Investigation of tribological properties of micro-arc oxidation ceramic coating on Mg alloy under dry sliding condition

To enhance wear resistance of Mg alloy, micro-arc oxidation (MAO) ceramic coatings on Mg substrate were prepared in silicate electrolyte under various currents. It was found that the surface roughness and thickness of MAO coating were increased with the increase of current. The dry tribological tests showed that the friction coefficient and wear resistance of thicker coatings (obtained under currents of 3?A and 4?A) were much higher than that of Mg alloy and the thin coating (obtained under current of 2?A), meanwhile the lifetime of the coating obtained under 4?A was longer than the other coatings under higher load. The wear type of thin MAO coating was slight abrasive wear under low load, whereas translated to severe adhesive wear under high load. While the main wear mechanism of thick MAO coating was slight abrasive wear or scratch under the given test condition, which was attributed to the thick intermediate layer improved load support for the soft substrate. The tribological study indicated that the MAO coating obtained under 4?A current had better wear resistance and life time due to its compact microstructure and thickness.     

Cr/CrAlSiN涂层海水环境摩擦学性能及耐蚀研究

采用多弧离子镀技术,在316不锈钢基底表面制备Cr/CrAlSiN涂层,通过SEM、XRD表征涂层成分,利用多功能摩擦试验机对涂层在海水环境下的摩擦学性能测试。结果表明:相对于316L基底,在摩擦实验中,由于海水的润滑作用,涂层表现了良好的摩擦性能。电化学阻抗谱测试中Cr/Cr Al Si N涂层有效的保护了基底。     

A study of biotribological behavior of DLC coatings and its influence to human serum albumin

Diamond-like carbon (DLC) coatings has been synthesized on NiTi alloy substrates by arc enhanced magnetic sputtering (AEMS) system using graphite targets. The tribological behavior indicates that the friction coefficient and wear rate of DLC coatings deposited on NiTi alloy substrates is relatively higher in ambient air than that in simulated body fluid (SBF). In human serum albumin (HSA) solution, though the friction coefficient is higher than that in SBF, but it has quite low wear rate. The Raman spectrum shows that the low friction coefficient of DLC coatings is due to the graphitization during sliding, and the degree of graphitization is relatively lower in both SBF and HSA solution than them in ambient air. The friction mechanism of DLC coatings at different environments is then proposed. On the other hand, the kinematic viscosity and sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) measurements show that the DLC coatings cannot induce the thermal and mechanical denaturation of HSA during sliding.     

Structures and tribological performances of PEEK (poly-ether-ether-ketone)-based coatings designed for tribological application

Driven by economical and ecological reasons, thermoplastic-based coatings become a potential solution for anti-wear purpose. Two coating design concepts, flame spraying and printing PEEK (poly-ether-ether-ketone)-based coatings on Al substrate, were introduced in this paper. An amorphous PEEK coating was obtained by these two techniques. After being annealed, the coating presents a semi-crystalline structure. The friction and wear behaviors of PEEK-based coatings were investigated by means of ball-on-disc tests. The results show that PEEK coatings exhibit an excellent tribological performance with a relatively low coefficient of friction and wear rate. The semi-crystalline PEEK coating exhibits a lower friction coefficient and wear rate than the amorphous one. The additions of micron-sized particles such as SiC and graphite in PEEK coating can improve significantly the coating wear resistance.     

Tribological behavior of the polyamide composite coating filled with different fillers under dry sliding

The polyamide (PA) composite coating filled with the particles of microsized MoS₂, microsized graphite, and nano‐Al₂O₃, respectively, were prepared by flame spraying. The friction and wear characteristics of the PA coating and composite coating filled with the varied content of filler under dry sliding against stainless steel were comparatively investigated using a block‐ring tester. The morphologies of the worn surfaces and transfer films on the counterpart steel ring were observed on a scanning electron microscope. The result showed that the addition of fillers to the composite coatings changed significantly the friction coefficient and wear rate of the coatings. The composite coatings filled with a low level content of fillers showed lower wear rate than did pure PA coating under dry sliding; especially the MoS₂/PA composite coating had the lowest wear rate among these composite coatings. The composite coatings with a high level content of fillers had higher wear rate than did pure PA coating, except of the Al₂O₃/PA composite coating. The bonding strengths between the polymer matrix and fillers changed with the content of the fillers, which accounted for the differences in the tribological properties of the composite coatings filled with the varied content fillers. On the other hand, the difference in the friction and wear behaviors of the composite coatings and pure coating were attributed to the difference in their worn surface morphologies and transfer film characteristics. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Effect of electrolyte concentration on the tribological performance of MAO coatings on aluminum alloys

