Effect of solid lubricant particles on the tribological properties of PTFE composites lubricated with natural seawater

An orthogonal test was used to design different mixture ratios of molybdenum disulfide(MoS₂), graphite, and SiO₂ particles, which were filled with polytetrafluoroethylene (PTFE) composite. MoS₂-, graphite-, and SiO₂-modified PTFE was obtained by pressing and sintering, and the processing parameters were determined using progressive studies and experiments. The friction and wear properties of different PTFE composites lubricated with natural seawater were analyzed using an MMU-5G wear tester. A laser scanning confocal microscope was employed to examine the morphological characteristics of the worn surface. Moreover, the influence of particle proportions on the tribological property of composites was analyzed. Results show that the addition of SiO₂, MoS₂, and graphite can increase the bearing capacity, improve the wear resistance, reduce the friction coefficient, and increase the self-lubricating ability of the PTFE matrix.     

Structural and tribological properties of polytetrafluoroethylene composites in atomic oxygen environment

Effects of atomic oxygen (AO) irradiation on the structural and tribological behaviors of glass fiber (GF) and MoS₂ filled polytetrafluoroethylene (PTFE) composites were investigated in a ground‐based simulation facility, in which the average energy of AO was about 5 eV and the flux was 5.0 × 10¹⁵ cm^–2 s^–1. The structural changes were characterized by XPS and attenuated total‐reflection Fourier transform infrared spectroscopy, and the tribological changes were evaluated by friction and wear tests and SEM analysis of the worn surfaces. It was found that AO irradiation induced the degradation of PTFE molecular chains, and the primary erosion mechanism is collisionally induced rather than chemically induced. The addition of MoS₂ filler significantly increased the AO resistance of PTFE composites. Friction and wear tests indicated that GF and MoS₂ improved the tribological properties of materials before and after AO irradiation. Short GF and MoS₂ exhibited a good synergistic effect for improving the AO resistant and tribological properties of PTFE material. Copyright © 2012 John Wiley & Sons, Ltd.     

Effect of atomic oxygen irradiation on the structural and tribological characteristics of polytetrafluoroethylene and its composites

Based on the ground‐based simulation facility, the effects of atomic oxygen (AO) irradiation on the structural and tribological properties of pure polytetrafluoroethylene (PTFE) and carbon fiber and MoS₂‐filled PTFE composites were studied by scanning electron microscopy, X‐ray photoelectron spectroscopy, and a ball‐on‐disc tribometer. The results shown that AO irradiation had significant effects on the structural and tribological properties of pure PTFE, in which the surface morphologies, mass loss, friction coefficient, and wear rate had been changed greatly after AO irradiation. However, it was noticeable that the addition of carbon fiber and MoS₂ filler to PTFE could improve the AO resist capacity and tribological properties of PTFE composites significantly. Copyright © 2016 John Wiley & Sons, Ltd.     

Effect of maleic anhydride‐grafted polytetrafluoroethylene on the tensile and tribological properties of blending polytetrafluoroethylene with polyamide‐6

Blending polytetrafluoroethylene (PTFE) to polyamide‐6 (PA6) with and without maleic anhydride‐grafted polytetrafluoroethylene (PTFE‐g‐MA) was produced in a corotating twin screw extruder, where PTFE acts as the polymer matrix and PA6 as the dispersed phase. The effect of PTFE‐g‐MA on the tensile properties and tribological propertiesof PTFE/PA6 polymer blends is studied. Results show that the structural stability and morphology of the blends were greatly improved by PTFE‐g‐PA6 grafted copolymers, which were formed by the in situ reaction of anhydride groups with the amino end groups of PA6 during reactive extrusion forming an imidic linkage. The presence of PTFE‐g‐PA6 in the PTFE continuous phase improves the interfacial adhesion, as a result of the creation of an interphase that was formed by the interaction between the formed PTFE‐g‐PA6 copolymer in situ and both phases. Compared with thePTFE/PA6 without PTFE‐g‐MA, the PTFE/PA6 with PTFE‐g‐MAhad the lowest friction coefficient and wear under given applied load and reciprocating sliding frequency. The interfacial compatibility of the composite prevented the rubbing‐off of PA6, accordingly improved the friction and wear properties of the composite. Copyright © 2009 John Wiley & Sons, Ltd.     

