Water Lubrication Research Articles

Effect of bionic shield texture on friction behavior of Silicon Carbide under water lubrication condition

Abstract Reasonable texture parameters can effectively generate local dynamic pressure effects and promote the formation of lubrication film. The synergistic friction reduction mechanism of the shield-shaped texture on the Silicon Carbide (SiC) surface under water-based lubrication conditions between the flow pressure effect and the "rolling ball" effect is investigated by combining simulation analysis and friction experiments. The effects of shield textured surface on the friction and wear characteristics of SiC surface and the characteristics of interfacial polarization electric field under different rotational speeds and different load conditions were analyzed. The results display that synergistic texture lubrication has a beneficial effect on improving tribological properties. The surface with 6% texture area occupancy showed the best tribological characteristics. The surface with a textured area occupancy of 6% displays the optimal tribological properties. Moreover, the friction reduction mechanisms under different working conditions are discussed, with the textured uniformly arranged surfaces being more suitable for high-speed and heavy load (140 N, 2000 rpm) conditions and the textured non-uniformly arranged surfaces being more suitable for low-speed and light load (40 N, 400 rpm) conditions.

Enhancing Water Lubrication in UHMWPE Using Mesoporous Polydopamine Nanoparticles: A Strategy to Mitigate Frictional Vibration.

Establishing a persistent lubrication mechanism and a durable tribo-film on contact surfaces is identified as crucial for improving the tribology and vibration characteristics of polymer materials under water-lubricated conditions. This study focuses on enhancing tribological performance and reducing frictional vibrations in ultrahigh molecular weight polyethylene (UHMWPE) through the incorporation of mesoporous polydopamine (MPDA) nanoparticles. In the experiments, MPDA nanoparticles were synthesized and blended with UHMWPE to create UHMWPE/MPDA composites. The interactions between these composites and zirconia (ZrO2) ceramic balls under water lubrication were examined. The results show that when the MPDA content of the composite is 1.5 wt %, the coefficient of friction and wear rate are reduced by 40% and 52% compared with those of pure UHMWPE, respectively. This notable enhancement helped to mitigate friction-induced vibrations, particularly those caused by intermittent sticking and slipping motions. MPDA nanoparticles were shown to act as reservoirs for water, releasing and replenishing water based on the loading conditions, which sustained continuous water-based lubrication at the composite surfaces. Additionally, the surface deformation behavior of the composite material is significantly weakened, which provides a more stable friction surface. This work introduces a novel approach to enhance the interface stability of polymers in water-lubricated environments, offering guidance for developing advanced materials and reducing friction and wear in engineering applications.

Evaluation of Fine Wear Particles Emission from Styrene-Butadiene Rubber Reinforced with Aligned Carbon Nanotubes: A Study Based on Unit Wear Mass Analysis

Rubber filled with carbon nanotubes (CNTs) oriented along a specific direction exhibits excellent tribological performance owing to the unique directional structure of the CNTs, and offers significant application potential. However, when CNT-reinforced rubbers are worn, fine wear particles (WPs), including CNTs, are emitted, creating a potential respiratory health risk. This study explores the relationship between the emission of fine WPs (with sizes ) against a frosted glass disc under sliding conditions and the tribological performance of styrene-butadiene rubber (SBR) reinforced by aligned CNTs. The number of WPs per unit worn mass (QwpS/uwm, where S is the upper limit to the particle size in μm), was defined to quantify the emissions after a unit mass was worn. Using a pin-on-disc test rig developed for this study, the results showed that SBR with CNTs oriented perpendicular to the wear surface (denoted as CNTs-z-SBR) exhibited higher Qwp3.0/uwm and Qwp5.0/uwm values owing to its superior wear resistance. A greater worn mass resulted in larger amounts of WPs, but smaller Qwp3.0/uwm and Qwp5.0/uwm. Furthermore, both water lubrication and lower coefficients of friction (COF) increased the value of Qwp3.0/uwm, whereas a larger load and velocity decreased the values of Qwp3.0/uwm and Qwp5.0/uwm.

