Synergetic Lubricating Research Articles

Multiscale study on the solid-liquid synergistic lubrication mechanism of graphite and liquid lubricant in polymer composites

Solid-liquid synergistic lubrication, in combination with the advantages of solid and liquid lubrication, has gained the great popularity in recent years. However, the mechanism of solid-liquid synergetic lubrication is still unclear. In this paper, graphite and poly α-olefin base oil (PAO) were used as self-lubricating additives to evaluate their synergistic effect. The results show that the composites possess good mechanical and excellent tribological properties with a nanoindentation modulus of 3.8 GPa, a coefficient of friction of 0.0998, as well as a wear rate of 1.3 × 10−14 m3/N·m. Both transfer film and lubricating oil film exist on the friction interface, and the lubricating oil film protects the counter ball from excessive oxidation. At the same time, with combination of molecular dynamics (MD) simulation and first-principles calculations, the synergistic lubrication mechanism of graphite and PAO was manifested. PAO destroyed the interlayer structure of graphite, making it easier to form a transfer film on the counter ball surface. The weak chemical bond between graphite and PAO facilitates more PAO molecules to gather at the interface while forming the transfer film, which benefits the formation of lubricating oil film. The synergistic effect of graphite and PAO molecules is critical in promoting the further reduction of COF.

Synergetic lubrication between self-lubricating ceramic tools and nanofluids: Advancing the application of self-lubricating ceramic cutting tools

In the field of ceramic tool processing, the incorporation of solid lubricants into self-lubricating ceramic tools forms a supportive lubricating film during the cutting process, effectively enhancing the cutting performance of the tools. Concurrently, Nanofluid Minimum Lubrication Technology (NMQL), as an emerging lubrication method, holds the potential to improve tool performance. However, due to significant cutting forces, NMQL faces challenges in effectively reaching the machining area, thereby limiting its cooling and lubricating efficiency. To overcome this challenge, our study proposes an innovative strategy by combining self-lubricating ceramic tools with nanofluids, aiming to enhance ceramic tool performance through synergistic lubrication effects. We conducted experimental studies under various lubrication conditions, comparing the performance of self-lubricating ceramic tools with traditional ceramic tools in cutting operations. A comprehensive evaluation of parameters such as tool life, cutting temperature, and cutting forces was performed. The results demonstrate that self-lubricating ceramic tools enable more efficient penetration of nanofluids into the machining area. In comparison to sole nanofluid lubrication, the synergistic effect significantly improves tool performance while substantially reducing production costs. This research contributes to advancing the development and widespread application of self-lubricating ceramic tools in the field of mechanical processing.

WS2-Ti-based solid-liquid synergetic lubricating coating with super-high wear resistance for space application

Solid-liquid lubricating technology is a quite effective approach to achieve long life for sliding components in space. Herein, the WS2-Ti films with porous and dense structures were prepared. The tribological performances of WS2-Ti films lubricated in two kinds of space liquid lubricants (P201 and PFPE) were mainly investigated in vacuum compared to the films in dry friction condition. The dense film exhibits the low friction coefficient of 0.02 and ultra-low wear rate of 2.3 × 10−8 mm3·N−1·m−1 in the dry friction condition. The dense film/oil coatings also show a very long wear life over 4.5 × 105 r, and their wear rates obviously decrease about 79 % and 67 % under harsh test condition compared to the porous film lubricated in P201 and PFPE, respectively. The related analyses indicate that nonpolar P201 molecule is found to have far better compatibility to WS2-Ti crystal surfaces than polar PFPE molecule. It contributes to forming compact tribolayer consisting of numerous ultrathin nanosheets, significantly extending wear life of the coating. Noteworthily, for the solid-liquid coatings, there is a new find that formation of transfer film firstly underwent amorphization and then occurred recrystallization. This reveals lubricating mechanism of the WS2-Ti/oil coating.

