Continuous Transfer Film Research Articles

Tribological synergy of copper‐based metal–organic frameworks, carbon fibers and SiO2 in modifying the friction and wear properties of epoxy composites

AbstractCopper‐based metal–organic frameworks is anticipated to find applications in the field of friction materials owing to its plentiful surface‐active groups and distinctive framework structure. In this study, copper‐based metal–organic frameworks was synthesized through ultrasound‐assisted method and incorporated alone into carbon fiber reinforced epoxy composites or together with SiO2 nanoparticles towards the goal of improving the composites' friction and wear properties. It is revealed that copper‐based metal–organic frameworks alone cannot improve the friction and wear of carbon fiber reinforced epoxy composites simultaneously. The combination of copper‐based metal–organic frameworks and SiO2 nanoparticles was more effective in enhancing both the mechanical and tribological properties of studied composites. The composite material exhibits a friction coefficient of 0.104 under the specified test conditions of 10 MPa and 3.75 m/s. Additionally, the specific wear rate is impressively low, measuring only 5.64 × 10−7 mm3 N/m. Through morphological and chemical analysis on the worn surfaces and transfer films, the functioning mechanism of copper‐based metal–organic frameworks in modifying the mechanical and tribological properties was discussed. It was discovered that a tribological synergy exists between short carbon fibers, copper‐based metal–organic frameworks, and SiO2 fillers, leading to a shift in the wear mechanism of the composite materials from abrasive wear to adhesive wear. Concurrently, a shear‐prone transfer film forms on the surface of the counter steel surfaces. Findings of the present study pave a new route of designing high performance epoxy based tribo‐composites by using metal–organic frameworks.Highlights Cu‐BDC nanosheets were synthesized using ultrasound‐assisted techniques and incorporated as tribological fillers in EP composites. The combined use of Cu‐BDC, SiO2, and SCF fillers synergistically enhances the mechanical and tribological properties of EP composites. The composite material exhibits a friction coefficient of 0.104 under the specified test conditions of 10 MPa and 3.75 m/s, the specific wear rate is impressively low, measuring only 5.64 × 10−7 mm3N/m. During the sliding friction process of the composite materials, Cu‐BDC and SiO2 play a crucial role in reducing SCF pull‐out wear through their anchoring effect. The dynamic coordination bond structure of Cu‐BDC contributes to the formation of uniform and continuous transfer films on counter metal surfaces.

Lubrication mechanism of polyimide/V2CTx MXene composites based on surface chemistry

AbstractA series of polyimide (PI)/V2CTx MXene composites was synthesized via polyamide acids (PAA) and two‐dimensional (2D) V2CTx MXene obtained by etching precursor V2AlC. PI/V2CTx MXene composites with different mass ratios were obtained by blending and heating with PAA. The results showed that V2CTx MXene has excellent dispersion in PI. In particular, V2CTx MXene exhibited excellent friction reduction and anti‐wear properties as a solid lubricant additive, and the wear rate (WR) was reduced by 43.2% by incorporating only 0.8 wt% of V2CTx MXene in the pristine PI and 71.9% by incorporating 1.2 wt%. Scanning electron microscopy (SEM) and x‐ray photoelectron spectroscopy (XPS) analyses showed that the continuous transfer film consisting of a high proportion of tribo‐chemical products formed on the contact surface is significant to improve the lubrication performances of the PI composites. This work broadens the application of MXene in the field of tribology and contributes to energy conservation and sustainable development of human society.Highlights The tribological properties could be tuned by changing the ratio of PI to V2CTx MXene. The WR of PI composites was reduced by 71.9% with incorporating 1.2 wt% of V2CTx MXene. The formation of transfer films on the contact surface is significant for improving anti‐wear of PI.