Influence of Variable-Depth Groove Texture on the Friction and Wear Performance of GCr15–SiC Friction Pairs Under Water Lubrication

Influence of Variable-Depth Groove Texture on the Friction and Wear Performance of GCr15–SiC Friction Pairs Under Water Lubrication

Mechanism of Wheel-Rail Adhesion Recovery during Large Sliding processes under Water Lubrication condition

The challenge of low adhesion between the wheel and rail constrains the advancement of train braking technologies, resulting in sliding during braking, increased braking distances, and even operational safety incidents. Low adhesion arises from the contamination of the rail surface by a third body, such as water or oil, significantly reducing adhesion. However, experimental studies have found that wheel-rail adhesion coefficient under water lubrication conditions possesses a recovery capability: In scenarios characterized by low adhesion in water lubrication conditions, a secondary rise in adhesion occurs when substantial wheel-rail sliding is present. This paper focuses on numerically modeling the unique phenomenon of adhesion recovery during large-sliding processes under water lubrication conditions. Considering the notable differences in frictional heating during wheel sliding, as opposed to pure rolling conditions, we construct a wheel-rail contact model under mixed lubrication conditions that incorporates the solid-liquid coupled heat transfer effect. This model achieves stable solutions for the wheel-rail contact relationship and the temperature at the wheel-rail interface. The impacts of velocity, axle load, water temperature, and slide ratio on the adhesion recovery phenomenon are discussed, revealing the underlying mechanism of adhesion recovery during large sliding processes. Finally, brake adhesion tests under water lubrication conditions are conducted on a scaled test rig to validate the proposed theoretical model.

A review: Enhancing tribological properties of journal bearings composite materials

Abstract Tribology is the science of studying friction, wear, and lubrication. Composite materials consist of two or more constituents (phases): the discontinuous phase represents the reinforcement and the continuous phase represents the matrix. Journal bearing is manufactured from various composite materials. This article reviews the literature on improving the tribological properties of journal bearings made of composite materials (polymer matrix composite materials and metal matrix composite materials) by dividing the previous studies into six primary sections depending on the kinds of composite materials. An efficient method was utilized to solve the problems of composite journal bearings in water lubrication such as wear resistance, reduced friction, and increased service life of journal bearings in various applications especially in ships. The impact of composite materials, which were added through thermoplastic such as polytetrafluoroethylene (PTFE), polyether-ether-ketone, POM, and PA66, thermoset such as epoxy, polyester, and phenolic reinforced with fibers, and thermoplastic with thermoset (PTFE/epoxy composite) to reduce wear rate and coefficient of friction, and also the addition of nanomaterials to composite journal bearing to enhance the tribological properties in various applications were examined. The last section used metal matrix composite reinforced to other metal or alloy to give the attractive mechanical properties used to improve wear resistance and friction coefficient of journal bearing. The novelty of this article lies in the comprehensive analysis of various composite materials and their effect on the tribological properties of journal bearings, providing future insights into bearing design and optimization to improve performance.

Interparticle friction behaviors of kaolinite: Insights into macroscale friction from nanoscale

The friction behavior of widespread clay minerals is a major concern in many geo-engineering problems, such as the stability of soft soil foundations and the induction of seismic fault zones. The present work aimed to study the friction behaviors of kaolinite at the particle level using the molecular dynamics method. The effects of normal force (Fn), shear velocity (v), and interfacial water film on nanofriction were discussed. The “stick-slip” phenomenon and periodic evolution of friction forces (Ff) were observed in dry friction and became less pronounced with water lubrication. The dry Ff of kaolinite was found to be insensitive to Fn. However, wet Ff exhibited a linear increase with Fn and then transitioned to a non-linear relationship as slip displacement increases due to the continuous loss of water molecules from the interface during friction. Notably, at high loads (Fn ≥ 30 nN), the peak friction of wet kaolinite showed characteristics similar to dry friction. A velocity-strengthening behavior of kaolinite at high velocities was observed in both dry and wet conditions. The macroscale friction coefficients of kaolinite were predicted from nanofriction data and results showed good agreement with experimental values. This study lays the foundation for bridging micro- and macro-mechanical behaviors, suggesting a new pathway for acquiring precise macroscopic friction of minerals through cross-scale studies.