Tribological performance of maintenance-free Cu-Sn-Ni-MoS2 composites over a wide temperature range

PurposeThe purpose of this paper is to investigate the friction and wear mechanisms in copper-based self-lubricating composites with MoS2 as the lubricating phase, which provides a theoretical basis for subsequent research on high-performance copper-based self-lubricating materials.Design/methodology/approachFriction tests were performed at a speed of 100 r/min, a load of 10 N, a friction radius of 5 mm and a sliding speed of 30 min. Friction experiments were carried out at RT-500°C. The phase composition of the samples was characterized by X-ray diffraction of Cu Ka radiation, and the microstructure, morphology and elemental distribution were characterized by scanning electron microscopy and energy dispersive spectroscopy. Reactants and valences formed during the wear process were analyzed by X-ray photoelectron spectroscopy.FindingsThe addition of MoS2 can effectively improve friction-reducing and anti-wear action of the matrix, which is beneficial to form a lubricating film on the sliding track. After analyzing different changing mechanism of the sliding tracks, the oxides and sulfides of MoS2, MoO2, Cu2O, CuO and Ni(OH)2 were detected to form a synergetic lubricating film on the sliding track, which is responsible for the excellent tribological properties from room to elevated temperature.Research limitations/implicationsFor self-lubrication Cu–Sn–Ni–MoS2 material in engineering field, there are still few available references on high-temperature application.Practical implicationsThis paper provides a theoretical basis for the following research on copper-based self-lubricating materials with high performance.Originality/valueWith this statement, the authors hereby certify that the manuscript is the results of their own effort and ability. They have indicated all quotes, citations and references. Furthermore, the authors have not submitted any essay, paper or thesis with similar content elsewhere. No conflict of interest exits in the submission of this manuscript.

Synergistic lubrication mechanism of core/shell C@MoS2 particles as lubricant additives

To unify the lubrication characteristics of carbon spheres (CS) with high load-bearing capacity and molybdenum disulfide (MoS2) with exceptional low-shear friction performance, CS wrapped with MoS2 (C@MoS2) were accomplished via an efficient and facile hydrothermal method based on the self-assembly principle. Then, 0.5 wt% C@MoS2 particles were dispersed into Poly Alpha Olefin 40 (PAO 40) for enhancing the anti-friction/wear abilities. Subsequently, 0.5 wt% of C@MoS2 particles were dispersed into Poly Alpha Olefin 40 (PAO 40) to enhance its anti-friction and wear-resistant capabilities. The excellent tribological properties of C@MoS2 particles were attributed to the synergistic lubrication between bearing and filling effect of CS as well as the superior antifriction capacity of MoS2 shell. Furthermore, the synergetic lubrication mechanism of C@MoS2 may be segmented into different stages: I. the shell crushing stage, corresponding to the rolling bearing effect of C@MoS2 particles at the friction interface; II. the core/shell separation stage, corresponding to the rolling bearing effect and self-repair effect of C@MoS2 particles; III. the core/shell recombination stage, corresponding to the construction and reinforcement of protective film and the great improvement of anti-friction/wear abilities performance.

Fabrication and tribological behavior of Fe-Cu-Ni-Sn-Graphite porous oil-bearing self-lubricating composite layer for maintenance-free sliding components

Fe-Cu-Ni-Sn-Graphite oil-bearing self-lubricating composite was prepared using powder metallurgy method through multiple sintering-rolling processes and oil impregnation vacuum-assisted method. The tribological property of the composite were characterized by a UMT-2 tribometer. And the micro-structure and worn surface of composite were investigated by an optical microscope, SEM (scanning electron microscopy), XRD (X-Ray Diffraction) and EDS (energy disperse spectroscopy). The results show that the porous oil-bearing self-lubricating composite exhibit an excellent long-term low-friction and antiwear properties. Especially, the friction coefficient of the composite after secondary rolling and sintering decreased by 38% compared to that of the sample without sintering-rolling. After sliding for 21 h, the friction coefficient of the composite still keep relatively stable at a low value. In addition, the wear resistance of the composite has greatly improved after secondary rolling and sintering. And the wear loss of the 40Cr counterpart is almost wear-free and presents oil-graphite mixture around the wear track, which reveals that solid-liquid synergetic lubrication is the potential lubrication mechanism during the sliding process.

