Solid Lubricant Films Research Articles

Using a bonded solid film lubricant to prevent fretting wear in the axle journal bearings of rail vehicles

Fretting degrades the inboard inner ring and the backing ring contact surfaces of axle journal roller bearings used in railway applications. This study attempts to prevent fretting wear between them as well as fretting wear particles from entering the axle bearing interior without introducing new bearing components. It has been reported that coating metallic surfaces with bonded solid film lubricants improves lubricity and wear resistance while reducing fretting wear. To evaluate the impact on fretting wear prevention, a full-size railway axle bearing that was coated a backing ring side face with a bonded solid film lubricant was rotated. The findings demonstrate that applying the bonded solid film lubricant to the backing ring side face does not prevent the axle bearings from fretting. The surface temperature probably exceeds the heat-resistant temperature of the solid film lubricant because of the fretting friction.

Amino-functionalized Ti3C2 and ZIF-8-induced high lubricity, friction robust self-healing polyurethanes as solid lubrication films

Self-healing polyurethane (SPU) has important applications in areas such as protective coatings, medical devices and solid lubrication. However, improving the lubricating properties of self-healing polyurethanes to reduce their friction and wear is still an important challenge. Herein, an amphoteric SPU is prepared and used as the solid lubrication matrix. NH2-Ti3C2-ZIF-8 is grown on NH2-Ti3C2 in situ to obtain NH2-Ti3C2-ZIF-8 as lubrication additive. The lubrication performance of NH2-Ti3C2-ZIF-8/SPU composites is the best when the NH2-Ti3C2-ZIF-8 content is 1.00 wt%. The coefficient of friction (COF) is only 0.10, and the wear rate is only 1.315×10−4 mm3/(N·m), which are reduced by 80.4 % and 99.4 % respectively compared with single SPU. By exploring the lubrication mechanism, it is found that NH2-Ti3C2-ZIF-8 participated in producing transfer film during friction, and the excellent lubricity and anti-wear effect of NH2-Ti3C2 and the unique adsorption and rolling effect of ZIF-8 jointly improved the friction performance of the samples. In addition, the composite material can realize rapid healing within 5 min at 75 %RH, 20℃, the self-healing efficiency can reach 84.7 %. Therefore, the SPU containing NH2-Ti3C2-ZIF-8 has potential applications in the field of solid lubricated materials.

The effect of MoS2 concentration on the thickness and tribology performance of electro-codeposited Ni–Cr–MoS2 coatings

A Ni–Cr–MoS2 coating with trivalent Cr was prepared on the surface of the cylinder liner by the composite co-deposition method to modify its tribology performance. The effects of MoS2 concentration on the properties of the coatings and tribological properties of cylinder liners were studied by surface detection methods and reciprocating wear tests. The results show that Ni–Cr–MoS2 coating has a smaller grain size, higher micro-hardness, and greater coating thickness, compared with Ni–Cr coating. Doping by MoS2 effectively reduces the friction coefficient of Ni–Cr coating from 0.142 to 0.107, the wear amount of coating decreases from 7.9 mg to 7.1 mg, and the scuffing time increases from 19 min to 56 min. It is found that the doping of MoS2 provided more nucleation sites and promoted the deposition of ions, which resulted in the refined grain and thicker coating. The formation of solid lubrication film by MoS2 during the wear process and more coating thickness are mainly responsible for the modification of the tribology performance of cylinder liners. This research provides a practical approach to prolong the service life of friction pairs.

Macroscale Ultradurable Anti‐wear Achieved on Graphene‐based Films via Multiphase Combination

Excellent anti‐wear performance, high bearing capacity, and long service life are essential prerequisites for the reliability and durability of Si‐based micro/nano device operation. To improve the anti‐wear property and prolong service life of Si‐based micro/nano devices under high loads, graphene oxide (GO) nanosheets, graphene quantum dots (GQDs) and ionic liquid‐capped GQDs (IL‐GQDs) were used to create three kinds of multilayer films as solid lubricant, that is, single‐component (GO)5, (GO/GQDs)5 and (GO/IL‐GQDs)5 multilayer films. The results showed that (GO/IL‐GQDs)5 composite multilayer possessed excellent wear resistance under a high load of 4 N with the wear rate of 4.9×10‐7 mm3·N‐1·m‐1. The superior anti‐wear performance of (GO/IL‐GQDs)5 composite film is mainly due to the unique 3D structure composed of GO nanosheets alternating with IL‐GQDs. The rigid GO nanosheets play the role in load‐carrying capacity, and the IL‐GQDs could delay the time of structure transformation and reduce the loss rate of transfer film, thereby effectively extending the service life of (GO/IL‐GQDs)5 composite multilayer. Such multilayers are expected to be good solid lubricating films suitable for Si‐based micro/nano devices.This article is protected by copyright. All rights reserved.