Rolling Contact Fatigue Life and Categorization of Failure in Experiment of Flat PEEK Race-Alumina Ball Bearings in Water Lubrication under 1700 N at 1000 rpm

Abstract The rolling contact fatigue tests of flat polyether-ether-ketone (PEEK) race-alumina balls bearings in water lubrication were done. From the experiments under 1700 N at 1000 rpm, three types of failures were obtained: a crater-shaped flaking, a rhombus-shaped flaking and a large cracking failures. To research the relationships between the failures and the lives, the surface properties near the failures were measured and observed. No relationships between the surface roughness and the life were found. On the other hand, the contact width of the shorter life specimen was larger than that of the longer life specimen. Two types of the flaking holes were compared to study the differences. The crater-shaped flaking hole exceeded the contact track, but the rhombus-shaped flaking hole existed inside the contact track. In addition, the crater-shaped flaking hole was shallower than the rhombus-shaped flaking hole. This means that the flaking mechanisms were different between them, i. e. the differences of the flaking mechanisms caused the differences of the life.

Hierarchical structure on tin bronze hydrostatic bearing surfaces to achieve ultra-high Cassie stability

The hierarchical structure represents a significant approach to enhance the Cassie stability on superhydrophobic hydrostatic bearing surfaces. However, the preparation of a robust hierarchical structure on tin bronze alloy remains unknown. In the present study, a hierarchical structure comprising micro-bulges and nanowires was fabricated on a tin bronze surface, exhibiting excellent superhydrophobicity (water contact angle, WCA = 163°). In contrast to the micro-bulge structure, the hierarchical structure surface exhibited a quasi-reversible trajectory after pressure, with the WCA recovered to 161°. For the same triple-phase contact line (TPCL), a higher Laplace pressure (3640 Pa) is required to destroy the Cassie state of the hierarchical structure. Droplets on the hierarchical structure can rapidly recover to a stable Cassie state after impact. It can be verified the hierarchical structure has higher Cassie stability to resist pressure, thermal exposure, and impact. The slip lengths of the hierarchical structure in water and VG5 lubricant are 18 μm and 27 μm, respectively. The hierarchical structure preparation is straightforward, and its application to hydrostatic bearings can enhance stability.

Study on properties of 6061 aluminum alloy coating by two-stage plasma electrolysis in two completely different electrolytes

In this paper, an innovative two-stage plasma electrolysis technology was used to prepare a coating with improved properties, and the growth mechanism, wear and corrosion resistance of it were studied. In the first stage, 6061 aluminum alloy discs were fluoridated in a non-aqueous electrolyte (NH4F-EG) to get a plasma electrolytic fluorination (PEF) coating, and then in the second stage, the samples with fluorinated coatings were transferred to a phosphate electrolyte for plasma electrolytic oxidation (PEO) treatment, resulting in a new coating. Also, two PEF coatings and PEO coatings obtained by processing in a single electrolyte were set up. The roughness, hardness, microstructure, and material composition were analyzed using a surface roughness meter, nano-indentation instrument, scanning electron microscope (SEM), energy dispersive spectrometer (EDS), X-ray diffractometer (XRD), and X-ray photoelectron spectroscopy (XPS). Furthermore, their wear resistance was evaluated through friction tests, and their corrosion resistance was assessed using corrosion tests. The results demonstrate that FF has a lower coefficient of friction (COF) and abrasion width under dry friction than conventional OO, but it has a higher coefficient of friction and abrasion width under water and oil lubrication than under dry friction. Furthermore, FF has a lower corrosion potential and higher corrosion current density than OO. However, FO fully combines and enhances the advantages of both coatings with lower energy consumption, exhibiting the highest corrosion potentials as well as the lowest friction coefficients, abrasion widths, and corrosion current densities in three different samples.

