Preparing SiC/diamond coatings via chemical vapor deposition of SiC on diamond-coated graphite and their frictional properties

SiC/diamond coatings with excellent frictional properties were successfully prepared using graphite as substrate. Diamond particles with size of 25–38 μm were firstly bonded on graphite substrate through PVA glue, followed by chemical vapor deposition (CVD) of SiC with varied MTS flow on the diamond-coated graphite substrate to enhance the adhesion of diamond particles. The influence of the MTS flow on the SiC coatings was investigated. The results showed that polycrystalline SiC coating with good crystallinity has been obtained. With MTS flow increasing, the SiC grains feature increased surface roughness and greater sizes of the SiC crystallite resulting from the co-deposition of SiC and carbon with increased carbon containing species. Reciprocating sliding wear tests were conducted to investigate the coefficient of friction. With increasing applied load, while the low-flow specimens showed a remarkable increase in the friction coefficient resulting from degradation of the SiC coatings, the high-flow specimens maintained a relatively low friction coefficient during wear tests indicating strong holding force to diamond particles of the SiC coatings. The reason for low friction coefficient of the high-flow specimens was that GCr15 steel ball was wearing by the SiC/diamond coatings with good affinity to the substrate resulting in a flat–flat contact on the contact area.     

Cr–C/h-BN 自润滑复合镀层的制备与摩擦学性能

在三价铬Cr–C镀液中添加1~5 g/L的h-BN自润滑微粒,运用直流电沉积技术在Q235碳素结构钢基体上制备了Cr–C/h-BN复合镀层。利用扫描电镜(SEM)、X射线衍射仪(XRD)、显微硬度计、摩擦磨损试验机等设备分析了h-BN微粒添加量、电流密度等工艺参数对镀层组织和性能的影响。结果表明:在电流密度20 A/dm2,h-BN添加量3 g/L的条件下,可获得h-BN微粒体积分数为6.15%的复合镀层。h-BN微粒的添加改善了Cr–C合金镀层的耐磨性,Cr–C/h-BN复合镀层在室温干摩擦条件下的磨损率减少了22%,平均摩擦因数由原先的0.49降低至0.31。     

Molten salt synthesis of a SiC coating on graphite flakes for application in refractory castables

A silicon carbide coating was formed on the surface of graphite flakes by reaction of molten Si with carbon at 1100–1300 °C in a 95%KCl-5%NaF molten salt under Ar atmosphere. The effect of temperature and Si/graphite ratio in the initial mixture on the quality and the amount of SiC were investigated by XRD and SEM/EDS analyses. Also, the water wettability, oxidation resistance and zeta potential of un-coated and coated graphite were examined by TGA analysis and sedimentation test. The results show the amount of coating to increase in the coated flakes with increasing temperature and Si/graphite ratio. The SiC coating improves water wettability of graphite and acts as a protective layer to enhance oxidation resistance. The zeta potential of coated graphite was also increased which indicated a better dispersion in water based systems. These improvements in both the water dispersivity and oxidation resistance of SiC coated graphite would make it as promising candidate raw materials for application in C-containing refractory castables.     

Green preparation of in situ Cr3C2 nano-coatings on graphite surface and their water-wettability and rheological properties

Cr₃C₂ coatings were successfully prepared on the surface of graphite flakes via a molten salt route by mixing Cr powders with natural graphite flakes in a binary LiCl-KCl salt at 450–950?°C for 4–12?h. The phases and microstructures of the coatings were verified by its XRD/XPS spectra and SEM/AFM observations, respectively. Together with the dissolution/dispersion evidence of chromium powders after interaction with the salt, and the slightly increased particle sizes due to the formation of Cr₃C₂ coatings on graphite flakes, a ‘template-growth’ kinetic process was therefore proposed on the formation of such coatings in the molten salt. The resultant coatings decreased the contact angle between water and graphite from 101° to ~ 75° and lowered the apparent viscosities of graphite water slurry by two orders of magnitude accordingly, suggesting that the coatings will afford graphite with good processing abilities for carbon-water based materials.     

