Search Results (123)

Poly-ether-ether-ketone (PEEK) is widely used in dynamic sealing applications due to its excellent properties. However, its tribological performance as a sealing material still has limitations, as its relatively high friction coefficient may lead to increased wear of sealing components, affecting sealing effectiveness and service life. To optimize its lubrication performance, this study employs surface modification techniques to synthesize a thin polyimide (PI) film on the surface of PEEK. When paired with bearing steel, this modification reduces the friction coefficient and enhances the anti-wear performance of sealing components. The tribological properties of a friction pair composed of GCr15 steel and PI-modified PEEK were systematically investigated using a nematic liquid crystal as the lubricant. The friction system was analyzed through various tests. The experimental results show that, under identical conditions, the friction coefficient of the PI-modified PEEK system decreased by 83.3% compared to pure PEEK. Under loads of 5 N and 25 N and rotational speeds ranging from 50 rpm to 400 rpm, the system exhibited induced alignment superlubricity. At 50 rpm, superlubricity was maintained when the load was below 105 N, while at 200 rpm, this occurred when the load was below 125 N. Excessively high rotational speeds (above 300 rpm) might affect system stability. The friction coefficient initially decreased and then increased with increasing load. The friction system demonstrated induced alignment superlubricity under the tested conditions, suggesting the potential application of PI-modified PEEK in friction components. Full article

Metalworking fluids (MWFs) are crucial in the manufacturing industry, playing a key role in facilitating various production processes. As each machining operation comes with distinct requirements, the properties of the MWFs have to be tailored to meet these specific demands. Understanding the properties of different MWFs is fundamental for optimizing processes and improving performance. This study centered on characterizing the thermal behavior of various cutting oils and water-based cutting fluids over a wide temperature range and sheds light on the specific tribological behavior. The results indicate that water-based fluids exhibit significant shear-thinning behavior, whereas cutting oils maintain nearly Newtonian properties. In terms of frictional performance, cutting oils generally provide better lubrication at higher temperatures, particularly in mixed and full-fluid film regimes, while water-based fluids demonstrate greater friction stability across a wider range of conditions. Among the tested fluids, water-based formulations showed a phase transition from solid to liquid near 0 °C due to their high water content, whereas only a few cutting oils exhibited a similar behavior. Additionally, the thermal conductivity and heat capacity of water-based fluids were substantially higher than those of the cutting oils, contributing to more efficient heat dissipation during machining. These findings, along with the reported data, intend to guide future researchers and industry in selecting the most appropriate cutting fluids for their specific applications and provide valuable input for computational models simulating the influence of MWFs in the primary and secondary shear zones between cutting tools and the workpiece/chiplet. Full article

This study explores the in situ measurement of contact temperature in thermo-elastohydrodynamic lubrication (TEHL) within cylindrical roller thrust bearings (CRTBs) utilizing vapour-deposited resistive thin-film sensors. The sensors, optimized for compactness and high spatial resolution, were strategically embedded on the stationary bearing raceways near the outer, inner, and mean radius. This configuration enabled a precise measurement of temperature variations in both pure rolling and rolling–sliding regions of the CRTBs. The experimental results revealed a consistent decrease in temperature from the inner and outer radius zones towards the mean radius as the slip-to-roll ratio (SRR) decreased in these regions. Temperature profiles showed an early rise in the inlet zone attributed to thermal inlet shear. At higher speeds, a secondary temperature peak indicative of full-film lubrication was observed in the outlet zone immediately following the Hertzian contact. The study further shows the influence of surface pressure, shear rates, sliding friction, and circumferential speed on contact temperature dynamics, offering insights into their complex interplay. Additionally, viscosity variations due to different oil temperatures were found to critically affect the rate of temperature rise and the propensity for mixed friction phenomena. A higher viscosity resulted in an earlier onset of the temperature rise in the contact, while a lower viscosity and higher speeds promote mixed lubrication, leading to reduced contact film temperatures. These findings provide valuable insights into the behaviour of CRTB-lubricated contacts under various operating conditions and serve as crucial validation data for advanced TEHL computational models. Full article

With the development of steel sheets towards higher strength and lower thickness, the process of rolling is facing more challenges, and one of the most important issues is lubrication, which directly determines the rolling stability, product quality, and production efficiency. This study focuses on the modeling and analysis of oil film thickness with viscosity–pressure–temperature (VPT) coupling effects under a hybrid lubrication system. Firstly, the mechanisms and limitations of direct spray and recirculation lubrication systems are systematically compared, highlighting the advantages of hybrid lubrication for high-speed tandem cold rolling. Subsequently, the mathematical models corresponding to different positions within the rolling interface between the roll and strip, are presented; the initial oil film thickness is described based on both plate-out and dynamic concentration formation mechanisms under the hybrid lubrication; and the model of inlet oil film thickness integrates the Reynolds equation, VPT effects, energy conservation, and continuity equations to quantify temperature-driven viscosity degradation. Furthermore, the influences of rolling process and lubrication parameters on the oil film thickness are analyzed, and a dynamic regulation strategy is proposed to optimize direct emulsion flow with regard to the actual rolling speed and the expected oil film thickness. This work bridges the gap between theoretical models and industrial requirements, providing actionable insights for high-speed rolling of advanced high-strength steel sheets. Full article