Effect of aqueous layer thickness on nano-scratching of single-crystal γ-TiAl alloys

ABSTRACT The study of nano-scratching under water lubrication is helpful to understand the role of lubrication mechanism in the machining of single crystal γ-TiAl alloy. In this paper, through the comparative analysis of nano-scratching under different thicknesses of water layers, it was found that under a water layer thickness of 1 nm, nano-scratching not only improves the surface quality but also achieves multiple reductions in scratch force, stress, temperature and subsurface structural damage. In order to deeply reveal the internal mechanism of workpiece temperature variation under different thicknesses of water layer lubrication, a fitting formula was innovatively adopted to conduct quantitative analysis. In addition, with the increase of the thickness of the water layer, it was observed that the water film effect was continuously enhanced, and this change caused the matrix stress to gradually increase, which hindered the forward motion of the nanoscratch, ultimately resulting in an increase in the friction coefficient. These findings provide valuable insights into the nanoscratching mechanism of monocrystalline γ-TiAl alloy in the presence of water film, and provide a new perspective for understanding the complex mechanism of nanoscratch behaviour under water lubrication, thus promoting the understanding of nanoscale lubrication effects.

Effects of liquid lubricants on the surface characteristics of 3D-printed polylactic acid

In this study, 3D-printed Polylactic acid (PLA) specimens were manufactured and polished using various lubricants to assess their surface, friction, and wear characteristics. After polishing, the surface roughness decreased by approximately 80% compared with that before polishing, except when acetone was used as the lubricant. In particular, under deionized (DI) water and acetone lubrication conditions, the friction coefficient decreased by 63% and 70%, respectively, whereas the specific wear rate decreased by 88% and 83%, respectively, compared with the unpolished specimens. In the case of dry polishing, adhesion, friction, and wear increase owing to surface damage. Ethanol and IPA polishing resulted in hydrolysis and increased friction, but slightly decreased wear rates. The surface of the specimen polished with acetone dissolved and became very rough. Only the surface polished with DI water exhibited hydrophobic properties. When acetone and DI water were used as lubricants, the surface adhesion force, adhesion energy, friction coefficient, and wear rate were lowest. The finite element analysis results showed that the polished surface exhibited stable contact pressure and friction force, while the unpolished surface showed large fluctuations in contact pressure and friction force owing to the laminated pattern. These results suggest that the polishing process is crucial for improving the surface characteristics and mechanical performance of 3D-printed PLA parts.

Effect of hygrothermal aging on the friction behavior and wear mechanism of the multi-filler reinforced epoxy composites for coated steel

Polymer-based composites for steel structure coating are an effective strategy to improve tribological properties and service durability under hygrothermal aging conditions. In the present paper, epoxy resin was improved by mechanical reinforcement and frictional lubrication fillers, and a kind of multi-filler reinforced epoxy composite (MFREC) was successfully prepared. Water uptake behavior, mechanical and thermal property evolution, friction behavior and wear mechanism as well as micro-topography analysis of MFREC under hygrothermal aging were conducted and discussed in detail. The research results showed that the water uptake curve of MFREC after distilled water and 5 wt% NaCl water solution immersions confirmed the two-stage diffusion model, where the quasi-equilibrium water uptakes were 4.23% and 3.67%, respectively. Additionally, the fundamental reason for the degradation of the mechanical and thermal properties of MFREC was the hydrolysis of the resin and the de-bonding of the fillers/matrix interface. The interface shear strength of MFREC adhesive and steel gradually decreased with the hygrothermal aging, but did not lose the bonding property, because the uniformly dispersed multi-fillers can fill the internal defects of the matrix and prolong the crack propagation path to block the effect. Before hygrothermal aging, MFREC had excellent friction and wear resistance compared to resin matrix, especially under water lubrication conditions. The anti-wear rate of MFREC increased by up to 59.6% compared to the room temperature dry test environment due to the coupling effects of the water lubrication and anti-friction characteristics of modified fillers. Hygrothermal aging had little effect (＜12%) on the friction coefficient of MFREC, but the anti-wear properties decreased significantly, especially the Ws increased by 255.1% under the 60 °C immersion condition. Because the degradation of thermal/mechanical properties was not enough to resist the high shear stress of the steel ball, leading to severe fatigue wear.