Preparation and tribological properties of PTFE/DE/ATF6 composites with self-contained solid-liquid synergetic lubricating performance

A new kind of PTFE composite with self-contained solid-liquid synergetic lubricating effect is prepared by the combination of PTFE, porous diatomite (DE), and immersed lubricating oil (ATF6). The tribological and mechanical properties of composites with different DE contents and varying cold-pressed pressures were investigated systematically. Due to the oil storage effect of DE particles, the maximum oil content of PTFE/DE composite is 16.4 wt%. With the increase of DE content, the surface hardness, elastic modulus and yield strength can be increased from 3.2 to 3.6 HV, 37.8–60.2 MPa and 8.7 MPa–12.8 MPa, respectively. With the addition of DE, the wear rate of PTFE decreases but the coefficient of friction (COF) increases. Meanwhile, with the addition of DE and ATF6, both the COF and wear rate of PTFE decrease. The COF can be reduced by 68% from 0.121 (specimen 0%-10 MPa-dry) to the minimum value of 0.039 (composite 10%-10 MPa-ATF6), and the wear rate can be reduced by 82% from 1.95 × 10−4 mm/Nm (0%-50 MPa-dry) to the minimum value of 0.35 × 10−4 mm/Nm (10%-50 MPa-ATF6). The enhanced antifriction performance of the composite PTFE/DE/ATF6 is contributed by the synergistic lubricating effect of self-contained liquid lubricant of ATF6 and the solid lubricant of PTFE. The prepared PTFE/DE/ATF6 composites exhibit excellent tribological performance as well as the mechanical properties, which can be used to fabricate a new kind of self-lubricating materials with high performance and long durability.

Excellent Water Lubrication Additives for Silicon Nitride To Achieve Superlubricity under Extreme Conditions.

Superlubricity has been recognized as the future of tribology. However, it is hard to achieve superlubricity under extreme conditions such as a high load and low sliding speed on the macroscale. In this paper, a remarkable synergetic lubricating effect between nanoparticles and silicon nitride (Si3N4) is demonstrated; this effect helps water-lubricated Si3N4 achieve superlubricity under extreme conditions successfully. Different kinds of hairy silica nanoparticles were prepared, dispersed into water, and characterized using a variety of methods. The tribological properties of water-lubricated Si3N4 with nanoparticle additives were tested using a ball-on-disk tribometer under different loads and sliding speeds. The coefficient of friction and wear scar diameter were measured and analyzed. Both the nanoparticle size and surface functional groups have a significant influence on the tribological properties of water-lubricated Si3N4. Amino-modified silica nanoparticles reduce the friction coefficient of water-lubricated Si3N4 by 82.9% under 60 N, compared with that achieved using deionized water, and induce superlubricity after the running-in process. Silica nanoparticles effectively form a homogenous film with silica gel on the worn surface under a high load and thus reduce the wear and maintain the superlubricity under extreme conditions.

Ultra-low friction of a-C:H films enabled by lubrication of nanodiamond and graphene in ambient air

Hydrogenated amorphous carbon (a-C:H) is subjected to abnormal high friction in ambient air, and the possibility to retain an ultra-low friction state remains as a great challenge. Here, nanodiamond and graphene were used as solid lubricants to improve the tribological properties of two representative types of a-C:H films with 20 at.% and 40 at.% hydrogen contents, respectively. The results emphasize the exceptionally synergetic lubrication effect of nanodiamond + graphene composite with a mass ratio of 1:1 and a solution-processed concentration of 0.1 mg/mL. An ultra-low friction coefficient of ∼0.02 was achieved for a-C:H (20 at.% H) film, and more strikingly, a dramatic reduction in COF from 0.52 to 0.07 was realized in a-C:H (40 at.% H) film. Meanwhile, the wear rates of the counterparts in both cases are significantly reduced in the presence of nano-lubricants. The lubricity mechanisms are mainly based on the in-situ growth of nanostructured tribolayers. The roles of a-C:H film bonding characteristic and the tribo-induced structural evolution of nano-lubricants in the build-up of anti-friction and wear-resistant tribolayers are discussed. These findings can enrich the understanding of surface modification pathways to a-C:H films via low-dimensional nano-lubricants and help to develop more adaptive and robust solid carbon films.

