Lubricant Film Research Articles

Research on the tribological properties of kaolin/MoDDP composite lubricant additives under heavy load and impact conditions

PurposeWith respect to severe working conditions such as heavy load and impact, this paper aims to investigate the friction reduction and anti-wear performance of kaolin and molybdenum dialkyl dithiophosphate (MoDDP) composite lubricant additives to improve the lubrication effect of a single additive.Design/methodology/approachA four-ball friction test was carried out to determine the optimal concentration of kaolin and organic molybdenum additives and the tribological properties of the kaolin/MoDDP composite lubricant additives. A ring block test of composite lubricant additives was designed to investigate its lubrication performance under the severe working conditions of low speed, heavy load and impact.FindingsThe results showed that the optimal addition mass fractions of kaolin and MoDDP were 4.0 and 1.5 Wt.%, respectively, when kaolin and MoDDP were used as single lubricant additives. Compared with the single additive, the 4.0 Wt.% kaolin/1.5 Wt.% MoDDP composite lubricant additive showed excellent friction reduction and anti-wear effects under heavy load and impact conditions. Physicochemical analysis of the wear surface revealed that the lamellar kaolin additive and MoDDP had excellent synergistic effects, and the friction process promoted the generation of lubricant films containing a chemically reactive layer of MoS2, MoO2, FeS2 and Fe2O3 and a physically adsorbent layer containing SiO2 and Al2O3, which play important roles in anti-wear and friction reduction.Originality/valueThe excellent friction reduction and anti-wear effects of lamellar silicate minerals and the excellent antioxidant properties and good synergistic effects of molybdenum were comprehensively used to develop the composite additives with great lubricating properties.

Microstructure and wear resistance of multi-layer graphene doped AlCoCrFeNi2.1 high-entropy alloy self-lubricating coating prepared by laser cladding

A novel AlCoCrFeNi2.1 high-entropy alloy self-lubricating coating was prepared by multilayer graphene (MLG) enhancement. The AlCoCrFeNi2.1-MLG (3 wt%) high-entropy alloy self-lubricating coating was prepared on AISI1045 steel using laser cladding by introducing lubricant named MLG. The microstructure, phase structure, wear resistance and corrosion performance of the AlCoCrFeNi2.1-MLG coating were studied. It is shown that the microstructure of the AlCoCrFeNi2.1-MLG coating has typical dendritic (DR) and interdendritic (ID) structures, with the dendrites consisting of high density M23C6 phase precipitation and FCC phase distributed in the interdendritic region. With the addition of MLG, the average hardness of the AlCoCrFeNi2.1 coating increases from 306.71 HV to 486.68 HV (an increase of 58.68 %). The average coefficient of friction decreases from 0.59 to 0.48 (a reduction of 22.92 %). The wear rate decreases from 1.678 × 10- 6 mm3·N− 1 m−1 to 0.825 × 10- 6 mm3·N− 1 m− 1 (a reduction of 50.83 %). This is due to the formation of a lubricant film in the AlCoCrFeNi2.1-MLG coating. The wear mechanism changes from plastic deformation and abrasive debris wear to slight delamination and spalling of the lubricant film. However, the corrosion performance of the AlCoCrFeNi2.1-MLG coating is slightly reduced by the occurrence of micro-electro-coupling corrosion on the corroded surface. The M23C6 phase is used as the anode and the FCC phase is used as the cathode. The subsequent generation of a passivation film prevents the appearance of severe electro-coupling corrosion. The wear resistance of the AlCoCrFeNi2.1-MLG coating is substantially improved while taking into account the corrosion performance. This study provides important values for laser cladding of self-lubricating composite coatings of high-entropy alloys.