Two-step printing Ni3Al/Cr3C2-Ti3SiC2/MoS2 composite films using electrohydrodynamic atomization with a biomimetic shark-skin mask

Natural structures with outstanding tribological properties have inspired mankind to imitate their designs, and the purpose is to minimize friction and wear. Herein, in consideration of the exceptional high-temperature strength and wear resistance of Cr3C2 reinforced Ni3Al matrix composite, Ni3Al/Cr3C2 convex texture was printed through the usage of electrohydrodynamic atomization (EHDA) technology, with a mask that simulated bioinspired sharkskin. Furthermore, the corresponding synergistic lubrication behavior between the convex texture and Ti3SiC2/MoS2 lubricants was explored. Experimental results indicated that the composite films consisting of inspired-sharkskin Ni3Al/Cr3C2 convex texture and Ti3SiC2/MoS2 lubricants exhibited favorable adhesive strength, giving long wear life and excellent stability in friction. This was mainly ascribed to the convex textured enhanced surface wettability of the polished substrate. The composite films performed a favorable friction coefficient of 0.17 at ambient temperature, which was decreased by 70.2 % and 39.3 %, with respect to the structure-less Ni3Al/Cr3C2 and Ti3SiC2/MoS2 composite films, respectively. This improvement could be explained by the sharkskin convex texture served as a reservoir for storing lubricants and supported to form more continuous transfer films. In this work, an efficient and potential approach was proposed for exploiting lubrication structures in future interfacial engineering and lubrication systems under peculiar service environments.

Improving the tribological performance of polyphenylene sulfide by incorporating irradiation treated polytetrafluoroethylene powders

AbstractIn this work, the efficacy of using irradiation treated polytetrafluoroethylene (i.e., i‐PTFE) powders on the tribological properties of polyphenylene sulfide (PPS)‐based composites was systematically investigated. The results showed that the addition of i‐PTFE powders significantly improved the friction and wear properties of PPS. The average friction coefficient and specific wear rate of PPS/i‐PTFE 20 wt% composite reached 0.129 and 1.75 × 10−5 mm3 N−1 m−1, which were 77.4% and 99.5% lower than those of pure PPS, respectively. SEM observations indicated that the i‐PTFE powders exhibited a relatively uniform distribution within PPS, which favored the formation of intact, uniform and continuous transfer film on the surface of friction pair, thereby resulting in a significant improvement of tribological properties for PPS/i‐PTFE composites. The worn surface of the testing specimen turned smoother and the wear debris became smaller with increasing addition of i‐PTFE powders, which was related to the improvement of tribological performance by forming transfer film at the sliding interface. This work provided a strategy to fabricate high performance self‐lubricating polymer composites that demonstrate potential applications in engineering sectors.

Effect of Square Texture on Tribological Properties of Nano-SiO2/POB-PTFE Composites

In order to study the seal design problem of piston rings in Stirling engine, on the basis of filling PTFE with Nano-SiO2 and POB and preparing the GCr15 contact surface with square texture by HM20-I laser marking machine, experiments were carried out on LSR-2M wear tester by indirect weighing and in-situ observation methods. Optical microscope (OM) and scanning electron microscope (SEM) were used to observe the evolution of Nano-SiO2/POB-PTFE composites’ transfer film on contact surface. The results showed that the square texture would shorten the running-in and transitionary periods of the composites’ tribological process, accelerate into the stationary period. The formation process of the composites’ transfer film on the square textured contact surface was also different from smooth contact surface. Although the square texture would increase wear rate, its ability to store wear debris is more conducive to the formation of reliable, uniform and continuous transfer film with a same friction direction. Obviously, reasonable design of surface texture can effectively improve the wear resistance of sealing parts made of filling modified PTFE composites, thus providing theoretical guidance for the seal design of Stirling engine piston ring.

MoS2 Lubricating Film Meets Supramolecular Gel: A Novel Composite Lubricating System for Space Applications.

In the field of space mechanical lubrication, to improve the reliability and life of space lubrication, solid lubricating film-liquid lubricant composite lubrication has been used in recent years. This lubrication method can improve the durability of sliding friction mating surfaces, reduce equipment wear, and extend the service life of motion mechanisms. However, due to unstable factors such as volatilization and creeping of liquid lubricants in microgravity and ultra-high-vacuum environments, the solid lubricating film wears out after long-term use and produces wear debris and other unfavorable factors. To solve the above problems, this study proposes a novel composite lubrication system constituting a MoS2 film in combination with a supramolecular gel. The tribological performance of this lubrication system establishes an extended service life with a lower wear rate compared to the MoS2 film, regardless of functioning in vacuum or atmospheric conditions. More importantly, the results of the irradiation experiment demonstrate that MoS2-gel exhibits better anticreep performance as compared to MoS2-oil when exposed to atomic oxygen and ultraviolet light for 4 h. The analysis of this composite lubrication mechanism also reveals the formation of a continuous transfer film on the surface of the friction pairs by virtue of the outstanding synergistic effect between the MoS2 film and the gel. MoS2 debris is present in the gel as an additive, and the gel is capable of replenishing automatically once the MoS2 film is depleted. Moreover, the strong anticreep properties of the gel are attributable to the multialkylated cyclopentane oil being trapped by the intricate reassembling of the gelator network. It is firmly believed that this novel MoS2-gel composite lubrication system may have good prospective applications in space and special machinery domains.