Synthesis of polyethylene glycol modified carbon dots as a kind of excellent water-based lubricant additives

The polyethylene glycol (PEG) modified carbon dots (CDs-PEG) were facile synthesized by one-pot pyrolysis of the mixture of gluconic acid and PEG. When the average molecular weight of PEG was 200, 600, 1000 and 4000 g/mol, the CDs-PEG were denoted as CDs-PEG200-4000, respectively. As the water-based lubricant additives, the tribological properties of CDs-PEG200 under four-ball mode and steel/steel contact were far superior to PEG200, CDs derived from gluconic acid only, and CDs-PEG600-4000, reflecting the carbon cores and surface groups of CDs-PEG200 should play a synergetic lubrication effect. Specifically, at load of 40 N, adding 0.20 wt% of CDs-PEG200 into base liquid resulted in the largest friction coefficient and wear volume reductions up to 83.5% and 90.9%. Meanwhile, the load carrying capacity of base liquid increased from 50 N to at least 200 N. Amazingly, the lubrication ability of base liquid containing 0.20 wt% of CDs-PEG200 sometimes was even comparable to some lubricant oils. The results of worn surface analyses revealed that the distinguished friction-reducing and antiwear performance of CDs-PEG200 as additives could be attributed to the formed composite lubrication film composed of CDs-PEG200 and Fe3O4 on the rubbing surfaces.

Facile pyrolysis synthesis of ionic liquid capped carbon dots and subsequent application as the water-based lubricant additives

Carbon dots (CDs) were facilely synthesized by one-pot pyrolyzing a lactic acid-ionic liquid (IL) gel with a relatively high yield of 34.9 wt%. The CDs, with a mean particle size of 4.4 nm and high thermal stability, were almost amorphous and capped by IL groups. The CDs-IL in water exhibited an obvious excitation-, concentration-, pH-dependent and high salt-tolerant photoluminescence property. Specifically, the CDs-IL emitted the strongest blue fluorescence at 454 nm under 365 nm excitation with a quantum yield of 16%. In addition, the CDs-IL, as a kind of water-based lubricant additives, greatly improved the tribological properties of base liquid. The loading capability of base liquid for steel–steel pair increased from 50 N to at least 80 N when only 0.015 wt% of CDs-IL was added. Meanwhile, the mean friction coefficient and wear volume of base liquid reduced by 57.5% and 64% at the load of 40 N, respectively. In addition, the friction-reducing and antiwear performance of CDs-IL was far superior to the CDs and IL, reflecting a synergetic lubrication effect between the IL groups and carbon cores. Based on the worn surface analyses, the CDs were prone to be squeezed out of the rubbing surfaces during the boundary shear friction process, while the CDs-IL were prone to quickly form ordered absorption layers on rubbing surfaces by electrostatic interaction between the IL groups and steel surface, which is of key importance for the formation of effective lubrication film to largely reduce friction and wear.

Probing carbon-based composite coatings toward high vacuum lubrication application

Abstract For challenges in minimizing friction and wear of spatial mechanical systems, synergetic lubrication coatings were prepared by spinning liquid lubricants and hybrid greases on the diamond-like carbon (DLC) films, and were evaluated whether they could achieve a long-term safe and reliable operation under high vacuum. Under high vacuum conditions, liquid lubricants significantly reduce the friction and wear of DLC films. Hybrid greases not only show excellent lubrication performance, but also greatly enhance the tribological behavior of DLC films, especially the grease with optimal proportion. Such excellent tribological performance of DLC-based composite coatings at low applied loads depends on the synergy of DLC and fluid film, in reverse the tribo-chemical reaction film under harsh working conditions.

Microstructures and Properties of Nanostructured TiN/MoS2/Ag Composite Film Prepared by Pulsed Laser Deposition

In this work, the structural and mechanical properties, tribological performance, and lubrication mechanism from room temperature to 900 °C of TiN/MoS2/Ag composite films were investigated in detail. Nanostructured TiN/MoS2/Ag composite film was obtained by assembling targets using pulsed laser deposition. The incorporation of lubricant layered MoS2 and soft metal Ag led to degraded mechanical properties, which could contribute to the lower friction coefficients at low temperatures. When the temperature increased to above 500 °C, the generated high-temperature lubricant MoO3 and silver molybdates played a critical synergetic lubrication effect, which formed a layer of lubricating film and reduced the friction coefficient. Thus, the cooperation of various lubrication phases contributed to improvement of tribological performance and resulted in continuous lubrication from room temperature to 900 °C.