Tribological Performance Study of Low-Friction PEEK Composites under Different Lubrication Conditions

This study introduces a low-friction composite based on PEEK to improve its friction and wear properties. The composite incorporates PTFE as a solid lubricant and utilizes PPTA as a reinforcing material within the PEEK matrix. These components were prepared utilizing a compression molding method, followed by a series of exploratory experiments to identify the optimal preparation conditions for PEEK. This research assesses how the PTFE/PPTA/PEEK composites perform in terms of friction and wear under dry and oil-lubricated conditions. By examining wear tracks using scanning electron microscopy and white light interference microscopy, this study aims to uncover the wear mechanisms of PEEK and its composites under different lubrication scenarios. Results show that the main wear mechanisms for the PTFE/PPTA/PEEK composites and bearing steel are ploughing and adhesive wear. The presence of PPTA helps reduce wear by leveraging its strong fibers and thermal stability, while the coefficient of friction decreases as PTFE creates a smooth, solid lubricating film on the surface. Notably, PEEK composites containing 25 wt% PTFE and 6 wt% PPTA demonstrate the lowest wear rates and reduced coefficient of friction in both dry and oil-lubricated conditions.

The effect of LaF3 in enhancing the atomic-oxygen-resistance of molybdenum-disulfide-based solid lubricant films

The effect of LaF3 in enhancing the atomic-oxygen-resistance of molybdenum-disulfide-based solid lubricant films

Microstructure, mechanical and tribological properties of multilayer graphene reinforced WC-10Ni3Al prepared by microwave sintering

The multilayer graphene (MLG) reinforced WC-10Ni3Al cemented carbide was prepared by microwave sintering. The effects of the sintering temperature and MLG content on the microstructure and mechanical properties of the WC-10Ni3Al cemented carbide were investigated. The promotion effect and strengthening mechanism of MLG on WC-10Ni3Al by microwave sintering were explored. The tribological properties of WC-10Ni3Al and Ti6Al4V(TC4) were studied, and the wear mechanism of WC-10Ni3Al was revealed. The experiment result show that the WC-10Ni3Al-0.5 wt.% MLG sample sintered at 1450 °C had its greatest mechanical properties with a relative density of 96.9%, hardness of 1430 HV, flexural strength of 1410 MPa and fracture toughness of 15.7 MPa mm1/2, which were 4.2%, 12.2%, 24.4%, and 29.6% greater than those of the sample without MLG added, respectively. The reinforcing and toughening mechanisms of adding MLG in WC-10Ni3Al samples consist of fine crystal strengthening, crack bridging and deflection, MLG pulling out and bridging. The results of friction experiment show that the friction coefficient and wear rate of the WC-10Ni3Al samples were lower than those of YG8 (WC-8 wt. % Co cemented carbide). The WC-10 Ni3Al-0.5 wt.% MLG sample obtained the lowest friction coefficient of 0.35 and the lowest wear rate of 1.69 × 10−5 mm3N−1m−1. A stable solid lubrication film was produced on the friction surface of the WC-10Ni3Al samples, which was conducive to reducing the breakage and wear of WC grains. MLG can enhance the stability of solid lubrication film and reduce its friction coefficient.

Influence of hardness of nanoparticle additive in PTFE solid lubricant on tribological properties of GCr15 steel with bionic texture

The surface microstructure of biomimetic Procambarus clarkia claw was prepared on the surface of GCr15 steel, then PTFE solid lubricants dispersed with three different hardness nanoparticles (C, ZnO, Al2O3) were filled in. The results of the tribological experiment show the textured surface lubricated by PTFE with Al2O3 nanoparticles reflected the best performances. Because PTFE stored by the bionic texture could be supplied to the friction surface to form a solid lubrication film. Due to the addition of Al2O3 nanoparticles, the hardness and wear resistance of the film are improved, thus avoiding a large loss of PTFE. And the process of "rolling-embedding PTFE surface-exposing-rolling" occurs. As a final, the surface tribological properties of GCr15 steel can be significantly improved.

