Effects of various kinds of fillers on the tribological behavior of polytetrafluoroethylene composites under dry and oil‐lubricated conditions

Polytetrafluoroethylene (PTFE)‐based composites filled with various inorganic fillers in a volume fraction of 30% were prepared. The tribological behavior of the PTFE composites sliding against AISI52100 steel under dry and liquid paraffin‐lubricated conditions was investigated on an MHK‐500 model ring‐on‐block test rig. The morphologies of worn surfaces and wear debris were observed with a scanning electron microscope (SEM) and an optical microscope. As the results, different fillers show different effects on the tribological behavior of the PTFE composites, while the composite shows much different tribological behavior under lubricated conditions as compared with dry sliding. The tribological behavior of the PTFE composites under dry sliding is greatly related to the uniformity and thickness of the transfer films. Only the PTFE composites with a transfer film of good uniformity and proper thickness may have excellent tribological behavior. The PTFE composites show much better tribological behavior under lubrication of liquid paraffin than under dry sliding, namely, the friction coefficients are decreased by 1 order of magnitude and the wear rate by 1–3 orders of magnitude. Observation of the worn composite surfaces with SEM indicates that fatigue cracks were generated under lubrication of liquid paraffin, owing to the absorption and osmosis of liquid paraffin into the microdefects of the PTFE composites. The creation and development of the fatigue cracks led to fatigue wear of the PTFE composites. This would reduce the mechanical strength and load‐supporting capacity of the PTFE composites. Therefore, the tribological behavior of the PTFE composites under lubrication of liquid paraffin is greatly dependent on the compatibility between the PTFE matrix and the inorganic fillers. In other words, the better is the compatibility between PTFE and fillers the better is the tribological behavior of the composites. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1891–1897, 2001     

Influence of solid lubricant reinforcement on wear behavior of Kevlar fabric composites

The friction and wear behavior of Kevlar fabric composites reinforced by PTFE or graphite powders was investigated using a Xuanwu‐III friction and wear tester at dry sliding condition, with the unfilled Kevlar fabric composite as a reference. The worn surfaces were analyzed by means of scanning electron microscope, and X‐ray photoelectron spectroscopy. It was found that PTFE or graphite as fillers could significantly improve the tribological behavior of the Kevlar fabric composites, and the Kevlar fabric composites filled with 20% PTFE exhibited the best antiwear and antifriction ability among all evaluated cases. The transfer films established with two lubricants in sliding wear of composites against metallic counterparts made contributions to reducing friction coefficient and wear rate of Kevlar fabric composites. In particular, FeF₂ generated in the sliding of Kevlar fabric composites filled with PTFE against counterpart pin improved the bonding strength between the transfer film and counterpart surface, which accounted for the lowest friction coefficient and wear rate of the Kevlar fabric composites filled with PTFE measured in the testing. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008.     

Mechanism of filler action in reducing the wear of PTFE polymer by differential scanning calorimetry

Two types of representative nanometer materials, i.e., fibroid nanometer attapulgite and approximate spherical ultrafine diamond, were selected as fillers of polytetrafluoroethylene (PTFE) to study the mechanism of the wear‐reducing actions of the fillers in PTFE composites. The friction and wear tests were performed on a block‐on‐ring wear tester under dry sliding conditions. Differential scanning calorimetry (DSC) was used to investigate material microstructure and to examine modes of failure. No significant change in coefficient of friction was found, but the wear rate of PTFE composites was orders of magnitude less than that of pure PTFE. DSC analysis revealed that nanometer attapulgite and ultrafine diamond played a heterogeneous nucleation role in PTFE matrix and consequently resulted in increasing the crystallinity of PTFE composites. Moreover, the PTFE composite with higher heat absorption capacity and crystallinity exhibited improved wear resistance. A propositional “sea‐frusta” frictional model explained the wear mechanism of filler action in reducing the wear of PTFE polymer, i.e., fillers in the PTFE matrix effectively reduced the size of frictional broken units for PTFE composites and restrained the flowability of the units, as well as supporting the applied load. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Mechanical and tribological properties of polyoxymethylene modified with nanoparticles and solid lubricants