Tribological properties and lubrication mechanism of in situ graphene-nickel matrix composite impregnated with lubricating oil

A solid-liquid synergetic lubricating system has been designed to develop a novel self-lubricating nickel matrix composite. The graphene-nickel (G-Ni) matrix composite with porous structure was fabricated by in situ growing graphene in bulk nickel using a powder metallurgy method. The porous structures of the composite were used to store polyalphaolefin (PAO) oil for self-lubricating. It is found that the G-Ni matrix composite under oil lubrication condition exhibited superior tribological properties as compared to pure nickel and the composite under dry sliding condition. The prestored oil was released from pores to the sliding surface forming a lubricating oil film during friction process. This lubricating oil film can protect the worn surface from severe oxidation, and help the formation and transfer of a carbon-based solid tribofilm derived from graphene and lubricating oil. This solid (graphene)-liquid (oil) synergistic lubricating mechanism is responsible for the reduction of friction coefficient and improvement of wear resistance of the in situ fabricated G-Ni matrix composite.

Controlled Friction Behaviors of Porous Copper/Graphite Storing Ionic Liquid through Electrical Stimulation

Porous copper/graphite composites storing stimuli‐responsive lubricant can be used to fabricate a new kind of electrical contact friction materials. However, the synergetic lubricating effect of solid and liquid lubricants incorporated into the copper matrix is rarely discussed. In this work, neat copper and its composites storing ionic liquids (ILs) have been successfully prepared via a template‐free strategy. The effect of frictional, electrical, and electro‐frictional coupling stimulation on the tribological behavior of the copper filled with graphite has been investigated using ball‐on‐disk friction tests. Results show that a high voltage may accelerate the release of the ILs stored in the composite to the friction interface, thereby resulting in a low coefficient of friction (COF) (ca. 0.14) at the voltage of 0.5 V, which is superior to those of the pure copper without applying voltage. The COF is more stable in copper/graphite composite storing ILs (SI) than in copper‐SI. Therefore, the graphite efficiently protects the surface of the sample from wear and electrochemical corrosion.

Synergistic role of carbonaceous reinforcements on multi length scale tribology of electrophoretically deposited nickel-boron nitride coatings

Electrophoretically deposited Ni-BN composite coating was strengthened with graphene (Ni-BN-Gr), carbon nanotubes (Ni-BN-CNT) and diamond (Ni-BN-D) carbonaceous reinforcements. Highest hardness (2.0GPa) and elastic modulus (133.5GPa) of Ni-BN-D coating than Ni-BN-CNT (1.96GPa and 102.1GPa, respectively), Ni-BN-Gr (1.94GPa and 92.0GPa respectively) and also from Ni-BN (1.89GPa and 91.5GPa, respectively) coatings was linked through high compressive stress (−601MPa), dislocation density (8.9×1015m−2) and yield strength (4.4GPa). The micro-scratching damage was contributed by ploughing and adhesion components, which were compared with that of experimental frictional values. Addition of graphene, CNT and diamond in Ni-BN composite showed a decrease in wear volume (from 1.66×10−8m3 to 0.45×10−8m3) due to the synergetic lubricating effect of BN and carbonaceous reinforcements. Thus, Ni-BN-D restrict inception of multiscale wear and can be a potential three phase metal-ceramic coating for engineering and industrial applications.

Effect of copper molybdate on the lubricating properties of NiCrAlY laser clad coating at elevated temperatures

The goal of the current work was to prepare a self-lubricating composite coating NiCrAlY/Cr3C2(NiCr)/Cu/MoO3 on GH4169 alloy substrate by laser cladding with hard phase Cr3C2(NiCr) as the reinforcing agent and Cu-MoO3 as the primary fillers. The composition and microstructure of the feedstock powders and corresponding composite coating were examined by scanning electron microscopy-energy dispersive spectrometry (SEM-EDS) and X-ray diffraction. The tribological behavior of the composite coating from 25°C to 800°C was performed in air with a ball-on-disk tribometer against Si3N4 ball counterfaces and a dual-mode three-dimensional surface profiler. It has been found that the composite coating shows the most serious abrasion at 200°C, the friction coefficient was 0.7 and the wear rate was 7.7×10−5mm3/N·m. Better tribological properties could be found when the temperature higher than 200°C, and the composite coating got the best wear resistance with the friction coefficient 0.34 and the wear rate was 1.0×10−5mm3/N·m at 800°C. The morphology and compositions of the worn surfaces were analyzed by SEM-EDS and Raman spectroscopy. Findings indicate that copper molybdate (CuMoO4) is converted by in situ reaction between Cu and MoO3 during friction at elevated temperatures. The synergetic lubricating effect between CuMoO4 and oxide lubrication (such as MoO3, Cr2O3, CuO, and NiO) is the principal reason for the anti-wear and self-lubricate of the composite coatings. Particularly, composite coating containing CuMoO4 and Cr2O3 exhibits the lowest friction coefficient and smallest wear rate when the temperature above 600°C. Abrasive wear, plastic deformation, delamination as well as adhesive wear was main wear mechanism of the composite coating during friction at different temperature.