Inspired by the ventral scale structure of the oriental sand boa, this study successfully fabricated multiscale bioinspired alumina (Al₂O₃) ceramics by combining the excellent mechanical properties, high-temperature resistance, and high hardness of ceramic composites with direct ink writing (DIW) 3D printing technology and femtosecond laser processing. A MoS₂ thin film was then deposited on the ceramic surface via radio frequency magnetron sputtering (PVD) to systematically investigate the impact of bioinspired structures on the tribological properties of ceramic composites under both dry and lubricated conditions. Experimental results demonstrated that bioinspired structures at different scales exhibited significant friction-reducing and wear-resistant characteristics compared to blank structures. Specifically, under room-temperature conditions, the friction coefficients of bioinspired ceramic composites with solid lubricants and oil lubrication were 0.3 and 0.148, respectively, indicating excellent tribological performance. These findings confirm the synergistic lubrication effect between bioinspired structures, two-dimensional solid lubricants, and lubricating oil, which significantly enhanced the friction-reducing and wear-resistant properties of ceramic components. Therefore, the synergistic design of multiscale bioinspired structures and solid lubricants provides an innovative strategy for the advanced application of ceramic components. Full article

Ionic liquid molecules exhibit a variety of properties that are well suited for use as lubricants or additives for lubricants, since they form tribolayers that reduce friction and wear. As additives in the design of new water-based biolubricants, ionic liquids present the advantages of polar nature to use in aqueous lubrication, whilst being biocompatible and with null toxicity, opening up the opportunity to develop novel biolubricants. Choline is a cation present in numerous ionic liquids and is widely recognized for its water solubility, biodegradability, low toxicity, and role as a green solvent in different applications. This work presents the comparative studies of several water-based biolubricants and thin-layer films on stainless steel using a low proportion of Choline-based ionic liquids. The results of friction and wear using water-based biolubricants with 1 wt% of different Choline-based ionic liquids showed good tribological performance. In addition, Choline Lysinate, an amino-acid ionic liquid which is biocompatible, nontoxic, and biodegradable, presented excellent performance and was used as a precursor of thin-layer films on stainless steel showing outstanding behavior in pin-on-disc configuration and sapphire/stainless-steel contacts. Subsequent X-ray photoelectron spectroscopy confirmed the presence of a tribolayer containing the amino acid compound on the metallic surface. Full article

This study focuses on addressing the pressing challenge of reusing plastic in an eco-friendly manner. This research aimed to produce synthetic grease through an environmentally friendly pyrolysis technique, utilizing 69% predegraded low-density polyethylene (LDPE) combined with visible-light-working TiO₂ thin film, protein-coated TiO₂ NPs, and Lactobacillus plantarum bacteria in a batch reactor. The optimized conditions of temperature (500 °C) and heating time (2 h) resulted in the creation of 166 gm of partially degraded polyethylene grease 2 (PDPLG2) with National Lubricating Grease Institute (NLGI 2) grade consistency. PDPLG2 grease exhibits a wide-range dropping point of 280 °C and effectively maintains lubrication under high friction and stress loads, thereby preventing wear. Thermal analysis using TG and DSC validated the grease’s stability up to 280 °C, with minimal degradation beyond this point. Taguchi analysis using substance, sliding speed, and load as factors identified the ideal process parameters as aluminum, 1500 rpm, and 150 N, respectively. The present study revealed that sliding speed has the greatest impact, contributing 31.74% to the coefficient of friction (COF) and 11.28% to wear, followed by material and load. Comparative tribological analysis with commercially available grease (NLGI2) demonstrated that PDPLG2 grease outperforms NLGI2 grease. Overall, this innovative eco-friendly approach presents PDPLG2 as a promising alternative lubricant with improved anti-wear and friction properties, while also contributing significantly to plastic waste reduction. Full article