Polyoxymethylene (POM) composites modified with nanoparticles, polytetrafluoroethylene (PTFE) and MoS₂ were prepared by a twin‐screw extruder. The effect of nanoparticles and solid lubricant PTFE/MoS₂ on mechanical and tribological properties of the composites were studied. Tribological tests were conducted on an Amsler friction and wear tester using a block‐on‐ring arrangement under dry sliding and oil lubricated conditions, respectively. The results showed that generally speaking POM nanocomposites had better stiffness and tribological properties than corresponding POM composites attributed to the high surface energy of nanoparticles, except that the tensile strength of three composites and dry‐sliding tribological properties of POM/3%Al₂O₃ nanocomposite decreased due to the agglomeration of nanoparticles. Tribological properties differed under dry sliding and oil lubricated conditions. The friction coefficient and wear volume of POM nanocomposites under oil lubricated condition decreased significantly. The increased deformation resistance supported the increased wear resistance of POM nanocomposites. POM/PTFE/MoS₂/3%Al₂O₃ nanocomposite had the best mechanical and tribological properties of all three composites, which was attributed to the synergistic effect of nanoparticles and PTFE/MoS₂. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

A study on the tribological behavior of hybrid PTFE/Kevlar fabric composites filled with nano‐SiC and/or submicron‐WS2 fillers

The tribological behaviors of hybrid PTFE/Kevlar fabric composites filled with nano‐SiC and/or submicron‐WS₂ fillers were studied. Scanning electron microscopy and energy‐dispersive X‐ray spectrometer were used for analysis of the worn surface, transfer film, and debris of the PTFE/Kevlar fabric composites. In addition, the wear volume loss of the composite was measured by means of a laser microscopic 3D and profile measurement apparatus. The results indicate that although both single fillers and hybrid fillers can reduce the wear rate of composites, but hybrid fillers filled composites could achieve the desired comprehensive tribological properties in dry sliding. The improved tribological performance of filled composites can be attributed to two aspects: the formation of a thin and tenacious transfer film on the counter‐surface, and the restrain the formation of larger debris. Tiny wear debris was easily trapped in the gap of a worn surface and can repair the damaged surface. In addition, the trapped debris could be considered as a secondary source of lubricant. POLYM. COMPOS., 37:2218–2226, 2016. © 2015 Society of Plastics Engineers     

混杂填料增强聚四氟乙烯复合材料的摩擦学性能研究

采用MM-200型摩擦磨损试验机对纳米SiC、MoS2和石墨填充聚四氟乙烯(PTFE)复合材料在干摩擦条件下与45#钢对摩时的摩擦磨损性能进行了研究,探讨了MoS2、石墨及纳米SiC的协同效应。认为纳米SiC的加入大大提高了复合材料的承载能力,石墨、MoS2的加入减少PTFE复合材料的摩擦因数。利用扫描电子显微镜(SEM)对PTFE复合材料的摩擦面进行了观察。结果表明:实验中5%nano-SiC和3%MoS2填充PTFE复合材料的摩擦磨损性能最好,且在高载荷下的摩擦磨损性能尤为突出,具有一定的应用价值。     

Tribological properties of porous PPS/PTFE composite filled with mesopore titanium oxide whisker

Nano‐micro hierarchical porous polyphenylene sulfide/polytetrafluoroethylene (PPS/PTFE) composites were prepared by mold‐leaching and vacuum melting process under high temperature condition. The tribological behaviors of porous PPS/PTFE composites and the synergism as a result of incorporation of both micro‐porogen (NaCl) and mesoporous TiO₂ whiskers were investigated. The effects of mesoporous TiO₂ whiskers and nonperforated TiO₂ whiskers on the friction and wear properties of PPS/PTFE composites were comparatively studied, respectively. Results indicated that the wear rate of porous PPS/PTFE composites with 30 wt % NaCl and 7 wt % mesoporous TiO₂ whiskers obtained the lowest values under the load of 100 N. Compared with pure PPS, the wear resistance of nano‐micro porous PPS/PTFE composite was enhanced by 6.45 × 10³ times, showing outstanding wear resistance. During sliding condition, grease could be squeezed through the nano‐micro pores under the coupling effect of load and friction heat, and formed a lubricanting layer on friction surface, providing self‐lubricating effect and high wear resistance. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Influence of organic montmorillonite nanoparticles on the microstructures and thermal and tribological properties of polyethersulfone and polytetrafluoroethylene composites

