Impact of fillers and counterface topography on wear behavior of PTFE polymers for ultrasonic motor

Aimed to study the effects of reinforcing or functional fillers on mechanical and tribological properties of PTFE‐based friction materials of ultrasonic motor, carbon fibers reinforced PTFE composites modified with different functional fillers with differences in dimension, size, and hardness are fabricated. The tribological performances of PTFE‐based friction materials are comparatively investigated under different sliding velocities and normal loads on different surface morphologies, respectively. The experimental results reveal that nano‐SiO₂ shows excellent performance in improving friction stabilities and wear resistance in different operating conditions. It is believed the silica‐based tribofilms, higher deformation resistance, and bearing capacity play a key role in improving friction stabilities. Furthermore, the results also show that the surface topography plays an important role in wear properties. The lower wear rate (sliding against with the disordered surface) is believed to be attributed to wear debris easy‐store characteristic of the topography, which promotes transfer films formation and decreases the wear rate effectively. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44835.     

Study on the tribological characteristics of solid lubricants embedded tin‐bronze bearings

The friction and wear characteristics of graphite, MoS₂, and PTFE embedded tin‐bronze bearings were studied using a pin‐on‐disc tester. The results indicated that solid lubricants decreased and stabilized the friction coefficient, and decreased the wear rate by two to three orders of magnitude. When the content of solid lubricants, PTFE mixed with graphite, was 20–40%, the performance of the solid lubricants embedded bearing (SLEB) was the best. Wear scar was analyzed by means of X‐ray diffraction (XRD), Auger electron spectroscopy (AES), and scanning electron microscopy (SEM). The results show that the transfer films of solid lubricants reduce adhesion between the SLEBs and the mating material, and the wear mechanism of SLEBs changes to fatigue and adhesive wear. The main reason for fatigue wear is microcracks expanding at Pb points in SLEBs. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2394–2399, 2001     

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     

Tribological behavior of carbon nanotube and polytetrafluoroethylene filled polyimide composites under different lubricated conditions

The friction and wear behavior of polyimide (PI) composites reinforced with carbon nanotube (CNT) and polytetrafluoroethylene (PTFE) were comparatively evaluated under dry sliding, water‐, oil‐ or alkali‐lubricated condition. The wear mechanisms of the composites were also discussed. Results indicate that, when comparison with the dry friction situation, PI‐based composites results lower friction coefficients and wear rates under oil‐ or alkali‐lubricated condition. The lowest wear rate of the CNT/PTFE/PI composite is recorded as 1.2 × 10⁻⁶ mm³/Nm during the composite sliding in alkali, which is only about 40% of the value sliding under dry friction condition. The worn surface of neat PI under dry sliding is characterized by severe adhesive wear, whereas abrasive wear is the main character for CNT/PTFE/PI composites. The worn surfaces of CNT/PTFE/PI composites sliding in oil or alkali lubricated condition are smoother than those under dry or water condition. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

半芳香族聚酰胺PA6T及其PTFE复合材料的摩擦磨损性能研究

对3种不同共聚结构的聚对苯二甲酰己二胺（PA6T）树脂——聚对苯二甲酰己二胺/己内酰胺（1132）、聚对苯二甲酰己二胺/己二酰己二胺（M21）和聚对苯二甲酰己二胺/己二酰己二胺（1252）以及其聚四氟乙烯（PTFE）复合材料在干摩擦条件下的摩擦磨损性能进行了研究,并使用扫描电子显微镜（SEM）对试样的磨损面进行了分析。结果表明,1252的摩擦磨损性能最好,M21次之,1132最差;PTFE的加入提高了3种树脂的摩擦磨损性能,其中对1252的摩擦磨损性能改善最大,当PTFE含量为30份（质量份,下同）时,其摩擦因数和磨损率分别降低到了0.16和1.00×10^-6;磨损机理方面,1132的磨损方式主要表现为粘着磨损和疲劳磨损,而M21和1252的主要磨损方式表现为磨粒磨损;随着PTFE含量的增加,复合材料的主要磨损方式均转变为粘着磨损。     

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     

Friction behavior of PTFE-coated Si3N4/TiC ceramics fabricated by spray technique under dry friction