Micro-arc oxidation (MAO) is an efficient approach to improve the hardness, wear resistance, and other properties of aluminum alloys. In order to investigate the effect of the electrolyte concentration on the properties of MAO coatings for LY12 alloy, the voltage variation during the MAO process was recorded. The surface morphologies and phase compositions of the coatings produced with different electrolytes were investigated using scanning electron microscopy and X-ray diffraction, respectively. The roughness and thickness of the coatings were measured using a pocket roughness meter and an eddy-current thickness meter, respectively. The tribological performances of the coatings were investigated against GCr15 bearing steel on a ball-on-disc wear tester in open air. The results showed that with an increase in the Na₂SiO₃ content, the working voltage of the MAO process decreased, the roughness and thickness of the coatings increased significantly, and the relative content of the α-Al₂O₃ phase decreased. With an increase in the KOH content, the working voltage decreased slightly, the roughness and thickness of the coatings increased slightly, and the α- and γ-Al₂O₃ phase contents remained unchanged. The friction coefficient and wear rate of the coatings increased with an increase in the Na₂SiO₃ and KOH concentrations. A decrease in the porosity and roughness and an increase in the α-Al₂O₃ content of the coatings reduced their wear mass loss.     

Effects of graphene content in alkaline silicate electrolyte on AA1060 pure aluminum micro-arc oxidation coating

Ceramic coatings were obtained by micro-arc oxidation (MAO) on the surface of AA1060 pure aluminum in alkaline silicate electrolyte with the addition of graphene. The effects of graphene contents in the range of 0–.30 g/L in the electrolyte on surface morphology, corrosion resistance, and wear resistance of the ceramic coatings were investigated. The outer surface structure, outer surface element content, coating cross-section structure, coating cross-section element content, coating/substrate interface structure, and coating phase were characterized by scanning electron microscope and X-ray diffraction. Potentiodynamic polarization and electrochemical impedance spectroscopy were used to evaluate the corrosion behavior of MAO samples in a 3.5-wt% NaCl solution. In addition, the resistance to sliding and abrasive wear of the oxide coating were studied experimentally. The results show that the alkaline silicate electrolyte with the addition of graphene has a significant effect on the characteristics of MAO coating. The performance of micro-arc oxide coatings is best when the graphene content in the electrolyte is .15 g/L, the average thickness of the film is 7.24 μm, the average pore size is 6.07 μm, the impedance value is approximately 4.01 × 106 Ω, and its friction coefficient is .55.     

Preparation and tribocorrosion performance of CrCN coatings in artificial seawater on different substrates with different bias voltages

The CrCN coatings have been prepared by multi-arc ion plating technology with different bias voltages on 316?L, TC4 and H65 substrates, respectively. The prepared CrCN coatings have been characterized by XRD, SEM, and EDS, respectively. The mechanical properties, electrochemical corrosion behavior, and tribological performance of prepared coatings were tested by microhardness tester, scratch tester, electrochemical workstation, and friction and wear tester, respectively. Results show that the CrCN coatings with bias voltage of ?50?V presented the finer grain size, denser structure, better comprehensive mechanical properties and friction, and better corrosion resistance than the CrCN coatings with a bias voltage of ?30?V. The coating on TC4 substrate show the lower hardness, the better adhesion, the better electrochemical properties and tribological properties than that on 316?L substrate. The coatings based on H65 Cu substrate presented the worst electrochemical and wear properties. The CrCN coating with a bias voltage of ?50?V on TC4 substrate is an optimal candidate in artificial seawater for tribocorrosion.     

Advanced TiC/a-C:H nanocomposite coatings deposited by magnetron sputtering

TiC/a-C:H nanocomposite coatings have been deposited by magnetron sputtering. They consist of 2–5 nm TiC nanocrystallites embedded in the amorphous hydrocarbon (a-C:H) matrix. A transition from a columnar to a glassy microstructure has been observed in the nanocomposite coatings with increasing substrate bias or carbon content. Micro-cracks induced by nanoindentation or wear tests readily propagate through the column boundaries whereas the coatings without a columnar microstructure exhibit substantial toughness. The nanocomposite coatings exhibit hardness of 5–20 GPa, superior wear resistance and strong self-lubrication effects with a friction coefficient of 0.05 in air and 0.01 in nitrogen, under dry sliding against uncoated bearing steel balls. Especially, reversible transitions from low to ultra-low friction are observed if the atmosphere is cycled between ambient air and nitrogen. The lowest wear rate is obtained at high humidity.     

