Interfacial structure and tribological behaviours of epoxy resin coating reinforced with graphene and graphene oxide

Graphene (G) and graphene oxide (GO) were added into epoxy resin (EP) respectively via chemical modification and physical ultrasound technology to improve the tribological behaviour of EP coating. The topographies of G and GO were detected by scanning probe microscopy. The chemical structures of the fillers before and after modification were identified by Fourier transform infrared spectrometer. The across‐section topographies of the coatings were detected by scanning electron microscopy. The tribological behaviour of the coatings was evaluated by UMT‐3 tribology tester, surface profiler and scanning electron microscopy. The results revealed that the coefficient of friction of the coatings decreased, and the wear resistance of the coatings improved with the addition of the G and GO. GO could improve the tribological performance of EP further compared to G. When containing 0.5 wt% G and 0.75 wt% GO, the coatings had the lowest coefficient of friction and best wear resistance. When the contents of G reached 0.75 wt%, and GO reached 1 wt%, the tribological performance of the composite coatings decreased as a result of the agglomeration of the fillers. Finally, the anti‐friction and anti‐wear mechanisms of G‐EP and GO‐EP composite coatings were discussed in detail based on the results obtained in the preceding texts. Copyright © 2016 John Wiley & Sons, Ltd.     

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     

Enhanced wear resistance of sol–gel TiO2 film on a carbon steel in unlubricated sliding against steel ball by stearic acid modification

Increasing wear resistance of steel is of great importance for their practical application. In this paper, we have studied the tribological performance of assembly of stearic acid on a carbon steel coated by sol–gel derived TiO₂ film. The samples were characterized by means of infrared spectroscopy, contact angle measurements, atomic force microscopy and a macro friction and wear tester. Enhanced wear resistance were clearly obtained after functionalization of stearic acid on the TiO₂ surface.     

Insight into the Excellent Tribological Performance of Highly Oriented Poly(phenylene sulfide)

Achieving low friction and wear of poly(phenylene sulfide)(PPS) without using fillers or blending is a challenging task, but one of considerable practical importance. Here we describe how neat PPS with high tribological performance is achieved by manipulating processing parameters(pressure, flow and temperature). The key to achieving high tribological performance is comparatively high molecular chain orientation, realized in neat PPS, at high shear rates and low pressure. The friction coefficient and wear rate are as low as ~0.3 and~10^-6 mm³·N^-1·m^-1, respectively, which break the record for neat PPS. These values are even better than those for PPS-based blends and comparable to PPS composites. Further studies show, for the first time, that wear rate decreases exponentially with increasing molecular chain orientation, prompting us to revise the classical Archard's law by including the effect of molecular chain orientation. These findings open the possibility of using neat PPS in highly demanding tribological applications.     

Effects of atomic oxygen irradiation on structural and tribological properties of polyimide/Al2O3 composites

To understand the effects of atomic oxygen (AO) irradiation on the structural and tribological behaviors of polymer composites, polyimide/Al₂O₃ composites were irradiated with AO in a ground‐based simulation facility. The structural changes were characterized by X‐ray photoelectron spectroscopy and attenuated total‐reflection FTIR, whereas the tribological changes were evaluated by friction and wear tests as well as scanning electron microscopy analysis of the worn surfaces. It was found that AO irradiation induced the oxidation and degradation of polyimide molecular chains, which increased the O concentration and decreased the C concentration in the composite surfaces. The destruction action of AO changed the surface chemical structure and morphology of the samples. Friction and wear tests indicated that AO irradiation decreased the friction coefficient but increased the wear rate of both pure and Al₂O₃ filled polyimides. In terms of the tribological properties, appropriate content of Al₂O₃ might be favorable for the improvement of tribological properties in AO environment. Copyright © 2011 John Wiley & Sons, Ltd.     

Preparation and investigation of tribological properties of ultra‐high molecular weight polyethylene (UHMWPE)/graphene oxide