Ni-P复合镀层摩擦磨损性能的研究

采用化学复合镀在碳钢基体上共沉积（Ni-P）-SiC和（Ni-P）-PTFE两种复合镀层,重点研究了两种复合镀层在相同对磨条件下的摩擦磨损性能及磨损机理表现形式,并与化学镀镍磷层进行对比。结果表明,本实验条件下所制备的（Ni-P）-SiC和（Ni-P）-PTFE两类复合镀层分别具有优异的耐磨和减磨性能,均能对所镀覆基体材料起到良好的保护作用;对磨实验过程中主要出现磨料磨损、粘着磨损和氧化磨损三种磨损方式,而且磨损方式不同,镀层的摩擦磨损性能表现也不尽相同。     

Low-Temperature Preparation of Titanium Carbide Coatings on Graphite Flakes from Molten Salts

Titanium carbide (TiC)-coated graphite for refractory castable applications was prepared via reacting titanium metal powder (∼45 μm) and natural graphite flakes (100–300 μm) for 5 h at 950°C in a KCl-based salt in Ar atmosphere. TiC coatings formed on graphite flakes were uniform, crack-free, and composed of nanosized particles (20–40 nm). The "template-growth" mechanism played a dominant role in the coating formation process.     

Effects of expandable graphite on char morphology and pyrolysis of epoxy based intumescent fire-retardant coating

The current study was designed to investigate the effects of expandable graphite (EG) on fire protection properties of intumescent fire-retardant coating for steel structures. Several formulations of intumescent coating were prepared and tested according to ISO 834 for char expansion. The chars were found without cracks and bonded with the steel substrate. The results showed that the coating slowly degraded during the test and char remained in contact with vertically tested coated substrate. The coated substrates were also tested for weather resistance using humid and ultraviolet environment. The char was characterized by using FESEM, XRD, FTIR, TGA, and XPS analysis. FESEM examined char morphology of the coatings after furnace fire test. XRD and FTIR showed the presence of graphite, borophosphate; boron oxide and sassolite in the char. TGA and DTGA results disclosed that EG improved the residual mass of coating. XPS analysis showed the percentages of carbon and oxygen are 48.50 and 43.45 in char of formulation with 12.8% EG. The results of weathering test coatings showed decreased in char expansion because of a humidity and UV light. The formulation with 9.8% EG showed the maximum char expansion and high residual mass among the formulations investigated in this study. The weathering tested coated samples showed their capability of fire protection.     

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     

Graphite particles in the diamond-like a-C films prepared with the pulsed arc-discharge method

Microparticle collection on the coating surface has been studied during the preparation of diamond-like amorphous carbon coatings with the pulsed arc-discharge method. The curved solenoid method was used for the particle filtering. The quality of the coatings was studied using profilometer, ESCA and SEM techniques and wear, friction and acid resistance tests. The coatings without and with filtering contained graphite particles (40% and less than 1% respectively) and the sp²/sp³-bonding ratios were 51% and 78% respectively. The acid resistance of the nonfiltered films was poor. On the contrary, in pin-on-disc experiments with both types of coating against polyethylene, steel and Al₂O₃ pins, no clear differences in the friction and wear measurements were observed.     

Hydrophobic Nano‐Silica for the Surface Modification of Graphite Flake

Graphite flake is an electromagnetic interference material of importance for IR screening. In this study, an attempt to improve the performance of graphite flake by coating it with nano‐silica using cyclomix (Hosokawa) and hybridizer (Nara) processes was made. Uncoated and coated graphite flakes were examined by scanning electron microscopy (SEM). It was shown that a more uniform coating was obtained using the hybridizer process. Coated graphite flake with a mass ratio of nano‐silica equal to 5.25 % exhibited the best hydrophobic properties. The test chamber experiments demonstrated that the deposition velocity of coated graphite flake decreased from 0.227 cm s⁻¹ to 0.187 cm s⁻¹ and its IR interference performance was improved, compared with uncoated graphite flake. The obtained results showed that the coatings on the graphite flake powder with hydrophobic nano‐silica enhanced the moisture resistance and electromagnetic interference performance of the graphite flake.     