Tribological properties of polyimide coatings filled with PTFE and surface‐modified nano‐Si3N4

Polyimide (PI) coatings filled with PTFE and nano‐Si₃N₄ were prepared by a spraying technique and successive curing. Nano‐Si₃N₄ particles were modified by grafting 3‐aminopropyltriethoxysilane to improve their dispersion in the as‐prepared coatings. Friction and wear performances and wear mechanisms of the coatings were evaluated. The results show that the incorporations of PTFE and modified nano‐Si₃N₄ particles greatly improve the friction reduction and wear resistance of PI coating. The friction and wear performance of the composite coating is significantly affected by the filler mass fraction and sliding conditions. PI coating incorporated with 20 wt % PTFE and 5 wt % modified nano‐Si₃N₄ displays the best tribological properties. Its wear rate is more than one order of magnitude lower and its friction coefficient is over two times smaller than that of the unfilled PI coating. Differences in the friction and wear behaviors of the hybrid coatings as a function of filler or sliding condition are attributed to the filler dispersion, the characteristic of transfer film formed on the counterpart ball and the wear mechanism of the coating under different sliding conditions. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40410.     

Tribological behavior of graphene reinforced chemically bonded ceramic coatings

To investigate tribological behavior of graphene reinforced chemically bonded ceramic coatings at different temperatures, tribological tests at room temperature, 200 °C and 500 °C were carried out. Results show that the fracture toughness and the hardness of the coating are improved with the introduction of graphene. Besides, the friction coefficient of the coating decreases with the addition of graphene at the room temperature and 200 °C. The coating without graphene achieves the similar friction coefficient at all temperatures. However, the coating with graphene achieves the lowest friction coefficient at 200 °C, and achieves the highest at 500 °C. In addition, the wear rate of the coating decreases with the increase of graphene. Besides, the wear rate at 200 °C is almost similar with that at room temperature. In contrast, the wear rate at 500 °C is much larger than those at room temperature and 200 °C. The mechanisms for graphene to decrease the friction coefficient and improve the wear resistance of chemically bonded ceramic coatings at evaluated temperatures are clarified.     

粘结剂对超音速火焰喷涂碳化钨涂层磨粒磨损性能的影响

采用超音速火焰喷涂(HVOF)工艺在35钢基体上制备了WC-10Ni涂层和WC-12Co涂层,研究了镍、钴这两种粘结剂对WC涂层的显微硬度、摩擦系数和抗磨粒磨损性能的影响,采用扫描电子显微镜观察涂层磨损前后的表面形貌,探讨了WC涂层的磨粒磨损机理。结果表明,以HVOF方法制备的2种WC涂层均有较高的显微硬度,WC-10Ni涂层和WC-12Co涂层与SiC砂纸摩擦副之间的干摩擦系数相差不大。2种涂层在低载荷下均有较好的抗磨粒磨损性能,但在较高载荷下WC-12Co涂层的抗磨性明显优于WC-10Ni涂层。2种涂层的磨粒磨损形式主要为均匀磨耗磨损,磨损机理以微切削和微剥落为主。WC-12Co涂层的磨损表面损伤较轻微,综合性能优于WC-10Ni涂层。     

Effect of specimen orientation and heat treatment on electroless Ni-PTFE-MoS<Subscript>2</Subscript> composite coatings

In this study, the effects of simultaneous co-deposition of polytetrafluoroethylene (PTFE) and MoS₂ particles on tribological properties of electroless nickel (EN) coating were studied. The influences of specimen orientation and heat treatment on EN-PTFE-MoS₂ composite coatings were also investigated. Scanning electron microscopy was used to study the morphology of coatings and the distributions of the lubricant particles in the deposits. Chemical analyses of coatings were done by electron dispersive spectrometry. The phases of the coatings were identified by X-ray diffraction utilizing CuKα radiation. Wear and friction properties of the coatings were also determined by pin-on-disk wear tester. The wear investigations showed that the EN-PTFE-MoS₂ composite coating performs better than EN-PTFE and EN-MoS₂ coatings in terms of friction coefficient and wear resistance. PTFE and MoS₂ contents of the EN-PTFE-MoS₂ coating were increased by changing the specimen orientation from vertical to horizontal configuration, which leads to enhancement in tribological properties of the coating. After heat treatment, the wear rate of EN matrix composite coating decreased with corresponding change in phase structure.     

