Water-lubricated Conditions Research Articles

Friction Behaviors and Wear Mechanisms of Carbon Fiber Reinforced Composites for Bridge Cable

Carbon fiber reinforced epoxy resin composites (CFRP) demonstrate superior wear resistance and fatigue durability, which are anticipated to markedly enhance the service life of structures under complex conditions. In the present paper, the friction behaviors and wear mechanisms of CFRP under different applied loads, sliding speeds, service temperatures, and water lubrication were studied and analyzed in detail. The results indicated that the tribological properties of CFRP were predominantly influenced by the applied loads, as the tangential displacement generated significant shear stress at the interface of the friction pair. Serviced temperature was the next most impactful factor, while the influence of water lubrication remained minimal. Moreover, when subjected to a load of 2000 g, the wear rate and scratch width of the samples exhibited increases of 158% and 113%, respectively, compared to those loaded with 500 g. This observed escalation in wear characteristics can be attributed to irreversible debonding damage at the fiber/resin interface, leading to severe delamination wear. At elevated temperatures of 100 °C and 120 °C, the wear rate of CFRP increased by 75% and 112% compared to that at room temperature. This augmentation in wear was attributed to the transition of the epoxy resin from a glassy to an elastic state, which facilitated enhanced fatigue wear. Furthermore, both sliding speed and water lubrication displayed a negligible influence on the friction coefficient of CFRP, particularly under water lubrication conditions at 60 °C, where the friction coefficient was only 15%. This was because the lubricant properties and thermal management provided by the water molecules, which mitigated the frictional interactions, led to only minor abrasive wear. In contrast, the wear rate of CFRP at a sliding speed of 120 mm/s was found to be 74% greater than that observed at 60 mm/s. This significant increase can be attributed to the disparity in sliding rates, which induced uncoordinated deformation in the surface and subsurface of the CFRP, resulting in adhesive wear.

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.

Comparative analysis of fretting wear behavior of steel wire subject to tensile-torsional coupling forces in typical mining environments

The complex mining environments can significantly accelerate the fretting wear among steel wires within wire rope, thereby diminishing its service life and posing severe risks to the safety of mine hoisting operations. To explore the fretting behavior of steel wires featuring complex contact structures in typical mining environments, a customized test rig was utilized to perform fretting wear experiments of steel wire under tensile-torsional coupling forces. The findings indicate that with increasing contact force, the coefficient of friction (CoF) between steel wires in different environments decreases, whereas the frictional force and wear degree increase significantly. The wear depth and wear coefficient under peak contact structure are markedly larger than those under valley contact structure. For the same contact force, the wear of steel wire without lubrication is the largest, the wear under water lubrication is the second, and the wear under grease lubrication is the least. The primary wear mechanisms of steel wire under grease lubrication are abrasive wear and fatigue wear. The presence of mineral particles in the grease can reduce the CoF, but it will exacerbate the wear and result in adhesive wear characteristics on the wear surfaces. Under no lubrication and water lubrication conditions, the wear mechanisms encompass abrasive wear, adhesive wear and fatigue wear. Furthermore, with increasing contact force, the fatigue wear of steel wire under no lubrication intensifies, while the abrasive wear characteristics become more pronounced under water lubrication.

Fabrication of covalently modified graphene oxide-based assembled polymer brushes as efficient aqueous lubricant additive

The present study demonstrates a facile and multistep chemical approach for preparing covalent functionalized graphene oxide (GO) followed by the layer-by-layer assembly of polymer brushes on functionalized GO for aqueous lubricants. Simultaneous reduction and surface modification of GO with 6-amino-4-hydroxy-2-naphthalenesulfonic acid (ANS) and polyethylenimine (PEI) was performed to synthesize functionalized GO (rGO-ANS and rGO-PEI) through a nucleophilic addition reaction pathway to enhance the thermal and dispersion stability in water. Polymer brush particles were fabricated on modified rGO-PEI using anionic polyelectrolytes to extend the load-bearing ability under water-lubricated conditions. The chemical, structural, wettability, and morphological features of functionalized GO and polymer brush particles were well characterized using standard spectroscopic and microscopic techniques. The macrotribological results showed that rGO-ANS (0.5 wt%) exhibited a steady coefficient of friction (COF) with increasing load-bearing ability up to 500 N load (Pm ∼ 4.8 GPa) compared to GO. Although the ANS chains helped to generate an antifrictional tribofilms, the smeared particle film was unable to decrease the COF and wear with increasing the contact pressure to a lower level. Whereas, the poly(sodium 4-styrenesulfonate) (PSS) containing polymer brush (rGO-PBS) showed a significant reduction of the COF (∼ 61.5 %) and wear volume (∼ 82.9 %) at a 147 N load compared to the GO under water lubricated conditions. rGO-PBS also exhibited higher load-bearing capacity up to 800 N load (Pm ∼ 5.8 GPa) with a significantly lower COF and wear among particles. The sulfonate groups containing PSS in rGO-PBS provided robust interfacial adhesive properties to the steel tribo pairs, which facilitated the formation of antifrictional protective tribofilm through well-hydrated polymeric cushioning layers to reduce the COF, wear, and enhance the load-affording ability. Therefore, the excellent dispersibility in water, strong adhesion properties, intrinsic low frictional properties, and strong load-bearing ability make rGO-PBS a potential candidate for aqueous lubricants.