This paper presents an analysis of the dynamic characteristics observed and studied during the startup process of a gas foil radial bearing. It utilizes a comparison of both experimental data and three-dimensional fluid–solid interaction computational fluid dynamics simulations to investigate a gas foil bearing with three bump-type pads. The analytical model employs the fluid–structure interaction finite element method to examine the relationship between the components and the thin working fluid film within the bearing. This analysis was conducted under various operational conditions, including ambient pressure and temperature, shaft rotational speed, and the load applied to the shaft within the bearing. The foil structure of the bearing was modeled by representing the top and bump foils as a series of linear springs that are interconnected with the rigid housing. Meanwhile, the hydrodynamic pressure distribution acting on the top foil was modeled as a gas film operating under steady-state lubrication conditions. The comprehensive three-dimensional multi-physics model was developed using a commercial computer-aided engineering package, enabling independent finite element calculations for both fluid and solid domains. Following these calculations, the model exchanged analysis results across the interface between domains, allowing simulations to continue until the system achieved a quasi-steady state. An in-house experimental system was designed to evaluate the performance of the gas foil bearing under different working conditions, including the load applied to the shaft and the rotational speed. The experiment investigated the operational state of a gas foil radial bearing under ambient pressure (1 bar), ambient temperature (303 K), rotational speeds ranging from 1.5 to 9.5 krpm, and a load of 0.5602 kgw. Some operational conditions of the bearing were defined as boundary condition inputs for the simulation model. The model’s results, notably the predicted lift-off rotational speed of the bearing, show strong alignment with results from in-house experiments. Full article

Fluorocarbon thin films are widely used in protective coatings due to their distinctive physical and chemical properties. However, their inherent lubricating nature often results in low scratch resistance and poor adhesion to substrates. In this study, a beam plasma source was employed to deposit fluorocarbon thin films, resulting in enhanced adhesion and scratch resistance while preserving optical transmittance and hydrophobicity. The beam plasma source can generate high-density plasma, resulting in the effective dissociation of the C4F8 source gas, as evidenced by the large ion current and high film deposition rates. A unique feature of this beam plasma source is that it can simultaneously emit a single broad beam of ions with independently controllable ion energy and flux to interact with the film. The fluorocarbon films exhibit high hydrophobicity with a contact angle of about 105°, a high optical transmittance of 85–90% in the visible wavelength range, and exceptional scratch resistance and durability. Full article

Understanding lubrication at the nanoscale is essential for reducing friction. While alkanes, the primary component in most lubricants, have been studied for their molecular structure’s impact on rheology and behavior when confined by solid surfaces, the influence of confining surface texture remains underexplored. This research uses molecular dynamics simulations to investigate the rheological behavior of thin film lubrication between various patterned rough surfaces. The study focuses on sinusoidal, sawtooth, and squaretooth wave-patterned surfaces, using hexadecane as the lubricant. The simulations examine the effects under different normal loads and shear rates. Surface patterns significantly influence the formation and structure of crystalline bridges, depending on shear rates and normal loads. The sawtooth wave-patterned surface exhibits the highest viscosity under low normal load and shear rate conditions, forming crystalline bridges with a molecular orientation perpendicular to the shear direction. The squaretooth patterns exhibit the lowest viscosities due to the nematic order in crystalline bridges with molecules aligned in the shearing direction. The sinusoidal wave-patterned surface shows intermediary viscosity with disordered crystalline bridge groups formed with random molecular orientation. The lowest viscosity provided by the squaretooth pattern surface persists across various conditions, including both transitory and steady states, under high and low loads, and over a wide range of shear rates. However, the difference in shear viscosity is reduced at higher normal loads. This research provides valuable insights for designing nanoelectromechanical systems (NEMS) and other applications where boundary conditions are critical to lubrication. Full article

This research follows closely previous findings in flow characteristics and phenomena that take place in the piston ring and cylinder liner interface during motoring and firing engine operation, and also compares results between different optical engine set-ups. Cavitation visualisation in a simulating lubrication single-ring test rig and oil transport and cavitation visualisation in custom made cylinder assemblies of optical engines are the tools used to quantify the transport process under the piston ring and cylinder liner. Simplification of the interface is an essential technique that enhances the researcher’s confidence in results interpretation. Engine complexity and severe oil starvation are impeding the analysis of the experimental results. Visualisation experiments constitute an effective way to test various lubricant types and assess their overall performance characteristics, including their properties and cavitation behaviour. The repeatability of the visualisation method establishes the parametric study effects and offers valuable experimental results. As a further step towards the lubricant composition effect, a link between the lubricant formulation and the operating conditions could be established as the oil performance is assessed with a view to its transport behaviour. Image processing is used to quantify the impact of cavitation on piston ring lubrication in conjunction with varied operating and lubricant parameters. The characteristics of the lubricant and the working environment have an impact on these types of cavities. Viscosity, cavitation, oil film thickness (OFT), lubricant shear-thinning characteristics and friction are all linked. Full article

