Search Results (345)

To improve the wear resistance of 45 steel, nano-agglomerated Al₂O₃-TiO₂-CeO₂/carbon nanotubes (CNT) composite powders were prepared by spray drying and ball milling, followed by plasma spraying to fabricate coatings. The effect of CNT content on microstructure and wear resistance was investigated. The powders showed uniform size and high sphericity. Coatings mainly consisted of α-Al₂O₃, γ-Al₂O₃, and TiO₂. CNT addition refined grain size to 18.3 ± 1.1 nm. The high thermal conductivity of CNT reduced unmelted particles, improving coating density and element uniformity. Average coating thickness was 200 μm. When the CNT content reached 3 wt.%, the coating porosity decreased to 5.01 ± 0.72%. TEM analysis indicated that CeO₂ was mainly located at the grain boundaries. Moreover, the interfaces between CNT (002) and CeO₂ (220) appeared clean and well-bonded. As CNT content increased, microhardness and wear resistance first increased then decreased. At 3 wt.% CNT, the volumetric wear rate was 0.87 ± 0.15 × 10⁻⁵ mm³·N⁻¹·m⁻¹, representing an 8.46-times improvement in wear resistance compared to the substrate. The presence of CeO₂ enhanced the surface activity of CNT, facilitating the formation of lubricating films during friction and contributing to the superior wear resistance of the composite coating. Full article

This work examines the machining responses of dry turning in ultrasonic-assisted stir-squeeze cast A356 hybrid nanocomposites reinforced with zirconia (ZrO₂) and graphene oxide (GO). Accordingly, flank wear (VBc) ranged from 0.061 to 0.238 mm, influenced by abrasion, adhesion, built-up edge (BUE) formation, and diffusion mechanisms. Cutting speed had the most significant effect on flank wear (65.65%), followed by depth of cut (18.2%) and feed rate (11.13%), supported by a well-fitted regression model (R² = 0.987; p < 0.05). Surface roughness (Ra) ranged from 1.733 to 7.012 μm, with cutting speed, feed rate, and depth of cut contributing 70.42%, 15.43%, and 9.56%, respectively. The cutting temperature was limited to 127 °C, primarily influenced by cutting speed (60.68%), whereas cutting power varied between 0.353 and 0.644 kW, mainly governed by cutting speed (68.71%) and depth of cut (25.92%). The chip morphology showed a segmented sawtooth pattern due to cyclic fracture initiation during material removal. Multi-criteria optimization using complex proportional assessment (COPRAS) identified v = 90 m/min, f = 0.06 mm/rev, and d = 0.1 mm as the optimal parameters, yielding a tool life of 22.6 min and a machining cost of INR 58.69 per item. This research is further focused on the implementation of different cooling lubrication techniques utilizing environmentally friendly cutting fluids, including Minimum-Quantity Lubrication and nano-MQL, among other types of environments. Full article

The rapid growth of electric vehicles and electrified systems has increased the risk of bearing failures due to combined mechanical and electrical stresses. This study investigated the performance of hexagonal boron nitride nanoparticle-enhanced lithium grease under electrified conditions. Experiments based on a Taguchi L9 orthogonal array were conducted on deep groove ball bearings using a full-scale test rig at 1200 rpm with varying loads (100–300 N), currents (6–10 A), and hBN concentrations (0.1–1 wt.%). The tribo-electrical performance of nano-enhanced grease was compared with the base grease and commercial grease. It was observed that the base grease exhibited superior performance with a lower current flow, reduced vibration, and minimal surface degradation. In contrast, the hBN-enhanced grease exhibited inferior tribo-performance, with high vibrations and surface damage in electrified conditions. The surface analysis revealed features morphologically similar to white etching areas and micro-pitting. The FTIR results indicated grease degradation, while ICP-OES confirmed higher wear debris generation in the commercial and hBN-added greases. The present work indicates that additives like hBN nanoparticles do not necessarily improve performance under electrified conditions, making it important to consider the type of additives to be added during lubricant formulation. Thus, the findings emphasize the importance of lubricant formulation for controlling electrically induced bearing failures and provide insights for developing advanced greases for electric machinery applications. Full article

