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Two-dimensional (2D) lamellar materials have unique molecular structures and mechanical properties, among which molybdenum disulfide (MoS2) and graphitic carbon nitride (g-C3N4) with different interaction forces served as reinforcing phase for polytetrafluoroethylene (PTFE) composites in the present study. Thermal stability, tribological and thermo...
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... morphologies are shown in Fig. 2. MoS 2 micropowders with an average diameter of 20 μm and purity of 99.9% were purchased from Beijing DK Nano technology Co. Ltd. The yellowish g-C 3 N 4 powders were synthesized by directly heating melamine (C 3 N 6 H 6 , Tianjin Kemiou Chemical Regant Co., Ltd.) at 550 ° C for 4 h following previous works [27,29]; the sizes are shown in Fig. 3. Detailed information on the other compositions is summarized in Table 2. The fillers were added and mixed in a shredding machine for 3 min. ...Citations
... The utilization of PTFE composites has been extensively observed in diverse industrial and scientific research domains owing to their chemical stability, high specific strength, superior process ability, lifetime service at 260 • C, and self-lubrication properties [1][2][3][4][5]. However, the advancement of technology and the increasing demands for applications have created new challenges concerning the development of products that are capable of operating under extreme working conditions due to uncertainties in terms of service characteristics and friction and wear mechanisms [6,7]. ...
Because of the complex nonlinear relationship between working conditions, the prediction of tribological properties has become a difficult problem in the field of tribology. In this study, we employed three distinct machine learning (ML) models, namely random forest regression (RFR), gradient boosting regression (GBR), and extreme gradient boosting (XGBoost), to predict the tribological properties of polytetrafluoroethylene (PTFE) composites under high-speed and high-temperature conditions. Firstly, PTFE composites were successfully prepared, and tribological properties under different temperature, speed, and load conditions were studied in order to explore wear mechanisms. Then, the investigation focused on establishing correlations between the friction and wear of PTFE composites by testing these parameters through the prediction of the friction coefficient and wear rate. Importantly, the correlation results illustrated that the friction coefficient and wear rate gradually decreased with the increase in speed, which was also proven by the correlation coefficient. In addition, the GBR model could effectively predict the tribological properties of the PTFE composites. Furthermore, an analysis of relative importance revealed that both load and speed exerted a greater influence on the prediction of the friction coefficient and wear rate.
... The F atoms are helically distributed around the C atoms in the main chain, the C-C bonds and/or C-F bonds in the polymer structure are broken during the friction process, and the active PTFE radicals and F ions react or bond with the counterpart metal ions to form a transfer film with strong adhesion. Therefore, PTFE has a lower coefficient of friction than other polymers [26]. High-performance polymer materials, such as polyimide (PI), polyphenylene sulfide (PPS), and polyetheretherketone (PEEK), have been used to prepare high-temperature self-lubricating and wear-resistant www.Springer.com/journal/40544 ...
... It is difficult to meet the actual high-temperature friction conditions. It has been found that PTFE coatings were easy to creep and worn severely under high load conditions [26,27], PI coatings exhibited high friction and severe wear [28], PPS coatings were fragile and lack of impact resistance [29]. Generally, inorganic lubricants, such as h-BN, carbon nano tube (CNT), and graphene [30][31][32][33], are used as fillers, which are added into polymers (PEEK, UHMWPE, PI, and PTFE, etc.) to obtain self-lubricating and wear-resistant. ...
High-temperature ablation is a common failure phenomenon that limits the service life of the transmission parts on heavy-duty machines used in heavy load, high temperature, high shock conditions due to in-sufficient supply of lubricating oil and grease. Traditional self-lubricating coatings prepared by inorganic, organic or organic-inorganic hybrid methods are prone to be oxidated at high temperatures to lose their friction reducing function, so that it is difficult to meet the engineering requirements of high-temperature lubrication. We design viscoelastic polymer coatings by a high-temperature self-lubricating and wear-resistant strategy. Polytetrafluoroethylene (PTFE, T m = 329 °C) and polyphenylene sulfide (PPS, T g = 84 °C, T m = 283 °C) are used to prepare a PTFE/PPS polymer alloy coating. As the temperature increases from 25 to 300 °C, the PTFE/PPS coating softens from glass state to viscoelastic state and viscous flow state, which is owing to the thermodynamic transformation characteristic of the PPS component. Additionally the friction coefficient ( µ ) decreased from 0.096 to 0.042 with the increasing of temperature from 25 to 300 °C. The mechanism of mechanical deformation and surface morphology evolution for the PTFE/PPS coating under the multi-field coupling action of temperature ( T ), temperature–centrifugal force ( T – F ω ), temperature–centrifugal force–shearing force ( T – F ω – F τ ) were investigated. The physical model of “thermoviscoelasticity driven solid–liquid interface reducing friction” is proposed to clarify the self-lubricating mechanism determined by the high-temperature viscoelastic properties of polymers. The high-temperature adjusts the viscosity ( η ) of the coating, increases interface slipping and intensifies shear deformation ( τ ), reducing the friction coefficient. The result is expected to provide a new idea for designing anti-ablation coatings served in high temperature friction and wear conditions.
