This study investigates the formation of electrical fluting erosion on bearing surfaces using a lubricated ball-on-disc tribometer. The “washboarding effect” is firstly proposed to account for fluting evolution during electrical erosion. Results show that elevated voltage extends the discharge region beyond the Hertzian contact area. Thicker oil films, resulting from higher velocity or viscosity, increase the critical breakdown voltage and decrease the fluting spacing. Additionally, mechanical-electrical coupling under slide-roll conditions significantly exacerbates surface degradation. Fluting is observed to evolve from initial frosting damage. Analogous to the “washboard” phenomenon on the unpaved roads, it is thought the initial ridge/flute morphology is irreversibly recorded and progressively amplified under follow-up rolling, forming fluting erosion with alternating “bright” and “dark” areas.

Water invasion is a primary cause of grease lubrication failure, the mechanisms of which can be effectively investigated using the ball-on-disc test rig. However, traditional experimental methods, such as pre-mixing grease with water or directly adding water into the contact, fail to accurately replicate the water distribution on the rolling track in humid environments. Here, a conventional ball-on-disc apparatus was modified by coupling it with a unit for precise relative humidity control. This paper investigates the influence of water on film formation, lubricant distribution, and replenishment for both oil and grease lubrication. The results showed that water plays an important role by influencing the lubricant flow and rheological properties of grease on film formation. For oil lubrication, higher relative humidity extended cavitation length in the outlet region by altering local pressure distribution, reducing oil-water surface tension. For grease lubrication, direct water mixing rapidly degrades performance through immediate thickener-water interaction, emulsification, and structural softening. In contrast, humidity-driven water invasion causes slower but progressive damage by gradually weakening the thickener network. These findings provide valuable insights into lubrication failure under humid conditions, support the development of water-resistant greases, and present a novel test method.

In this paper, we prepared series of DLC-Si films on 304 stainless steel by adjusting the flux of C6H18OSi2 (HMDSO) using the high-power pulse magnetron sputtering (HiPIMS) system. The effects of different Si contents on the tribology performance and electrochemical properties of DLC-Si films were evaluated. The results suggested that the film showed favorable tribological properties and corrosion resistance with 9.26 at.% Si content, and this can be attributed to the incorporation of Si elements changed its graphitization ratio, friction chemistry, and plastic transfer behavior. Furthermore, the formation of hydrated silica gel during the friction process resulted in the lowest coefficient of friction (0.084) and wear rate (2.124 x 10_ 7 mm3/(Nm)) in seawater. Furthermore, icorr of DLC film reduced three orders of magnitude (3.397 x 10_8 A/cm2) when compared to the 304 substrate, this is due to its inherent chemical inertness and the compact structure of films. The results suggested that the DLC-Si films with low friction coefficients and high corrosion resistance, could effectively prolong the service life of moving components in seawater environments. This provides a theoretical foundation for the application of these films in such environments.

In this work, the idea of water lubrication enhanced with a small quantity of oil was tested for the first time in a rubber journal bearing. A small quantity of silicone oil was supplied to an eight-groove rubber bearing through a small nozzle, aiming to improve the lubrication of the bearings under short-term severe working conditions. The results demonstrated that the addition of small quantities of silicon oil can significantly reduce friction, with the coefficient of friction (COF) at certain speeds being lower than that achieved with either pure water or pure oil. If the oil was given under frequent and small-quantity supply, a smaller time interval of oil supply has little impact on friction reduction. Moreover, a simple method based on the Stribeck curve was proposed to roughly predict the COF reduction of water-lubricated journal bearings with a small quantity of oil supply at low speeds. Additionally, computational fluid dynamics (CFD) simulations provided insights into the migration/diffusion of injected oil within the bearing, revealing a correlation between the oil-side leakage and the COF.