Tribological properties of high-speed steel surface with texture and vertical fibers

Inadequate lubrication of the two touching surfaces during friction can lead to severe wear, especially in metal cutting. Therefore, a surface with synergistic anti-friction effect of texture and solid lubricant was proposed to improve lubrication. A mesh texture with excellent wettability was prepared on the high-speed steel (HSS) surface by laser, and then nylon fibers were vertically implanted into the grooves of the texture using the electrostatic flocking technology. The friction and wear state of different surfaces (smooth, textured, flocking) under dry/oil-lubricated were studied by a linear reciprocating wear tester. The coefficient of friction (COF) under different working conditions was used to analyze the anti-friction properties, and the wear rate was used to evaluate the wear resistance of the surface. The results showed that the tribological properties of flocking surfaces were better than those of the other two surfaces. This is because the addition of nylon fibers eases shear at the edges of the texture. The broken fibers form a solid lubricating film on the specimen surface, which prevents the surface from being scratched by debris. In addition, it is found that COF decreases with increasing load. Finally, the rapid wettability of the oil droplets on the flocking surface shows the great potential of the surface for lubrication and anti-friction.

Tribological properties of AISI 4140 steel reinforced by bioinspired topological texture and multi-solid lubricants under starved lubrication

Improving the tribological properties of AISI 4140 steel (AS) by texture combined with SnAgCu (SAC) will cause the loss of lubricants too fast. Herein, problem was solved by adding MXene-Ti3C2/nano-TiC (MNT) into SAC to prepare multi-solid lubricants. Friction tests with contact pressures of 219.07, 347.76 and 471.98 MPa were respectively carried out to study effect of lubricant components and contents (0–10 wt%) on tribological properties of AS under starved lubrication. Compared with those of AS-SAC, COF and wear depth of AS-SAC-MNT containing 4 wt% MNT were decreased by 24.29% and 41.59%, respectively. The excellent tribological properties of AS-SAC-MNT were attributed to the formation of a stable solid lubricating film and improved adsorption ability of material to oil.

Ice Adhesion Evaluation of PTFE Solid Lubricant Film Applied on TiO2 Coatings

Ice formation affects the performance of many industrial components, including aircraft wings, spacecraft, and power transmission cables. In particular, ice build-up on airplane components increases drag and fuel consumption. A large number of studies have been carried out to reduce ice adhesion by developing passive methods such as icephobic coatings and active ice removal approaches such as mechanical vibrations or chemical-based solutions. Despite remarkable recent breakthroughs in the fabrication of icephobic coatings, passive ice removal solutions require higher durability to resist cyclical mechanical ice detachment treatments. Functionalized TiO2 coatings, applied using the suspension plasma spray (SPS) technique, have been shown to be robust and to have dual-scale characteristics in an ice accretion analysis. In this study, the icephobicity and mechanical durability of a novel duplex coating consisting of polytetrafluoroethylene (PTFE) solid lubricant films on TiO2-coated substrates were evaluated. Notably, various amounts of PTFE were applied on top of the TiO2 coating to identify the ideal quantity required to obtain optimal icephobic properties. Ice was generated in an icing wind tunnel, and the amount of accreted ice was evaluated to assess the anti-icing properties. Wettability parameters, including static water contact angle and contact angle hysteresis, were measured to determine the water mobility and surface energy. Ice shear adhesion to the PTFE-TiO2 duplex coating was measured using a custom-built test rig. The mechanical durability was assessed by measuring the ice shear strength for almost twenty icing–deicing cycles, and after five cycles, the roughness parameters and images taken from the surface of the samples were compared. The combination of PTFE solid lubricant film and TiO2 coating reduced ice adhesion by 70%–90% compared to that of a bare aluminum substrate (reference material). Additionally, the results showed that the application of a uniform layer of PTFE solid lubricant film on dual-scale TiO2 coating significantly reduced ice adhesion and maintained mechanical durability for 25 deicing cycles, making this combination a promising candidate for deicing approaches.