Corrosion and friction resistance of TiVCrZrWNx high entropy ceramics coatings prepared by magnetron sputtering

High entropy alloy coatings have attracted much attention because of their high hardness, low-level fault energy, and chemical stability. Nevertheless, this type of coating would inevitably suffer from wear, corrosion, aging, and so on. Hence, a novel coating with corrosion and friction resistance would be constructed for broadening its application scenarios. In this work, TiVCrZrWN_x high entropy ceramics coatings were prepared by reactive magnetron sputtering. The microstructure, mechanical properties, friction, and corrosion resistance of the coatings deposited at different nitrogen flow rates have been studied. The microstructure of TiVCrZrWN_x coatings is strongly dependent on the nitrogen flow rate and forms a stable FCC structure when the nitrogen flow rate reaches 24 sccm. The pure TiVCrZrW coating is 15.65 GPa, with the increase of nitrogen flow rate (24 sccm), the coating hardness reaches 21.27 GPa. The corrosion resistance of the coatings also increases continuously. According to the results of the impedance spectrum and polarization curve, the charge transfer resistance value of the coating gradually increases with the content of nitrogen, the current density rapidly decreases to a minimum as the potential increases. In terms of tribological behavior, the formation of V₂O₅ during the sliding in seawater could significantly reduce the coefficient of friction from 0.603 to 0.383. Therefore, TiVCrZrWN_x HECs coatings simultaneously possess high hardness, toughness, and excellent resistance to friction and corrosion, which is expected to provide a new and reliable method for the research field of coatings in the maritime field.     

Effect of multi-walled carbon nanotubes as reinforced fibres on tribological behaviour of Ni–P electroless coatings

After multi-walled carbon nanotubes (MWNTs) were modified and dispersed uniformly in electrolyte, the MWNTs composite coatings were prepared by electroless deposition. Hardness tests were carried out using a Vickers Hardness indenter. The friction and wear behavior of the Ni–P–MWNTs composite coatings in carbon-steel rings were investigated by using a ring-on-plate wear tester at pure liquid paraffin. Moreover, the friction and wear behavior of nine kinds of wear combinations, which were composed of plates and rings of different composite coatings, were studied. The experimental results indicated that addition of MWNTs would result in an increase in microhardness and an improvement of tribological properties of the Ni–P composite coating significantly. The Ni–P–MWNTs composite coatings revealed lower wear rate and friction coefficient compared with Si–C composite coatings. Moreover, the wear combination, which composed of the Ni–P–MWNTs composite coatings, showed a more excellent ability of friction-reduction and wear resistance than other combinations, and their friction coefficient and wear rate were 0.1087 and 1.49 × 10^− 6 kg/m, respectively.     

配副材料对镍-磷-碳化硅化学复合镀层摩擦磨损性能的影响

利用化学复合镀技术制备了Ni-P-SiC复合镀层,研究了镀层的表面形貌、组织、显微硬度等性能,并对比研究了不同配副材料对Ni-P-SiC复合镀层和Ni-P镀层摩擦磨损性能的影响。结果表明,Ni-P-SiC复合镀层的显微硬度较Ni-P镀层有所提高;与GCr15钢球对磨时,Ni-P-SiC复合镀层发生严重的塑性变形和粘着磨损,但磨损率比Ni-P镀层稍有降低;与Si3N4陶瓷球对磨时,两者的磨损率相当,且均比与GCr15球对磨时小1个数量级,其主要磨损机理为磨粒磨损。配副材料的磨损率变化规律与镀层一致。在一定条件下,陶瓷材料与Ni-P镀层或Ni-P-SiC复合镀层是较匹配的摩擦副。     

Effect of current density and polytetrafluoroethylene on the properties of micro-arc oxide coating of pure aluminum

Micro-arc oxidation (MAO) is a surface treatment technology that enhances the surface properties of valves by creating a ceramic oxide layer on the metal surface. The goal of this study is to investigate the influence of current density on the properties of aluminum coatings during preparation and to improve the tribological properties of MAO/PTFE self-lubricating films on the coating surface. The characterization of the coating was performed using X-ray photoelectron spectroscopy, X-ray diffraction, Raman spectra, and energy dispersive spectroscopy. The roughness, hardness, and elastic modulus of the coatings were tested using atomic force microscopy and nanoindentation. Tribological experiments were conducted to evaluate the tribological properties of the coatings. The experimental results show that the friction coefficient (COF), roughness, hardness, and elastic modulus of the MAO coating increase with the increase of current density. Additionally, the friction coefficient of the MAO composite coating significantly decreases after the addition of polytetrafluoroethylene (PTFE), improving the service life and application range of the metal coating. These findings are expected to promote the development of valve metal in various application fields.     