Because of high wear rate and low thermal deformation temperature, the generalization and application of polytetrafluoroethylene (PTFE) in the field of tribology is restrained to a certain extent. In order to improve the wear resistance and thermal stability of this self‐lubricating polymer, organic montmorillonite (OMMT) nanoparticle reinforced polyethersulfone (PES) and PTFE ternary composites were prepared by the cold molding and vacuum sintering technology. The effects of sodium montmorillonite (Na‐MMT) and OMMT on the microstructures, thermal stabilities and tribological properties of PTFE composites were comparatively studied. The results show that the thermal stability of the PES/PTFE composites is clearly improved by the incorporation of OMMT nanoparticles. Not only the friction coefficients but also the wear rates of OMMT/PES/PTFE composites are less than those of Na‐MMT/PES/PTFE composites under identical tribological tests. Of all these PTFE composites, the PES/PTFE composite containing 10.0 wt% OMMT nanoparticles exhibits the best friction and wear properties (μ = 0.14, k = 5.78 × 10^?15 m³ N^–1 m^?1). This can be attributed to the existence of a polymer multicomponent layer consisting of PTFE, PES and OMMT on the composite surface as well as the formation of uniform PTFE transfer film on the worn surfaces of metal counterparts.     

Tribological properties of polyimide coatings filled with PTFE and surface‐modified nano‐Si3N4

Polyimide (PI) coatings filled with PTFE and nano‐Si₃N₄ were prepared by a spraying technique and successive curing. Nano‐Si₃N₄ particles were modified by grafting 3‐aminopropyltriethoxysilane to improve their dispersion in the as‐prepared coatings. Friction and wear performances and wear mechanisms of the coatings were evaluated. The results show that the incorporations of PTFE and modified nano‐Si₃N₄ particles greatly improve the friction reduction and wear resistance of PI coating. The friction and wear performance of the composite coating is significantly affected by the filler mass fraction and sliding conditions. PI coating incorporated with 20 wt % PTFE and 5 wt % modified nano‐Si₃N₄ displays the best tribological properties. Its wear rate is more than one order of magnitude lower and its friction coefficient is over two times smaller than that of the unfilled PI coating. Differences in the friction and wear behaviors of the hybrid coatings as a function of filler or sliding condition are attributed to the filler dispersion, the characteristic of transfer film formed on the counterpart ball and the wear mechanism of the coating under different sliding conditions. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40410.     

Enhanced thermal conductivity and wear resistance of polytetrafluoroethylene composites through boron nitride and zinc oxide hybrid fillers

In this study, the thermal conductivity and wear resistance of the polytetrafluoroethylene (PTFE)/boron nitride (BN), PTFE/zinc oxide (ZnO), PTFE/tetra‐needle‐shaped zinc oxide whiskers (T‐ZnO), and PTFE/hybrid filler composites were investigated. Moreover, hot‐press molding was used to prepare the composites, and scanning electron microscopy was used to observe the morphology of the fillers and the friction interface of the composites. The results show that continuous thermally conductive paths could be formed in the PTFE/hybrid fillers (T‐ZnO and BN) composites so that the thermal conductivity of the PTFE was improved through addition of the hybrid fillers. Meanwhile, the synergistic effects of the hybrid fillers were useful for reducing the wear rate of the composites. In addition, for the pure PTFE, abrasive and adhesive wear was found. Compared to the worn surface of the pure PTFE, the worn surface of the PTFE composites filled with ZnO, T‐ZnO, BN, and hybrid fillers presented much smoother surfaces, and slighter ploughing occurred. Therefore, the hybrid fillers improved not only the thermal conductivity but also the wear resistance of the PTFE composites. The data obtained in this study contributed to the construction of a technical foundation for the preparation of composites with a high thermal conductivity and wear resistance. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42302.     

Tribological performance of DLC-coated ceramics against cemented carbide under dry sliding conditions

In order to improve the tribological behavior of Si₃N₄/TiC ceramics, DLC coating was fabricated on the ceramic surface through magnetron sputtering technology. The surface and cross-section micrographs, the adhesion between coating and substrate, the surface roughness and microhardness of the DLC-coated ceramics were investigated. Reciprocating friction tests sliding against cemented carbide ball were conducted under dry sliding conditions. The test results indicated that the DLC coating possessed superior tribological performance, which was conductive to decreasing the friction coefficient and enhancing the wear resistance of ceramics. The primary mechanisms responsible for performance improvement of the DLC-coated ceramics were attributed to the combined effects of low shear stress, excellent adhesion with substrate, high microhardness and good surface roughness. It was believed that the DLC coating was efficient in improving the load-carrying capacity and expanding the application area of ceramic materials.     