Study on the effect of counter ball materials on fretting wear behavior of solid lubricating films

Solid self-lubricating film can undoubtedly play a superior role in improving the micromotion behavior. The friction pairs of different materials have different fretting behavior and wear mechanism due to their different mechanical properties and surface adhesion properties. Investigating the influence of mechanical properties and surface adhesion on the fretting behavior can make the self-lubricating solid film play a better effect in the practical fretting working conditions. Here, DLC film and MoS2 film are deposited on AISI 304 stainless steel using a TeerUDP-650 unbalanced magnetron sputtering system. The fretting performance of DLC and MoS2 films resistance to GCr15, Al2O3, SiC and Si3N4 balls are studied. The results demonstrate that the fretting characteristics of DLC film are highly dependent on the mechanical properties and adhesion behavior of counter balls. Thereinto, Al2O3 balls show excellent fretting behavior, while SiC and Si3N4 balls make DLC film ineffective due to their high hardness and high adhesion. The MoS2 film maintains low friction and low wear state against any counter ball. DLC film achieves anti-fretting wear via graphitization, while MoS2 film primarily relies on slip and plastic flow. This work provides a theoretical reference for proper selection of solid lubricating films and counter balls under practical fretting conditions and reveals the different tribological mechanisms of friction pairs.

Fretting wear behavior of aluminum coatings

The aluminum bronze coating is a type of soft solid lubricant film with excellent performance. In this work, to improve the wear resistance and tribological behavior of the aluminum alloy, the aluminum bronze coatings were prepared on aluminum alloy substrates using the High- Velocity Oxygen Fuel (HVOF) system. Fretting wear tests were performed on the coatings at 200 °C with different frequencies to analyze the wear behavior. The worn surface was characterized by scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS). The results showed that as the frequency increased from 5 Hz to 15 Hz, the coefficient of friction increased from 0.653 to 0.929. It then decreased to 0.890 at 20 Hz. There was an overall trend of the coefficient of friction increasing and then decreasing. The worn surface’s morphology changed from pits to bulges. At a low frequency, the wear mechanism was abrasive wear with delamination. As the frequency increased, adhesive wear was observed and gradually became the dominant wear form. Oxidation occurred on the surface of the worn tracks caused by the high temperature and thermal effect of high-frequency micromotion. Due to the intensification of the oxidation phenomenon, oxidation films formed on the worn surface. The wear rate of the coating was significantly reduced. The oxide was identified as mainly CuO and Cu2O. The presented results confirmed that the aluminum bronze coating fabricated via HVOF exhibited a great resistance performance even at a high frequency.

Influence of different loads and temperatures on solid lubricant-filled micro-dimples existing on both cylinder liner and piston ring

In order to meet the increasing demands of friction reduction and wear resistance in heavy-duty diesel engines, the refined design of surface topography of cylinder liner and piston ring (CLPR) has been a major concern. Based on electrolytic micro-texturing and electrochemical deposition methods, micro-dimples filled with solid lubricant have been separately applied to the CLPR surfaces. This double-sided textured design of CLPR exhibited significantly lower friction coefficient and wear depth than the non-dimpled CLPR when the lubricating oil containing zinc dialkyldithiophosphates (ZDDP) was used under different strengthening loads and temperatures. Solid lubricants were released from the double-sided textures, forming mutually transferable solid lubricant films on the sliding surface. Although various products containing molybdenum oxides, molybdenum sulfides, phosphate of different chain lengths, zinc compounds, iron sulfide, etc. Appeared in the tribochemical reactions of ZDDP and MoS2 with increasing temperature and load, but the lubricating effect was still maintained. These results can provide some insight into the design of CLPR surfaces in order to achieve a high quality tribofilm under heavy load conditions.