This article has been devoted to investigation of the tribological properties of ultra‐high molecular polyethylene/graphene oxide nanocomposite. The nanocomposite of ultra‐high molecular polyethylene/graphene oxide was prepared with 0.5, 1.5, and 2.5 wt% of graphene oxide and with a molecular weight of 3.7 × 10⁶ by in‐situ polymerization using Ziegler–Natta catalyst. In this method, graphene oxide was used along with magnesium ethoxide as a novel bi‐support of the Ziegler–Natta catalyst. Analyzing the pin‐on‐disk test, the tribological properties of the nanocomposite, such as wear rate and mean friction coefficient, were investigated under the mentioned contents of graphene oxide. The results showed that an increase in graphene oxide content causes a reduction in both wear rate and mean coefficient friction. For instance, by adding only 5 wt% graphene oxide to the polymeric matrix, the wear rate and mean coefficient friction decreased about 34% and 3.8%, respectively. Also, the morphological properties of the nanocomposite were investigated by using X‐ray diffraction and scanning electron microscopy. In addition, thermal properties of the nanocomposite were analyzed using differential scanning calorimetry, under various contents of graphene oxide. The results of the morphological test indicated that the graphene oxide was completely exfoliated into the polymeric matrix without any agglomeration. Copyright © 2016 John Wiley & Sons, Ltd.     

Carbon‐ion implantation improves the tribological properties of Co?Cr?Mo alloy against ultra‐high molecular weight polyethylene

Amorphous diamond‐like carbon (DLC) has drawn a great deal of attention for its superior wear properties against ultra‐high molecular weight polyethylene (UHMWPE). Its rate of wear, however, is not necessarily maintained within a specific range. The aim of this study was to evaluate the mechanical features and tribological properties of three types of surfaces: (i) uncoated, (ii) carbon‐ion implantation (CII)‐treated, and (iii) DLC‐film‐coated substrate. The surface alterations were carried out on cobalt–chrome (Co? Cr? Mo) alloy by the plasma‐source ion implantation (PSII) method. The wear properties and friction coefficient were estimated by a pin‐on‐plate wear‐tester. We found, as a result, that the implanted carbon penetrated the substrates in which good adhesion was expected. Though the surface modifications by CII and DLC hardened the surfaces, the surface with DLC was also roughened (R_a = 39 nm). In contrast, the surface modified by CII had a very smooth surface (R_a = 15 nm) and low friction coefficient (ranging from 0.15 to 0.20), resulting in a low rate of wear. Our findings suggest that CII on the Co? Cr? Mo alloy/UHMWPE pair offers potential benefits as a hard coating for artificial total‐joint arthroplasty. Copyright © 2008 John Wiley & Sons, Ltd.     

The mechanical properties and tribological behavior of epoxy resin composites modified by different shape nanofillers

Mechanical properties and tribological behavior of epoxy resin (EP) and EP nanocomposites containing different shape nanofillers, such as spherical silica (SiO₂), layered organo‐modified montmorillonite (oMMT) and oMMT‐SiO₂ composites, were investigated. The SiO₂‐oMMT composites were prepared by in situ deposition method and coupling agent modification, and transmission electron microscopy (TEM) analysis shows that spherical SiO₂ is self‐assembled on the surface of oMMT, which forms a novel layered‐spherical nanostructure. The mechanical properties test results show that oMMT obviously improves the strength of EP and SiO₂ enhances its toughness, but oMMT‐SiO₂ exhibits a synergistic effect on toughening and reinforcing EP simultaneously. A pin‐on‐disc rig was used to test friction and wear loss of pure EP and EP nanocomposites. The tribological test results prove that these nanofillers with different shapes play different roles for improving the wear resistance of EP nanocomposites. Morphologies of the worn surfaces were studied further by scanning electron microscopy (SEM) observations, and it was clarified that the EP and EP nanocomposites undergo similar wear mechanisms. Copyright © 2006 John Wiley & Sons, Ltd.     

硅表面复合自组装膜的制备及其摩擦性能

采用自组装技术在单晶硅表面制备了3-氨基丙基三乙氧基硅烷(APTES)-SiO2-APTES复合膜,并对其表面的组成、结构及摩擦性能进行了表征.结果表明:复合膜表面对水的接触角约为63°,且表面平整、致密,其平均粗糙度(Ra)约为0.963nm.通过原子力显微镜(AFM)和透射电子显微镜(TEM)观察到夹层中SiO2颗粒的粒径约为20-50nm,较均匀地分布在第一层APTES膜的表面.与APTES自组装单层膜(SAMs)相比,APTES-SiO2-APTES复合膜由于纳米SiO2颗粒的引入而表现出更低的摩擦系数和更长的耐磨寿命.     