PTFE coatings were deposited on the Si₃N₄/TiC ceramic substrate by using spray technology. The surface and cross-section micrographs, adhesive force of coatings with substrate, surface roughness and micro-hardness of the coated ceramics were examined. The friction and wear behaviors of ceramic samples with and without coatings were investigated through carrying out dry sliding friction tests against WC/Co ball. The test results indicated that the coated ceramics exhibited rougher surface and lower micro-hardness, and the PTFE coatings can significantly reduce the surface friction and adhesive wear of ceramics. The friction performance of PTFE-coated sample was affected by applied load due to the lower surface hardness and shear strength of coatings, and the main wear failure mechanisms were abrasion wear, coating delamination and flaking. It can be considered that deposition of PTFE coatings is a promising approach to improve the friction and wear behavior of ceramic substrate.     

Properties of carbon fiber reinforced poly(vinylidene fluoride)‐based friction materials of ultrasonic motors

In order to improve output properties and anti‐irradiation capability of ultrasonic motors (USMs), which are driven by friction forces of friction material between the stator and rotor, a type of friction material is fabricated by composite materials consist of carbon fiber (CF) and polyvinylidene fluoride (PVDF). The effects of different contents of CF on the mechanical and tribological properties of PVDF‐based friction materials are studied, and the mechanical features of the relative USMs are measured. Further, the worn surface morphology of PVDF composites is observed by means of scanning electron microscope and the wear mechanisms are also discussed. In addition, the anti‐irradiation capability of the type of friction materials is measured by the γ‐ray irradiation at room temperature environment with the total radiation dose of 4.0X rad (Si). The experimental results show that the incorporation of CF into PVDF can effectively improve the friction and wear properties of the friction materials, and the mechanical properties of TRUM‐60 used by relative PVDF composites are also increased with the increase of CF. For TRUM‐60, both the no‐load speed and holding torque of the USMs were high, and the wear of friction material was lowest, when the CF content is 15 wt%. The experiment results also show that this PVDF‐based friction material has a good anti‐irradiation property. Therefore, the composite materials consist of CF and PVDF are beneficial for the applications in USMs, especially for some radiation environment. POLYM. COMPOS., 37:547–552, 2016. © 2014 Society of Plastics Engineers     

Evaluation of fretting wear behavior of PEEK by analyzing the change of crystallinity: The high temperature effect

In this study, the high‐temperature tribological behaviors of poly‐ether‐ether‐ketone (PEEK) under fretting wear condition have been evaluated by using a SRV‐IV oscillating reciprocating ball‐on‐disk tribometer. It can be found that the noticeable transitions of the friction coefficient and wear rate occurred when the test temperature was 150°C. Based on the observations of the morphologies of worn surfaces, the transition of wear mechanisms of PEEK actually occurred at 150°C. In addition, by investigating the change of the crystalline structure of PEEK, results showed that the wear contributed to the formation of a higher crystallinity of PEEK. The change of the crystallinity further affected the tribological behavior of PEEK. According to the result of permanganate etching, it also can be observed that the main component of plastic deformation resulting from adhesive wear was the amorphous phase. POLYM. ENG. SCI., 57:1340–1348, 2017. © 2017 Society of Plastics Engineers     

Friction and wear studies of polyetherimide composites under oscillating sliding condition against steel cylinder

Tribological properties of neat polyetherimide (PEI), glass, carbon fiber, and solid lubricants filled PEI composites are presented in this article. The aim of this study was to investigate the friction and wear properties of these composites under dry oscillating sliding condition at room temperature (RT) as well as at elevated temperature (120°C). The polymer specimens were made to oscillate against steel cylinder as a counterpart. The friction and wear properties of PEI and composites were strongly influenced by the temperature. Incorporation of carbon fiber in the PEI matrix has increased the wear rate at RT, while at elevated temperature this trend was opposite. Abrasive action of carbon fibers has severely damaged the counterpart and resulted in accelerated wear of the composite at RT. Solid lubricants filled (PTFE, MoS₂, graphite) along with glass fiber is beneficial in improving the friction and wear performance of the PEI composite at RT, whereas at elevated temperature wear performance was deteriorated. Tribological performance of neat PEI and glass fiber composite was similar with each other at RT. Scanning electron micrographs and optical micrographs of the worn polymer specimens and the steel cylinders was used to study the possible wear mechanisms. The present test results were also compared with data available on the reciprocating wear of PEI and composites in the literature and trends have been reported. POLYM. COMPOS., 38:48–60, 2017. © 2015 Society of Plastics Engineers     