Tribological properties of PEEK-based composite coating prepared by thermal spraying

To improve the friction wear performance of the aluminum alloy scroll disc of the scroll compressor under dry friction conditions, the C-MoS2-PTFE-PEEK coating was prepared on the surface of the 4032 aluminum alloy substrate by thermal spraying. The friction and wear performance of C-MoS2-PTFE-PEEK coating under dry friction conditions was investigated via friction wear test, hardness test, coating adhesion scratch test, x-ray diffraction analysis test, morphological characteristics, element distribution test, And XPS photoelectron spectrometer. Moreover, the frictional wear performance of the C-MoS2-PTFE-PEEK coating was compared with that of the anodic oxide film of 4032 aluminum alloy and the Ni-plated coating of 4032 aluminum alloy. The results show that the hardness of C-MoS2-PTFE-PEEK coating is 102.8 HV0.2. The C-MoS2-PTFE-PEEK coating has good lubrication properties under dry friction conditions due to the synergistic effect of MoS2 and PTFE, which can effectively resist deformation and reduce the coefficient of friction. The average friction coefficient under 5N, 10N, and 15N loads are 0.12, 0.15, and 0.23, respectively. The Graphite can effectively form a solid lubricating film, improve the adhesion resistance of the composite, and cause the shallow and small wear mark of C-MoS2-PTFE-PEEK coating; The wear rate and friction coefficient of C-MoS2-PTFE-PEEK coating under different loads are lower than that of the anodic oxidation film of 4032 aluminum alloy and the Ni-plated coating of 4032 aluminum alloy, showing excellent anti-friction and wear resistance. The wear mechanism of C-MoS2-PTFE-PEEK coating under different loads is mainly fatigue wear, adhesive wear, and abrasive wear.

Fabrication of HAp/rGO nanocomposite coating on PEEK: Tribological performance study

Polyetheretheretherketone (PEEK) is a prominent alternative material in medical applications because of its lower stress shielding impact than metal. Friction and wear characteristics have a large impact on the long-term in vivo performance of load-bearing implants. As a result, orthopaedic polymer implants have been subjected to a myriad of surface changes to increase their biofunctionality. In this study, wear resistant coatings, including hydroxyapatite (HAp) and reduced graphene oxide (rGO) as HAp/rGo, rGo/HAp and HAp+rGO nano composites were applied to the polyetheretherketone (PEEK) sample through dip coating method. The characterization of various coating combinations and patterns was accomplished by FESEM, XRD, AFM, and FT-IR. It was observed that the inclusion of rGO with HAp enhanced the friction and wear behaviour, with the HAp+rGO composition achieving the best wear resistance. In addition, carbonaceous films formed between the composite surfaces and counter body operated as solid lubricating films, resulting in a drop in the coefficient of friction (COF) from to 0.23 r min−1 on the coating and even helps to increase hydrophobicity state of the coating. Nevertheless, because rGO functions as an interstitial bonding agent between PEEK and HAp, bond strength increases, with the HAp+rGO combination having the highest bond strength of 35 MPa.

Tribological Behavior and Self-Healing Properties of Ni3Al Matrix Self-Lubricating Composites Containing Sn-Ag-Cu and Ti3SiC2 from 20 to 800 °C

As a high-temperature structural material, Ni3Al matrix composites are often used to manufacture basic mechanical components that need to be used in high-temperature conditions. To meet the increasing demand for metal matrix composites with an excellent tribological performance over a wide temperature range, Ni3Al matrix self-lubricating composites containing Sn-Ag-Cu and Ti3SiC2 (NST) were synthesized via laser-melting deposition. Dry sliding friction tests of NST against Si3N4 ball were undertaken from 20 to 800 °C to investigate the tribological behavior and wear-triggered self-healing properties. The results show that the tribological behaviors of NST are strongly dependent on the testing temperature and self-healing properties. At low and moderate temperatures from 20 to 400 °C, as the Sn-Ag-Cu flows into the cracks and is oxidized during sliding friction, while the cracks on the worn surface are filled with oxides consisting mainly of Al2O3, SnO2 and CuO. At higher temperatures of 600 and 800 °C, the cracks are filled by the principal oxides of Al2O3, TiO2 and SiO2 due to the partial decomposition and oxidation of Ti3SiC2. Compared with other testing temperatures, the recovery ratio relative to the Ni3Al base alloy of the cracks on the worn surface of NST is the highest at 400 °C, which is about 76.4%. The synergistic action mechanisms of Sn-Ag-Cu and Ti3SiC2 on the crack self-healing from 20 to 800 °C play a significant role in forming a stable solid lubricating film, improving the anti-friction and wear resistance of NST. The results provide a solution allowing for metal matrix composites to achieve excellent lubrication stability over a wide temperature range by virtue of the crack self-healing properties.