The influence of BN particle size on lithium grease performance was systematically compared among a base grease (Li), a micro-BN (3 µm, 0.1 wt%) modified grease (Li + 0.1% mBN), and a nano-BN (50 nm, 0.1 wt%) modified grease (Li + 0.1% nBN). SEM shows that addition nano-BN leads to a more compact soap fiber networks, whereas micro-BN tends to agglomerate and provides limited reinforcement, leaving the base grease with a loose, porous network. Consequently, Li + 0.1% nBN outperforms both Li and Li + 0.1% mBN in dropping point (199.5 °C vs. 194.9 °C and 198.6 °C), oil separation (0.39% vs. 0.64% and 0.44%), and flow point (49% vs. 45% and 47%). Its plateau modulus is significantly higher, reflecting stronger network entanglement. However, Li + 0.1% nBN shows lower structural recovery (61.0%) than Li (65.8%) and Li + 0.1% mBN (67.2%) due to rigid particle–fiber junctions. Notably, Li + 0.1% mBN exhibits a unique frequency-dependent viscoelasticity: higher tanδ at low frequencies but lower tanδ at high frequencies relative to Li. Tribologically, Li + 0.1% nBN reduces friction coefficient by 35% and wear scar diameter by 12.7% compared with Li, outperforming Li + 0.1% mBN. XPS confirms a protective hybrid tribofilm (BN + organic nitrogen species + iron oxides) on the nano-BN lubricated surface. Particle size critically governs BN–fiber interactions and the resulting rheological and tribological performance. Full article

In response to the harsh operating conditions of high-speed, high-temperature bearings in new energy vehicle drive motors, this study focuses on enhancing the performance of polyurea-based gel greases through the use of nano-additives. Using polyurea-based gel grease as the matrix, nano-composite gel greases with different CeO₂ loadings were prepared, and their tribological properties and rheological behavior were characterized using four-ball friction tests, rheological testing, and SEM analysis. The results indicate that adding 0.5 wt% CeO₂ increased the grease’s yield stress by approximately 75.4% and significantly raised its apparent viscosity. This rheological enhancement effect may be attributed to the physical adsorption of ultrafine particles onto the polyurea fiber network and potential interfacial interactions between the particles and the fiber surfaces. Compared to the original grease, the average coefficient of friction decreased by 10.4%, and the average wear scar diameter decreased by 12.7%. Meanwhile, the shear stress increased by 110.41 Pa, and the viscosity increased by 1102 Pa·s. This study provides experimental evidence and technical references for the development of high-performance gel lubricants suitable for motor bearings operating under high-temperature conditions. Full article

Under complex friction conditions, base oils usually exhibit insufficient friction-reducing and anti-wear performance, poor shear resistance of the lubricating film, and weak interfacial adsorption stability. Herein, graphene oxide (GO) was surface-modified with the silane coupling agent KH550 and compounded with Ag nanoparticles to fabricate a silver/modified graphene oxide (Ag/KGO) composite lubricant additive. The microstructure and chemical characteristics of the Ag/KGO composite were characterized by SEM, XRD, FTIR, and Raman spectroscopy. Tribological tests performed on a Si₃N₄/GCr15 friction pair demonstrated that the lubricant containing 0.15 wt% Ag/KGO achieved the optimal tribological performance, with the average friction coefficient decreasing to 0.053, 51.8% lower than that of the base oil, and the wear scar width and depth decreasing by 34.5% and 75.7%, respectively. Molecular dynamics simulations revealed that Ag/KGO enhanced the interfacial adsorption strength and improved the shear stability of the lubricating film. Mechanism analysis indicated that KGO facilitated the formation of a stable lubricating film at the friction interface, while Ag nanoparticles acted as nano-bearings. Their synergistic effect reduced interfacial shear resistance and alleviated wear. These findings provide theoretical support for the design and development of high-performance composite lubricant additives. Full article

Cellulose ether, like hypromellose (HM), is an extremely versatile material that is widely used in pharmaceutical products as film coatings. To modify the surface properties of HM films, additives are routinely included during the film formulation process, which are typically hydrophobic lubricants or hydrophilic plasticizers. Plasticizers increase the flexibility and reduce the brittleness of the film. The first goal of this study is to demonstrate that plasticization of HM films by low-molecular-weight (400 g∙mol⁻¹) polyethylene glycol (PEG) allows tuning adhesion and friction properties of HM films, both at nano- and macroscales. Surface morphology, surface energy, nano/macro adhesion, and nano/macro friction coefficient were studied by atomic force microscopy (AFM) in adhesion or friction modes at the nanoscale, wettability, and probe-tack adhesion, as well as pin-on-disk friction experiments at the macroscale. The results show that the addition of PEG decreases the Young’s modulus and the Tg of HM-plasticized films while increasing their strain at break and surface energy. The macroadhesion force increases from 9 to 90 mN by the addition of 40% w/w of PEG, whereas the macrofriction coefficient is reduced by 50%. The hypothesis of insertion of plasticizer molecules in HM chains’ nano-domains is evidenced and explains these results. The second goal of this study is to investigate nanoscale versus macroscale correlation of adhesion and friction properties and the role of adhesion in friction experiments. The results show, first, that the evolution of the adhesion energy at the macroscale as a function of adhesion energy at the nanoscale is linear. On the contrary, a high friction coefficient at the nanoscale corresponds to a low friction coefficient at the macroscale and vice versa, showing a first linear decrease for PEG contents ranging from 0 to 30% (w/w) and the second linear decrease, less pronounced, is observed for PEG contents ranging from 30 to 40% (w/w). The hypothesis of a difference in contact pressure applied on the probe at both scales, as well as HM-PEG surface phase separation at a high PEG content (>30% w/w), is proposed to explain this difference. The variations in friction coefficients are linear according to the PEG plasticizer content and suggest its lubricant role in HM-Plasticized films. Finally, the interplay between adhesion and friction, in friction experiments, is evidenced and appears dominant at the nanoscale. Full article