Tribological application of carbon nanotubes in a metal-based composite coating and composites

Ni-P-carbon nanotube (CNT) composite coating and carbon nanotube/copper matrix composites were prepared by electroless plating and powder metallurgy techniques, respectively. The effects of CNTs on the tribological properties of these composites were evaluated. The results demonstrated that the Ni-P-CNT electroless composite coating exhibited higher wear resistance and lower friction coefficient than Ni-P-SiC and Ni-P-graphite composite coatings. After annealing at 673 K for 2 h, the wear resistance of the Ni-P-CNT composite coating was improved. Carbon nanotube/copper matrix composites revealed a lower wear rate and friction coefficient compared with pure copper, and their wear rates and friction coefficients showed a decreasing trend with increasing volume fraction of CNTs within the range from 0 to 12 vol.% due to the effects of the reinforcement and reduced friction of CNTs. The favorable effects of CNTs on the tribological properties are attributed to improved mechanical properties and unique topological structure of the hollow nanotubes.     

Strongly adherent Al2O3 coating on SS 316L: Optimization of plasma spray parameters and investigation of unique wear resistance behaviour under air and nitrogen environment

Plasma spray deposition of Al₂O₃ is a well-established technique for thick ceramic coatings on various substrates to shield them from corrosion and wear. Owing to its high hardness, aluminum oxide is known to protect stainless steel substrates from wear. However, the plasma process requires optimization for desired coating thickness and adhesion strength. It is also necessary to understand the sensitivity of friction and wear resistance of the deposited coating on exposed environment for evaluation of service life. The study offers comprehensive investigation on plasma process parameters for the development of strongly adherent aluminium oxide coatings on SS 316L substrate. Impact of environment like dry air and dry nitrogen on tribological properties of the coatings was also investigated. Dense adherent coatings of alumina could be deposited on SS 316L at a plasma power of 20 kW with an intermediate bond coat of NiCrAlY to enhance the adhesion properties. The effects of stand-off distance and bond coat thickness on adhesion strength were additionally examined. Further, the coatings were characterised for phase composition, microstructure, microhardness and wear resistance potential. Reciprocating wear tests of the coatings were carried out using ball on disc reciprocating tribometer at different loading conditions (5, 10 and 15 N) at constant (5 Hz) sliding frequency. Unlike the coefficient of friction (COF), wear volume was found to increase with an increase in normal load. These adherent coatings revealed promising properties for the applications where the tribological failure of SS 316L in dry air or dry nitrogen environment is to be controlled.     

Effect of ultra accurate control of electrolyte temperature on the performance of micro arc oxidation ceramic coatings

The technique of micro arc oxidation (MAO) uses arc discharge and high-voltage breakdown to produce a ceramic layer on valve metal surfaces. However, the common method of MAO requires immersing the workpiece in an electrolyte solution, which can result in elevated temperatures due to the arc discharge, thus negatively affecting the coating's quality and performance. This article investigates the influence of electrolyte temperature on the performance of MAO ceramic coatings, with the assistance of a robotic arm enabling valve metal reaction without immersion in the electrolyte, and precise control of electrolyte temperature through a MAO temperature monitoring system. Various techniques, such as scanning electron microscopy (SEM), hardness testing, electrochemical corrosion experiments, and friction-wear experiments, were utilized to characterize the performance of the prepared coating. The results indicate a nonlinear correlation between the temperature of the electrolyte and the thickness and hardness of the ceramic coating. The corrosion and wear resistance of the MAO ceramic coatings initially improve with increasing electrolyte temperature but eventually deteriorate. At an electrolyte temperature of 40 °C, the MAO ceramic coating exhibits the optimal corrosion and wear resistance. The variation in electrolyte temperature affects the reactivity of the electrolyte ions, leading to changes in the morphology and properties of the resulting MAO ceramic coating. These findings offer valuable insights into the interaction mechanism between electrolyte temperature and the properties of the resulting MAO ceramic coating. This is of great significance in optimizing the MAO process for specific applications and improving the overall performance of ceramic coatings.