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.     

Comparative study of the effects of nano‐sized and micro‐sized CF and PTFE on the thermal and tribological properties of PEEK composites

The tribological characteristics of PEEK composites fretting against GCr 15 steel were investigated by a SRV‐IV oscillating reciprocating ball‐on‐disk tribometer. In order to clarify the effect of type and size of fillers on the properties of PEEK composites, nano‐sized and micro‐sized CF and PTFE fillers were added to the PEEK matrix. The thermal conductivity, hardness, and fretting wear properties of PEEK composites reinforced by CF or PTFE were comparatively studied. The results showed that the type and size of the fillers have an important effect on both the friction coefficient and wear rate, by affecting their thermal conductivity, hardness, as well as the surface areas of their transfer films. In comparison, the effect on improving the tribological properties of micro‐sized CF was superior to that of nano‐sized CF, while the effect of nano‐sized PTFE was superior to that of micro‐sized PTFE. Considering the acceptable friction coefficient and wear rate of the composite under the fretting wear test, it seemed that 4% nCF, 20% mCF, 2% nPTFE and 10% mPTFE were desired additive proportions. And it also can be found that during the fretting wear test, the abrasive and adhesive wear resulted in accumulative debris at the contacting surface. The transfer films made of debris were formed on the counterfaces.     

Effect of nano‐modified SiO2/Al2O3 mixed‐matrix micro‐composite fillers on thermal,mechanical, and tribological properties of epoxy polymers

Thermo‐mechanically durable industrial polymer nanocomposites have great demand as structural components. In this work, highly competent filler design is processed via nano‐modified of micronic SiO₂/Al₂O₃ particulate ceramics and studied its influence on the rheology, glass transition temperature, composite microstructure, thermal conductivity, mechanical strength, micro hardness, and tribology properties. Composites were fabricated with different proportions of nano‐modified micro‐composite fillers in epoxy matrix at as much possible filler loadings. Results revealed that nano‐modified SiO₂/Al₂O₃ micro‐composite fillers enhanced inter‐particle network and offer benefits like homogeneous microstructures and increased thermal conductivity. Epoxy composites attained thermal conductivity of 0.8 W/mK at 46% filler loading. Mechanical strength and bulk hardness were reached to higher values on the incorporation of nano‐modified fillers. Tribology study revealed an increased specific wear rate and decreased friction coefficient in such fillers. The study is significant in a way that the design of nano‐modified mixed‐matrix micro‐composite fillers are effective where a high loading is much easier, which is critical for achieving desired thermal and mechanical properties for any engineering applications. Copyright © 2016 John Wiley & Sons, Ltd.     

Comparative study of the mechanical and wear performance of short carbon fibers and mineral particles (Wollastonite,CaSiO3) filled epoxy composites

To improve the mechanical and tribological performance, two kinds of wollastonite fillers (fine or coarse) and short carbon fibers (5–15 vol %) were, respectively, incorporated into an epoxy resin. Fine wollastonite fillers remarkably enhanced the flexural modulus, strength, and toughness of the resin at some filler contents (i.e., 10 vol %) simultaneously, while coarse wollastonite fillers and short carbon fibers impaired most of mechanical properties except the modulus. The small particle size, low aspect ratio as well as the good adhesion to the epoxy matrix of the fine wollastonite particles are believed to be responsible for the improved strength and toughness. Tribological tests were performed under sliding and low amplitude oscillating wear conditions. All fillers enhanced the wear resistance and reduced the sliding coefficient of friction but to a different extent. Under sliding wear conditions, fine wollastonite particle‐filled epoxy displayed the highest wear resistance because of the formation of an effective transfer film and the low abrasiveness of the fillers. Under low amplitude oscillating wear conditions, both wollastonite fillers showed much higher wear resistance than short carbon fibers regardless of the filler content. The better adhesion between the wollastonite fillers and the epoxy matrix is responsible for the higher wear resistance under oscillating conditions. The wear tracks were inspected by microscopy to analyze the corresponding wear mechanisms. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 854–863, 2006     

Effect of nano/micro‐mixed ceramic fillers on the dielectric and thermal properties of epoxy polymer composites

Nano/micro ceramic‐filled epoxy composite materials have been processed with various percentage additions of SiO₂, Al₂O₃ ceramic fillers as reinforcements selected from the nano and micro origin sources. Different types of filler combinations, viz. only nano, only micro, nano/micro, and micro/micro particles, were designed to investigate their influence on the thermal expansion, thermal conductivity, and dielectric properties of epoxy polymers. Thermal expansion studies were conducted using thermomechanical analysis that revealed a two‐step expansion pattern consecutively before and after vitreous transition temperatures. The presence of micro fillers have shown vitreous transition temperature in the range 70–80°C compared with that of nano structured composites in which the same was observed as ~90°C. Similarly, the bulk thermal conductivity is found to increase with increasing percentage of micron‐size Al₂O₃. It was established that the addition of micro fillers lead to epoxy composite materials that exhibited lower thermal expansion and higher thermal conductivity compared with nano fillers. Moreover, nano fillers have a significantly decisive role in having low bulk dielectric permittivity. In this study, epoxy composites with a thermal expansion coefficient of 2.5 × 10^?5/K, thermal conductivity of 1.18 W/m · K and dielectric permittivity in the range 4–5 at 1 kHz have been obtained. The study confirms that although the micro fillers seem to exhibit good thermal conductivity and low expansion coefficient, the nano‐size ceramic fillers are candidate as cofillers for low dielectric permittivity. However, a suitable proportion of nano/micro‐mixed fillers is necessary for achieving epoxy composites with promising thermal conductivity, controlled coefficient of thermal expansion and dielectric permittivity. Copyright © 2013 John Wiley & Sons, Ltd.     