Polyvinyl alcohol gel/micro-arc oxidation 3D-printed porous structural aluminium for oil-water separation

Traditional oil-water separation membranes still face challenges in designing membrane structures and pore sizes. In this study, we successfully prepared a PVA@MAO 3D-Al material with an internal porous structure using 3D printing technology and micro-arc oxidation (MAO). Compared to the base 3D-Al material, the fabricated PVA@MAO 3D-Al exhibits excellent wear resistance, with an average friction coefficient reduced by 66 % in dry friction and 22 % in water lubrication. In electrochemical experiments, corrosion current density decreased by an order of magnitude, indicating higher stability of PVA@MAO 3D-Al in corrosive environments. In oil-water separation experiments, PVA@MAO 3D-Al achieved separation efficiencies exceeding 97 % for mixtures of white oil, kerosene, liquid paraffin, and cyclohexane with water. Moreover, even after undergoing 600 cycles of reciprocating friction and exposure to various environmental solutions, the separation efficiency of PVA@MAO 3D-Al for white oil/water mixtures remained above 96 %, demonstrating outstanding physical and chemical stability. This suggests that PVA@MAO 3D-Al is suitable for use in extremely harsh environments. This study introduces a simple and efficient approach to manufacturing oil-water separation membranes using 3D printing technology, coupled with MAO technology to enhance the base material's performance. The combination of these techniques opens up new avenues in the field of oil-water separation.

Tribological Effects of Quaternary Ammonium-Functionalized Montmorillonite as Water-Based Additives.

In this study, a water-soluble quaternary ammonium salt (QAS)-functionalized montmorillonite (MMT) was fabricated using a mechanochemical method as a high-performance water lubrication additive. The intercalation of QAS into the MMT layer expands the layer spacing of MMT, but does not affect the hydrophilicity of MMT. The ultrathin layer QAS-functionalized montmorillonite (QAS-MMT) demonstrated excellent water-stable dispersion and can be used as a water-based lubrication additive. Only 0.1% addition can reduce the friction coefficient by more than 71.4% and the wear volume by about 58.8% when compared to water, demonstrating its excellent friction reduction and antiwear performance. The frictional mechanism indicates that the physical adsorption film, together with the chemical reaction film, endows the QAS-MMT additives with outstanding tribological performance, provides excellent lubrication for the contact of steel/steel pairs, and prevents the steel surface from being further worn.

Dramatic changes in water lubrication aroused by light

Light-controlled friction and lubrication has a wide prospect in industry and life. The friction coefficient of water lubrication between silicon nitride and titanium dioxide was found to be significantly changed by ultraviolet treatment from superlubricity to near lubrication failure. Under fully flooded conditions, the relative difference in wettability between wear and non-wear zone determined film formation of water lubrication, and its change after ultraviolet treatment aroused the failure of lubrication. While for the starved water lubrication, ultraviolet treatment slowed down the tribo-chemical reaction rate to form smaller particles on wear area, which was more conducive to lubrication and even reduced to superlubricity. Such enormous changes of water lubrication in macroscale may throw a new light on light-controlled friction and lubrication.

Friction and corrosion characteristics of microarc oxidation/laser cladding palygorskite coating on 6061 aluminum alloy substrates

In this study, micro arc oxidation (MAO) technology was used to surface coating of 6061 aluminum (Al) disk. Then laser is used to clad palygorskite (Pal) on the surface of the MAO coating to improve the protection of the coating against the Al substrate. The laser irradiates heat onto the Pal powder, the Pal is heated and at the same time the MAO coating is affected by the heat, and the MAO coating is cooled and cured along with the Pal to form the MAO- Pal composite coating. The surface morphology, elemental composition and phase composition of the MAO-Pal coating were analyzed using scanning electron microscopy, energy spectroscopy and X-ray diffraction. And friction experiments were performed on the MAO- Pal coating. The results showed that the coefficient of friction (COF) of the MAO-Pal coating was reduced by 27 % compared to the Al substrate and 19 % compared to the MAO coating under water lubrication conditions. Through the corrosion resistance experiments, the corrosion potential (Ecorr) of the MAO- Pal coating increased by 0.197 V compared to the Al substrate and 0.280 V compared to the MAO coating, and the corrosion current density (Icorr) simultaneously decreased by three orders of magnitude compared to the Al substrate and one order of magnitude compared to the MAO coating. The MAO- Pal coating prepared by laser cladding Pal had good wear and corrosion resistance, which improved the service life and application range of Al alloy and was expected to promote the development of Al alloy in the application field.

