Veränderung des elektrochemischen Korrosionsverhaltens und der mechanischen Eigenschaften von C/Al-Verbunden durch Faserbeschichtungen aus SiC und pyrolytischem Kohlenstoff

Changes of the electrochemical corrosion behavior and the mechanical properties of C/Al-composites due to SiC and pyrolytic carbon fiber coatings The following contribution describes the modification of the electrochemical and mechanical behavior of carbon fiber reinforced pure aluminum (C/Al-composite) due to two different fiber coatings. Tests include potentiodynamic corrosion tests, Transmission electron microscopy, bending tests and single fiber-“push in”-tests. The potentiodynamic corrosion tests were carried out in 3,5 wt.% NaCl solution. The results give evidence of a considerable decrease of the corrosion resistance of the C/Al-composites due to the application of the pyrolytic fiber coating. The SiC coating improves the corrosion resistance of the composite. However, the mechanical properties of the composites were harmed by the SiC coating. The pyrolytic carbon coating leads to a remarkable energy dissipation due to “stick-slip” effects on the interface under load. Consequently, the application of suitable multilayers of pyrolytic carbon and SiC fiber coatings could result in improved electrochemical and optimized mechanical properties of the C/Al-composite.     

Aluminium based composites reinforced with alumina coated carbon fibres

Abstract

A fine Al₂0₃ coating could be obtained from alumina sols modified by chelator acetylacetone, with exact control of parameters. Coating with alumina by the sol–gel method on a carbon fibre surface was investigated in detail to improve the oxidation resistance of carbon fibre. Further study focused on making the alumina coated fibre reinforced aluminium composite prefabrication. X-ray diffraction and SEM methods were used to analyse the alumina gels and the carbon fibre/aluminium (CF/Al) preformed wire. After the coating treatment, oxidation resistance of carbon fibres is enhanced, the wettability between the fibres and melting aluminium is greatly improved, and the tensile strength of CF/Al preformed wire is increased.     

Evaluation of corrosion resistance of diamond-like carbon films deposited onto AISI 4340 steel

The corrosion resistance of amorphous diamond-like carbon (DLC) coatings deposited by radio frequency plasma enhanced chemical vapor deposition (rf-PECVD) technique on AISI 4340 steel substrates was evaluated under saline (5% NaCl) and acid (1700 ppm H₂SO₄) atmospheres. The corrosion process was investigated by surface characterization and electrochemical methods, such as potentiostatic polarization and electrochemical impedance spectroscopy (EIS). DLC coatings effectively protected the substrate after 48 h in a salt fog chamber and after the first Kesternich cycle. For comparison, under the same conditions, titanium nitride (TiN) coatings did not protect the substrate even for 2 h of saline exposure and even for the first Kesternich cycle. Although the DLC coatings resisted well to the corrosive action of the aggressive media, nucleation and growth of homogenous and micro-sized pinholes uniformly distributed on DLC coatings were observed as a result of the corrosion processes. The observed results suggest that the development of techniques which would reduce the porosity of the DLC films could promote further improvement on their corrosion protection ability.     

Coating NiTi archwires with diamond-like carbon films: reducing fluoride-induced corrosion and improving frictional properties

This study aims to coat diamond-like carbon (DLC) films onto nickel–titanium (NiTi) orthodontic archwires. The film protects against fluoride-induced corrosion and will improve orthodontic friction. ‘Mirror-confinement-type electron cyclotron resonance plasma sputtering’ was utilized to deposit DLC films onto NiTi archwires. The influence of a fluoride-containing environment on the surface topography and the friction force between the brackets and archwires were investigated. The results confirmed the superior nature of the DLC coating, with less surface roughness variation for DLC-coated archwires after immersion in a high fluoride ion environment. Friction tests also showed that applying a DLC coating significantly decreased the fretting wear and the coefficient of friction, both in ambient air and artificial saliva. Thus, DLC coatings are recommended to reduce fluoride-induced corrosion and improve orthodontic friction.     

Reinforcing effect of carbon nanotubes on PEEK composite filled with carbon fibre

Abstract

The main objective of the present paper is to develop high wear resistance carbon fibre reinforced polyether ether ketone composite with addition of multiwall carbon nanotubes. These compounds were well mixed in a batch mixer, and compounded polymers were fabricated into sheets of known thickness by compression moulding. Samples were tested for wear resistance with respect to different concentration of fillers. The wear resistance properties of these samples depend on filler aspect ratio. Wear resistance of composite with 20 wt-% of carbon fibre increases when multiwall carbon nanotubewas introduced. The worn surface features have been examined using scanning electron microscope. Photomicrographs of the worn surfaces revealed higher wear resistance with the addition of carbon nanotube. Also better interfacial adhesion between carbon and vinyl ester in carbon reinforced vinyl ester composite was observed.     

Dry sliding wear behavior and corrosion resistance of NiCrBSi coating deposited by activated combustion-high velocity air fuel spray process

NiCrBSi is a Ni-based superalloy widely used to obtain high wear and corrosion resistant coatings. This Ni-based alloy coating has been deposited onto 0Cr13Ni5Mo stainless steel using the AC-HVAF technique. The structure and morphologies of the Ni-based coatings were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive spectrometer (EDS). The wear resistance and corrosion resistance were studied. The tribological behaviors were evaluated using a HT-600 wear test rig. The wear resistance of the Ni-based coating was shown to be higher than that of the 0Cr13Ni5Mo stainless steel because Fe₃B, with high hardness, was distributed in the coating so the dispersion strengthening in the Ni-based coating was obvious and this increased the wear resistance of the Ni-based coating in a dry sliding wear test. Under the same conditions, the worn volume of 0Cr13Ni5Mo stainless steel was 4.1 times greater than that of the Ni-based coating. The wear mechanism is mainly fatigue wear. A series of the electrochemical tests was carried out in a 3.5 wt.% NaCl solution in order to examine the corrosion behavior. The mechanisms for corrosion resistance are discussed.     