In this study, nanolubricants based on SAE 5W-30 mineral oil were formulated using oleic acid-functionalized graphene nanoplatelets (GNPs), and their colloidal stability, rheological behaviour, thermal stability, and tribological performance under cold rolling conditions were systematically investigated. The nanolubricants were prepared at GNP concentrations of 0.05, 0.1, 0.2, 0.4, and 0.6 wt%. FT-IR analysis confirmed successful functionalization, evidenced by the characteristic C=O band at approximately 1710 cm⁻¹ and changes in CH₂ stretching vibrations in the 2850–3000 cm⁻¹ range. UV–VIS results indicated initially homogeneous dispersions; however, after three days, relative concentrations decreased to 95%, 90%, and 75% for 0.05, 0.2, and 0.6 wt% GNPs, respectively. Viscosity measurements showed minimal variation at low concentrations, with only a 0.64% increase at 0.2 wt% compared to the base oil. TGA revealed enhanced oxidative stability at low GNP contents, with the oxidation onset temperature increasing from 205.3 °C to 207.2 °C at 0.05 wt%, while a marked decline was observed at higher concentrations (176.8 °C at 0.6 wt%). In cold rolling experiments at a 3% reduction ratio, the rolling force was measured at 1341 N/mm with the neat lubricant, decreasing to 1210 N/mm with a lubricant containing 0.1 wt% GNPs, corresponding to an approximate 10% reduction. Compared with dry conditions, this reduction was approximately 21%. Surface roughness and 3D topography analyses further showed that GNPs-containing lubricants reduced asperities and promoted the formation of a more uniform tribofilm. At low concentrations, the improved lubrication performance of oleic acid-functionalized graphene nanoplatelets is attributed to their homogeneous dispersion in mineral oil, where physically adsorbed oleic acid improves colloidal stability by reducing agglomeration and promotes the formation of a stable tribofilm, facilitating interlayer sliding under boundary lubrication conditions. Overall, the findings demonstrate that oleic acid-functionalized GNPs, when used at optimal concentrations, significantly enhance both lubricant stability and cold rolling performance. Full article

Rolling bearings operate under complex contact conditions, and their tribological and dynamic behaviors are highly sensitive to their lubrication performance. Based on previous studies on surface texturing, three types of representative textures (wholly distributed dimples, locally distributed dimples, and grooves) with optimized parameters were fabricated on the shaft washers using the laser marking method. This was done to investigate the synergistic effect of surface textures and polytetrafluoroethylene (PTFE) nano-additives on the tribological and friction-induced vibration performance of cylindrical roller thrust bearings under starved lubrication. Lubricating oils containing various mass fractions (0.5 wt%, 1.0 wt%, and 3.0 wt%) of PTFE nano-additives were prepared and employed. The coefficients of friction (COFs), wear losses, worn morphologies, and time/frequency-domain vibration responses were analyzed. The results show that the appropriate integration of surface textures and solid lubricant additives can establish a highly effective synergy for rolling bearings under starved lubrication. PTFE nano-additives significantly improved the tribological performance of the smooth bearings and those with dimples (both wholly distributed and locally distributed), with the optimal performance observed at a mass fraction of 3.0 wt%. In contrast, the tribological performance of the groove-textured bearings noticeably deteriorated with the addition of PTFE nano-particles, especially at higher mass fractions. The bearing with wholly distributed dimples exhibited the best overall tribological performance at a mass fraction of 3.0 wt%, achieving a 61.8% reduction in the average COF, a 99.6% reduction in wear loss, and significantly suppressed vibration amplitudes. Full article

