motions, the critical speed of the sliding bearing-rotor system remains nearly unchanged, while the resonance amplitude increases significantly, and the instability speed occurs earlier. In addition, base rocking motion not only induces periodic and uniform changes in the vibration amplitude of the shaft system but also demonstrates a strong positive correlation between the amplitude of system vibration and the amplitude of base rocking. Full article

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16 pages, 4930 KiB

Open AccessArticle

Trade-Off for CFRP Quality Using High-Frequency Ultrasonic-Assisted Drilling Under Lubricant Absence

by Khaled Hamdy and Saood Ali

Lubricants 2025, 13(6), 241; https://doi.org/10.3390/lubricants13060241 - 26 May 2025

Abstract

Carbon fiber reinforced polymers (CFRPs) are significantly vital for industries. However, the drilling process of a CFRP is considered a challenge due to its nature, which causes delamination, fiber pull-out, peel-up, high friction, and a decrease in cutting tool life. Wet drilling is [...] Read more.

Carbon fiber reinforced polymers (CFRPs) are significantly vital for industries. However, the drilling process of a CFRP is considered a challenge due to its nature, which causes delamination, fiber pull-out, peel-up, high friction, and a decrease in cutting tool life. Wet drilling is necessary for minimizing defects, and lubricants are very costly. In the current work, ultrasonic-assisted drilling (UAD) with a longitudinal vibration of 39.7 kHz was applied to the drill bit in the feed direction, used for CFRPs, and compared with conventional drilling (CD). Low spindle speeds under 5000 rpm were applied with different feed rates. The morphology, delamination factor, and cutting forces were investigated through the specific input machining parameters for CD and UAD. SEM was applied to study the morphology of the hole entrance and exit as well as the burr heights of evacuated chips. UAD with 39.7 kHz succeeded in minimizing the surface roughness by 50% compared with the surface roughness resulting from CD and could drill high-precision holes for CFRPs with a trade-off concept, besides achieving near-zero delamination (K ≃ 1) in the absence of a lubricant, which is being extended for industrial application. Full article

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17 pages, 2429 KiB

Open AccessArticle

Experimental Investigation on Cutting Forces in Sustainable Hard Milling of Hardox 500 Steel Under Al₂O₃/MoS₂ Hybrid Nanofluid MQCL Environment

by Tran The Long

Lubricants 2025, 13(6), 240; https://doi.org/10.3390/lubricants13060240 - 26 May 2025

Abstract

Hardox 500 is a special low-alloy, martensitic steel possessing extraordinary wear resistance, high hardness, and high ductility; thus, it has been widely used in many industrial applications. Nevertheless, this type of steel has a low machinability and is grouped among the difficult-to-machine materials. [...] Read more.

Hardox 500 is a special low-alloy, martensitic steel possessing extraordinary wear resistance, high hardness, and high ductility; thus, it has been widely used in many industrial applications. Nevertheless, this type of steel has a low machinability and is grouped among the difficult-to-machine materials. Hence, this paper’s objective was to study its hard milling performance under minimum quantity cooling lubrication (MQCL) conditions using an Al₂O₃/MoS₂ hybrid nano cutting oil. The Box–Behnken response surface methodology was used to investigate the effects of the nanoparticle concentration (NC), cutting speed (v), and feed rate (f) on the total cutting force F and cutting force coefficient F_y/F_z. The obtained results indicate that the cutting efficiency of Hardox 500 steel was improved thanks to the enhancement in cooling lubrication from the MQCL using the Al₂O₃/MoS₂ hybrid nano cutting oil. The applicability of vegetable oil and coated carbide inserts is thus extended to the hard milling of difficult-to-cut materials. Moreover, the provision of the appropriate ranges and optimal set of investigated variables obtained in this paper will be useful guides for technologists and further studies. Concretely, NC = 0.5–0.7%, v = 110–115 m/min, and f = 0.08–0.10 mm/tooth are the optimal set for the total cutting force F, while NC = 0.5%, v = 138–140 m/min, and f = 0.08–0.09 mm/tooth are suggested for the cutting force coefficient F_y/F_z. Full article

(This article belongs to the Special Issue Recent Advances in Tribological Properties of Machine Tools)

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18 pages, 5787 KiB

Open AccessArticle

Use of Advanced Piston Ring Coatings on Agricultural Engines

by Xiaochao He, Bang Liu, Eduardo Tomanik, Grzegorz Koszalka and Anna Orlova

Lubricants 2025, 13(6), 239; https://doi.org/10.3390/lubricants13060239 - 26 May 2025

Abstract

The use of combustion engines on agricultural vehicles will persist much longer than on-road vehicles. Introducing new technologies in agricultural engines is crucial to mitigating emissions while accounting for customer cost-sensitivity, harsh operation conditions, and typically sub-optimal maintenance. This work describes the use [...] Read more.