The Impact of Pad Elasticity on Frequency-Dependent Linear Dynamic Coefficients of Tilting-Pad Journal Bearings

Abstract The frequency-dependent dynamic coefficients of tilting-pad bearings are significantly influenced by the pad pivot elasticity. In addition to the elasticity of the pivot, there is also the flexibility of the structure that predominantly leads to a bending of the pad. For the calculation of the dynamic coefficients, it is common to describe the structural stiffness by a support stiffness in series with the lubricant film. For this purpose, the stiffness according to Hertz's theory is widely used. This approach only allows the rigid body motion of the pad in the theoretical model. However, the elasticity of the pad leads to a film thickness characteristic, which cannot be represented with a pure rigid body motion. Additionally, the structural elasticity already includes the stiffness of the contact between the pad and the support, and therefore the elasticity according to Hertz cannot simply be added. This paper investigates the influence of dynamic pad deformation on dynamic bearing coefficients considering the contact boundary conditions and examines whether it can be replaced by a suitable support stiffness. A three-dimensional finite element model provides the eigenmodes for calculating the dynamic coefficients by perturbed Reynolds equations within a thermo-elasto-hydrodynamic bearing analysis. The model is validated with measurement data.

Effect of Surface Texturing on Friction and Lubrication of Ti6Al4V Biomaterials for Joint Implants

The number of endoprosthetic implants for both large and small joints is increasing at a steady rate, thereby creating a growing demand for durable products that closely replicate the functionality of human joints. Notwithstanding the aforementioned advancements, challenges pertaining to implant fixation and tribological surfaces persist. The advent of progressive technologies, such as three-dimensional printing, offers a promising avenue for addressing these challenges in implant design and surface engineering. The Ti6Al4V and CoCrMo alloys, renowned for their biocompatibility and osseointegration properties, represent promising printable materials, although they are susceptible to wear on articulating surfaces. In order to mitigate the effects of abrasion, it is essential to implement surface treatments to facilitate the formation of a robust lubricating film. This research investigates the potential of texturing and electrochemical polishing to enhance protein aggregation in the contact area. The study employs a reciprocating simulator and colorimetric interferometry to observe the contact area and measure the coefficient of friction (CoF) of modified surfaces. The findings demonstrate that textured surfaces and the combination of electrochemical polishing result in an increase in the thickness of the protein lubrication film, which may potentially reduce wear. These outcomes suggest the potential for the utilization of Ti6Al4V alloy implants with fewer elements manufactured by additive technology.Graphical

Improved Friction Reduction and Wear Resistance of Steel Using a Subnanometer Nanowires-Poly-α-Olefin Gel Lubricant.

Lubricating oil is commonly utilized due to its excellent lubricating properties in mechanical motion systems. However, high fluidity in lubricating oil often leads to leakage during machine operation, causing mechanical components to fail. Herein, a gel lubricant of SNWs-PAO6 was devised by combining subnanometer nanowires (SNWs) with poly α-olefin 6 (PAO6) at room temperature, effectively confining PAO6 and preventing PAO6's creeping and leakage while enhancing its load-bearing capacity. SNWs-PAO6 outperforms PAO6 in reducing friction and wear for steel-on-steel interfaces. The friction coefficient is markedly diminished by 57.53%, from 0.223 to 0.095, while the wear rate is significantly curtailed by 84.98%. Furthermore, SNWs-PAO6 remains stable even after 180 000 cycles at 200 N and 25 Hz, withstanding high-speed centrifugation without releasing PAO6. It remained stable over 6 months of resting and can well withstand low temperatures. Surface analysis of the wear scar and the formed tribochemical film after friction has demonstrated that PW12O403- is more likely to adsorb onto the steel surface, forming a lubricating medium film through tribochemical reactions and thus reducing interfacial friction and wear. This method facilitates the development of domain-limited nanomaterials-based gels for mass production and their applications in engineering moving parts.