A new family of low wear,low coefficient of friction polymer blend based on polytetrafluoroethylene and an aromatic thermosetting polyester

To improve the wear resistance of polytetrafluoroethylene (PTFE), a crosslinked aromatic thermosetting polyester (ATSP) has been blended directly with PTFE. Cured ATSP powder which was directly synthesized as a cured powder form was used for this application. Because of the similar processing temperature range of cured ATSP and PTFE, composites within the entire composition range were successfully prepared by blending these two powders using a hot press. Tribological pin‐on‐disk tests (composite pins sliding against gray cast iron disks) showed improvement on friction coefficient of all composites and much less wear than pure PTFE. The composites survived at contact pressures of 7 MPa, which is higher than either pure PTFE or pure ATSP could sustain. With an increase in the amount of ATSP in the composites, storage modulus, and glass transition temperature were higher, and the wear resistance was enhanced. SEM images helped provide explanations for the unusually low mean wear rates that were observed for these composite samples. Copyright © 2008 John Wiley & Sons, Ltd.     

Tribological behavior of polyurethane-based composite coating reinforced with TiO2 nanotubes

The unmodified and hexamethylene diisocyanate (HDI) modified TiO₂ nanotubes, were used for fabricating TiO₂ nanotubes (TiNTs)/polyurethane (PU) composite coating. The effects of applied load and sliding speed on the tribological behavior of the composite coating were investigated using a block-on-ring wear tester. Compared to the TiO₂ nanotubes filled PU composite coating, the HDI modified TiO₂ nanotubes (TiNTs-HDI) filled one had the lower friction coefficient and higher wear life under various applied loads and sliding speed. Scanning electron microscope (SEM) investigation showed that the TiNTs-HDI filled PU coating had smooth worn surface under given applied load and sliding speed, and a continuous and uniform transfer film formed on the surface of the counterpart ring, which helped to reduce the wear of the coating. The improvement in the tribological properties of TiNTs-HDI/PU composite coating might due to an improvement in interfacial adhesion between TiNTs and PU after HDI treatment. The strong interfacial coupling of the composite coating made TiNTs-HDI not easy to detach from the PU matrix, and prevented the rubbing-off of PU composite coating, accordingly improved the friction and wear properties of the composite coating.     

The Wear Resistance of Composite Materials Based on Ultra-High-Molecular-Weight Polyethylene with Fillers of Various Types

The tribological properties and wear resistance under different action of composite materials based on of ultra-high-molecular-weight polyethylene (UHMWPE) and fillers of various types such as organomodified montmorillonite (MMT), graphite nanoplates (GNP), molybdenum disulfide, and shungite prepared via polymerization in situ are studied. According to the obtained results, the introduction of these fillers to UHMWPE in the amount of 0.4–7 wt % has almost no effect on the value of the coefficient of sliding friction on steel in the mode of dry friction. Composites with GNP, MoS₂, and shungite are characterized by a significant (two- to threefold) increase in the wear resistance in the case of sliding friction on steel. The abrasive wear of composites in the case of friction on an abrasive paper is substantially affected by the type of filler, the use of MMT was the most effective for increasing the wear resistance of composites. In the case of a highspeed impact effect of water–sand suspensions all the studied composites are characterized by increased wear resistance in comparison with industrial UHMWPE at a low concentration of fillers and by an increase in the wear with the increase of the filler content.     

Strong interfacial modified aramid fabric reinforced degradable thermosetting composites: reinforcing and tribological effects

In this work, dense molybdenum disulfide (MoS₂) nanosheets were grown onto polydopamine (PDA) functionalized aramid fabric (AF) surface via a simple hydrothermal method to improve the wettability between AF surface and polyhexahydrotriazine (PHT) resin, thus resulting in stronger AF/resin interfacial bonding. The PDA-assisted surface modification on AF generated a high active interface allowing the nucleation and subsequent growth of MoS₂. Moreover, this nanosheet-coated reinforcement fiber enabled the viscous liquid of resin precursor to spread over and form intimate contact with its surface, which eventually promoted the formation of strong interfacial bonding between AF-MoS₂ and cured resin matrix. In addition, the enhanced interfacial bonding between the reinforcement and matrix generated stable mechanical interlock within the resulting AF-MoS₂/PHT composites, and thus, contributed better thermal stability, higher tensile strength, and tribological properties. Compared with AF/PHT composites, the tensile strength and elongation at break of the AF-MoS₂/PHT composites increased by 32.5% and 50%, and the average friction coefficient and wear rate of AF-MoS₂/PHT composites decreased by 43.9% and 86.3%, respectively. Furthermore, the composites realized the non-destructive recovery of expensive AF at 25 °C. Overall, our study demonstrates a dependable strategy to construct the recyclable AF-MoS₂/PHT composites, which exhibit valuable applications in tribology.     