Fabrication and effect of heat treatment on the microstructure and tribology properties of HVOF-sprayed CoMoCrSi coating

A type of CoMoCrSi coatings were fabricated by using HVOF technique, and the microstructures, mechanical properties and tribological behaviors at room temperature (RT) of the coatings annealed at 800 °C for different time were investigated in detail. Annealed CoMoCrSi coatings exhibited better crystallization and more compact microstructures compared to as-sprayed coatings. The porosity of the annealed coatings reduced to 0.32–0.2%, and adhesive strength increased to 63.8–68.5 MPa, both of that were all reached at an equivalent level with the variation of the annealed time. The surface microhardness could be enhanced from 902.8 HV0.3 for the as-sprayed coating to 1237.6 HV0.3 for the coating annealed for 10 h, which could be attribute to more compact microstructures and hard nano-sized Cr2O3 layer, that resisted indentation effectively. With the increasing of sliding distance at room temperature, the friction coefficients of the annealed coatings reached at 0.39–0.4, and the wear rates decreased to 0.88–1.59 × 10–6 mm3 N−1 m−1, demonstrating enhanced tribological performance of the CoMoCrSi coating after heat treatment. Numerous metallic oxides, i.e., Cr2O3 played a critical role in sustaining and anti-wear, and oxides, i.e., Co3O4, MoO3, and CoMoO4 transferred to the Al2O3 pair surface and formed a continuous transfer film during the friction test at RT, which directly reduced friction and leading to a low friction coefficient and wear rate.

Tribological Performance Studies of Waterborne Polyurethane Coatings with Aligned Modified Graphene Oxide@Fe3O4.

In this study, the chemical graft method was used to connect modified graphene oxide (GO) and Fe3O4 through covalent bonds. To make full use of the tribological properties of graphene, aligned graphene oxide@Fe3O4/waterborne polyurethane (GO@Fe3O4/WPU) was prepared in a magnetic field and tribological experiments were carried out on it. The GO@Fe3O4 was characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and a transmission electron microscopy (TEM). The characterization results show that Fe3O4 is successfully loaded on the surface of GO and GO@Fe3O4 has better dispersibility in WPU. Among the coatings without alignment inducement of GO@Fe3O4, 0.5 wt % GO@Fe3O4/WPU has the lowest friction coefficient and wear rate. In addition, the 0.5 wt % aligned GO@Fe3O4/WPU composite coating has the lowest friction coefficient and wear rate compared with nonaligned and pure WPU coatings. The excellent tribological properties of the aligned composite coating come from its ability to quickly form a uniform and continuous transfer film on the friction counterpair, which avoids direct friction between the friction counterpair and the coating.

The effect of oxygen on the tribology of (PEI/GO)15 multilayer solid lubricant coatings on steel substrates

Multilayers of polyethyleneimine and graphene oxide, (PEI/GO)15, were coated onto steel substrates via electrostatic layer-by-layer (LbL) deposition, and their tribological properties were investigated as solid lubricants. The coefficient of friction (COF) and specific wear rate (SWR) were measured against a poly(methyl methacrylate) (PMMA) counterface ball, in various gas environments with different oxygen concentrations. The COF and SWR both significantly decreased with decreasing oxygen content. Detailed surface characterization of the contact area of the counterface ball revealed that continuous transfer films were formed in oxygen-free environments, but not in oxygen-rich environments. This is attributed to an increased proportion of sp3 bonding in the wear debris in the presence of oxygen (as confirmed by Raman spectroscopy), as well as possible suppression of wear debris adhesion on the counterface ball due to oxygen adsorption on the surface.