Tribological Performance of Nano-CeO2/BNH2 Compound Lubricant Additive

To improve lubricant performance and extend the service life of machinery, the friction reduction and anti-wear performance of nano-cerium oxide (nano-CeO2) and nitrogen-containing heterocyclic borate (BNH2) composite additives were studied in this work, with the goal of obtaining better lubrication effects than a single additive. The results showed that the nano-CeO2 modified with Span80 had good dispersion stability in the base oil. The optimal addition mass fractions of single nano-CeO2 and BNH2 were 0.6 wt% and 1.0 wt%, respectively. Compared with the base oil, 0.6 wt% nano-CeO2 reduced the coefficient of friction by 44.9% and the wear spot diameter by 27.8%, while 1.0 wt% BNH2 reduced the coefficient of friction by 49.1% and the wear spot diameter by 32.8%. Compared with the single additions of nano-CeO2 and BNH2, the compound nano-CeO2/BNH2 further improved the friction reduction and anti-wear performance of the lubricating oil. Compared with the base oil, the 0.8 wt% nano-CeO2/1.0 wt% BNH2 composite additive reduced the coefficient of friction by 55.9% and the diameter of the abrasive spot by 48%. Physicochemical analysis of the wear surface revealed that the combination of nano-CeO2 and BNH2 had excellent synergistic effects. The generated lubricant films of nano-CeO2/BNH2 contained a chemical reactive layer of organic nitride (C–N), Fe2O3, FeO, and B2O3 and a physical adsorbent layer of CeO2 that provided great friction reduction and anti-wear effects during friction.

Advanced Research on Graphene‐Based Nano‐Materials: Synthesis, Structure, Dispersibility and Tribological Applications

AbstractIn recent years, graphene‐based nanomaterials have attracted extensive attention because of their excellent physical and chemical properties, such as high strength, high conductivity, high thermal conductivity and excellent lubrication performance. Here, the latest research progress of graphene‐based nanomaterials is reviewed in this paper, and their synthesis method, unique structure, dispersion improvement strategy and wide application in tribology are emphatically discussed. Graphene‐based materials are synthesized by typical chemical vapor deposition and reduced graphene oxide, showing nanoporous structure characteristics and excellent layered structure. Furthermore, through adjusting the chemical structure for the material, the graphene‐based materials with specific lubricating properties can be designed to meet the use requirements under different working conditions. In view of the easy agglomeration of graphene, physical and chemical dispersion methods, such as in‐situ polymerization and functionalization treatment, were introduced, which significantly improved its dispersibility in the matrix. In tribology, graphene‐based nanocomposites present the excellent anti‐friction and anti‐wear properties, which effectively reduce the coefficient of friction and prolong the service life of materials with forming the stable lubricating films. The summary for graphene‐based materials provides theoretical basis and technical support for applications in high‐end manufacturing, energy storage, and protective coatings.

A Minimal-Data Approach for Film Thickness Prediction in Tribological Contacts Using Venner’s Equation

The accurate design of tribological contacts, such as those in bearings and gearboxes, makes them highly efficient and helps reduce emission in all driven systems. Traditionally, this process requires more lubricant data than data sheets typically provide, mainly kinematic viscosity at 40 °C and 100 °C and density, which limits the design process. This study introduces a simplified methodology for determining lubricant film thickness, one of the main design critical parameters, using minimal viscosity measurements obtained with a high-pressure viscometer. The researchers demonstrate that essential lubricant parameters can be derived effectively from a few measurements. By combining state-of-the-art models for film thickness with practical measurements from an EHL tribometer, this study confirms that reliable film thickness predictions can be made from basic viscosity data. This approach streamlines the design process, making tribological simulations more accessible and cost-effective, and enhances the design of tribological contacts under extreme conditions.