High-performance transformer oils require excellent thermal stability and electrical insulation, making polyol esters (POE) synthesized from trimethylolpropane (TMP) and fatty acids ideal base oils for advanced transformers. The synthesis efficiency of POE is largely dependent on the catalytic system employed. This work employs acetic acid (HAc) as a green, low-cost modulator to fabricate defective UiO-66 for the esterification of TMP esters, a key reaction in transformer base oil production. The UiO-66 were characterized, and their catalytic performance was evaluated via single-factor tests, response surface methodology (RSM)-Box-Behnken design (BBD) optimization, density functional theory (DFT) calculations, and reusability experiments. HAc modification introduced controllable linker defects while preserving the crystal framework, creating abundant coordinatively unsaturated Zr4+ (CUS-Zr4+) Lewis acid sites, raising specific surface area by 40.89% and total acidity by 10.20%. Under optimized conditions, esterification conversion exceeded 95%, and the catalyst showed outstanding reusability and stability. DFT revealed that CUS-Zr4+ strengthened substrate adsorption, promoted electron transfer, polarized n-octanoic acid C--O, and weakened TMP O-H bonds, thus activating key sites and accelerating the nucleophilic step of esterification.

In this study, an elastoplastic finite element (FE) contact model was developed to evaluate the plastic deformation of a surface induction-hardened tapered roller bearing used in wind turbines, incorporating depth-dependent material properties and heat treatment-induced residual stress distribution. The validity of this model was confirmed by comparing the calculated plastic deformation with measured profiles from static compression experiments. The results show that the residual stresses generated by induction hardening have a significant influence on the elastoplastic behavior of bearings. Based on this model, a parametric analysis was performed to investigate the effects of surface hardening depth (SHD), contact pressure, and residual stress on surface plastic deformation. Empirical formulas were developed to predict surface plastic deformation and evaluate material yielding for surface-hardened tapered roller bearings, thereby preventing excessive deformation during service. This allows for the rapid estimation of the maximum plastic deformation for different hardening depths and provides an efficient approach for assessing the yielding risk.

Rolling contact fatigue(RCF)failures in critical components such as precision gears and high-performance bearings have become increasingly prominent under demanding conditions.Conventional lubricant additives struggle to reduce friction simultaneously,resist wear,and repair dynamic micropitting.To address this challenge,a composite material of ionic liquid-functionalized magnesium silicate hydroxide(MSH)([DDP][TOA]/MSH(DDP=dialkyl dithiophosphate,TOA=trioctylamine))was synthesized using hydrothermal synthesis and noncovalent modification.This composite exhibited remarkable dispersion stability and copper corrosion inhibition,as well as superior tribological properties,including friction reduction,wear mitigation,and micropitting repair during rolling-sliding contact.Tribological evaluations revealed that 1.0 wt%[DDP][TOA]/MSH reduced the friction coefficient by 17.2%and the wear volume by 52.5%,demonstrating unprecedented load-bearing capacity and frequency adaptability.Notably,under rolling-sliding contact fatigue conditions,commercial gear oil exacerbated micro-pitting damage continuously,whereas the composite material repaired damage,with a repair efficiency of 72.0%.Surface characterization reveals a three-stage mechanism for the dynamic repair of worn metal surfaces:(1)micro-asperities are removed through mechanical grinding,(2)micro-cracks are filled via tribochemical deposition of FeS/phosphate phases,and(3)a hybrid a-SiC/a-SiOx repair layer is formed with improved mechanical strength,effectively preventing fatigue wear propagation.This work demonstrates the synergistic effect of ionic liquids and layered silicate additives on micropitting repair under rolling contact fatigue,expanding the application of MSH in the field of commercial lubricant additives.

This study examines how the molecular structures of oiliness additives affect the lubrication performance of a step slider bearing. Here an optical step-slider-on-disc tribometer was used to measure interferometric film thickness together with friction force under the present test conditions. Seven representative molecules (undecanedioic acid, undecanoic acid, palmitic acid, stearic acid, oleic acid, oleylamine and oleyl alcohol) were each blended into PAO8 at 0.15 wt% to separately probe headgroup polarity, alkyl-chain length, saturation and the number of polar heads. Compared with neat PAO8, every formulation produced a thicker film (up to 106% increase) and a lower coefficient of friction (up to 65.9% reduction), with stearic acid delivering the best overall improvement. To interpret the trends, wettability of the step-slider surface after lubricant treatment was assessed by deionized-water contact-angle measurements. The observed inlet-outlet wetting asymmetry is consistent with a possible asymmetry in interfacial slip, which may contribute to the experimentally observed combination of film-thickness increase and friction reduction.