超声波功率对Cu-SiO_2复合镀层形貌与性能的影响

采用超声波辅助电沉积工艺制备Cu-SiO_2复合镀层,借助扫描电镜、粗糙度仪、显微硬度计和摩擦磨损试验机,研究超声波功率对复合镀层形貌、显微硬度和摩擦磨损性能的影响。结果表明,较低功率(0~160 W)超声波起不到改善和提高复合镀层形貌与性能的效果,较高功率(240~400 W)超声波能够明显改善复合镀层的形貌平整性和致密性,并且提高性能;超声波功率过高,反而使复合镀层形貌变差,性能下降。超声波功率为400 W时,复合镀层呈颗粒状形貌,表面粗糙度仅为0.42μm,显微硬度达到166.8 HV,磨损质量损失率为1.07 mg/min,表现出良好的摩擦磨损性能。     

Effects of the combination of solid lubricants and short carbon fibers on the sliding performance of poly(ether imide) matrix composites

Solid lubricants, that is, graphite flakes and poly(tetrafluoroethylene) powders, were incorporated with short carbon fibers into a poly(ether imide) matrix to improve the tribological performance. Wear tests were performed with a polymer pin against a mild steel counterpart at a constant sliding speed of 1 m/s under various temperatures and contact pressures. Composites filled with equilibrium contents of solid lubricants and short carbon fibers, that is, 10 vol % of each filler, exhibited the lowest wear rate and friction coefficient. The relatively lower concentration of solid lubricants adversely affected the wear resistance, whereas the friction coefficient did not vary significantly in comparison with the friction coefficient of the composites filled with only short carbon fibers. The improved tribological behavior was attributed to more continuous and effective friction films formed on the material pairs during sliding. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1428–1434, 2004     

脉冲喷射电沉积纳米晶镍工艺优化研究

采用脉冲喷射电沉积方法在钢基体表面制备了纳米晶镍镀层,研究了占空比、频率、平均电流密度对镀层硬度的影响,并通过正交试验对工艺参数进行优化,用扫描电镜和X-射线衍射仪对镀层表面形貌和晶粒尺寸进行分析。结果表明,制备纳米晶镍镀层的优化工艺参数为:平均电流密度39.8 A/dm2、频率1 000 Hz和占空比20%,此时镀层最致密,硬度最高(530.6 HV),纳米晶镍平均晶粒尺寸最小(13.7 nm)。     

Characterization of wear surfaces in dry sliding of steel and alumina on hydrogenated and hydrogen-free carbon films

Hydrogenated amorphous carbon coatings were deposited by r.f. plasma and hydrogen-free carbon films in pulsed arc discharge on stainless steel substrates. The coatings were characterized and evaluated in tribological tests. Pin-on-disc tests were used over a wide range of test parameters: normal load, 5–40 N; sliding velocity, 0.1–3.0 m s⁻¹. The wear of both coatings was of the same order of magnitude (0.7 × 10⁻³−5.1 × 10⁻³ mm³). However, the wear of the counterface was one order of magnitude higher for the hydrogenfree carbon coatings. Increasing the normal load generally caused an increase in coating wear and in most cases also an increase in counterface wear. When the steel pin was sliding against the hydrogenated carbon coating with a high sliding velocity and load, a rather thick tribofilm was formed on the pin wear surface, lowering the coefficient of friction and reducing the pin wear. The tribofilm formed on the alumina pin sliding against the hydrogenated carbon film also seemed to reduce the friction coefficient but could not prevent the pin wear. A tribofilm was also formed on the pin wear surface when the hydrogen-free carbon coating was sliding against the steel and alumina pins, but the layer was not able to protect the pins. The tribofilm did, however, lower the coefficient of friction, which was rather insensitive to the different test parameters used. According to secondary ion mass spectroscopy analyses, material transfer of the pin was detected on the disc (coated) wear surfaces. The tribofilms formed on the pin wear surfaces consisted of pin material, hydrogen, oxygen, and carbon.     

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.     

Semiconductive polyaniline melamine–formaldehyde blend electronic barrier to corrosion

Abstract

Polyaniline (PANI) is one of the intrinsic semiconductive polymers and shows some useful properties: high conductivity, transparency for the red and violet domain of spectrum, good elasticity and processability, superficial tension and chemical, photochemical and electrochemical behaviour. A PANI primer coat has been developed to act as an active electronic barrier to corrosion. When overlaid with a conventional durable topcoat, the coating has been shown to protect steel against salt, pollutants and other harsh environments.