The Effect of Ni Nanoparticles on the Lubrication of a DLC-Based Solid–Liquid Synergetic System in All Lubrication Regimes

Ni nanoparticles (with average diameter 7 nm) capped with oleylamine and oleic acid were added to a DLC/DIOS solid–liquid synergetic lubricating system. The tribological behavior rubbed with steel balls in three lubricating regimes (boundary, mixed and elasto-hydrodynamic lubrication) has been systematically studied by surface analyses techniques such as SEM, EDX and XPS. It was found that, in all the lubricating regimes, the system’s lubricating performance was substantially improved because of the addition of the Ni nanoparticles. For all the lubrication regimes, the COF decreased by 10.3–19.1%. In the boundary lubrication regime, the wear rate of DLC could be decreased by 50%. Ni nanocores facilitate the adequate oxidation of the steel surface and the transformation of C=C (sp2) to C–C (sp3) of the DLC sliding surface. The tribo-film containing ferrous oxides, Ni and its oxides, presents low shearing strength and good cohesion to the DLC coating, which greatly improves the lubricating behaviors of the DLC/DIOS solid–liquid synergetic system. In the elasto-hydrodynamic lubrication regime, the Ni nanoparticles cause the occurrence of obstructed or plug flow in the oil films, which in turn reduces friction by reducing the layers of lubricant molecules to slide on each other.

The fracture mechanism and the corresponding optimization strategy for nonhydrogenated amorphous carbon film in dimethyl silicone oil

Abstract The synergetic lubrication effects between amorphous carbon (a-C) films and lubricating oils have drawn much attention for the past decades, and related researches suggest that the molecular structure and physicochemical properties of base oil could strongly affect the tribological behavior of a-C films. Here, we report a unique tribological behavior of nonhydrogenated a-C film when slides against the steel counter-parts in polydimethylsiloxane (PDMS), where the a-C film is severely fractured at the onset of sliding, but achieves a very low steady friction coefficient which is only about 50% of the one obtained in the poly-alpha-olefin (PAO). Via detailed morphological, chemical analysis and designed verification experiment, it is proposed that the initial high adhesion between a-C and steel in PDMS accounts for the fracture failure of the analyzed a-C film, while the chemical adsorption of decomposed PDMS on a-C surface is responsible for the reduced friction. Finally, we present an effective method to eliminate the cracking behavior while retain the low friction performance for steel/a-C contacts in PDMS.

The Influence of Total Acid Number of Ester Oil in Tribological Behavior of DLC Contacts

The synergetic lubrication effects between diamond-like carbon (DLC) coatings and lubricating oils have draw much attention for the past decades, and promising results have been reported between DLC and biodegradable synthetic ester, which might be a potential solution in energy conservation and environmental protection. However, the challenges lie in that the synthetic ester oils exhibit lower oxidation stability than the hydrocarbon oils and are prone to produce organic acids in the aging process. Thus, investigating the tribological behavior of DLC coating in acidified ester oil is meaningful to the long-term reliability of ester-lubricated DLC contacts. In this article, the friction and wear behavior of DLC–DLC, DLC/steel, and steel–steel contacts in acidic ester oils with different total acid values (TANs) is systematically studied. It was found that acidification of ester oil showed certain beneficial tribological effects for the self-mated steel and DLC contacts but could cause severe wear loss on steel counterparts with a special polished appearance for steel–DLC hybrid contacts. By focusing on the properties of the tribofilm formed on the contact surfaces, a possible tribological mechanism was discussed. Finally, it was proposed that the steel–DLC contacts exhibited low tolerance to organic acids and thus the additives that could dissipate the produced organic acids are a critical component in lubricating oils that were tailored for the steel–DLC contacts.