Fluting damage has been extensively studied, and its formation mechanism involves mechanical action and periodic electrical discharges. In this study, periodic discharges induced by film reconstruction were simulated using modified hybrid bearings, repeatedly reproducing fluting damage. It is confirmed that periodic discharges induced by film reconstruction are the key factor leading to the fluting formation. The fundamental cause of periodic discharge lies in the interplay between the discharge-induced film suppression effect and the hydrodynamic pressure effect, which occurs under the influence of lubricant replenishment. The introduction of ceramic balls further intensifies film reconstruction by altering the lubricant flow distribution, thereby causing more severe damage in the modified hybrid bearings. The surface characteristics suggest that under high power conditions, fluting damage is more likely to occur. Moreover, test results show that conductive grease based on ionic liquids can reduce the contact resistance in the resistive state, while in the capacitive state it facilitates current transfer through the contact. A 3D energy model was established, further elucidating the relationships between fluting damage pattern, contact zone geometry, and the surrounding oil film distribution.

Fatigue wear under rolling-sliding contact remains a critical constraint on gear and bearing service life in highstress applications. This study employed coupled SRV and MPR tribological platforms to conduct extendedduration tests, elucidating the contact-mode-dependent synergy between zinc dialkyldithiophosphate (ZDDP) and friction modifiers (FMs: MoDTC, ODMP, DFA). Key findings demonstrate that contact stress modes govern failure mechanisms. Synergistic friction/wear reduction occurred under sliding (e.g., ZDDP-MoDTC reduced COF by 34% versus ZDDP), whereas oscillating Hertzian stress induced antagonistic effects under rolling-sliding. Organic phosphorus-containing tribofilm exacerbated micropitting, while DFA inhibited crack propagation via viscoelastic dissipation; A critical ZDDP concentration threshold exists - 3%ZDDP minimized wear but amplified micropitting risk due to film brittleness, triggering a sharp increase in centre line average (CLA) after 4 h, while 2%ZDDP balanced wear and micropitting resistance. Long-term stability testing revealed DFA's superior performance beyond 30 h, maintaining CLA stability through dynamic film reconstruction, whereas ODMP accelerated failure at 12 h via spallation cascades. This work establishes interfacial film toughness and dynamic stability as pivotal design criteria for lubricants, ultimately providing technical support for developing fatigueresistant lubricants in wind turbines and electric vehicle transmissions.

The incorporation of calcium carbonate as an additive into calcium sulfonate grease poses significant challenges in achieving stable extreme pressure and anti-wear effects due to the complex thickening mechanism inherent in calcium sulfonate grease. To address this issue, using the synergistic effect between graphene oxide (GO) and calcium carbonate (CaCO3) could provide a promising solution to exhibit a substantial reduction in friction and wear. In this paper, oleic acid modified CaCO3 deposited on graphene oxide (CaCO3@GO) was prepared and used as additives in calcium sulfonate grease. Tribological results indicated that the introduction of an optimal quantity of CaCO3@GO (3 wt %, CaCO3: GO with 2:1) exhibited a substantial steady friction coefficient for CSG under high load (500 or 600 N) compared to pure CSG, CSG with GO (1 wt%), CaCO3 (2 wt%), and mixed GO (1 wt%) with CaCO3 (2 wt%). In particular, CaCO3@GO could reduce the wear volume by 88% compared with pure CSG. In comparison with single (GO or CaCO3) or mixed additive (GO with CaCO3), the good lubricating performance was ascribed to the formation of continuous and enhanced protective films by the synergistic tribological effect in the structure of CaCO3@GO.

Open-water-lubricated thrust bearings in rim-driven thrusters (RDTs) suffer severe sediment intrusion in coastal environments, destabilizing the water film and accelerating wear. This study investigates the effects of quartz particle size (4.5, 25, and 50 μm) on the friction and wear of a polymer/ZCuAl9Mn4 thrust-bearing pair under varying loads and speeds. Particle intrusion shifts the interface toward mixed or boundary lubrication. Higher speeds and loads suppress friction fluctuations by enhancing hydrodynamic lift and promoting particle embedment, respectively. At intermediate and high speeds, entrained quartz and metallic debris embed into the polymer, forming a composite layer. This mitigates pad wear but acts as an abrasive surface, increasing disc wear via micro-cutting. Conversely, at low speeds, insufficient metallic debris prevents composite layer formation, allowing trapped quartz to severely plough the exposed polymer. Characterization confirms a particle-embedding-assisted abrasive wear mechanism, where larger particles cause more severe ploughing. An Archard-based model identifies rotational speed as the dominant factor governing disc wear, with its sensitivity index increasing with particle size. Overall, friction and wear do not vary monotonically with particle size but are governed by coupled effects of size, film thickness, embedment, and fluid transport. These findings elucidate sediment-induced wear mechanisms and provide data for the service-life prediction of water-lubricated thrust bearings.