The antioxygen radiation properties of the nanocomposite film consisted of hydrogenated amorphous carbon (a-C:H) and MoS2

MoS₂/a-C:H multilayer film and MoS₂/a-C:H composite film exhibit excellent tribological properties in vacuum, which can be used as the potential space lubricant. The radiation-protective properties of these two films in atomic oxygen (AO) are evaluated. The influences of AO radiation on structure, morphology, and tribological properties of the films were investigated. The results show that AO radiation mainly causes oxidation and increases sp² C content in both of the films. Furthermore, the MoS₂ sublayer on the surface of the multilayer film is oxidized heavily, whereas both the MoS₂ and the a-C:H matrix on the surface were oxidized in the composite film. As a result of this, the multilayer film exhibits high friction coefficient and short sliding lifetime in vacuum after AO radiation. Compared with that, the composite film exhibits lower friction and longer sliding time more than 3600 seconds in vacuum, which illustrates it has a good AO radiation protection. This indicates that MoS₂/a-C:H composite film is more likely to be used as a potential space lubricant.     

Study of mechanical and tribological properties of nylon 66‐titanium dioxide microcomposite

Nylon 66 microcomposites with various weight percentage of titanium dioxide (TiO₂) were prepared by a twin screw extruder and investigated for mechanical and tribological properties. Mechanical properties of the composite such as tensile strength/modulus, flexural strength/modulus, impact, and compressive strength first showed an increase up to 6 wt% TiO₂ followed by a decrease at higher filler loading. The value of heat deflection temperature increased with the increase in wt% of TiO₂. Sliding wear tests were performed on pin‐on‐disk equipment under different loads, sliding velocity, and sliding distance combinations. It was found that micro‐TiO₂‐Nylon 66 composite exhibited reduced wear and coefficient of friction up to 6 wt% TiO₂. Micro‐TiO₂ at 2 wt% was most effective in improving the tribological properties of plain nylon 66. The worn surfaces were examined by scanning electron microscopy to understand the wear mechanism. The optimal combination from 2 wt% to 6 wt% micro‐TiO₂‐Nylon 66 can be used depending upon the application requiring improvement in tribological or mechanical properties, respectively.     

Composite tribological materials based on molybdenum disulfide nanoparticles and polytetrafluoroethylene microgranules

Tribological materials based on molybdenum disulfide nanoparticles localized on the surface of ultradispersed polytetrafluoroethylene were prepared. The composition and properties of the new composite materials were studied. Introduction of ultradispersed additives based on polytetrafluoroethylene with MoS₂ and on polytetrafluoroethylene and nanodiamonds prepared by detonation synthesis (taken as reference samples) decreases the viscosity of MS-20 aviation oil. The dependence of the friction coefficient on the Sommerfeld number for the composites obtained was examined. Introduction of additives leads to a decrease in the friction coefficient with increasing linear sliding velocity, in contrast to the initial oil for which the trend is opposite. The dependence of the friction coefficient on the concentration of additives in the initial oil was demonstrated. Modification of polytetrafluoroethylene microgranules with 3 wt % MoS₂ nanoparticles allows the amount of additive to the oil to be considerably reduced.     

Effect of surface texturing on friction behaviour of 3D printed polylactic acid (PLA)

Additive manufacturing is gaining a remarkable importance in manufacturing industries because of the ability to build parts with complex and intricate shapes. The most widely used material in additive manufacturing is the polymer. In this paper, circular textures have been 3D printed on the surface of Polylactic Acid (PLA) polymer using fused deposition modelling technique. Experiments were performed under dry and lubricated conditions by varying the texture size. The results were obtained for high and low speeds with varying loads of 10, 20, 30, 40 and 50 N. It was observed that coefficient of friction was minimum for texture T₂ at both high and low speeds under dry sliding conditions. This is due to the less real area of contact than texture T₁ and more effective formation of transfer film in case of texture T_3. The entrapment of wear debris is more effective which helps in the formation of transfer layer that acts as solid lubricant. Under lubricated conditions, it was observed that for low speed, texture T₃ has least coefficient of friction while at high speed texture T₁ resulted in the minimum coefficient of friction. This is mainly due to the more retention of lubricating oil for texture T₃ at low speed in comparison to the high speed. Surface analysis carried out for all the textures under dry sliding conditions revealed that the wear is mainly to adhesive and abrasive action.     

