Electrodeposition and characterization of chromium–tungsten carbide composite coatings from a trivalent chromium bath

The electrodeposition of chromium from a trivalent chromium bath has been described in this work. The electrocomposite coatings of chromium with hard abrasive particles were investigated. The chromium–tungsten carbide (Cr? WC) composite coatings were obtained by suspending different concentrations of WC particles in a trivalent chromium plating solution to improve the various properties of the chromium deposit layers. The effect of operating conditions on the deposit layers has been studied. On the other hand, the effect of non‐ionic polymeric surfactant [nonyl phenol ethoxylate with 12 units of ethylene oxide (NPE)] as an additive in enhancing the incorporation of the WC ceramic particles in the chromium metal matrix was investigated. It was found that the co‐deposition of the WC ceramic particles depends on the concentration of the additive and its efficiency in reducing the surface tension of the electroplating solution. The mechanism of incorporation of WC particles into a growing deposit was suggested and discussed in view of the zeta potential and degree of wetability of WC particles in the plating solution. Furthermore, the adsorption behaviour of the additive on WC particles was analysed according to the Frumkin isotherm. The surface morphology and the distribution of WC in the chromium metal matrix were investigated. The properties of the deposit layers, hardness, corrosion resistance and wear resistance were determined and compared with free chromium deposits. The test results reveal that the Cr? WC deposit layer shows better performance compared with the chromium‐free deposit. Copyright © 2005 John Wiley & Sons, Ltd.     

Micromechanical and tribological properties of nanocrystalline coatings of iron-tungsten alloys electrodeposited from citrate-ammonia solutions

The correlation between the composition, morphology, and properties of Fe-W alloy coatings containing up to 29 at % tungsten was investigated by means of scanning electron microscopy, X-ray diffraction analysis, and the wear resistance and nanohardness measurements. The coatings were deposited from the citrate-ammonia bath at a direct current, the current densities were ranged from 10 to 100 mA/cm². It is shown that, in contrast to metallurgical iron, the Fe-W coatings are nanocrystalline (amorphous, the grain size is 3.0–4.0 nm). This structure of alloys allows us to produce the coatings with a nanohardness of ～13 GPa, which is comparable to the electrolytic chromium coatings. The study of wear resistance of thus obtained coatings reveals their oxidation in the course of dry friction; as a result, the oxygen content in the debris increases by 2–3 times, and the wear volume due to the tribooxidation exceeds that for similar hard Co-W and electrolytic chromium coatings.     

Preparation of NiCrBSi‐WC brazed coating and its microstructure characteristics

WC–Ni composite coatings were developed by the powder cloth and the vacuum brazing technology. The wear resistance and the corrosion resistance of the brazed WC–Ni coatings were investigated. The peeling coating samples were prepared by using solder mask during brazing. The microstructures for the powder cloth and for the brazed coatings were characterized by scanning electron microscopy. The distribution of elements in the different area of the brazed coatings was determined by energy dispersive X‐ray maps. It shows that the segregation of chromium carbides occurs during brazing. Apart from penetrating into the interspaces of WC particles, the Ni‐based filler can also infiltrate and spread on the substrate surface. Copyright © 2012 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.     

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.     

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.     

Enhancement of tribological performance of epoxy bulk composites and composite coatings using micro/nano fillers: a review

Epoxies in the form of bulk and coatings have been used throughout the years for a wide spectrum of applications in various industries ranging from aerospace, oil and gas, petrochemical and marine to several others. Their use in tribological applications, those involving a range of contact conditions and where the requirement is exceptionally low wear and friction coefficient, is often limited by the properties of the pristine epoxy matrix such as low load bearing capacity combined with low thermal conductivity values. These properties have been improved by the addition of nano‐fillers, and numerous studies have been carried out in this regard. This paper presents a detailed review of the works carried out in the recent years where addition of nano‐fillers to formulate epoxy‐based composites and coatings has shown a substantial improvement in wear and friction properties thereby enhancing their potential to be used in demanding tribological applications such as solid lubricant in bearings, as wear‐resistant protective coatings in rotating and stationary equipment and for applications in the construction industry such as floorings and airport runway repairs. Copyright © 2016 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.     