Dispersion and Tribological Behaviors of Modified Functionalized Surfaces of Single and Hybrid Nanoparticles in Water-Based Lubrication

This study investigated the dispersion and tribological effetcs of modifying surface functionalization on single (GO, Al2O3, MgO, SiC) and hybrid (SiC/MgO, Al2O3/MgO) nanoparticles in water-based lubricant (WBL) formulations. Polyvinylpyrrolidone (PVP) and glycerol were utilized to further enhance dispersion and viscosity. The experimental findings revealed that incorporating modified nanoparticles surfaces in WBLs improved hydrophilicity and dispersion by introducing additional oxygen functional groups. This effectively reduced direct metal-to-metal contact, resulting in lower interface temperatures and enhanced tribological performance. Hybrid Al2O3/MgO nanoparticles exhibited a significant 76.69 percent enhancement in tribological performance in wear mechanisms, synergistically filling microcracks to improve lubricant film formation, bearing, and mending effects. Using a single nanoparticle was found to be insufficient for achieving enhanced tribological effects. All nanoparticles improved bearing effects, except for GO, which promoted a shearing effect. High-hardness nanoparticles such as SiC and Al2O3 demonstrated an additional polishing effect.

Effect of squeeze motion on the tribo-performances of molybdenum disulfide powder lubricated textured cemented carbide specimens

Purpose This study aims to improve the lubrication performance of molybdenum disulfide powders at textured surface of cemented carbide materials, a squeeze motion of vibration assistance method was introduced and investigated. Design/methodology/approach Surface texture was fabricated on YT15 cemented carbide samples using a laser marking machine. After that, a tribological experiment was carried out on a self-built friction testing machine under different amplitude and frequency of squeeze motion conditions. Moreover, a simulation model was also established to verify the principle of squeeze motion on the lubrication performance improving of MoS2 particles at textured interfaces. Findings Analysis results indicated that surface texture on test sample can increase the storage ability of solid lubrication particles, and the lubrication film at the contact interface is more easily formed due to the reciprocating action. Squeeze motion can improve the storage ability of it due to an intermittent contact, which provides an opportunity for MoS2 particles infiltration, and then a more uniform distribution and load-bearing properties of force chain are also established and formed simultaneously. Thus, a better tribological performance at the contact interface is obtained. Originality/value The main contribution of this work is to provide a reference for the molybdenum disulfide powder lubrication with textured surface of cemented carbide materials. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-05-2024-0166/

Effects of contact path on lubricant distribution and EHL film formation

Effects of contact path on lubricant distribution and EHL film formation

Super wear-resistant WB 4–B super-hard ceramic by in-situ formed lubrication film in high moisture

Super wear-resistant WB ₄–B super-hard ceramic by <i>in-situ</i> formed lubrication film in high moisture

Preparation and tribological properties study of a novel self-lubricating Alumina-based composite coating

A self-lubricating composite coating Al2O3/C was designed and sprayed via atmospheric plasma spraying (APS), in order to endow the alumina coating with certain lubricating properties under room temperature conditions. The raw feeding powders of boehmite-alumina-graphite (AlO(OH)/Al2O3/C) with particle sizes of 30–50 µm were prepared through hydroxylation treatment, physical stirring, and spray granulation process. The tribological properties of the Al2O3/C composite coating were systematically studied using a CSM friction tester. The prepared Al2O3/C composite coating exhibited fewer defects, lower coefficient of friction (COF), and slighter adhesion wear degree compared to single-component Al2O3 coating. The graphite lubrication film was discovered on both the worn surface of the composite coatings and the friction pair after friction. The existence of the graphite lubrication film decreased the COF, and the reduction extent depended on the load, with a maximum reduction of 55 %. The composite coatings presented the best tribological properties when sliding against Si3N4 balls at a higher load (5 N) because of the diverse wear mechanisms and the influence of graphite lubrication film, resulting in a reduction in the COF and wear rate by approximately 48 % and 11 times respectively. In addition, part of γ-Al2O3 in the Al2O3/C composite coating transformed into α-Al2O3 after the friction test. But the Al2O3 coating remained phase stable, with no phase change occurring before and after the friction. The transformation from the γ-Al2O3 to the α-Al2O3 phase was positive as for the tribological performance. It could reduce the COF as well as improving the thermal conductivity and mechanical properties of the coating.