One-step synthesis of g-C3N4 nanosheets to improve tribological properties of phenolic coating

Abstract In the present work, g-C3N4 nanosheets are prepared by calcination the mixture of urea and melamine. Resulting production is characterized by transmission electron microscope (TEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, indicating an effective synthesis of g-C3N4 nanosheets. Phenolic coatings with addition of different content of g-C3N4 nanosheets are used to evaluate the tribological performance of g-C3N4 nanosheets as a role of enhancement phase. Bulk g-C3N4 and graphite are also utilized as fillers to further insight different wear mechanism under dry sliding condition. Experimental results show 1 wt% g-C3N4 nanosheets/phenolic coating exhibit the optimal tribological properties. A higher surface area with more active sites and formation of a continuous transfer film are two important factors for the improvement.

Tribological properties of Ti‐doped diamond‐like carbon coatings under dry friction and PAO oil lubrication

Titanium‐doped diamond‐like carbon (Ti‐DLC) coatings with Ti concentration of 4 at.% (Ti4at.%‐DLC) and 27 at.% (Ti27at.%‐DLC) were prepared by a hybrid ion beam deposition system for comparison. The tribological behaviors of Ti‐DLC coatings under dry friction and boundary lubrication conditions were systematically investigated. Results showed that, under dry friction, the Ti4at.%‐DLC coating displayed lower friction coefficient (0.07) and wear rate due to the continuous transfer film formed in the sliding interface, while Ti27at.%‐DLC coating was worn out at initial stage due to severe abrasive wear. And under boundary lubrication, both the Ti4at.%‐DLC and Ti27at.%‐DLC coatings showed excellent tribological properties attributing to the formation of oil film between sliding interface. In particular, Ti27at.%‐DLC performed the lowest wear rate of 1.12 × 10−16 m3 N−1 m−1 in this friction case. In conclusion, compared with Ti27at.%‐DLC coating, Ti4at.%‐DLC coating exhibited better tribological performances both under dry friction and boundary lubrication. The present result provides guidance for the selection of DLC coatings according to the realistic environment of starved‐oil and rich‐oil conditions.

Development of Wear Mechanism Maps for Acrylonitrile Butadiene Styrene Hybrid Composites Reinforced With Nano Zirconia and PTFE Under Dry Sliding Condition

Acrylonitrile butadiene styrene (ABS) polymer is cost-effective and also possesses high toughness and resistance to corrosive chemicals. However, pure ABS does not show significant wear resistance and also it has a high friction coefficient. Incorporation of a solid lubricant and nanofiller in a polymer matrix improves its tribological properties significantly. The addition of solid lubricant makes it suitable for application where self-lubrication is desirable (sliding bearings, gears). This paper deals with the study of tribological behavior of ABS hybrid composites reinforced with nano zirconia and polytetrafluoroethylene (PTFE). ABS hybrid composites with varying proportions of nano zirconia and PTFE were prepared using melt blending. Dispersion of reinforcement in the polymer matrix has been studied with the help of transmission electron micrographs. Influence of reinforcements on the mechanical behavior is studied by tensile testing according to the ASTM standard. The tribological behavior of composites was determined in a pin-on-disk tribometer according to the ASTM G99 standard. Worn surfaces were analyzed using scanning electron microscope (SEM) in order to identify the different types of wear and various wear mechanisms. Transfer film formation was studied by analyzing the counterbody surface. A wear mechanism map has been developed, which helps in identifying various wear mechanisms involved under given loading conditions. The results reveal that the addition of PTFE reduces the wear rate and coefficient of friction (COF) significantly. Nano zirconia effectively transfers the load, thereby improving wear resistance, and the addition of PTFE results in continuous transfer film formation thereby reducing the COF. Also from the wear map, it has been identified that abrasion, adhesion, plowing, plastic deformation, melting, and delamination are the dominant wear mechanisms involved.