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.

Molecular Dynamics Simulation and Experimental Study of Friction and Wear Characteristics of Carbon Nanotube-Reinforced Nitrile Butadiene Rubber

Nitrile butadiene rubber (NBR) and its various composite materials are widely employed as friction materials in mechanical equipment. The use of carbon nanotube (CNT) reinforcement in NBR for improved friction and wear characteristics has become a major research focus. However, the mechanisms underlying the improvement in the friction and wear characteristics of NBR with different CNT contents remain insufficiently elucidated. Therefore, we conducted a combined analysis of NBR reinforced with varying CNT contents through molecular dynamics (MD) simulations and ring–block friction experiments. The aim is to analyze the extent to which CNTs enhance the water-lubricated friction and dry wear properties of NBR and explore the improvement mechanisms through molecular chain characteristics. The results of this study demonstrate that as the mass fraction of CNTs (0%, 1.25%, 2.5%, 5%) increases, the water-lubricated friction coefficient of NBR continuously decreases. Under water-lubricated conditions, CNTs improve the water storage capacity of the NBR surface and enhance lubrication efficiency. In the dry wear state, CNTs help reduce scratch depth and dry wear volume.

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.

An enhanced water-lubrication method: Friction-reducing and diffusion properties of secondary lubricants

To prevent severe friction between water-lubricated bearings (WLBs) and stern shafts under harsh conditions, a method is introduced that uses a lubrication pump to supply a small amount of secondary lubricant into the bearing for a short period of time. The effect of the secondary lubricant viscosity on friction-reducing performance is investigated by a modified block-on-ring friction and wear tester. The transfer process of the secondary lubricant within the bearing is observed with a self-designed visualization experimental platform. A flow model for capturing the diffusion of the secondary lubricant is developed, and the flow velocity equations are used as a “bridge” to link the mixed lubrication model and Volume-of-Fluid (VOF) model. The results indicate that injecting the secondary lubricant in the mixed lubrication state has the effect of rapidly reducing the friction coefficient, while supplying the lubricant in the elastohydrodynamic lubrication state tends to increase the friction coefficient. The backflow zones are primarily located at the bearing inner surface and the upper half of the fluid. The high-viscosity secondary lubricant separates into “free lubricant” and “adhesive lubricant” during the transfer process. The “oil-free zone” appears in the lubricating film due to the obstruction of lubricant diffusion by the “backflow effect”. The area of the “oil-free zone” decreases with increasing lubricant viscosity and decreasing load. This study provides a reference for friction-reducing technologies of friction pairs under water-lubrication conditions.

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.

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.

Tribological Properties of Al2O3/Graphite-Al2O3 Laminated Composites under Water Lubrication Conditions

High-performance Al2O3/graphite-Al2O3 laminated composites exhibit an excellent self-lubricating ability for moving components, such as sliding shaft sleeves and dynamic seals. The tribological behaviors of Al2O3/graphite-Al2O3 laminated composites should be studied extensively under water working conditions. Here, we attempted to explore the practicability of the Al2O3/graphite-Al2O3 laminated composite as a sealing material from a tribological point of view under water lubrication conditions. The tribological properties and mechanism of friction and wear of laminated composite ceramics were investigated under dry sliding friction, water environment, and suspended particle working conditions. It was found that the Al2O3/graphite-Al2O3 laminated composite has a better friction performance under water lubrication compared to dry sliding because of the separation effects formed by a water molecule film and a transfer film. Meanwhile, the wear rate under dry contact was found to be approximately six times that under water lubrication conditions. Under the water lubrication conditions, the formation of graphite films and water-adsorbed layers improved the anti-wear properties of the laminated materials, and the friction coefficient and the wear rate were as low as 0.16 and 1.76 × 10−6 mm3/Nm, respectively. Under the suspended particle working condition, the solid particles destroyed the graphite lubricating film and abrasive wear dominated the wear mode. The Al2O3/graphite-Al2O3 laminated composite demonstrates a potential for application in dynamic sealing and sliding components.