The use of combustion engines on agricultural vehicles will persist much longer than on-road vehicles. Introducing new technologies in agricultural engines is crucial to mitigating emissions while accounting for customer cost-sensitivity, harsh operation conditions, and typically sub-optimal maintenance. This work describes the use of CrN and tetrahedral amorphous carbon (ta-C) DLC-coated rings in small agricultural diesel engines. Compared with the gas nitride rings, the CrN and the ta-C DLC coatings exhibited, respectively, 74% and 86% lower wear in rig tests. The DLC also presented a very low coefficient of friction and high resistance to scuffing. A similar wear trend was observed on durability engine tests, where the CrN top ring showed an 80% lower wear rate than the GNS used in a similar engine. Wear on the DLC oil ring was below the measurement capability. Liner radial wear was measured on the piston ring reversal points in four angular positions, and except for one position, was lower than 3 µm. At the end of the test, engine performance and emissions are nearly identical to those at the test’s start, demonstrating that the use of advanced tribological solutions can significantly contribute to emissions mitigation in agricultural engines. Full article

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

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15 pages, 5949 KiB

Open AccessArticle

The Influence of Graphite Orientation on the Current-Carrying Friction Performance of Copper–Graphite Composite Materials

by Zhenghai Yang, Wenbo Li, Yingjian Song, Xiaomeng Zheng and Yongzhen Zhang

Lubricants 2025, 13(6), 238; https://doi.org/10.3390/lubricants13060238 - 26 May 2025

Abstract

In response to the need to optimize the performance of copper–graphite current-carrying friction materials, spark plasma sintering (SPS) technology was used to prepare copper–graphite composite materials with different graphite orientations. A self-made current-carrying friction testing machine was used to study the effect of [...] Read more.

In response to the need to optimize the performance of copper–graphite current-carrying friction materials, spark plasma sintering (SPS) technology was used to prepare copper–graphite composite materials with different graphite orientations. A self-made current-carrying friction testing machine was used to study the effect of graphite orientation on the current-carrying friction performance of copper–graphite composites. The results showed that as the graphite orientation increased, the current-carrying friction performance of the copper–graphite composites initially improved and then deteriorated. The performance was optimal when the graphite orientation of the 7.5 wt% graphite–copper composite was 90°, primarily constrained by the wear rate. The main wear mechanism was furrowing, and graphite enrichment occurred on the worn surface, where the graphite content on the wear surface was higher than that in the bulk material. The degree of enrichment varied under different wear mechanisms. The graphite content near the entry region of the friction surface was significantly lower than that near the exit region. Full article

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22 pages, 7683 KiB

Open AccessArticle

Surface Characterization of Cylinder Liner–Piston Ring Friction Pairs Under Different Temperature and Load by Power Spectral Density Method

by Xiaori Liu, Xiaofei Cao, Xuan Ma and Menghan Li

Lubricants 2025, 13(6), 237; https://doi.org/10.3390/lubricants13060237 - 25 May 2025

Abstract

Piston ring–cylinder liner is one of the most important friction pairs in internal combustion engines. The surfaces of the piston ring and the cylinder liner are affected by high temperature and high pressure, and the influence mechanism of temperature and pressure on their [...] Read more.

Piston ring–cylinder liner is one of the most important friction pairs in internal combustion engines. The surfaces of the piston ring and the cylinder liner are affected by high temperature and high pressure, and the influence mechanism of temperature and pressure on their microscopic morphology parameters is yet to be revealed. In this paper, high temperature friction and wear experiments on the piston ring and cylinder liner are carried out to obtain the microscopic morphology of the cylinder liner and piston ring at different temperatures and pressures, and their changes under different temperatures and pressures are investigated by using two methods, namely, fractal dimension and three-dimensional surface roughness characterization. The results show that, as the temperature increases, the texture patterns on the cylinder liner’s friction surface become simpler, with the fractal dimension showing a decreasing trend while the roughness shows an increasing trend. Compared to the condition at 80 °C, the surface roughness (Sa) of the cylinder liner increased by approximately 58.43% at 190 °C, while that of the piston ring increased by about 96.5%. With increasing pressure, both the fractal dimension and the roughness of the friction surface first decrease and then increase. Full article

(This article belongs to the Special Issue Thermal Hydrodynamic Lubrication)

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17 pages, 3922 KiB

Open AccessArticle

Effect of Post-Aging on Laser-Boronized Surface of 18Ni-300 Maraging Steel with Hypoeutectic Structure

by Jelena Škamat, Olegas Černašėjus, Kęstutis Bučelis and Oleksandr Kapustynskyi

Lubricants 2025, 13(6), 236; https://doi.org/10.3390/lubricants13060236 - 25 May 2025

Abstract

Laser-boronized parts manufactured by a selective laser melting process from 18Ni to 300 maraging steel are investigated in this study. Two main issues are addressed, namely (i) the possibility to restore the hardness of the heat-affected zone (HAZ) formed during laser processing and [...] Read more.

Laser-boronized parts manufactured by a selective laser melting process from 18Ni to 300 maraging steel are investigated in this study. Two main issues are addressed, namely (i) the possibility to restore the hardness of the heat-affected zone (HAZ) formed during laser processing and (ii) the effect of re-aging on the hardness and wear resistance of the laser-boronized layer with a hypoeutectic structure. Optical microscopy, scanning electron microscopy, energy-dispersive spectroscopy, X-ray diffraction analysis, microhardness measurements, the “ball-on-plate” dry sliding test, and the two-body dry abrasive wear test were employed to answer the questions. The results confirmed that HAZ is formed with the dissolution of intermetallides formed before and undergo full (near the molten pool) or partial (at some distance from the molten pool) iron–base matrix recrystallization. The hardness of HAZ (350–550 HK0.05) has been restored after re-aging to the 550–600 HK0.05 level. Moreover, a certain positive effect of re-aging on the laser-boronized layer with a hardness of ~470–750 HK0.2 is established, associated with structural transformations induced by aging in the iron-based solid solution phase. The hardness increased by ~9–25%. The wear resistance of the hardest boronized samples (~750 HK0.2) under dry sliding and dry abrasive wear conditions was ~5.8 times and 3.7 times higher than that of the aged control sample, while re-aging provided further improvement of these characteristics. The presented results provide insights into the effectiveness of laser-boronized layers having a hypoeutectic structure in terms of increasing the wear resistance of maraging steel. Full article

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