Computer Vision-Based Research on the Mechanism of Stick–Slip Vibration Suppression and Wear Reduction in Water-Lubricated Rubber Bearing by Surface Texture

Water-lubricated rubber bearings are a critical component of the propulsion systems in underwater vehicles. Particularly under conditions of low speed and high load, friction-induced vibration and wear often occur. Surface texturing technology has been proven to improve lubrication performance and reduce friction and wear; however, research on how different texture parameters affect friction-induced vibration and wear mechanisms remains insufficient. In this study, various texture patterns with different area ratios and aspect ratios were designed on the surface of water-lubricated rubber bearings. By combining these designs with an in situ observation system based on computer vision technology, the effects of texture parameters on bearing friction, vibration, and wear were thoroughly investigated. The experimental results show that surface textures play a critical role in improving hydrodynamic effects and stabilizing the lubrication film at the friction interface. Specifically, textures with a high area ratio (15%) and aspect ratio (3:1) exhibited the best vibration suppression effect, primarily due to the reduction in actual contact area. However, excessively high area ratios may lead to increased surface wear. This study concludes that a reasonable selection of texture area and aspect ratios can significantly reduce frictional force fluctuations and vibration amplitude, minimize surface wear, and extend bearing life.

Wear performance of electro-jet mask in-situ forming (CFx)n/CaF2-ZrO2/TiO2 composite films

In this paper, the electrojet mask in-situ forming technology was used to prepare (CFx)n/CaF2-ZrO2/TiO2 composite films with different ZrO2/TiO2 texture distributions, to improve the adhesion properties and tribological performance of (CFx)n/CaF2 lubricant films. The microstructure, mechanical properties, and reciprocating wear characteristics between the composite films and 304 stainless steel counterparts were studied. The results showed that the textured hard film significantly improved the adhesion strength of the soft film and the tribological properties of the composite film. The composite film sample B had the lowest friction coefficient (∼0.100) and a lower film wear rate of ∼2.85 × 10−7 mm3 N−1 mm−1, and also showed good self-lubricating properties in the high-temperature wear process. Sample C had a lower friction coefficient of ∼0.107 and the lowest film wear rate of ∼2.75 × 10−7 mm3 N−1 mm−1. Compared with untextured composite film sample DC, sample B showed a 21.3 % reduction in friction coefficient, while sample C showed a 54.8 % decrease in film wear rate. This was because the surface texturing treatment of hard films enhanced the storage and flow of lubricant particles, and maintained a stable self-lubricating film during reciprocating wear. Moreover, (CFx)n and CaF2 have a synergistic effect in a wide temperature range of 25 °C–600 °C.

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.

PDA Nanoparticle-Induced Lubricating Film Formation in Marine Environments: An Active Approach

The low viscosity of water-lubricated films compromises their load-bearing capacity, posing challenges for practical application. Enhancing the lubrication stability of these films under load is critical for the successful use of seawater-lubricated bearings in engineering. Polydopamine (PDA) shows great potential to address this issue due to its strong bio-inspired adhesion and hydration lubrication properties. Thus, PDA nanoparticles and seawater suspensions were synthesized to promote adhesive lubricating film formation under dynamic friction. The lubrication properties of PDA suspensions were evaluated on Cu ball and ultra-high molecular weight polyethylene (UHMWPE) tribo-pairs, with a detailed comparison to seawater. The results show PDA nanoparticles provide excellent adhesion and lubrication, enhancing the formation of lubricating films during friction with seawater. Under identical conditions, PDA suspensions demonstrated the lowest friction coefficient and minimal wear. At 3 N, friction decreased by 56% and wear by 47% compared to distilled water. These findings suggest a novel strategy for using PDA as a lubricant in seawater for engineering applications.