高性能耐高温聚合物复合材料的摩擦磨损性能研究

介绍了一些常见的高性能耐高温聚合物及其复合材料的摩擦与磨损性能的研究及其新进展,包括聚四氟乙烯(PTFE)、聚醚醚酮(PEEK)、聚苯硫醚(PPS)、聚酰亚胺(PI)等.并讨论了不同种类的填料,如纤维、固体润滑剂、无机化合物以及无机纳米粒子对高性能耐高温聚合物基复合材料摩擦系数及磨损率的影响,许多研究结果表明,适量填料的加入能提高聚合物基复合材料的耐磨性能,特别是填料的协同作用对降低复合材料的摩擦系数及磨损率有更大的帮助.     

Wear and friction in glassy polymers: Microscratch on blends of polystyrene and poly (2,6-dimethyl-1,4-phenylene oxide)

The microscopic process of abrasive wear and friction in glassy polymers was studied by using a special microscratch technique. A miscible blend of polystyrene (PS) and poly(phenylene oxide) (PPO) was used. It was found that as the composition varies there seems to exist two wear regimes in the blends controlled by different breakdown mechanisms corresponding to the brittle—ductile transition. Detailed study of the contact loads and SEM micrographs indicate that abrasive wear in the glassy polymers is controlled by microcracking under the asperity contacts. The critical load τ_c for initiating microscopic cracks can be linked to the macroscopic wear via a statistical Weibull model where τ_c is taken to be the mean of a strength distribution function. On the other hand, the friction coefficient was found to be independent of the composition but to vary strongly with the contact load. It approaches zero at the extrapolated zero load, but increases rapidly and eventually levels off with contact load. This behavior can be understood by a simple frictional adhesion model in which the polymer deformation during a frictional contact is analyzed by considering the compressive plastic ploughing and shearing yielding around the asperity contact. The shear strength S_o of the polymer/asperity contacts was found to vary with the normal load. The vertical scratch hardness H_v, which characterizes the spontaneous indentation yielding on the polymer surface, was found to be independent of scratch length and depth, and indeed can be regarded as a material constant. Although both S_o and H_v can accurately describe the frictional behavior of the glassy polymers, they bear no correlation to abrasive wear in the same materials. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 1295–1309, 1997     

Organohydrogels with High-Speed Lubrication by Confining Polymer Chain Mobility by an Interpenetrated Heteronetwork

Hydrogels with pure hydrophilic network have received much attention due to their excellent low frictional behavior. However, the lubrication performance of hydrogels is not satisfied under high-speed condition due to the energy dissipation caused by adsorbed polymer chains as well as the failure of lubricating mechanisms accompanied by the transition of lubrication regime. In this work, interpenetrating double-network organohydrogels were constructed by combining hydrophilic and oleophilic polymer networks to modify the physiochemical properties of surface polymer chains, especially the chain mobility. The oleophilic polymer network spatially restricting the mobility of the swollen hydrophilic network in water, resulted in a low coefficient of friction (ca. 0.01) compared with conventional hydrogels at high speed (0.1 m s⁻¹). Meanwhile, the organohydrogels had superior wear resistance, with almost no wear observed on the sliding track after 5 k cycles of rubbing at high speed. The design concept of organohydrogels can be extended to a variety of low-wear, highly-lubricating materials.     

Structure–tribological property relationship of nanoparticles and short carbon fibers reinforced PEEK hybrid composites

In a previous work, the roles of low‐loading, that is, 1 vol %, nano‐SiO₂ particles on the tribological behavior of short carbon fibers (SCFs)/polytetrafluoroethylene (PTFE)/graphite filled polyetheretherketone (PEEK) were studied. In the present work, the effects of nanoparticle content, varying from 1 to 4 vol %, on the structure and the tribological performance of the composite was investigated. The polished cross sections of the composites were inspected using a scanning electron microscope (SEM). The incorporated nanoparticles significantly reduce the friction coefficients of the composite. With low pressure‐sliding velocity (pv) factors, nanoparticle agglomerates seem to exert an abrasive effect on SCF, and thereby lead to high wear rates. Under such conditions, an increase in nanoparticle content decreases the wear resistance. With high pv factors, the nanoparticles remarkably improve the wear resistance of the composite and the nanoparticle contents do not play an important role on the wear resistance. The worn surfaces, transfer films and wear debris of the composites were analyzed. The tribological mechanisms were discussed. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 801–811, 2010     