Tribological evaluation of thermoplastic polyurethane-based bearing materials under water lubrication: Effect of load, sliding speed, and temperature

Polymers are widely used in bearing applications. In the case of water-lubricated stern tube bearings, thermoplastic polyurethane (TPU)-based composites are used due to their excellent wear resistance, corrosion resistance, and tunable mechanical properties. Their tribological performance, however, depends on operating conditions. In this work, TPU was blended with carbon fiber, graphene platelet, and ultra-high molecular weight polyethylene (UHMWPE). Friction tests of TPU based-composites against copper countersurface were carried out in water to mimic the actual operating conditions of the bearing. Most of the resulting contacts were in the boundary lubrication regime, in which friction was attributed to both contact mechanics of asperities as well as water lubrication. Our results show that the viscoelasticity of TPU has a considerable impact on its tribological performance. Water lubrication at 50 °C promotes the softening of polymer surface material during sliding, resulting in higher fluctuation in the coefficient of friction and wear loss. This is attributed to the reduced thermomechanical properties. In addition, Schallamach waviness is observed on worn surface. The tribological properties of TPU are significantly improved by the inclusion of carbon fiber, graphene platelet, and UHMWPE. The formation of graphene transfer-layers and UHMWPE transfer film reduces friction and wear loss, while the inclusion of carbon fiber enhances wear resistance due to improved mechanical properties and load bearing capacity.

Dual-Function Hybrid Coatings Based on Polytetrafluoroethylene and Cu2O for Anti-Biocorrosion and Anti-Wear Applications

Corrosion and wear issues of motion components exposed to water-based corrosion mediums, e.g., naval vessels and oil extraction equipment, pose challenges for the lifespan and reliability of the motion systems. In this work, epoxy-based coatings modified with polytetrafluoroethylene (PTFE) and cuprous oxide (Cu2O) nanoparticles were prepared. The anti-corrosion performance of the coatings was comparatively investigated by electrical impedance spectroscopy and Tafel tests in sterile and sulphate-reducing bacteria (SRB) mediums. Moreover, the tribological behaviors of the coatings were examined under water lubrication conditions. Our results demonstrate that the epoxy coatings lower significantly the corrosion current density icorr and the charge transfer resistance of the electrical double layer Rct of the carbon steel substrate. Interestingly, the hybrid coatings filled with both PTFE and Cu2O exhibit excellent anti-corrosion and anti-wear performance. After being immersed in the SRB medium for 18 days, the icorr of the pure EP coating and hybrid coatings are 1.10 × 10−7 Amp/cm2 and 0.3 × 10−7 Amp/cm2, and the Rct values are 1.04 × 103 Ω·cm2 and 3.87 × 103 Ω·cm2, respectively. A solid tribofilm forms on the stainless steel counterface sliding against the hybrid coating, which is surmised to be essential for the low friction coefficients and wear. The present work paves a route for formulating the dual-function coatings of anti-biocorrosion and anti-wear.

Impact of oil supply conditions on water lubrication assisted with minimal secondary lubricating medium

Abstract Previous research has revealed that introducing a secondary lubricating medium can temporarily enhance water-lubricated bearing performance, thereby reducing the risk of lubrication failure under challenging conditions. This study aims to identify the optimal injection point for the secondary lubricating medium and evaluates oil supply rate effects. Experiments are conducted using a block-on-ring test rig, complemented by CFD simulations to elucidate the underlying mechanisms. Three oil supply settings, upstream, inlet and outlet of the contact region, are compared. Results shows that upstream oil supply led to a lower critical speed at which the added oil loses any effect compared to the inlet oil supply and outlet oil supply. The effect of oil supply rates on friction reduction varies among the oil supply settings and ring rotational speeds. In conclusion, the most effective oil supply setting positions the injector at the outlet of the contact region, outperforming placement at the entrance of the contact region.