Optimization of tribological behavior of nano clay particle with sisal/jute/glass/epoxy polymer hybrid composites using RSM

The tribological properties are one of the most significant properties in many automobile components such as clutch plate, break shoe, engine liner, piston pin, etc. At present work, attempt on nano clay is loaded with natural fibers (sisal and jute), artificial fiber (E‐glass), and epoxy resin. In this investigation, the specific wear rate and coefficient of friction are analyzed by pin on disc apparatus under dry sliding conditions. The experiment design carried by Box–Behnken design on design of experiment techniques with influence wear parameters, namely, filler content, applied load, sliding distance, and sliding velocity; its responses are analyzed by response surface methodology. The regression mathematical models performed for all the responses, and the most influential factors determined by analysis of variance technique, S/N ratio. The results indicate that the coefficient of friction and specific wear rates are minimized with the addition of filler content to the developed composites and further increasing, the response of composites may be varied. Copyright © 2017 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.     

Tribological properties of epoxy/polyurea composite

The tribological behavior of epoxy/polyurea composite under dry friction was investigated. The worn surface morphologies of epoxy and epoxy/polyurea composite have been analyzed using scanning electron microscopy (SEM), and the functional group of epoxy and epoxy/polyurea composite before and after wear have been analyzed by a Fourier transform infrared spectrometer (FT‐IR). It has been found that epoxy terminal groups, which exist in an epoxy molecule, can react with the end group amine of the polyurea copolymer, generating more H? O bonds, which enhances the deformation capacity. Polyurea particles are dispersed uniformly in epoxy matrix before wear, while plastic deformation and distorted domains occur on the worn surface of epoxy/polyurea composite. This indicates that the wear resistance of epoxy/polyurea composite was greatly improved by the addition of polyurea elastomer, which led to low frictional coefficients and wear mass losses. Copyright © 2008 John Wiley & Sons, Ltd.     

The influence of polypyrrole coatings on the mechanical and friction and wear properties of bamboo fiber filled PA6 composites

The effects of polypyrrole coatings on the tensile and tribological properties of bamboo fiber reinforced polyamide 6 (PA6) composites were studied. Tribological tests were conducted using a block‐on‐ring arrangement. It was observed that the polypyrrole coatings played a main role in the tensile‐resistant and wear‐resistant properties of the PA6 composites. The tensile properties were ruled by the fiber‐matrix adhesion. And the excellent tribological performance of the fillers improved the tribological properties of PA6 composites. The optimum content of polypyrrole coating concentration is 7vol%.     

Comparative study of microstructure and tribological behavior of TiC/a‐C:H and a‐C:H coatings in a sand‐dust environment

TiC/a‐C:H and a‐C:H nanocomposite coatings were prepared on AISI 440C steel substrates using magnetron sputtering process. A comparative study was made on their composition and microstructure by Raman spectroscopy and high‐resolution transmission electron microscopy (HRTEM). The tribological properties of two types of carbon‐based coatings were investigated by pin‐on‐disc tribometer under the sand‐dust conditions concerning the influence of applied load, amount of sand and sand particle sizes. The results show that these carbon‐based coatings exhibited high tribological performance with low friction coefficient and wear rate under the sand‐dust environments. However, the TiC/a‐C:H coatings exhibit relatively higher fluctuant friction coefficient as well as higher wear rate in comparison with the a‐C:H coatings under sand‐dust environments. The formation of nanocrystalline hard TiC phase distributed in amorphous carbon matrix decreased the residual stress but significantly increased the hardness and Young's modulus of TiC/a‐C:H coatings, and consequently caused a relatively higher abrasive and fatigue wear loss under the sand‐dust conditions. Copyright © 2010 John Wiley & Sons, Ltd.     

Tribological evaluation of HVOF thermal‐spray coatings as a hard chrome replacement