Effect of temperature on friction and wear behaviors of polyimide (PI)‐based solid–liquid lubricating materials

The tribological properties of polyimide (PI) under four oils (including two perfluoropolyether oils and two silicon oils) lubricated conditions were comparatively investigated at room temperature in vacuum and Fomblin M30 and chlorine‐containing silicon oil were selected to study the friction and wear behaviors of PI‐based solid–liquid lubricants against steel at different temperatures in vacuum. Significant improvement in tribological performance of PI was found under oil‐lubricated conditions. The friction coefficient increased as the test temperature decreased for the mobility of liquid lubricant was limited at lower temperatures, while the wear rate exhibited distinct rule. Besides, no tribochemical reaction was detected at the contact surface of PI and chlorine‐containing silicon oil. However, the –CF₃ and fluorinated C? O groups were detected on the worn tracks of PI/Fomblin M30 by X‐ray photoelectron spectroscopy, which indicated that tribochemical reaction happened to PI and Fomblin M30 under high temperature as well as the simulation of friction heat. Copyright © 2015 John Wiley & Sons, Ltd.     

Friction and Wear of Semi-Crystalline Polytetrafluoroethylene with Spherulitic Micro-Morphology

Polytetrafluoroethylene (PTFE) is an important engineering material with a low coefficient of friction but a high rate of wear. As a semi‐crystalline polymer, its wear resistance is related to its micro‐morphology. Friction and wear properties of semi‐crystalline non‐spherulitic PTFE have been widely studied, but no investigation is reported about tribological properties of spherulitic PTFE due to difficulties in finding such properties. In this paper, friction and wear properties of PTFE with spherulitic micro‐morphology are studied for the first time. The results show that, first, under the same experimental condition, when two kinds of PTFE are rubbed against the steel disc, the number and size of debris of spherulitic PTFE are much less and smaller than that of debris of PTFE without spherulitic crystals. This means that the wear resistance of spherulitic PTFE is better than that of semi‐crystalline PTFE without spherulitic micro‐morphology. Second, the friction property of spherulitic PTFE is also different from that of PTFE without spherulitic crystals. Finally, the friction and wear mechanisms of spherulitic PTFE and non‐spherulitic PTFE are compared.     

The oxidation‐treated interface on tribological properties of carbon fibers‐reinforced PTFE composite under oil‐lubricated condition

The effect of air oxidation and ozone surface treatment of carbon fibers (CF) on tribological properties of CF reinforced polytetrafluoroethylene (PTFE) composites under oil‐lubricated condition was investigated. Experimental results revealed that ozone treated CF reinforced PTFE (CF–PTFE) composite had the lowest friction coefficient and wear under various applied loads and sliding speeds compared with untreated and air‐oxidated composites. X‐ray photoelectron spectroscopy (XPS) study of carbon fiber surface showed that, after ozone treatment, oxygen concentration was obviously increased, and the amount of oxygen‐containing groups on CF surfaces was largely increased. The increase in the amount of oxygen‐containing groups enhanced interfacial adhesion between CF and PTFE matrix. With strong interfacial adhesion of the composite, stress could be effectively transmitted to carbon fibers; carbon fibers were strongly bonded with PTFE matrix and large scale rubbing‐off of PTFE was prevented, therefore, the tribological properties of the composite were improved. Copyright © 2009 John Wiley & Sons, Ltd.     

The mechanical and tribological behaviors of PI composite filled with plasma treated UHMWPE fiber

The friction and wear behaviors of ultra‐high molecular weight polyethylene (UHMWPE)/PI composite were investigated in a ring‐on‐block wear tester. Ti6Al4V alloy ring were selected as the counterbody in this study. It was found that the detachment of particles, ripples, and ploughs were observed under higher load. Plasma treatment efficiently improves the interfacial adhesion of UHMWPE/PI composite. Both the friction coefficient and wear increased with load, and the plasma treated one shows lower friction coefficient and wear.