Effect of WS 2 particle size on mechanical properties and tribological behaviors of Cu-WS 2 composites sintered by SPS

Abstract The mechanical properties and tribological behaviors of Cu-WS2 composites fabricated by spark plasma sintering (SPS) using two different WS2 particle sizes of 0.6 and 5.0 µm and Cu powders as raw materials were investigated. The results indicate that the bending strength and tribological behavior of Cu-WS2 composites are greatly affected by the size of WS2 particles. The bending strength of Cu-WS2 composites with the WS2 particle size of 5.0 μm is 292.2 MPa. As the size of WS2 particle decreases to 0.6 µm, the bending strength also decreases to 181.5 MPa. Moreover, as the WS2 particle size decreases from 5.0 to 0.6 µm, the wear rate of Cu-WS2 composite sharply increases from 2.99×10−14 to 6.13×10−14 m3/(N·m) and its friction coefficient increases from 0.158 to 0.172. The size of WS2 particle (5.0 μm) plays an important role in forming transfer film formed on the counter-face. The sample with 5.0 μm WS2 particle forms smoother and more continuous transfer film, which results in a low wear rate and friction coefficient of the Cu-WS2 composites.

Enhanced tribological performance of hybrid polytetrafluoroethylene/Kevlar fabric composite filled with milled pitch‐based carbon fibers

ABSTRACTAs self‐lubricating bearing liner materials, tribological properties of milled pitch‐based carbon fibers (CFs) modified polytetrafluoroethylene (PTFE)/Kevlar fabric composites were investigated, and the microscopic morphology of worn surface was studied. The results show that the appropriate incorporation of CFs can obviously reduce the wear rate of the fabric composite with almost unchanging friction coefficient. The wear rates of 5 wt % CF‐filled PTFE/Kevlar fabric composites are decreased by 30% and 48% for two kinds of composites made with fibers from different producers compared with unfilled fabric composites. Scanning electron microscopy observations show that the appropriate incorporation of CFs obviously improves the interfacial bonding and reduces pull‐out and fracture of Kevlar fiber. Meanwhile, the introduction of CFs at proper fraction is helpful to form smooth and continuous transfer film on the surface of metal counterpart. The improving mechanism of the CF is attributed to increasing mechanical strength, thermal conductivity and self‐lubricating effects. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46269.

Comparative Tribological and Mechanical Property Analysis of Nano-Silica and Nano-Rubber Reinforced Epoxy Composites

Nano-filler reinforced epoxy composites has been investigated in this study subjected to various mechanical and pin-on-disk tribological tests. Two different types of nano-filler were used namely, rigid nano-silica (SiO2) particles and soft nano-rubber particles. Incorporation of nano-filler in polymer matrix enhance mechanical properties. In addition, tribological response of composites are also better compared to neat epoxy polymer. However, the effect of nano-silica addition is much more pronounced than that of nano-rubber due to the high rigidity of nano-silica reinforced epoxy composite. This was mainly attributed to transfer film layer (TFL) formation. The TFL was further investigated by electron microscope and nanoindentor. The best set of tribological properties was achieved at 8 wt. % nano-silica addition. This was due to better reinforcement dispersion and continuous transfer film layer formation which eventually control the overall friction and wear mechanism.

Tribological investigations of UHMWPE nanocomposites reinforced with three different organo‐modified clays

Nanocomposites of ultra‐high molecular weight polyethylene (UHMWPE) were developed via the ball milling method followed by hot pressing. Three different organically modified clays of 1.5 wt%, Nanomer I.28E, Nanomer I.30E, and Closite C15A, were used as reinforcements in the UHMWPE matrix. Ball on disc wear tests showed that all of the clay composites resulted in an improved wear resistance when compared to that of pristine UHMWPE. Scanning electron microscopy‐Energy dispersion spectroscopy, X‐ray diffraction, and optical profilometry are used to characterize the nanocomposites and the wear morphology. Among all the types of tested nanoclays, 1.5 wt% of C15A reinforced UHMWPE nanocomposite exhibited the highest wear resistance and the lowest coefficient of friction. Addition of 1.5 wt% C15A to UHMWPE reduced its wear rate by 41% and the coefficient of friction by 38% under dry sliding conditions. These improvements are attributed to the uniform dispersion of the clay platelets in the polymer matrix, preventing large scale material removal and also to the formation of a thin tenacious, continuous transfer film on the counterface. POLYM. COMPOS., 39:2224–2231, 2018. © 2016 Society of Plastics Engineers