PPESK／PTFE共混物摩擦行为研究

采用溶液共混法制备了不同质量比的新型含二氮杂萘酮结构聚芳醚砜酮（PPESK）与聚四氟乙烯（PTFE）共混物。利用磨损试验机对该共混体系进行摩擦性能研究测试。结果表明，在干摩擦条件下，PPESK中共混加入PTFE可以明显降低其磨损量，当PTFE质量分数为20％时，摩擦系数达到最小。同时采用扫描电镜、扫描探针显微镜对共混物摩擦表面及摩擦副表面进行观察，分析了该共混体系的磨损机理。研究表明，负荷、共混组分等因素对摩擦形貌均有较大影响，在不同摩擦条件下摩擦机理不同。黏着磨损和犁耕磨损随着负荷的增加由明显转变为不明显；随着共混物中PTFE含量增加，由犁耕磨损和黏着磨损变为以黏着磨损为主。     

Friction and wear properties of basalt fiber reinforced/solid lubricants filled polyimide composites under different sliding conditions

Short basalt fibers (BFs)‐reinforced polyimide (PI) composites filled with MoS₂ and graphite were fabricated by means of hot‐press molding technique. The tribological properties of the resulting composites sliding against GCr15 steel ring were investigated on a model ring‐on‐block test rig. The wear mechanisms were also comparatively discussed, based on scanning electron microscopic examination of the worn surface of the PI composites and the transfer film formed on the counterpart. Experimental results revealed that MoS₂ and graphite as fillers significantly improved the wear resistance of the BFs‐reinforced polyimide (BFs/PI) composites. For the best combination of friction coefficient and wear rate, the optimal volume content of MoS₂ and graphite in the composites appears to be 40 and 35%, respectively. It was also found that the tribological properties of the filled BFs/PI composites were closely related with the sliding conditions such as sliding speed and applied load. Research results show that the BF/PI composites exhibited better tribological properties under higher PV product. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Tribological behaviors of polytetrafluoroethylene composites under dry sliding and seawater lubrication

The composites of polytetrafluoroethylene (PTFE) filled with expanded graphite (EG), poly(p‐oxybenzoyl) (POB), and basalt fiber (BF) were prepared by heating compression and sintering molding. The tribological behavior of PTFE composites was investigated with a pin‐on‐disk tester under dry conditions and seawater lubrication. The worn surface of PTFE composites and the transfer film on the counterface were observed with a scanning electron microscope. The results indicated that the incorporation of EG and POB improved the hardness of PTFE composites, and addition of BF led to greater load‐carrying capacity. Compared to pure PTFE, the coefficients of friction of PTFE composites slightly increased, but the wear rates were significantly reduced (the wear rate of composite with 3% EG being only 10.38% of pure PTFE). In addition, all the composites exhibited a lower coefficient of friction (decreases of about 0.03–0.07) but more serious wear under seawater lubrication than under dry sliding. The wear mechanism changed from serious abrasive wear of pure PTFE to slight adhesion wear of PTFE composites under both conditions. A transfer film was obviously found on the counterface in seawater, but it was not observed under dry conditions. Among all the materials tested, the PTFE‐based composite containing 20% POB (mass fraction), 2% EG, and 3% BF exhibited the best comprehensive performance. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2523–2531, 2013     

Mechanical and tribological properties of PA66/PPS blend. II. Filled with PTFE

The mechanical and tribological properties of 70 vol % PA66/30 vol % PPS blend filled with different content of polytetrafluoroethylene (PTFE) were studied in this paper. It was found that the addition of PTFE impairs the mechanical properties of PA66/PPS blend, but greatly increases the wear resistance and decreases the friction coefficient. When PTFE content exceeds 20 vol %, the friction coefficient of composite is minimum (0.15) and lower than that of pure PTFE under the same conditions (0.22). The lowest wear volume (0.44 mm³) is obtained with PA66/PPS/30 vol % PTFE composite, which decreased by 91% compared with unfilled PA66/PPS blend (4.99 mm³). The topography of transfer film and the elemental distribution were investigated by Scanning Electron Microscopy (SEM) and Energy Dispersive Spectrometer (EDS), respectively. Because of the characteristic crystalline structure, PTFE preferentially transferred to the steel ring surface and formed a thin, uniform and firmly adhered transfer layer, which reduced the ability of PA66/PPS blend to transfer and prevent the adhesion between the sample and the couterface. In addition, the superior lubrication of PTFE inhibited the frictional heat melting during sliding. All these aspects are close related to the friction and wear behavior of PA66/PPS/PTFE composite. Upon the addition of PTFE, thermal control of friction regime is not applicable to the PA66/PPS blend. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 969–977, 2006     

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

The 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.     