... SL refers to the use of solid powders or films to reduce friction and wear and protect surface from damage [5][6][7]. However, the high coefficient of friction (COF), inevitable abrasion, the difficulty of discharging wear debris, and large vibration of SL (such as graphite, molybdenum disulfide, and Polytetrafluoroethylene (PTFE)) limit their application in high-precision and long-life motion components [8][9][10]. Instead, the EOL boost lubrication equipment and lubricant consumption [11]. ...
Herein, a porous oil-containing material with hierarchical pore structure was successfully prepared through microtexturing large pores on the surface of porous polyimide (PPI) with single-level small pores. Compared to the conventional oil-containing material, the hierarchically porous oil-containing material exhibited high oil-content, and retained excellent mechanical properties and high oil-retention because of the synergistic effects of large pores and small pores. Furthermore, the lubricant stored in the hierarchically porous polyimide could release to the interface under thermal-and-mechano-stimuli, and the released lubricant could be reabsorbed into the hierarchically porous polyimide via the capillary-force offered by the porous channel. Based on the high oil-content and recyclable oil release/reabsorption, the hierarchically porous oil-containing polyimide exhibited excellent lubrication performance (coefficient of friction was 0.057). Furthermore, the composite could perform 1,069 cycles of smart lubrication (1 h per cycle), which significantly extended the service life of the hierarchically porous oil-containing smart lubrication material.
... The ball-on-flat contact mode, which was widely used in previous studies [27][28][29], presents the characteristics of a good contact state and high-test repeatability. Therefore, in order to obtain a good contact state simulation of the wear failure process of joint bearings, the preparation of samples and the wear tests were based on this contact form. ...
... Fig. 18 shows the schematic of the proposed wear mechanism and how it changes with the increasing temperature. The wear mechanism of PTFE/Kevlar composite is thought to be closely related to the formation and evolution of the transfer film during the friction process [13,29]. Theoretically, the contact interface between the 100Cr6 bearing ball and the fabric material inevitably has rough peaks, although it looks smooth (Fig. 18a). ...
The tribological properties of PTFE/Kevlar fabric are extremely important for the service behavior of self-lubricating and maintenance-free joint bearings in aviation, aerospace and other fields that require high wear performance at different temperatures. This paper aims at investigating the influence of the ambient temperature on the tribological properties of hybrid PTFE/Kevlar fabric through reciprocating wear tests. The wear loss, surface damage morphology and tribo-chemical behaviors of PTFE/Kevlar at the temperature range of 25~200 °C are first analyzed. The wear mechanisms, damage behaviors and their transitions with the increase in the ambient temperature and reciprocating cycles are then systematically discussed. This information can provide a guide to master the range of safe use and the optimization of materials.
... Depending on formulations and service conditions, polymeric composites can exhibit a "self-lubricating" feature [8][9][10]. That is, low friction and wear can be obtained even under unlubricated and harsh lubrication conditions. ...
It is of great interest to realize controllable tribo-designs of a large variety of motion components operating under starved lubrication conditions. In this work, g-C3N4 nanosheets were prepared and uniformly dispersed into pure epoxy (EP) matrix. Especially for sliding with only 5 μL oil supply. In comparison to neat EP, friction coefficient and wear rate are reduced by up to 27% and 83% with addition of only 1% g-C3N4. Research illustrates a small amount of two-dimensional g-C3N4 nanosheets promote the growth of robust tribofilm on oil starved interface. The carbonous top layer of tribofilm benefits the boundary lubrication effect of the sliding pair, whereas the beneath layer confers a high load-bearing ability to tribofilm. It is anticipated that this work will pave a route for designing new polymer nanocomposites serving under oil starved conditions.
... Thus, the impact and tensile strengths of porous oil-impregnated GO/PA6 composites were improved as a result. At higher GO content, GO would be agglomerated in the porous PA6 matrix, which may lead to stress defects within the matrix [26,27]. In addition, the excessive introduction of GO will stiffen the molecular chain structure in the polymer composite. ...