Friction and wear behavior of PI and PTFE composites for ultrasonic motors

High‐performance polymer‐based frictional materials have become increasingly important to improve the mechanical output properties of ultrasonic motors. This study discussed the friction and wear behavior of 2 dominating frictional materials of polymer composites for ultrasonic motors, polyimide (PI), and polytetrafluoroethylene (PTFE) filled by aramid fibers (AF) and molybdenum disulfide (MoS₂). To explore the wear mechanisms, the tribo‐pair contact stress was theoretically characterized, and the interface temperature rise was numerically predicted. The predictions showed that the flash temperature on asperity tips could reach the glass transition temperature of the polymer materials. The experimental results indicated that the contact stress and sliding speed have a small effect on the friction of the PI composite but influence considerably the friction of the PTFE composite. A higher contact stress brings about a higher specific wear rate, but a higher sliding speed reduces the wear rate. Compared with AF/MoS₂/PTFE, the AF/MoS₂/PI has much better tribological performance under high loads and speeds.     

Functionalized imidazolium wear‐resistant ionic liquid ultrathin films for MEMS/NEMS applications

As a kind of new material, ionic liquids (ILs) are considered a new type of lubricant for micro/nanoelectromechanical system (M/NEMS) due to their excellent thermal and electrical conductivity. However, so far, only a few reports have investigated the friction and wear of thin films of these materials at the micro scale. Evaluating the nanoscale tribological performance of ILs when applied as films of a few nanometers thickness on a substrate is a critical step for their application in M/NEMS devices. To achieve this purpose, IL thin films with four kinds of anions were synthesized and prepared on single‐crystal silicon wafers by the dip‐coating method. Film thickness was determined by the ellipsometric method. Their surface morphologies were observed by means of atomic force microscopy (AFM). The nano and micro tribological properties of the IL films were investigated by a friction force microscope (FFM)with a spherical probe and a UMT‐2MT tribotester, respectively. The corresponding morphologies of the wear tracks of the IL films were examined using a three‐dimensional non‐contact interferometric microscope. The impact of temperature on the adhesion behavior was studied, as well as the effect of sliding frequency and load on the friction coefficient, load bearing capacity and anti‐wear durability. It was found that friction, adhesion and durability of IL films were strongly dependent on their anionic molecular structures, wettability and ambient environment. Copyright © 2010 John Wiley & Sons, Ltd.     

Effects of UV irradiation on tribological properties of nano‐TiO2 thin films

One‐layer and two‐layer nano‐TiO₂ thin films were prepared on the surface of common glass by sol–gel processing. Water contact angle, surface morphology, tribological properties of the films before and after ultraviolet (UV) irradiation were investigated using DSA100 drop shape analyzer, scanning probe microscopy (SPM), SEM and universal micro‐materials tester (second generation) (UMT‐2MT) friction and wear tester, respectively. The stored films markedly resumed their hydrophilicity after UV irradiation. But UV irradiation worsened tribological properties of the films. After the film was irradiated by UV, the friction coefficient between the film and GCr15 steel ball increased about 10–50% and its wear life shortened about 20–90%. Abrasive wear, brittle break and adherence wear are the failure mechanisms of nano‐TiO₂ thin films. It was believed that UV irradiation increased surface energy of the film and then aggravated adherence wear of the film at initial stage of friction process leading to severe brittle fracture and abrasive wear. Copyright © 2009 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.     

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.     

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.     

The tribological behaviours of dithiocarbamate‐triazine derivatives as additives in mineral oil

Ashless and non‐phosphorus hydroxyl‐containing dithiocarbamate‐triazine compounds,2,4,6‐tri[N,N‐di‐i‐octyldithiocarmate‐(2′‐hydroxyl)‐propionylthio]‐1,3,5‐s‐triazine (LDION) were prepared and their tribological behaviour as additives in mineral oil were evaluated using a four‐ball tester. Thermal degradation tests were conducted to identify their thermal stabilities using a thermo‐gravimetric analyser. The worn surfaces were investigated by X‐ray photoelectron spectroscopy (XPS) and X‐ray absorption near edge structure (XANES) spectroscopy. The results indicate that the additive LDION possesses high thermal stabilities and good load‐carrying capacities. Moreover, it has good anti‐wear property at all test concentration and under all test loads. The results of XPS and XANES analyses illustrate that the prepared compounds as additives in mineral oil forms a protective film containing oxidised compounds and organic nitrogen‐containing compounds and inorganic sulfate on the metal surface during sliding process. Copyright © 2008 John Wiley & Sons, Ltd.     