Skidding and spinning investigation for dry-lubricated angular contact ball bearing under combined loads

AbstractSliding and spinning behaviors significantly affect the performance of rolling bearings, especially for dry-lubricated bearings, micro and macro sliding may lead to increased wear of the solid lubricating film. A unified rolling contact tribology analytical model is proposed for dry-lubricated angular contact ball bearings (ACBBs) considering the extreme conditions including high combined loads and rolling contact effects. A comprehensive solution framework is proposed to ensure the robustness of the model under different loading conditions. Equilibrium equations are solved to study the effects of friction coefficients, rotating speeds, and combined loads on the skidding and spinning characteristics of the ACBB. The results show that the rolling contact effects and combined loads significantly affect the skidding and spinning performance of the ACBB. Further analysis reveals that the skidding mechanism is related to the interaction between ball kinematical motion and traction forces. The developed analytical model is proved to more accurately predict the bearing kinematical and tribological behavior as it discards the raceway control hypothesis and considers the macro/micro-slipping, creepage, and self-spinning motions of the ball, which is validated using both the existing pure axial loading dry-lubricated ACBB model and the classical Jones—Harris model. The study would provide some guidance for the structure and lubrication design of dry-lubricated ACBBs.

Comparative Evaluation of the Shear Adhesion Strength of Ice on PTFE Solid Lubricant

The development of a durable and green icephobic coating plays a vital role in the aviation industry due to the adverse impact of ice formation on aircraft performance. The lack of study into how temperature and surface roughness impact icephobicity is the main problem with present icephobic coatings. This study aims to qualitatively evaluate the icephobicity performance of a polytetrafluoroethylene (PTFE) solid lubricant film, as an environmentally friendly solution, with a custom-built push-off test device in different icing conditions utilizing a wind tunnel. The ice-adhesion reduction factor (ARF) of the film has been assessed in comparison to a bare aluminium substrate (Al 6061). The impact of surface energy was investigated by comparing the water contact angle (WCA), the contact angle hysteresis (CAH), and the pull-off force of the PTFE solid lubricant and Al with an atomic force microscope (AFM). The results of ice shear adhesion on the PTFE solid lubricant film showed a significant reduction in the ice adhesion force at various substrate temperatures and surface roughness compared to the bare aluminium substrate. The difference in the ice adhesion between the solid lubricant and aluminium alloy was attributed to the differences in the detachment mechanism. For the PTFE-based solid lubricant, the interfacial detachment mechanism was based on the formation of interfacial blisters towards the centre of the ice. Consequently, upon continued application of the shear force, most of the energy injected would be distributed throughout the blisters, ultimately causing detachment. In the comparison of ice adhesion on PTFE solid lubricant and bare aluminium, the film showed minimal ice adhesion at −6 °C with an adhesion force of 40 N (ARF 3.41). For temperature ranges between −2 °C and −10 °C, the ice adhesion for bare aluminium was measured at roughly 150 N.

Effects of frequency on the fretting wear behavior of aluminum bronze coatings

The aluminum bronze coating is a type of soft solid lubricant film with excellent performance. In this work, to improve the wear resistance and tribological behavior of the aluminum alloy, the aluminum bronze coatings were prepared on aluminum alloy substrates using the High-Velocity Oxygen Fuel (HVOF) system. Fretting wear tests were performed on the coatings at 200 °C with different frequencies to analyze the wear behavior. The worn surface was characterized by scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS). The results showed that as the frequency increased from 5 Hz to 15 Hz, the coefficient of friction increased from 0.653 to 0.929. It then decreased to 0.890 at 20 Hz. There was an overall trend of the coefficient of friction increasing and then decreasing. The worn surface's morphology changed from pits to bulges. At a low frequency, the wear mechanism was abrasive wear with delamination. As the frequency increased, adhesive wear was observed and gradually became the dominant wear form. Oxidation occurred on the surface of the worn tracks caused by the high temperature and thermal effect of high-frequency micromotion. Due to the intensification of the oxidation phenomenon, oxidation films formed on the worn surface. The wear rate of the coating was significantly reduced. The oxide was identified as mainly CuO and Cu2O. The presented results confirmed that the aluminum bronze coating fabricated via HVOF exhibited a great resistance performance even at a high frequency.