Dry blends were prepared by blending the powders of doped PANI and the host polymer, a commercial melamine–formaldehyde resin AZAMIN M514 in a mixer. The hardness, elasticity, resistance and protective behaviour of melamine–formaldehyde resin films were determined. The protective behaviour of obtained melamine–formaldehyde resin blend was evaluated from quantity of Fe (II) released by the coated carbon steel samples (exposed area 1·0 cm^–2) immersed for 1 month in 50 mL 3·5%NaCl solutions. The prepared coatings protect substrate from corrosion by stabilising the oxide layer formed on the metal surface and thus prevent the metal dissolution process. An optimum formulation of melamine–formaldehyde resin coatings with 5 wt-% doped PANI exhibits good protective behaviour.     

Evaluation of Ni‐Mo and Ni‐Mo‐P Electroplated Coatings on Stainless Steel for PEM Fuel Cells Bipolar Plates

Stainless steel bipolar plates (BPPs) are the preferred choice for proton exchange membrane fuel cells (PEMFCs); however, a surface coating is needed to minimize contact resistance and corrosion. In this paper, Ni–Mo and Ni–Mo–P coatings were electroplated on stainless steel BPPs and investigated by XRD, SEM/EDX, AFM and contact angle measurements. The performance of the BPPs was studied by corrosion and conduction tests and by measuring their interfacial contact resistances (ICRs) ex situ in a PEMFC set‐up at varying clamping pressure, applied current and temperature. The results revealed that the applied coatings significantly reduce the ICR and corrosion rate of stainless steel BPP. All the coatings presented stable performance and the coatings electroplated at 100 mA cm⁻² showed even lower ICR than graphite. The excellent properties of the coatings compared to native oxide film of the bare stainless steel are due to their higher contact angle, crystallinity and roughness, improving hydrophobicity and electrical conductivity. Hence, the electroplated coatings investigated in this study have promising properties for stainless steel BPPs and are potentially good alternatives for the graphite BPP in PEMFC.     

Corrosion and wear behavior of alumina‐polyester nanocomposite coatings

The corrosion and wear behavior of powder coatings fabricated by the electrostatic method was investigated in this study. Pure polyester coating and fabricated nanocomposite powder coating with 10 and 20 mass.% alumina nanoparticles were coated with electrostatic spraying method on the surfaces of carbon steel substrate. Coatings were cured in two regimes by oven and microwave for the appropriate time. The effects of alumina nanoparticles on the corrosion resistance of coated samples were studied by immersion and electrochemical impedance spectroscopy (EIS) tests. Also, pin‐on‐disk test was applied to evaluate the wear properties and coefficient of friction (COF) of the coatings. The results of the corrosion test reveal that the samples with 10 mass.% alumina show the best corrosion resistance and cause a reduction in corrosion rates which is about 36 times to that of the pure sample. The wear rate of nanocomposite coatings is 10 times lower than that of pure ones and also the coefficient of friction of nanocomposite samples is almost half of the pure samples. Furthermore, the nanocomposite coatings cured in the microwave show better protection properties and wear resistance than that of ones cured in an oven. POLYM. ENG. SCI., 57:846–856, 2017. © 2016 Society of Plastics Engineers     

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。     

Effect of expandable graphite and ammonium polyphosphate on the thermal degradation and weathering of intumescent fire-retardant coating

This research aims to study the effect of ammonium polyphosphate and expandable graphite on the intumescent coating formulations (ICF). The coating presented in this research article is based on carbon source expandable graphite (EG), blowing agent melamine, acid source ammonium polyphosphate (APP), epoxy resin as a binder with polyamide amine. The stability of the developed coating was verified at 950°C for 1-hour fire test. The results showed that the coating is stable and well bond with the steel substrate. The char was characterized by using FESEM, XRD, FTIR, DTA, TGA, XPS, Py-GCMS and Weathering Test. The morphology of the char was studied by SEM of the coating after furnace fire test. XRD and FTIR show the presence of graphite, borophosphate; boron oxide and sassolite in the residual char. TGA and DTG disclosed that EG improved the residual mass of coating. XPS analysis showed the char residue of IF5-APP-EG contains carbon and oxygen contents 47.50 and 40.70, respectively. Py-GCMS analysis described that the IF5-APP-EG released less gaseous compounds. The weathering test illustrated that's the char expansion of coatings samples was decreased due to the presence of a humid environment and UV light. The IF5-APP-EG showed the maximum char expansion, lower substrate temperature and high residual weight among the studied formulations.