Study on the Friction and Wear Behaviors of Modified PA66 Composites

The wear-resistant polyamide 66 (PA66) composites were prepared and the mechanical properties, friction and wear properties were inspected. Results show that GF, PTFE and MoS₂ can improve the mechanical, friction and wear properties of PA66 composites. PTFE is more effective on the friction and wear properties than MoS₂ when GF is 30%wt. The best effect of the modification is 35%wt GF when both PTFE and MoS₂ were added. Friction coefficient first increase, then reduce to be stable as sliding time increases. Friction coefficient and wear mass loss increase as load increases. The main wear mechanisms are fatigue and abrasion wears.     

Friction and wear characteristics of metal sulfides and graphite‐filled PTFE composites under dry and oil‐lubricated conditions

Five kinds of polytetrafluoroethylene (PTFE)‐based composites, pure PTFE, PTFE + 30(v)% MoS₂, PTFE + 30(v)% PbS, PTFE + 30(v)% CuS, and PTFE + 30(v)% graphite (GR) composites, were first prepared. Then the friction and wear properties of these PTFE composites, sliding against GCr15‐bearing steel under both dry and liquid paraffin‐lubricated conditions, were studied by using an MHK‐500 ring‐on‐block wear tester. Finally, the worn surfaces and the transfer films of the PTFE composites formed on the surface of GCr15 bearing steel were investigated by using a scanning electron microscope (SEM) and an optical microscope, respectively. Experimental results show that filling with MoS₂, PbS, CuS, or graphite to PTFE can reduce the wear of the PTFE composites by two orders of magnitude compared to that of pure PTFE under dry friction conditions. However, the friction and wear‐reducing properties of these PTFE composites can be greatly improved by lubrication with liquid paraffin. Investigations of transfer films show that MoS₂, PbS, CuS, and graphite promote the transfer of the PTFE composites onto the surface of GCr15‐bearing steel under dry friction conditions, but the transfer of the PTFE composites onto the surface of GCr15‐bearing steel can be greatly reduced by lubrication with liquid paraffin. SEM examinations of worn surfaces show that with lubrication of liquid paraffin, the creation and development of the cracks occurred on the worn surfaces of the PTFE composites under load, which reduces the load‐supporting capacity of the PTFE composites. This would lead to the deterioration of the friction and wear properties of the PTFE composites under higher loads (>600N). © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 751–761, 1999     

热处理温度对C／C复合材料摩擦磨损性能的影响

利用销一盘式摩擦磨损试验机研究了不同热处理温度制备C／C复合材料与GCrl5钢配副在油润滑务件下的摩擦磨损行为。结果表明,在油润滑条件下,材料摩擦系数低,其值在0．06～0．17范围内,磨损率在（1．03～2．56）×10^4mg／N·m范围,其中2100℃热处理的材料具有最低的摩擦系数和磨损率。在摩擦试验过程中,2000℃以上热处理的材料可以形成完整致密的摩擦膜,能起到润滑作用。结果还表明,随热处理温度的提高,材料石墨化程度提高,硬度降低,其磨损机制以磨粒磨损为主转向以疲劳磨损和粘着磨损占据主导地位。     

Modification of Cu‐PE‐PTFE composite coatings on rubber surface by low‐energy electron beam dispersion with glow discharge

Polytetrafluoroethylene (PTFE) composite coatings doped with copper acetate and polyethylene (PE) were fabricated on rubber substrate by electron beam dispersion technique. The effects of dopant nature and glow discharge treatment on morphology, structural and tribological properties of the coatings were investigated. The results showed that Cu and PE doping change the surface structure of PTFE‐based composite coatings due to the chemical reactions between the dispersion products. Cu‐PE‐PTFE coatings show the columnar and layered growth models without and with discharge treatment. Cu adding decreases the crystallinity, branched degree and unsaturated degree of PE coatings, but increases the branched degree and unsaturated bonds in the PE‐PTFE coatings. Glow discharge enhances the crystallinity and ordering degree of composite coatings. Friction experiments indicated the significant difference of composite coatings in the nature of their destruction during friction. PE‐PTFE coating is characterized of the brittle fracture with clear failure boundaries but Cu‐PE‐PTFE coating shows a rough surface without cracking and delaminating after friction. Cu doping increases the dynamic coefficient of friction of PE and PE‐PTFE composite coatings, but discharge plasma decreases the dynamic coefficient of friction. Cu‐PE‐PTFE composite coating after discharge treatment has the decreased dynamic coefficient of friction and improved wear resistance. POLYM. ENG. SCI., 58:103–111, 2018. © 2017 Society of Plastics Engineers     

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.     