Despite the growing adoption of Ti6Al4V-ELI made by Laser Powder Bed Fusion (LPBF) in tribologically demanding applications, the influence of hybrid nanoparticle additives on its lubrication behavior under starved contact conditions remains insufficiently explored. The tribological performance of Ti6Al4V was investigated under starved boundary-to-mixed lubrication conditions using engine oil modified with Ag-doped TiO₂ nanoparticles. Double-scan LPBF-fabricated discs were tested in a ball-on-disc configuration against AISI 52100 bearing steel using a TRB³ tribometer. Nanolubricants were prepared by dispersing TiO₂ and Ag–TiO₂ nanopowders with different Ag⁺/Ti⁴⁺ ratios (0.5%, 1.5%, and 2.5%) in SAE 10W-40 engine oil at a constant nanoparticle concentration of 0.05 wt%. Comprehensive physicochemical characterization of the nanopowders and nanolubricants was performed through structural, chemical, optical, morphological, rheological, and stability analyses. Tribological experiments were conducted following a full-factorial design combining three normal loads (5–15 N), three sliding speeds (0.10–0.20 m·s⁻¹), and four lubricant formulations. The steady-state coefficient of friction ranged between 0.281 and 0.359, while the specific wear rate varied from 2.81 × 10⁻⁴ to 4.83 × 10⁻⁴ mm³·N⁻¹·m⁻¹. The contact temperature rise remained relatively moderate, within the interval of 1.9–9.4 °C. Among the investigated formulations, the lubricant containing 1.5% Ag–TiO₂ exhibited the lowest friction coefficient, whereas the formulation with the highest Ag content showed improved stability of tribological performance across the investigated operating domain. These results indicate that Ag-modified TiO₂ nanoparticles are consistent with the formation of protective tribofilms and contribute to the stabilization of friction, wear, and thermal behavior under starved lubrication conditions. ANOVA confirmed that sliding speed and the load–lubricant interaction are the dominant factors governing friction and wear, while normal load controls the thermal response. These findings support the use of Ag–TiO₂ nanolubricants as a viable strategy for stabilizing interfacial behavior in LPBF-fabricated titanium components operating under starved lubrication conditions. Full article

PEEK coatings have been applied to sliding bearings in marine machinery and equipment, but their low bonding force, poor thermal conductivity and weak oleophilicity result in insufficient anti-adhesive wear performance. To solve this problem, the textured surface of the substrate was fabricated using laser texturing technology to enhance the bonding force. The PEEK coatings were reinforced by introducing oleophilic-modified nano-SiO₂ and graphene. The tribological properties of the PEEK composite coatings were studied using the ball–disc reciprocating friction wear test and Abaqus wear simulation. The results show that the texturing treatment of the substrate surface improves the bonding force of the coating. The addition of nano-SiO₂ and graphene enhances the hardness, thermal conductivity and oleophilicity of the composite coating, which shifts the wear mechanism from adhesive to abrasive. Under dry friction conditions, the composite coating containing 5 wt% SiO₂ and 1 wt% graphene exhibits a low friction coefficient and the lowest wear rate. Under oil lubrication conditions, the composite coating containing 2 wt% graphene shows the lowest friction coefficient and wear rate. In summary, under the load-bearing capacity enhancement of nano-SiO₂ and the thermal conductivity enhancement of graphene, the composite coating exhibits excellent anti-adhesive wear performance. Full article

Water-based lubricants (WBLs) are increasingly being considered for electrified drivetrain applications; however, their electrochemical stability toward bearing steels remains insufficiently understood. This study evaluated the corrosion behavior of through-hardened AISI 52100 bearing steel in novel WBLs to elucidate the corrosion kinetics and surface degradation mechanisms. Round steel disks were cleaned and tested in 50 wt% aqueous dilutions of glycerol, ethylene glycol (MEG), polyethylene glycol (PEG), and polyalkylene glycol (PAG). Electrochemical measurements were conducted using a three-electrode cell in accordance with ASTM G3-14, employing open circuit potential (OCP), linear polarization resistance (LPR), electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization curves. Among the uninhibited fluids, DI water exhibited the highest corrosion current density (19.85 µA/cm²), while glycerol- and PEG-based systems showed the lowest values (0.79 and 0.85 µA/cm², respectively), attributed to organic adsorption at the steel/electrolyte interface. EIS analysis revealed a single charge-transfer-controlled process across all fluids, consistent with a weak, non-passive interfacial oxide whose protective character is modulated by organic adsorption. The addition of NaNO₃ produced divergent effects depending on the base fluid chemistry: the corrosion activity was reduced in DI water and glycerol systems through enhanced passivation, while PEG- and PAG-based formulations showed increased corrosion current densities and reduced charge transfer resistance, attributed to competitive disruption of the polymer boundary layer by nitrate ions. Surface characterization by SEM/EDAX and white-light interferometry corroborated the electrochemical findings, revealing fluid-dependent corrosion morphologies ranging from uniform attack in DI water to localized pitting in polymer-based systems, with NaNO₃ shifting the corrosion mode in PEG/PAG systems from localized to combined localized and uniform attack. These findings highlight the critical role of fluid chemistry in controlling corrosion processes in water-based lubricants and provide mechanistic insight for the development of corrosion-stable formulations for high-performance electrified drivetrain applications. Full article