Using carbon nanomaterials to construct self-lubricating polymer materials with porous self-lubricating structures has become an effective way to improve the tribological performance of polymer composites. The synergistic effect between 1.0 wt% graphene oxide (GO) and lubricating oil resulted in excellent tribological properties of polyamide 6 (PA6) composites under different loads and speeds. It indicated that the introduction of GO in porous PA6 matrix (GO/PA6) would provide enhanced tribological performance with the friction coefficient reduction by 23.4% and wear resistance improvement by 36.2%. This was explained by the lubricating oil stored in the pores of PA6 material would be released to the surface of the matrix material under the dual effect of load and temperature during the friction process. The released lubricating oil would formed a solid-liquid double lubrication structure with the well-dispersed GO in the matrix, thus the porous oil-immersed GO/PA6 composite materials demonstrates excellent tribological performance. This work provides a solid-liquid double lubrication strategy for enhancing the tribological properties of self-lubricating polymers, which would promote the self-lubricating polymer composites more widely applied in the field of friction materials.
... [1][2][3][4] Among them, polytetrafluoroethylene (PTFE) has attracted tremendous attention in the field of sliding bearings, seals, and washers because of its excellent self-lubricating characteristic and high chemical resistance. [5][6][7][8] However, single component material is difficult to meet actual application due to complicated and extreme condition. 9 Therefore, filler-reinforced polymer composites have become an effective way to enhance tribological performance. ...
The mechanism of enhancing the mechanical and tribological properties of polytetrafluoroethylene (PTFE) via the addition of nano-ZrO 2 was investigated by virtue of molecular dynamic (MD) simulation from an atomic level. The MD was used to explore stretch and break of molecular chains for understanding the inherent mechanism of nanocomposites. The results found that elastic modulus of PTFE and PTFE/ZrO 2 were 1.42 GPa and 6.43 GPa, respectively. The average friction coefficients of PTFE and PTFE/ZrO 2 were 0.168 and 0.113, respectively. Compared to PTFE, the friction coefficient of PTFE/ZrO 2 decreased by 32.7%. To explore the microscopic friction mechanism, the radial distribution function, atomic concentration, and atomic velocity were simulated and interpreted accordingly during the tribological process.
... This superb combination of concurrent ultralow friction coefficient and wear rate makes DPNC TiB 2 / MoS 1.7 B 0.3 an outstanding USL material. In Figure 2c, we show a wear rate versus friction-coefficient plot for the recently reported self-lubricating materials based on MoS 2 , including MoS 2 -metals (Au, 33 Ti, 34 Pb, 35 Cr, 36 Zr, 11 W, 11 Nb 37 ), MoS 2nonmetals (C, 38 N, 14 B, 15 Si, 39 GLC, 40 a-C:H 41 ), and MoS 2others (PTFE, 42 Pb/Ti, 43 CrMoN, 44 Ag/C, 45 Sb 2 O 3 /Au 6 ); for comparison, MoS 2 , TiB 2 , TiN, 46 and several other typical wearresistant materials 3,47−50 are also included. All of the data shown here are obtained in the self-lubricating mode, i.e., without any external input, and measured in ambient air. ...
... This is justified knowing the poor molecular interaction between polymers and BN nanosheets [28,29]. Such weak molecular interaction is responsible for (as a contributor of) higher wear rates and interfacial thermal resistance resulting in lower thermal conductivity, as reported in numerous publications [30][31][32]. Therefore, increasing the molecular interaction between BN nanosheets and polymer materials is vital to improving the wear-resistant properties and thermal conductivity. ...
The heat generated by friction and wear between contact surfaces is detrimental to the performance of polymeric materials due to the low thermal conductivity of polymer materials. This work presents the effect of boron nitride (BN) nanosheets on the thermal and tribological properties of polyethylene (PE) materials. The molecular interaction between BN nanosheets and PE matrix was enhanced by functionalizing BN nanosheets with silane functional groups. It was observed that adding just 5 wt.% silane modified BN (sBN) nanosheets can increase the thermal conductivity of PE materials by 33% and minimizes the generation of hot spots due to fast heat dissipation. In addition, the wear rate is reduced by 35% in PE-sBN composites in comparison to PE materials.
... Pressure and shear forces are believed to be essential for graphene to reduce defects while stacking layer-by-layer, resulting in a reduced coefficient of friction. It is well known that in the tribological study of polymer materials, the friction coefficient is inversely proportional to the load [47], according to the following equation: ...
With the development of energy-saving industries, the tribology and thermal management of composites were increasingly urgent. Here, we explored the dual-network graphene/epoxy composites with enhanced tribological and thermal management. The 3D graphene was prepared using calcium ions as the crosslinker and melamine foam as template. Subsequently, the reinforced concrete-like composites were obtained by dipping in silica-filled epoxy. The research results show that the thermal conductivity of the composites was enhanced by 1015.52% compared to the silica-filled epoxy. Simultaneously, the friction coefficient of the composites was reduced to 0.29 with the wear rate be reduced to 0.19×10⁻⁵ mm³/N∙ m under the condition of 5 N and 2 cm/s. This dual-network model provides a new strategy for the development of solid lubricating materials with excellent thermal management.