Effect of Y2O3 on microstructural characteristics and wear resistance of cobalt‐based composite coatings produced on TA15 titanium alloy surface by laser cladding

The effects of Y₂O₃ on the microstructure, phase composition of the coatings, microhardness and wear resistance of cobalt‐based composite coatings prepared by laser cladding were investigated. The TA15 titanium alloy was selected as substrate which the cobalt‐based composite powder with different content of Y₂O₃ was cladded on. The microstructure of the coatings was observed by scanning electron microscope (SEM) and metallurgical microscope. The phase structure of the coatings was determined by X‐ray diffraction (XRD), and the microhardness and wear resistance of the coatings were measured by hardness tester and wear testing machine. The results show that the rare earth oxide Y₂O₃ can refine and purify the microstructure of the coatings, reduce the porosities and cracks and improve compactness of the coatings. Moreover the addition of Y₂O₃ improves the microhardness of the coatings and reduces the friction coefficient, thus improving the wear property of the coatings. And the wear resistance of the coating with Y₂O₃ has improved about 50 times; the highest value of microhardness in the coating is HV1181.1. And 0.8 wt% content of Y₂O₃ in the coating is the best choice for improving the microhardness and wear resistance of the coating. It is feasible to improve the microstructure and tribological properties of laser cladding coatings by adding of Y₂O₃. Copyright © 2014 John Wiley & Sons, Ltd.     

Effects of intermediate Ar plasma treatments on CrN coating microstructures and property evolutions

Chromium nitride (CrN) coatings with different steps of intermediate argon plasma treatments were deposited with primary (200) orientation by multi‐arc ion plating technique. By virtue of scanning electron microscopy, X‐ray diffraction and high‐resolution transmission electron microscopy, the influence of intermediate argon plasma treatments on the coating microstructures, mechanical properties and corrosion properties as well as tribological behaviors in artificial seawater solutions were systematically investigated. It was assumed that the mechanical properties, adhesion strength, corrosion and tribological performances of coatings depended on argon plasma treatment steps. High‐performance coatings could be obtained by proper plasma treatment steps. The superior anti‐corrosion ability of coating with appropriate treatment steps may be ascribed to the increased charge transfer resistance due to alternative interface and CrN layer and the compact microstructure. On the other hand, the excellent tribological performances in seawater conditions may be attributed to the enhanced mechanical properties. Otherwise, further increase in treatment steps was assumed to distinctly increase defects and deteriorate the coating integrity thus weakening coating properties and behaviors. Copyright © 2016 John Wiley & Sons, Ltd.     

Influence of powder-characteristics on the microstructure of ceramic plasma spray coatings

Summary The relationship between the properties of plasma spray powders and the resultant coating has been investigated. ZrO₂ powders, differing in grain size, state of agglomeration and morphology, have been used and coating properties such as microstructure, porosity, roughness, hardness, and wear resistance are described. Agglomerated powders cause high porosity, while sphericalized particles yield very dense layers. The homogeneity of an agglomerate is also responsible for the homogeneity of the microstructure of the coating. By selecting powders with defined characteristics it is possible to produce plasma spray coatings with defined properties; the microstructure of the layers can be varied over a wide range.     

Protective yttria coatings of melting crucible for metallic fuel slugs

As one of the candidate coating materials for a melting crucible, yttrium oxides were deposited on graphite and niobium substrates using slurry and plasma spraying methods. Thermal cycling tests and interaction studies between U–Zr/U–Zr–RE fuel melt and the Y₂O₃ coatings were carried out to evaluate the performance as reusable coatings for a melting crucible. A multi‐layer coating method was also applied to overcome the issue of a thermal expansion mismatch between the coating and substrate. The results showed that the plasma‐sprayed coatings showed a good consolidation after deposition compared to slurry coating. The plasma‐sprayed Y₂O₃ coating on the niobium substrate showed better thermal cycling resistance than those coated on a graphite substrate. The proposed TaC/Y₂O₃ double‐layer coating which was plasma‐sprayed on the niobium substrate showed improved characteristics with no reaction layer formation and no separation from the substrate after the interaction with the U–Zr–RE melt. Copyright © 2014 John Wiley & Sons, Ltd.     

The influence of anti‐wear additive ZDDP on doped and undoped diamond‐like carbon coatings

Diamond‐like carbon (DLC) coatings are recognised as a promising way to reduce friction and improve wear performance of automotive engine components. DLC coatings provide new possibilities in the improvement of the tribological performance of automotive components beyond what can be achieved with lubricant design alone. Lubricants are currently designed for metallic surfaces, the tribology of which is well defined and documented. DLC does not share this depth of tribological knowledge; thus, its practical implementation is stymied. In this work, three DLC coatings are tested: an amorphous hydrogenated DLC, a silicone‐doped amorphous hydrogenated DLC and a tungsten‐doped amorphous hydrogenated DLC. The three coatings are tested tribologically on a pin‐on‐reciprocating plate tribometer against a cast iron pin in a group III base oil, and a fully formulated oil that consists of a group III base oil and contains ZDDP, at 100 °C for 6 h and for 20 h in order to determine whether a phosphor‐based tribofilm is formed at the contact. The formation of a tribofilm is characterised using atomic force microscopy and X‐ray photoelectron spectroscopy techniques. The main findings of this study are the formation of a transfer film at the undoped, amorphous hydrogenated DLC surface, and also the tungsten amorphous hydrogenated DLC having a significant wear removal during the testing. The three coatings were found to have differing levels of wear, with the tungsten‐doped DLC showing the highest, the silicon‐doped DLC showing some coating removal and the amorphous hydrogenated DLC showing only minimal signs of wear. Copyright © 2015 John Wiley & Sons, Ltd.     