Hard chrome plating has been used in several different applications in industries that require abrasive sliding wear resistance, such as hydraulic pistons, shafts or bearings. However, the increasing environmental and worker safety pressures on electrolytic hard chrome are leading companies to adopt alternatives. The improvements of the high‐velocity‐oxy‐fuel (HVOF) thermal spray process allow the chromium coating replacement with a comparable or superior surface treatment and are more environmentally friendly. This HVOF process, as a flexible dry‐coating technology, avoids high‐volume waste streams and enables a flexible choice of coating material for each application. The cobalt–chromium‐cemented tungsten carbides are some of the easiest materials to spray and the WC‐10Co‐4Cr coatings have demonstrated superior performance over hard chrome with regard to mechanical and tribological properties. In this work, this coating has been deposited with a Sulzer Metco WokaJet‐400 kerosene fuel spray gun, and the spray conditions have been optimized in order to ensure the best properties of the coatings. The mechanical and tribological properties have been evaluated in coatings sprayed with four deposition conditions that involve different gas flow rates. The most wear‐resistant coating is obtained with those HVOF parameters that prevent decarburization of WC particles and, at the same time, allow an adequate agglomerate melting giving a good intersplat adhesion. The results indicate that HVOF‐sprayed WC‐CoCr coatings are a reliable alternative to electrolytic hard chrome (EHC) in the aeronautical industry to coat landing gear components. In particular, in the dry wear tests, the WC‐CoCr coatings outperform hard chrome coatings in wear resistance. Copyright © 2010 John Wiley & Sons, Ltd.     

高性能耐高温聚合物复合材料的摩擦磨损性能研究

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

A comparative study on wear and friction characteristics of phenolic composite coatings filled with different morphologies ZnO

In this paper, different morphologies ZnO (disk‐like, rod‐like, and nanoparticles) were introduced into phenolic composite coatings to comparatively investigate the tribological properties. The structural and morphological characterization was conducted with Raman spectroscopy, X‐ray diffraction, and scanning electron microscopy. The tribological performances of composite coatings were evaluated using ring‐on‐block tester under dry condition at room temperature. Experimental results indicated that composite coatings filled with 1 wt% ZnO micro‐disks possessed the optimal tribological performances. It was attributed to the strong interfacial interaction between ZnO micro‐disks and phenolic matrix induced by their specific polar structure. Moreover, different loads and sliding speeds were employed to further evaluate the tribological performances of ZnO micro‐disks/phenolic composite coatings. The outcome revealed that ZnO micro‐disks were potential anti‐wear fillers under harsh condition.     

A review on plant fiber reinforced thermoset polymers for structural and frictional composites

In recent past years, utilization of synthetic materials has become a matter of immense concern due to increasing environmental awareness in terms of safety, sustainability and maintaining ecological balance. A substantial amount of work has been carried out on various aspects of plant based natural fiber reinforced thermoset polymer composite materials due to their numerous inherent properties like high specific strength, low cost and degradability. Current issues and challenges associated with mechanical and tribological properties of only plant based natural fiber reinforced thermoset composites have been highlighted in the present study. Various factors influencing mechanical and tribological characteristics have been discussed keeping the focus on plant fiber reinforced thermoset composites. A detailed discussion on mechanical (tensile, compressive, flexural, impact strength) and tribological properties (friction and specific wear rate) have been reported. Interfacial adhesion was found to be a dominating factor with respect to mechanical and tribological properties. Wear and frictional characteristics of plant fiber based thermoset composites can be controlled using suitable fillers and reinforcement orientation. A discussion on interfacial adhesion and its effect on composite performance have also been included.     

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

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

Deposition and characterization of TiAlSiN coatings prepared by hybrid PVD coating system

TiAlSiN coatings with different Si contents were deposited on silicon and high‐temperature alloy by using a hybrid physical vapor deposition coating system, where the cathodic arc ion plating was combined with a twin target mid‐frequency magnetron sputtering. The chemical composition, microstructure, cross‐sectional structure and morphology were carried out by X‐ray photoelectron spectroscope (XPS), X‐ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and transmission electron microscope (TEM), respectively. NanoTest 600 nanomechanical system and ball‐on‐disc friction tester were used to investigate the mechanical and friction properties of TiAlSiN coatings. The worn surface of the TiAlSiN coatings and counterballs were investigated by means of surface profilometer and optical microscope. The wear rates were also measured by surface profilometer. The results showed that the Si addition did not change the coatings growth orientation, and the coating transfered into amorphous phase when the Si content reached about 13.9 at.%. The tribological properties and the hardness were improved by solid solution of Si atoms and grain boundary strengthening of SiN_x amorphous phase with moderate Si content addition. In addition, the SiNx amorphous phase improved oxidation resistance of TiAlN coating, but with a high Si content (more than 8.3 at.% in this work) the agglomeration of SiN_x amorphous phase would reduce the mechanical properties and oxidation resistance of the coating. Copyright © 2014 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.     

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

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

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.     

Modified epoxy coatings on mild steel: Tribology and surface energy

A commercial epoxy diglycidylether of bisphenol-A (DGEBA) was modified by adding fluorinated poly(aryl ether ketone) fluoropolymer and in turn metal micro powders (Ni, Al, Zn, and Ag) and coated on mild steel. Two curing agents were used; triethylenetetramine (a low temperature curing agent) and hexamethylenediamine (a high temperature curing agent) for understanding the curing temperature effect on the properties. Variations in tribological properties (dynamic friction and wear) and surface energies with varying amounts of metal powders and curing agents were evaluated. When cured at 30 °C, dynamic friction and wear decrease significantly due to phase separation reaction being favored between the fluoropolymer and the epoxy. However, when cured at 80 °C, friction and wear increase; this can be explained in terms of a crosslinking reaction favored at that temperature. There is a significant decrease in surface energies with the addition of modifiers.