热力耦合下TC4合金微动磨损行为影响的研究

为了研究TC4合金在300℃和500℃下的微动磨损行为,利用扫描电子显微镜和激光共聚焦显微镜分别表征表面磨痕形貌、磨损体积和磨痕轮廓,探究两种温度中TC4合金不同接触载荷作用下的微动磨损机制。结果表明： 磨损体积与接触载荷呈现正相关的关系,而摩擦系数和磨损率则呈现负相关的关系。两种温度下的无润滑微动摩擦磨损过程中,小载荷作用时磨损形式表现为氧化磨损和磨粒磨损;大载荷作用时磨损形式为氧化磨损和黏着磨损。与300℃相比,500℃时合金接触表面塑性变形严重,摩擦系数小,氧化磨损加剧,疲劳裂纹扩展严重。TC4合金高温环境中微动磨损机制为黏着磨损、磨粒磨损、氧化磨损和疲劳磨损,其中氧化磨损在TC4合金高温微动磨损中占据主导地位。     

玻璃纤维填充改性PTFE复合材料的摩擦磨损性能

为改善聚四氟乙烯(PTFE)高磨耗的缺点,通过冷压烧结成型工艺制备了玻璃纤维(GF)填充改性PTFE复合材料,探究了不同GF添加比例的PTFE/GF复合材料在不同转速下的摩擦磨损情况。采用三维视频显微镜观察了样品的表面磨痕深度,并借助扫描电子显微镜观察摩擦表面形貌同时分析磨损机理。结果表明,填充GF后的PTFE复合材料其摩擦系数虽有一定程度的升高,但其体积磨损率却大幅降低。当GF质量分数为20%时,复合材料的体积磨损率降到最低,并在转速为80 r/min时较纯PTFE降低了93.56%。观察分析微观形貌发现,随着GF含量的增大,复合材料的磨损机理逐渐由纯PTFE的犁耕磨损和粘着磨损向磨粒磨损转变,当GF含量为25%时,出现轻微的疲劳磨损。     

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     

Effect of irradiation modification above melting point on the wear resistance of polytetrafluoroethylene

The cross-linked polytetrafluoroethylene (PTFE) and PTFE/carbon fiber (CF) composites were synthesized through electron beam irradiation in the molten state of PTFE at a controlled temperature of 340 ± 3°C under an inert gas atmosphere for this study. The wear resistance of raw (raw-PTFE), irradiated modified PTFE (RM-PTFE), and CF-reinforced PTFE composites were evaluated using a friction and wear testing machine. The testing was conducted under varying ambient temperatures and dynamic loads. After irradiation, the samples were sectioned into specific sizes for subsequent testing purposes. Under the test conditions of 4.64 MPa positive pressure, 800 rpm speed, and a duration of 300 s at 20°C, the wear amount of PTFE after irradiation modification is significantly reduced from 1.4103 mm to only 0.0233 mm, representing a remarkable reduction by a factor of 60. Similarly, under the test conditions of 4.64 MPa positive pressure, 200 rpm speed, and a duration of 300 s at 20°C, the friction coefficient of PTFE after irradiation modification is substantially decreased from an initial value of 0.13 to just 0.03. The observed improvement can be attributed to the transformation of PTFE's crystalline form into spherulite, accompanied by a significant enhancement in the degree of cross-linking within its molecular chain. The PTFE was supplemented with 10% CF prior to irradiation. Under the test conditions of a positive pressure of 4.64 MPa, rotation speed of 800 rpm, and a duration time of 300 s at 20°C, the wear amount of the composite material measured only 0.0007 mm, representing a reduction by a factor of 2000 compared to that observed for pure PTFE. This improvement can be attributed to the CF filler's high wear resistance properties and the composite's enhanced thermal conductivity.