Tribological properties of reaction-formed graphite/SiC composites under water-lubricated conditions

Graphite/SiC composites with excellent tribological properties and chemical stability are ideal bearing materials for use in water-lubricated conditions. The composites can be fabricated rapidly by reactive melt infiltration (RMI) with near-net advantages. However, maintaining an adequate carbon content in the matrix after the violent reaction between carbon and liquid silicon is the critical requirement for wear rate and more stable friction coefficient. In this study, a carbon-composite-powder (PFC@G) constructed of graphite particles and glassy carbon derived from phenolic resin, was used as the main carbon source with a larger size (∼200 μm) to improve the carbon content of the graphite/SiC composites. The tribological properties of the composites were measured by a block-on-ring tribometer under water-lubricated conditions. The weight ratio of phenolic resin to graphite particles was adjusted to manipulate the microstructure of PFC@G, which can affect the carbon content of the composites in the course of RMI. The composites with high carbon content (34.47 vol%) were successfully fabricated when the weight ratio is 0.8, which exhibited the most outstanding tribological properties with low friction coefficient (∼0.014) and wear rate (∼10−6 mm3 N−1m−1) at a load of 15 N.

Fluid dynamics simulation on water lubricating performance of micro-/nano-textured surfaces considering roughness structures

With the development of surface precision machining technology and extensive studies on lubrication and friction reduction, the use of surface texture to reduce friction has attracted widespread attention, but few studies have considered the influence of surface roughness on lubrication characteristics. By employing the computational fluid dynamics (CFD) simulation method, the lubrication models with rectangular textures and the introduction of rough asperity structures at the same time are established. The effects of the corresponding structure parameters on the lubrication performance of textured and roughed surfaces are studied under water lubrication conditions. Our results suggest that the adjustment of geometric parameters on the micro-/nano-structured surfaces can influence the load-bearing capacity of the water lubrication film, thus affecting the hydrodynamic lubrication performance on the surface. In addition, the generation of vortex in the micro-textures can bring changes in vorticity, which causes energy dissipation and affects frictional forces. In the lubrication model with rectangular textures, optimal hydrodynamic lubrication performance is obtained under the appropriate depth ratio <i>H</i> = 0.6. Meanwhile, the corresponding lubrication performance can be enhanced by increasing the width ratio (<i>W</i>) of surface texture. After introducing random asperity structures on the micro-textured surface with a standard deviation <i>δ</i> = 0.5, the bearing capacity is increased by 44%, and the friction coefficient is reduced by 30.9%. Moreover, the introduction of half-sine rough asperity structures can only result in relatively minor differences in the lubrication performance, i.e. the changes of bearing capacity and friction coefficient are less than 10%. However, the introduction of compound hierarchical structure consisting of random asperity structures and half-sine rough asperity structures can result in an increase in the corresponding bearing capacity by 42% and a reduction in the friction coefficient by 31.1%, which implies a significant enhancement in the hydrodynamic lubrication performance.

Tribological Behavior of Cotton Fabric/Phenolic Resin Laminated Composites Reinforced with Two-Dimensional Materials.

In this study, cotton fabric-reinforced phenolic resin (CPF) composites were modified by adding four two-dimensional fillers: graphitic carbon nitride (g-C3N4), graphite (Gr), molybdenum disulfide (MoS2), and hexagonal boron nitride (h-BN). The tribological properties of these modified materials were investigated under dry friction and water lubrication conditions. The CPF/Gr composite exhibits significantly better tribological performance than the other three filler-modified CPF composites under dry friction, with a 24% reduction in friction coefficient and a 78% reduction in wear rate compared to the unmodified CPF composite. Under water lubrication conditions, all four fillers did not significantly alter the friction coefficient of the CPF composites. However, except for an excessive amount of Gr, the other three fillers can reduce the wear rate. Particularly in the case of 10% MoS2 content, the wear rate decreased by 56%. Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) were employed for the analysis of the morphology and composition of the transfer films. Additionally, molecular dynamics (MD) simulations were conducted to investigate the adsorption effects of CPF/Gr and CPF/MoS2 composites on the counterpart surface under both dry friction and water lubrication conditions. The difference in the adsorption capacity of CPF/Gr and CPF/MoS2 composites on the counterpart, as well as the resulting formation of transfer films, accounts for the variation in tribological behavior between CPF/Gr and CPF/MoS2 composites. By combining the lubrication properties of MoS2 and Gr under dry friction and water lubrication conditions and using them as co-fillers, we can achieve a synergistic lubrication effect.