P(MMA-GMA-AM-St) as transition layer for constructing GO@pPTFE core-shell nanoparticles as hydro-based lubricant additives towards excellent friction reduction and wear resistance

Although polytetrafluoroethylene (PTFE) has attracted significant attention in the lubrication field, it is still challenging for PTFE with low surface energy to achieve uniform dispersion in hydro-based lubricant. Interface regulation is considered as an effective strategy to enhance the dispersibility of PTFE nanoparticles in water. Here, we proposed to improve the interfacial property of PTFE via constructing a poly(methyl methacrylate-co-glycidyl methacrylate-co-acrylamide-co-styrene) transition layer (P(MMA-GMA-AM-St)), which containing rich hydrophilic groups on the surface. Then, graphene oxide@pPTFE (GO@pPTFE) core-shell nanohybrids were prepared by hydrogen bonding-driven self-assembly. Water contact angle (WCA) of GO@pPTFE nanohybrids showed ultra-hydrophilic properties. With the addition of 0.05 wt% GO@pPTFE nanohybrids, friction coefficient (COF) and wear rate (Wr) of the hydro-based lubricant were greatly reduced by 69.4 % and 61.8 %, respectively. Even after a long period of friction (extending up to 120 min), the Wr of GO@pPTFE nanohybrids was an order of magnitude lower than that of pristine PTFE nanoparticles. The improved tribological performance of GO@pPTFE nanohybrids could be benefited from the synergistic effect of the PTFE and GO. Our study advanced the understanding of the intrinsic mechanisms underlying friction and wear by establishing a robust connection between morphological evolution, lubricant film stability, theoretical calculation, and tribological property at the microscopic scale.

Improved tribological properties of MXene nanosheet filler-modified PPO composites

MXenes, a class of two-dimensional (2D) nanomaterials, exhibit exceptional properties such as outstanding mechanical and thermal stability, along with diverse surface characteristics, making them highly promising in the tribology. However, their tendency to aggregate within the polymeric matrix adversely affects the tribological performance of the polymer. In this study, glass fiber (GF) surfaces were modified with polydopamine (PDA), allowing smaller MXene nanosheets to adhere to the GF surface, whereas the larger MXene nanosheets were dispersed throughout the matrix. This approach effectively enhanced the dispersion of MXene nanosheets in the polymeric matrix, facilitating the preparation of polyphenylene oxide (PPO)/MXene composite materials. Compared with the pure PPO sample, the results showed that the average friction coefficient and wear rate of the PPO/MXene composites were reduced by 46.25% and 98.34%, respectively, due to the distinct roles of different MXene nanosheet sizes in the polymeric matrix. Furthermore, a uniform lubricating film was formed during the friction of the polymer composite, enhancing its tribological performance. This study proposes a novel design strategy to enhance MXene nanosheet dispersion and optimize their lubricating properties.

Tribological Properties of 7A04 Aluminum Alloy Enhanced by Ceramic Coating

The 7A04 Al alloy is a commonly used lightweight metal material; however, its low wear resistance limits its application. In this study, the wear resistance of this alloy was improved by preparing micro-arc oxidation (MAO) coatings, MAO/MoS2 composite coatings, and hard-anodized (HA) coatings on its surface. The friction and wear behaviors of these three coatings with diamond-like coated (DLC) rings under oil lubrication conditions were investigated using a ring–block friction tester. The wear rates of the coatings on the block surfaces were determined using laser confocal microscopy, and the wear trajectories of the coatings were examined using scanning electron microscopy. The results indicated that, among the three coatings, the MAO/MoS2 coating had the lowest coefficient of friction of 0.059, whereas the HA coating had the lowest wear rate of 1.47 × 10−6 mm/Nm. The MAO/MoS2 coatings exhibited excellent antifriction properties compared to the other coatings, whereas the HA coatings exhibited excellent anti-wear properties. The porous structure of the MAO coatings stored lubricant and replenished the lubrication film under oil lubrication. Meanwhile, the introduced MoS2 enhanced the densification of the coating and functioned as a solid lubricant. The HA coating exhibited good wear resistance owing to the dense structure of the amorphous-phase aluminum oxide. The mechanisms of abrasive and adhesive wear of the coatings under oil lubrication conditions and the optimization of the tribological properties by the solid–liquid synergistic lubrication effect were investigated. This study provides an effective method for the surface modification of Al alloys with potential applications in the aerospace and automotive industries.