Structure and tribological properties of Cu–PU–PTFE composite coatings prepared by low‐energy electron beam dispersion with glow discharge

Polytetrafluoroethylene (PTFE) composite coatings doped copper acetate and polyurethane (PU) were prepared on rubber substrate by low‐energy electron beam dispersion technique. The effects of dopant and glow discharge treatment on the surface morphology, structure and tribological properties of the coatings were investigated. The results showed that Cu–PTFE composite coatings form uniform surface and dense column structure with spherical aggregations under glow discharge treatment. PU coating shows the large size of protuberance structure but PU–PTFE coating presents spherical structure. Both of the coatings become relative dense and smooth after discharge treatment, and Cu–PU–PTFE composite coatings possess a smoother surface and lower polar component of surface energy. Cu doping weakens the crystallinity and ordering degree of composite coatings, but glow discharge increases the ordering degree and branched structure of C―H groups. Friction experiment indicated that Cu fails to improve the wear resistance of PTFE coatings but glow discharge treatment can do it. Cu–PU–PTFE coatings after discharge treatment have the higher wear resistance and lower coefficient of friction. Copyright © 2016 John Wiley & Sons, Ltd.     

Surface/interface phenomena in nano‐multilayer coating under severing tribological conditions

An extensive study of surface/interface phenomena during wear of an adaptive TiAlCrSiYN/TiAlCrN nano‐multilayer coating deposited using physical vapor deposition was undertaken under increasingly severe tribological conditions associated with dry end milling of H13 hardened tool steel. The results of FEM modeling on the temperature/stress distribution at different cutting speeds outline actual cutting conditions on the both rake and flank frictional surfaces of the coated tool. Studies of the surface/interface phenomena were made by means of SEM/high‐resolution transmission electron microscopy/XPS analyses. Results demonstrate that intensifying tribological conditions facilitates improved wear performance of the adaptive coating layer. In extreme tribological conditions of ultra‐performance machining (cutting speed of 500 m/min), the self‐organization process establishes entirely through the formation of a nano‐scale layer of dynamically re‐generating tribo‐ceramic films. The formation of these surface nano‐films results in exceptionally efficient protection of the underlying coating layers. In response to the extreme external environment, the coating layer remained almost undamaged during a long run, demonstrating the capacity to efficiently replenish necessary tribo‐ceramic films. In this way, interconnection of various surface and undersurface processes is established in the hierarchically structured tribo‐films/coating layer. This integral performance is responsible for exceptional wear resistance under intensifying and extreme tribological conditions. Copyright © 2016 John Wiley & Sons, Ltd.     

碳钢低压冷喷涂铝涂层的海水耐蚀性

本文以Al和10%体积比Al2O3的混合粉末为原料,使用便携式低压冷喷涂设备,在Q235碳钢基体上喷涂了Al涂层. 测试涂层自腐蚀电位及动电位极化曲线,结合扫描电镜观察涂层表面及截面微观形貌,研究了低压冷喷涂Al涂层在海水中电化学腐蚀行为,并与高压冷喷涂和热喷涂铝涂层的耐蚀性比较. 结果表明,低压冷喷涂铝涂层结构较为致密,其耐蚀性比高压冷喷涂铝涂层的略低,而明显优于热喷涂铝涂层.     

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.     

三种微弧氧化镁合金高温油润滑条件下的摩擦学性能

选择三种常用的基础电锯液：硅酸盐、磷酸盐、铝酸盐制备了镁合金微弧氧化（MAO）膜,研究了这三种氧化膜在高温油润滑条件下的摩擦学性能．利用SRV摩擦实验机,使样品在20N的外加载荷,振幅3mm,频率5Hz的条件下,与直径10mm的CCr15钢球分别在室温、80℃、100℃和120℃四个温度,油润滑条件下对磨,结果表明硅酸盐膜层具有最好的摩擦性能,另外两种膜层不仅没有起到抗磨损的作用,反而使磨损加剧．     

Properties of composite nickel-cobalt-aluminum oxide coating deposited from chloride electrolyte

Effect of the cathodic current density, pH value, electrolyte temperature, and concentration of aluminum oxide introduced into the electrolyte on the wear, microhardness, and internal stresses in nickel-cobalt-aluminum oxide composite electrolytic coatings was studied. It is shown that the coatings under consideration can be used instead of chromium coatings.