The Influence of Scratches on the Tribological Performance of Friction Pairs Made of Different Materials under Water-Lubrication Conditions

Water-lubricated bearings are widely used in marine equipment, and the lubricating water often contains hard particles. Once these particles enter the gap between the bearing and the shaft, they can scratch the smooth surfaces of the shaft and bearing, influencing the working performance of the bearing system. To investigate the effect of scratch parameters on tribological performance, this paper conducts multiple block-on-ring experiments and constructs a mixed-lubrication model under water-lubrication conditions. The results show that among the three commonly used bearing materials, the tribological performance of graphite block is the most sensitive to scratches on the test ring surface. Under the condition of one scratch (N = 1), the loading area of water film pressure is divided into two separate zones (a trapezoidal pressure zone and an extremely low-pressure zone). In addition, the variation of maximum water film pressure is determined by the positive effect (hydrodynamic pressure effect of fluid) and negative effect (“piercing effect” of the asperities). Compared with the scratch depth and scratch location, the scratch width has the most significant effect on the tribological performance of the block-on-ring system. The maximum contact pressure is located at both edges of the scratch due to the formation of a water sac structure. The scratch has a great influence on the transition of the lubrication state of the block-on-ring system. The existence of scratches increases the critical speed at which the lubrication state transits from mixed-lubrication to elastohydrodynamic lubrication, and the critical speed is directly proportional to the scratch width.

Insight into the biomimetic vessel structure of Lignum vitae on its tribological performances

Lignum vitae is well-known as the construction material of water-lubricated bearings due to its excellent tribological performance. Except for the included component, the effect of vessel structure on tribological performance is lack of analysis. In this study, a novel bionic polymer was manufactured based on the arrangement, size and density of Lignum vitae’s vessel. The results of experimental tests showed that the friction coefficient was down 43% and the wear volume is down nearly 38.3% at harsh condition. The tribological performance of Lignum vitae was concluded positively correlates to the size and density of the vessel. The findings reveal a more direct relation between internal structure and tribological properties of Lignum vitae and mechanisms for excellence in water-lubricated conditions.

Tribological Performance of Natural Resin Urushi Containing Graphite under Dry and Water Lubricated Conditions

Tribological Performance of Natural Resin Urushi Containing Graphite under Dry and Water Lubricated Conditions

Effect of picosecond laser texturing on the friction behavior of silicon carbide in hybrid ceramic bearings under dry and water lubrication

Hybrid ceramic bearings consisting of silicon carbide (SiC) and GCr15 steel have a wide range of applications. However, under unlubricated and water lubricated conditions, friction between SiC and GCr15 steel inevitably occurs due to interfacial contact (e.g. dry friction and boundary friction). Laser surface texturing, as a promising surface modification technique, has a significant impact on the material friction and wear characteristics aspects. In this paper, the UV picosecond laser was used to process a groove-textured structure on the surface of silicon carbide ceramics with the aim of comparatively investigating the effect of frictional properties of textured SiC surfaces and untextured SiC surfaces under dry friction and water lubrication conditions. The results showed that the picosecond laser successfully machined surface textures on the hard-to-process SiC surface, and the picosecond laser texturing had a significant effect on the tribological behavior of SiC ceramics. Under dry friction conditions, the coefficient of friction (COF) of picosecond laser-textured SiC with GCr15 steel increased (from 0.249 to 0.296) due to the micro-cutting effect and high surface roughness caused by the texture. In contrast, the COF of picosecond laser-textured SiC with GCr15 was significantly reduced under water-lubricated conditions (from 0.22 to 0.167), due to the facilitated frictional chemical reaction on the laser-textured surface, which favors the improved tribological properties of the silicon carbide friction interface.

Performance of Polymer Composites Lubricated with Glycerol and Water as Green Lubricants

The study analysed the tribological performance of five different polymer composites: polyetheretherketone reinforced with 30% carbon fibres—PEEK CF30, polyetheretherketone reinforced with 10% carbon fibres, 10% graphite and 10% polytetrafluoroethylene—PEEK MOD, polytetrafluoroethylene reinforced with 25% carbon fibres—PTFE CF25, polyoxymethylene with 30% carbon fibres—POM CF30 and ultra-high molecular weight polyethylene—UHMW PE. The polymers were tested under the sliding regime of a reciprocating stainless-steel ball on a polymer disc, with test parameters expected for hydraulic valves. Two environmentally safe lubricants were used: glycerol and water. The selected polymer materials and their tribological properties were compared based on the coefficient of friction and the specific wear rate. The worn surfaces were examined using scanning electron microscopy, and the transfer film was analysed using the energy dispersive spectroscopy technique. When tested in glycerol, a comparable and low coefficient of friction was measured for all polymers (~0.02). At the same time, a significantly lower coefficient was measured for all polymers in glycerol compared to water-lubricated conditions (~0.06–0.22). The polymers differed in the measured specific wear rate, which increases significantly in water for all polymers. A lower specific wear rate was measured for three polymers with higher microhardness: PEEK CF30, PEEK MOD and POM CF30. In water, PEEK CF30 showed superior tribological properties under harsh conditions but was well followed by POM CF30, which showed the most intense transfer film.