In this study, Fe2CrNiNbx (x = 0 – 1.0) medium-entropy alloy (MEA) coatings were fabricated by laser cladding to systematically investigate the effect of Nb content on phase evolution, microstructural refinement, and cavitation erosion resistance. X-ray diffraction (XRD) Rietveld refinement revealed that Nb addition promoted the transition from a single-face-centered-cubic (FCC) solid solution to an FCC + Laves-type dual-phase structure, with the Laves-type phase fraction increasing from 12.4% for Fe2CrNiNb0.4 to 25.7% for Fe2CrNiNb1.0. EBSD analysis demonstrated significant grain refinement with increasing Nb content, as evidenced by a reduction in average grain size from 65.79 μm in the Nb-free coating to 23.80 μm in the Fe2CrNiNb1.0 coating, corresponding to an approximately 64% decrease. This microstructural refinement is associated with rapid solidification, Nb-assisted heterogeneous nucleation, and grain-boundary pinning during laser cladding. Consequently, the average microhardness increased monotonically from 177.8 HV in the Nb-free coating to 554.3 HV in the Fe2CrNiNb1.0 coating. Nanoindentation results further showed that the Fe2CrNiNb1.0 coating exhibited the highest H3/E2 value of 7.05 × 10−5 GPa, suggesting improved resistance to localized plastic deformation. Ultrasonic cavitation tests demonstrated that the cumulative mass loss after 12 h decreased substantially from 73.9 mg for the 316L stainless-steel substrate to 4.7 mg for the Fe2CrNiNb1.0 coating, whereas the erosion rate stabilized at 0.79 mg/h. Moreover, the surface roughness (Ra) after cavitation erosion decreased from 3.2478 μm for the Nb-free coating to 0.2830 μm for the Fe2CrNiNb1.0 coating, confirming the suppression of surface roughening and local spallation. The enhanced cavitation erosion resistance was attributed to the synergistic strengthening-toughening effect of grain refinement, increased hardness, and the FCC + Laves-type dual-phase architecture. Within this architecture, Nb-rich Laves-type regions constrain localized plastic flow and crack propagation, whereas the FCC matrix provided strain accommodation. These findings suggest that Nb-mediated dual-phase microstructural engineering is an effective strategy for improving the surface stability of Fe–Cr–Ni-based MEA coatings under fluid-impact conditions.

Environmentally benign water-based lubricants are attracting increasing attention as alternatives to conventional oil-based lubricants that may cause environmental pollution. Herein, three protic poly(ionic liquid)s (PPILs) are synthesized by combining a copolymeric cation with carboxylate anions of different alkyl chain lengths. The PPILs are employed as additives in aqueous lubricants, and their viscosity-enhancing capability and tribological performance are systematically evaluated. Quartz crystal microbalance (QCM), electrical contact resistance (ECR), X-ray photoelectron spectroscopy (XPS), and time-of-flight secondary ion mass spectrometry (TOF-SIMS) are used to elucidate the lubrication mechanism. The results demonstrate that PPILs significantly improve the viscosity, corrosion resistance, and tribological properties of water-based lubricants. Notably, the kinematic viscosity of a 6% PPD-Oa aqueous solution increases by two orders of magnitude compared with deionized water, while the corresponding wear volume and coefficient of friction are reduced by approximately 77% and 70%, respectively. Mechanistic investigations indicate that interfacial adsorption and friction-induced chemical processes jointly generate a protective layer at the sliding interface, thereby imparting excellent lubricity and load-bearing capability to the lubricant. Moreover, the three sulfur-free and halogen-free PPILs represent environmentally benign additives with strong potential for application in metalworking fluids and hydraulic systems.