Preparation and properties of Ni–Co–P/nano‐sized Si3N4 electroless composite coatings

Ni–Co–P/nano‐sized Si₃N₄ composite coating was successfully fabricated on aluminum alloys by electroless plating in this work. The surface and cross‐sectional morphologies, composition, microstructure, microhardness, friction and wear behavior of deposits were investigated with SEM, EDS, XRD, Vickers hardness and high‐speed reciprocating friction, respectively. It was found that a Ni–Co–P/nano‐sized Si₃N₄ composite coating on aluminum alloy substrate is uniform and compact. The existence of nano‐sized Si₃N₄ particles in the Ni–Co–P alloy matrix causes a rougher surface with a granular appearance, and increases the microhardness but decreases the friction coefficients and wear rate of electroless coatings. Meanwhile, the effects of heat treatment at 200, 300, 400 and 500 °C for 1 h on the hardness and tribological properties were researched. It is revealed that both of the microhardness and tribological properties of Ni–Co–P coatings and Ni–Co–P/Si₃N₄ composite coatings increase with the increase of heating temperature in the range of 200–400 °C, but show different behavior for the two coatings after annealing at 500 °C. Copyright © 2011 John Wiley & Sons, Ltd.     

Superlubricity behaviors of Si3N4/DLC Films under PAO oil with nano boron nitride additive lubrication

The tribological properties of Si₃N₄ ball sliding against diamond‐like carbon (DLC) films were investigated using a ball‐on‐disc tribometer under dry friction and oil lubrications, respectively. The influence of nano boron nitride particle as lubricant additive in poly‐α‐olefin (PAO) oil on the tribological properties of Si₃N₄/DLC films was evaluated. The microstructure of DLC films was measured by Raman spectroscopy and X‐ray photoelectron spectroscopy. The experimental results show coefficient of friction (COF) of Si₃N₄/DLC films was as low as 0.035 due to the formation of graphite‐like transfer films under dry friction condition. It also indicates that the tribological properties of Si₃N₄/DLC films were influenced significantly by the viscosity of oil and the content of nano boron nitride particle in PAO oil. COF increases with the viscosity of PAO oil increasing. Si₃N₄/DLC films exhibit the superlubricity behaviors (μ=0.001 and nonmeasurable wear) under PAO 6 oil with 1.0 wt% nano boron nitride particle lubrication, indicating that the improved boundary lubrication behaviors have indeed been responsible for the significantly reduced friction. Nano boron nitride additive is used as solid lubricant‐like nano scale ball bearing to the pointlike contact and a soft phase bond with the weak van der Waals interaction force on the contact surface to improve the lubrication behaviors of Si₃N₄/DLC films. The potential usefulness of nano boron nitride as lubricant additive in PAO oil for Si₃N₄/DLC films has been demonstrated under oil lubrication conditions. The present work will extend the wide application of nano particle additive and introduce a new approach to superlubricity under boundary lubrication in future technological areas. Copyright © 2013 John Wiley & Sons, Ltd.     

Antibacterial photocatalytic self‐cleaning poly(vinylidene fluoride) membrane for dye wastewater treatment

Membrane technology has been successfully applied for the removal of dyes from wastewater in the textile industry. A novel poly(vinylidene fluoride) (PVDF) membrane was prepared via blending with different dosages of Ag‐TiO₂‐APTES composite for dyeing waste water treatment in our study. And the effect of Ag‐TiO₂‐APTES blended into the PVDF membrane was discussed, including the rejection rate of methylene blue (MB) dye, membrane morphology, surface hydrophilicity, antibacterial activity, and a certain photocatalytic self‐cleaning performance. X‐ray diffraction and Fourier transform infrared characterization confirmed that Ag‐TiO₂ was functionalized by amount of hydroxyl group (−OH) and amino group (NH−), which provided by APTES. Contact angle measurement certified that the hydrophilicity of the membrane surface increased, with the contact angle decrease to 61.4° compared with 81.8° of original PVDF membrane. MB rejection rate was also increased to 90.1% after addition of Ag‐TiO₂‐APTES, and the rejection of original membrane was only 74.3%. The morphologies of membranes were observed by scanning electron microscope, which indicated that Ag‐TiO₂‐APTES had a good dispersion in membrane matrix and also improved the microstructure of membranes. Besides, UV irradiation experiments were performed on the composite films contaminated by MB, and the result showed that Ag‐TiO₂‐APTES nanoparticle provided PVDF membrane with a certain photodegradation capacity under UV irradiation. Moreover, antibacterial activity of the composite membrane was also demonstrated through antibacterial experiment, Escherichia coli as the representative bacteria. Perhaps, this research may provide a new way for PVDF blending modification.     

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.