Evaluation of Tribological Properties of Organoclay Reinforced UHMWPE Nanocomposites

The current study is aimed to investigate the tribological properties of ultrahigh molecular weight polyethylene (UHMWPE) reinforced with organoclay Cloisite (C15A). Nanocomposites are prepared using a high energy ball milling process followed by hot pressing. Three different loadings of 0.5 wt.%, 1.5 wt.%, and 3 wt.% of C15A, respectively, are used as reinforcement. Results from the ball-on-disk wear tests showed that nanocomposites reinforced with 1.5 wt.% of C15A exhibited best wear resistance and lower coefficient of friction (COF), with C15A reducing the wear rate by 41% and the COF by 38%, when compared to the pristine UHMWPE. These improvements are attributed to the uniform dispersion of the nanosized clay platelets preventing large-scale material removal and formation of a thin tenacious, continuous transfer film on the counterface for C15A organoclay composites. X-ray diffraction (XRD), scanning electron microscopy (SEM), and optical profilometry are used to characterize the morphology of the nanocomposites and the wear tracks. SEM images of worn surfaces indicated more abrasive wear for the case of pristine UHMWPE as compared to organoclay composites.

Tribological behaviors of carbon series additions reinforced CF/PTFE composites at high speed

ABSTRACTThe tribological, mechanical, and thermal properties of carbon series additions reinforced CF/PTFE composites at high speed were investigated. In this work, carbon fiber (CF) filled polytetrafluoroethylene (PTFE) composites, which have excellent tribological properties under normal sliding speed (1.4 m/s), were filled with some carbon materials [graphene (GE), carbon nanotubes (CNTs) and graphite (Gr)] respectively to investigate the tribological properties of CF/PTFE composites at high sliding speed (2.1 and 2.5 m/s). The results reveal that the carbon series additions can improve the friction and anti‐wear performances of CF/PTFE, and GE is the most effective filler. The wear rate of 0.8 wt % GE/CF/PTFE was decreased by 50 − 55%, 55 − 60%, 40 − 45% at 1.4, 2.1, and 2.5 m/s compared with CF/PTFE. SEM study shows GE could be helpful to form smooth and continuous transfer film on the surface of counterparts. Meanwhile, GE can improve its tensile strength and elastic modulus obviously. Thin layer structure of GE could enhance the thermal conductivity, which can be helpful to dissipate heat of CF/PTFE composites wear surface. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43236.

Fretting experiments of advanced polymeric coatings and the effect of transfer films on their tribological behavior

The tribological performance of PTFE and PEEK-based polymeric coatings was evaluated under aggressive small amplitude reciprocating (fretting) conditions. Such a condition is encountered in modern machinery, including air-conditioning and refrigeration compressors. Unlubricated step load-to-failure experiments to determine their scuffing resistance have been performed. It was found that the tribological performance depends on the transfer film formed on the counterface. The PTFE coatings were able to form stable and continuous transfer films on the counterface and exhibited lower friction coefficient and wear without catastrophic failures. In the presence of liquid lubricant, the coatings showed worse performance than under dry conditions because the lubricant prevented the formation of transfer films on the counterface.

Investigation of the influence of solid lubricants on the tribological properties of polyamide 6 nanocomposite

The tribological properties of nano titanium dioxide filled polyamide 6(TiO2/PA 6 nanocomposite, 5/95 by weight) and its composites filled with single and combined solid lubricants were systematically investigated. It was found that all the solid lubricants except molybdenum disulfide (MoS2) could significantly enhance the tribological performance of TiO2/PA 6 nanocomposite; and the nanocomposite filled with polytetrafluroethylene (PTFE) exhibited lower friction coefficient and wear rate than that filled with ultra-high molecular weight polyethylene (UHMWPE); but it was interesting that the nanocomposite filled with MoS2 combined with UHMWPE had better tribological performance than that filled with MoS2 combined with PTFE, and the nanocomposite filled with MoS2 together with both UHMWPE and PTFE performed the best among the combination solid lubricants. XPS and SEM results showed that the synergism of fillers in helping the formation of thin, uniform and continuous transfer film was responsible for the enhancement in tribological properties.