A limited supply of lubricant can minimize energy dissipation and waste, enabling lean lubrication. However, insufficient lubricant supply can lead to a critical issue known as starved lubrication, emphasizing the need to address this concern under limited lubricant supply (LLS) condition. In this study, a ball-on-disc lubricating film test rig, with a circular contact, was employed. The impact of zinc dialkyl dithiophosphate (ZDDP) interfacial adsorption on the lubrication characteristics under LLS condition was investigated by introducing ZDDP as an anti-wear additive. A dichromatic interference intensity modulation (DIIM) approach was utilized to reveal the evolution of the lubricant film at various lubricant supply stages under LLS. Three distinct lubricant supply stages were identified: the fully flooded stage, the transition stage from fully flooded to starved lubrication, and the starved lubrication stage. The mechanism of ZDDP interfacial adsorption during different lubricant supply stages was evaluated by analyzing variations in oil reservoir morphology, lubricant film thickness, and friction coefficient. The results indicate that, under LLS conditions, changes in the oil reservoir directly influence the transition between lubricant supply stages. The adsorption effect of ZDDP was found to promote lubricant entrainment and improve the lubricant supply in the inlet area during the second and third lubricant supply stages, thereby enhancing the anti-collapse capacity of the lubricant film. Additionally, in the LLS condition, the improved anti-friction effect of ZDDP is attributed to the synergistic impact of enhanced lubricant entrainment and increased shear resistance.

Great attention has been focused on the IrOx with enriched oxygen vacancies as the exceptional oxygen evolution reaction (OER) catalyst due to its remarkable stability and catalytic performance during operations. The systematical quantify of the oxygen vacancies on the OER performance of the IrOx has not been previously reported to the best of our knowledge. Herein, series IrOx catalyst films with various oxygen vacancies concentrations were fabricated on the titanium felt surface (IrOx@Ti) through magnetron sputtering by adjusting the oxygen partial pressure during the deposition process. In addition, the iridium loading significantly reduced to 0.06 mg cm-2 comparing to the traditional commercial membrane electrode (more than 2 mg cm-2). Electrochemical experiments and electrolytic cell testing demonstrated that the IrOx@Ti possesses excellent catalytic performance and stability under a current density of 1 A cm-2. This research offers valuable insights into the correlation between oxygen vacancy levels and the high OER performance of IrOx catalysts, as well as guidelines for the design and synthesis of high-performance OER catalysts.

Gears are key components in the transmission system of high-speed railway trains, and their reliability is critical for the safe operation of trains. This study investigates the commonly used high-speed railway gear steel, 20CrNi2Mo, through systematic experimental and theoretical analysis. Based on the experimental results, it was found that the viscous effects of 20CrNi2Mo steel can be neglected, while the material exhibits significant changes in the hysteresis loop shape under cyclic loading. As the number of loading cycles increases, the hysteresis loop gradually becomes shorter and wider. Even when the applied stress is below the yield limit, initial deformation is primarily elastic, but plastic deformation and hysteresis loops develop over time. This phenomenon demonstrates a gradual reduction in the yield stress of the material under identical loading conditions, accompanied by a decline in elastic modulus. It further elucidates the evolution mechanism from elastic deformation to plastic failure during the fatigue process. Based on these experimental findings, the proposed constitutive model integrates improved fatigue damage evolution laws and coupling methods, incorporating elastic modulus and yield stress as damage factors. This model effectively explains material softening, hysteresis loop rotation, and widening observed during the fatigue process. Simulation results confirm that the model accurately captures the mechanical behavior at each stage of fatigue, with predicted life expectancy closely aligning with experimental outcomes. These findings provide a solid theoretical foundation and valuable reference for the failure analysis of gear transmission.