With the changing demands of society, gears, as fundamental components of mechanical devices, are evolving towards higher reliability and longer service life. To address the issue of thermal scuffing at the gear meshing interface, we propose the introduction of micro/nano-textures to improve the thermal elastohydrodynamic lubrication characteristics of the meshing surfaces, thereby enhancing the lubrication performance and anti-scuffing load capacity of the gear surfaces. First, finite element models with different microstructural features were established. Then, numerical calculations were conducted using computational fluid dynamics (CFD) software to analyze the impact of various micro-texture configurations on the lubrication performance of the tooth surface. Finally, an orthogonal experiment was performed to optimize the groove length, groove width, and areal density of the micro-textures in order to obtain the best processing parameters. The results show that, compared with the triangular, rectangular and trapezoidal micro-textures, the wedge-shaped micro-texture produces the largest pressure difference at the meshing-in and meshing-out points of the texture grooves, which causes the dynamic pressure effect to be more obvious. Compared with the triangular, rectangular and trapezoidal micro-textures, the wedge-shaped micro-texture has the largest bearing capacity and the smallest friction coefficient, so it has better bearing capacity and anti-friction and wear performance. The process parameters were optimized through orthogonal experiments, and the optimal combination of process parameters was obtained as the areal density of 50%, the depth of micro-pits of 12 µm, and the width of micro-pits of 200 µm. Under these optimal parameters, the pressure difference at the meshing-in and meshing-out points of the wedge micro-texture increased significantly by 255.6% compared to the initial model, and the oil film friction coefficient decreased by 17.857% relative to the initial model. These results demonstrate that the micro-texture with optimal parameters significantly enhances the lubrication and anti-friction/wear performance of the tooth surface. Full article

The compressor in automotive air-conditioning systems consumes a significant fraction of the vehicle’s energy, thereby reducing driving range. Consequently, developing more efficient compressor operation is essential for improving overall thermal management. Nano-enhanced lubricants have emerged as a promising passive strategy to reduce compressor power consumption, enhance thermodynamic performance, and improve tribological behavior by minimizing friction and wear. This review critically examines existing nano-lubricant research with a focus on automotive compressor and system-level performance, friction and wear reduction mechanisms, and the influence of nanoparticle type and concentration on lubricant thermo-physical properties. The analysis reveals that nano-lubricants consistently enhance compressor operation by lowering discharge temperature and reducing power consumption, while improving coefficient of performance and cooling capacity. However, these benefits have been validated primarily under cooling-mode conditions and predominantly for reciprocating-piston compressors. Tribological studies further demonstrate substantial reductions in coefficient of friction and surface roughness, with improved anti-wear characteristics compared to virgin lubricants. Four principal mechanisms—rolling, polishing, protective-film formation, and self-repairing—have been identified as contributors to these enhancements. Nevertheless, most tribological investigations rely on simplified test rigs that do not fully represent the complex contact, loading, and thermal environments inside actual automotive compressors. This review underscores the need for system-level, mechanism-driven, and compressor-architecture-specific investigations covering both cooling and heating modes of automotive air-conditioning operation. The insights presented aim to guide future development of reliable, durable, and refrigerant-compatible nano-lubricant technologies for next-generation automotive air-conditioning systems. Full article

Surface and interface science play an important role in the tribological properties of materials. Recently, research in this field has extended from the macroscopic scale to the molecular level to elucidate energy dissipation and structural evolution mechanisms at sliding interfaces. In this work, we propose a nanolubricant strategy based on carbon nanocages (CNCs). Three types of lubricating molecules—oleylamine (amine), oleic acid (carboxyl), and stearyl alcohol (hydroxyl)—were encapsulated into a polytetrafluoroethylene (PTFE) matrix to construct a composite tribological interface model. Molecular dynamics simulations were employed to investigate the interfacial enrichment, diffusion, and interaction mechanisms of these molecules with PTFE chains and the Fe counterface. Particular emphasis was placed on how different functional groups regulate energy transfer and dissipation pathways. This study deepens the molecular–level understanding of structure–lubrication relationships and provides theoretical guidance for designing high–performance polymer–based tribological materials. Full article