In recent years, the exponential growth of the machining industry and its needs has driven the development of new manufacturing technologies, more advanced cutting tool types, and new types of coatings to extend tool lifespan. New coating solutions have been studied and implemented for machining tools, which provide a low friction coefficient and lubrication, thus increasing tool lifespan. Following this line of reasoning, it is relevant to develop scientific work aimed at studying the behavior of cutting tools coated with thin films that promote low friction and high lubrication, as is the case with DLC (diamond-like carbon) coatings. These coatings promote good resistance to oxidation and allow high machining speeds, properties also exhibited by TiAlN (titanium aluminum nitride) coatings. In fact, there is a gap in the literature studying the performance of cemented carbide tools provided with multilayered coatings in milling operations of Cu–Be alloys, commonly used in inserts of plastic injection molds. This study’s objective was to investigate the effect of a multilayer coating (TiAlN/DLC) on end-milling tools to analyze their cutting performance when milling a Cu–Be alloy known commercially as AMPCOLOY^®83. The quality of the machined surface was evaluated, and the wear of the cutting tool was studied. A comparative analysis of milling parameters with respect to their effect on the condition of the surface after machining and the resulting wear on the tools, using coated and uncoated tools and different machining parameters, allowed us to verify a better quality of the machined surface and wear quantified in approximately half when used coated tools. Full article

The loosening or fracture of the prosthetic abutment screw is the most frequently reported complication in implant dentistry. Thin diamond-like carbon (DLC) films offer a low friction coefficient and high wear resistance, functioning as a solid lubricant to prevent the weakening of the implant–abutment system. This study evaluated the effects of DLC nanofilms on the reverse torque of prosthetic abutments after simulated chewing. Abutments with 8° and 11° taper connections, with and without DLC or silver-doped DLC coatings, were tested. The films were deposited through the plasma enhanced chemical vapor deposition process. After two million cycles of mechanical loading, reverse torque was measured. Analyses with scanning electron microscopy were conducted on three samples of each group before and after mechanical cycling to verify the adaptation of the abutments. Tribology, Raman and energy-dispersive spectroscopy analyses were performed. All groups showed a reduction in insertion torque, except the DLC-coated 8° abutments, which demonstrated increased reverse torque. The 11° taper groups experienced the most torque loss. The nanofilm had no significant effect on maintaining insertion torque, except for the DLC8 group, which showed improved performance. Full article

Hypromellose (HM) is a cellulose-derived polymer of pharmaceutical grade that forms easily from thin films and coatings. As few studies concern HM-formulated systems, this study focuses on the formulation of HM films by incorporating a fatty acid additive, making it possible to control surface properties such as wetting and slip behavior for pharmaceutical or medical applications. The results show that the addition of a very small amount (from 0.1 to 1% w/w) of fatty acid additive reduces HM film affinity for water and water vapor transmission rate, while film appearance and gloss are rather preserved. Surface properties were probed using wettability measurements, Tapping Mode AFM, ATR-FTIR spectrometry, and friction measurements. Tapping Mode AFM images show that the surface roughness reduces by up to 65%. Wettability results show that the surface energy decreases from 43 to 31 mJ.m⁻², whereas surface FTIR spectrometry measurements demonstrate that fatty acid molecules migrate on the surface of the formulated films, the driving force being the microphase separation between the polar HM macromolecules and the hydrophobic additive, leading to the formation of a weak boundary layer with poor cohesion. As a consequence, the surface coefficient of friction significantly reduces from 0.38 to 0.08, and fatty acid molecules thus act as a lubricant, improving the sliding properties of HM-based coatings. Full article

Molybdenum disulfide coatings, particularly Microseal 200-1, have been extensively used as dry film lubricants for actuating mechanisms in space applications. Although Microseal 200-1 has historically been a popular choice for space missions, recent assessments indicate a need for reexamination. This study evaluates sliding friction in air and dry gaseous nitrogen atmospheres at ambient temperatures with both linear reciprocating and rotary unidirectional tribo-tests. Measurements are performed for Microseal 200-1 applied on substrates and surface treatments commonly used in aerospace components, particularly stainless steel and a titanium alloy. Our findings indicate that the friction of stainless steel balls sliding on Microseal 200-1-coated disks is significantly influenced by the environment as well as the disk substrate material. The average friction coefficient ranges from 0.12 to 0.48 in air and from 0.04 to 0.41 in dry gaseous nitrogen, and the amount of friction is consistently much higher for the Microseal 200-1 on the stainless steel than on the titanium alloy. Microscopy and surface analyses, including scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray fluorescence, of the coatings on stainless steel substrates reveals that the coatings are sparse and relatively thin, likely a key factor contributing to their high friction. This insight underscores the substrate dependence of this widely used coating and highlights the importance of detailed tribological testing in accurately assessing the tribological performance of commercial dry film lubricants, a key step towards improving the reliability and effectiveness of actuating mechanisms for space applications. Full article