The mechanical and tribological properties of PTFE filled with PTFE waste powders

Polytetrafluoroethylene (PTFE) composites filled with PTFE waste offer interesting combination of tribological properties and low cost. PTFE composites waste was mechanically cut and sieved into powders. PTFE composites filled with PTFE waste powders were prepared by compression molding. Friction and wear experiments were carried out in a reciprocating sliding tribotester at a reciprocating frequency of 1.0 Hz, a contact pressure of 5.5 MPa, and a relative humidity of (60 ± 5)%. PTFE materials slid against a 45 carbon steel track. Results showed that a PTFE composite (B) filled with 20 wt % PTFE waste exhibited a coefficient of steady‐state friction slightly higher than that of unfilled PTFE (A), while wear resistance over two orders of magnitude higher than that of unfilled PTFE (A). Another PTFE composite filled with PTFE waste and alumina nanoparticles exhibited the highest wear resistance among the three PTFE materials. This behavior originates from the effective reinforcement of PTFE waste as a filler. It was experimentally confirmed that the low cost recycling of PTFE waste without by‐products is feasible. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1035–1041, 2007     

Tribological properties of PTFE‐filled PMIA

The polytetrafluoroethylene‐filled (PTFE) poly(m‐phenylene isophalamide) (PMIA) composite blocks are prepared by compression molding. The friction and wear of PTFE‐filled PMIA are investigated on a block‐on‐ring machine by running the PMIA composite block against plain carbon steel (AISI 1045 steel ring). The worn surface of PMIA composite and the steel counterface are examined by using electron probe microanalysis (EPMA). It is found that PTFE‐filled PMIA exhibited considerably lower friction coefficient and wear rate than pure PMIA. Furthermore, the lowest wear rate is obtained when the composite contains 20 vol % PTFE. EPMA investigations show that there are some debris that could restrain the wear of the PMIA composites oriented along the sliding track and embedded in the surface of PMIA composite. A kind of stripe transfer film that contains abundant F element should be the main reason for the improvement of the tribological properties of PTFE‐filled PMIA composites. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 747–751, 1999     

Study on the tribological properties of modified polyurethane material for water‐lubricated stern bearing

Polyurethane (PU) has been studied as alternative bearing material for marine water‐lubricated stern tube due to its excellent wear resistance, remarkable mechanical properties and so on. In this study, nine types of PU samples which are composed of different additives were prepared and tested in order to investigate their tribological properties under various working conditions. A pin‐on‐disc tribo‐tester was used to conduct tests. Then comparison analyses were conducted from three aspects, including the friction coefficient, wear mass loss, and the wear surface topography. The analysis results showed that: (1) the different additives as well as the mass fraction of these additives lead to significant difference in terms of tribological properties of PU; (2) the lubricating grease, as one of additives, improved the wear resistance and friction performance effectively; (3) modified PU is eligible to work as matrix because of satisfied mechanical properties and specific internal morphology. It is believed that understandings in this study are beneficial to the improvement of the tribological properties of PU and also provide the real practical basis for the studies of polymer materials which applied on water‐lubricated marine stern tube bearing. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46305.     

Tribological properties of PTFE‐filled thermoplastic polyimide at high load,velocity, and temperature

The effect of 20 wt% polytetrafluoroethylene (PTFE) fillers on the friction and wear properties of thermoplastic polyimides (TP) are investigated, under dry sliding in line contact against steel under 50 to 200 N, 0.3 to 1.2 m/s, and 60 to 260°C. Besides the lubricating mechanisms of PTFE based on mechanical shear, the thermal and tribophysical interactions in the sliding interface are considered in this research by using thermoanalytical measurements, Raman spectroscopy, and calculating the maximum polymer sliding temperature T*. The effect of hydrolysis of the TP bulk material, causing high friction at 100 to 140°C, is covered by PTFE. A transition at pv‐values 2.2 MPa m/s (T* = 120°C) is due to thermally controlled sliding of PTFE, while a transition at pv‐values 3.2 MPa m/s (T* = 180°C) remains controlled by degradation of the TP bulk material into monomer fractions. The reduced coefficient of friction in the presence of PTFE leads to smaller degradation and orientation of the molecular back‐bone and side‐chains within the TP structure. The formation of a homogeneously mixed transfer film is only observed at 180 to 260°C. The PTFE forms a fibrillar structure during wear at high sliding velocities, while they wear as separate particles at high normal loads. POLYM. COMPOS., 2009. © 2009 Society of Plastics Engineers