Four FeCrCoMn high-entropy alloy coatings with different preset body sizes are prepared on the surface of 45 steel substrates by laser cladding technology, and the effect of preset body size on the corrosion performance of the coatings is analyzed. The results show that the phase composition of samples with various preset body sizes are all FCC and HCP solid solution structures. However, the microstructure and morphology of the coating are transformed from equiaxial crystals to columnar dendritic crystals with the increase in the preset body size and the size of more than 10-mm grains coarsen obviously, which results in the gradual decrease in hardness and aggravation of the abrasion. The corrosion mechanism of the coating is mainly pitting, and the wear mechanism is mainly abrasive wear, adhesive wear and corrosive oxidative wear. With the increase in the preset body size, the corrosion and abrasion resistance of the coating increases first and then decreases. When the preset body size is 15 mm, the coating has high corrosion protection efficiency due to the dense structure of the coating and few solidification defects, which makes the coating show excellent corrosion and abrasion resistance.

ObjectivesDue to the complexity of the grinding process, the study of the grinding mechanism has always been a research hotspot in the field of precision grinding. The establishment of an accurate surface topography model of the grinding wheel circumference is an important basis for studying the grinding mechanism. The surface topography of the corundum grinding wheel is accurately described using four parameters, namely the shape of the abrasive grain, the size of the abrasive grain, the height of the abrasive grain bulge and the number of abrasive grains per unit area. The corresponding grinding wheel model is established using Matlab.MethodsTo construct a circumferential surface morphology model of the corundum grinding wheel using Matlab simulation software, the geometric shape of the abrasive particles is first simplified to a truncated cone with a cone angle of 45° based on the actual shape of the abrasive particles in the corundum grinding wheel. By using the center coordinates of the large and small circular surfaces of the truncated cone abrasive particles and the radius variation relationship at different axial heights, an arbitrary truncated cone particle with size d is constructed using the cylinder function. Secondly, based on the corresponding grinding wheel circumferential surface established in the cylindrical coordinate system, the rand random function is used to randomly generate Nt grinding particle position coordinates on the circumferential surface. Based on the phenomenon that the grinding particle size and the protrusion height both follow the normal distribution law, the normrnd function is used to generate circular truncated grinding particles with randomly distributed positions on the grinding wheel circumferential surface. Then, a collision detection method is used to check whether there is interference between the abrasive grains, that is, the distance between the centers of the small circular surfaces of any two adjacent truncated cone abrasive grains should be greater than or equal to the sum of the radii of the large circular surfaces of the two abrasive grains. Finally, the real grinding wheel surface topography and the constructed grinding wheel surface topography model are compared and analyzed to determine the accuracy of the modeling method in this paper.ResultsA corundum grinding wheel model is constructed with a diameter and width of 20 mm and 4.5 mm, particle size code of F80, grinding wheel structure number of 7, abrasive rate of 48% and grinding particle size of 152 to 178 μm. The following results are obtained: (1) The distance between any adjacent truncated cone abrasive grains is narrow, and there is no interference between abrasive particles. The position distribution of abrasive particles on the surface of the grinding wheel is in accordance with the random distribution characteristics, and the surface topography of the grinding wheel produces blocky and narrow strip-shaped gap areas. (2) The total number of abrasive grains calculated theoretically is 9 342, while the total number of abrasive grains generated in the model is 8 626, with a relative error between the two of only 7.66%. (3) The size distribution of the abrasive grains and the protrusion height distribution of the abrasive grains in the model are statistically analyzed, and it is found that the distribution patterns are consistent with the normal distribution curve set in the modeling.ConclusionsThe abrasive grain shape can be set to a truncated cone with a cone angle of 45°, and the size of the truncated cone abrasive grains can be converted from spherical abrasive grains based on the principle of volume invariance, which aligns with the actual abrasive grain shapes observed in real grinding wheels during the grinding process. Compared with the traditional modeling method for grinding wheel morphology, the modeling method proposed in this paper does not require complex coordinate transformations between the grinding wheel circumferential surface and its unfolded plane, and can obtain a model of the grinding wheel circumferential surface morphology where the size of the truncated cone abrasive grains and the height of the protrusions follow the normal distribution law, and the position of the abrasive particles are randomly distributed. The model has high similarity to the distribution characteristics of real grinding wheel topography, and the grinding wheel surface forms irregular block-shaped and narrow strip-shaped gap areas. Therefore, this modeling method is suitable for the establishment of a corundum grinding wheel circumferential surface topography model. The microscopic contact mechanism between the grinding wheel and the workpiece surface can be further explored through this model, and a grinding surface topography prediction and analysis model can be established.