Electrochemical performance of diamond-like carbon thin films

Diamond-like carbon (DLC) thin films used in this study were intended for their electrochemical properties. The DLC films were deposited by a filtered cathodic vacuum arc (FCVA) process on p-type silicon (100) substrates biased at different pulse voltages (0-2000 V). The chemical bonding structures of the DLC films were characterized with micro-Raman spectroscopy and the electrochemical properties were evaluated by means of electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization. The DLC films showed high impedance, high polarization resistance and high breakdown potential in a 0.5 M H₂SO₄ aqueous solution, which were attributed to the high sp³ content and uniformity of the films. The excellent chemical inertness of the DLC films made them promising corrosion resistant coating materials.     

Relative performance of hydrogenated, argon-incorporated and nitrogen-incorporated diamond-like carbon coated Ti-6Al-4V samples under fretting wear loading

Hydrogenated diamond-like carbon (DLC) (H-DLC), argon-incorporated DLC (Ar-DLC) and nitrogen-incorporated DLC (N-DLC) coatings were deposited on flat rectangular Ti-6Al-4V samples. The DLC coatings were characterised by Raman spectroscopy and nanoindentation. Fretting wear tests were conducted on uncoated and DLC coated samples with an alumina ball as the counterbody. As the Ar-DLC and N-DLC coatings had relatively more sp² network compared to the H-DLC coating, they exhibited lower values of hardness and elastic modulus. At both loads of 4.9 N and 14.7 N, all DLC coated specimens showed lower values of tangential force coefficient (TFC), wear volume and specific wear rate compared to the uncoated samples. While the Ar-DLC coated sample exhibited the lowest TFC, wear volume and specific wear rate at 4.9 N load, the N-DLC coated specimen exhibited the lowest TFC, wear volume and specific wear rate at 14.7 N load.     

In vitro corrosion testing of PVD coatings applied to a surgical grade Co–Cr–Mo alloy

Toxic effects and biological reaction of metallic corrosion and wear products are an important concern for metal on metal artificial joints. Corrosion tests were conducted to study the susceptibility to pitting and localized corrosion, with three coatings, CrN, TiN and DLC, applied to a wrought high carbon Co–Cr–Mo alloy substrate material. Corrosion testing involved the measurement of potential time transients during immersion in a physiological solution and cyclic polarization of specimen potentials into the transpassive range followed by reversal of the potential to scan in the cathodic direction to regain the rest potential E_rest. Resistance to pitting and localized corrosion was assessed by determining the transpassive breakdown potential E _bd and if any hysteresis generated during the reverse cyclic scan may have caused crossover with the original anodic scan. Three different surface coating conditions were tested namely: (1) as-coated, (2) polished, and (3) indented to penetrate the coating by diamond pyramid hardness indentor. Results showed that all three coatings produced significant improvements in corrosion resistance compared to performance of the wrought cobalt alloy but that some corrosive attack to both the CrN and TiN coatings occurred and some risk of attack to the cobalt alloy substrate existed due to coating defects or when damage to the coating occurred. TiN coatings were highly effective in preventing corrosion provided they were thick enough to produce complete coverage. Thin TiN coatings displayed some tendency to encourage localized attack of the cobalt alloy at coating defects or where the coating suffered mechanical damage. CrN coatings underwent transpassive breakdown more easily and some degree of pitting at defects within the coating was observed, especially when the CrN coating was polished before the test. No corrosive attack of the cobalt alloy substrate was observed when the CrN coating was mechanically damaged by indentation. DLC coatings produced were much thinner than either of the other two coatings and proved to be rather fragile. They were less effective in preventing apparently high corrosion currents and possibly high rates of corrosion.     

Cell attachment on diamond-like carbon coating

Preliminary results of diamond-like carbon (DLC) coating with its novel properties with no toxicity have caused a strong interest of commercial manufacturers of surgical implants. DLC coatings were prepared on polymethylmethacrylate (PMMA) at room temperature using ion beam assisted deposition (IBAD). It could be shown by X-ray photoelectron spectroscopy, Auger electron spectroscopy, and Raman spectroscopy that DLC coating prepared by 800 eV CHⁿ⁺ beam bombardment possessed a higher fraction ofsp ³ bonds in the structure of mixedsp ⁿ³ +sp ⁿ² bonding, resulting in a higher hydrophobicity. The results of the cell attachment tests indicated that DLC coatings exhibited low macrophage attachment and provided desirable surface for the normal cellular growth and morphology of the fibroblasts. At the same time, the number of both neutral granulocytes and platelets adhering to DLC coatings decreased significantly. These findings showed that DLC was a better coating with desirable tissue and blood compatibility.     

Characteristics and performance of hard Ni60 alloy coating produced with supersonic laser deposition technique

A novel coating fabrication technique, known as supersonic laser deposition (SLD), which combines cold spray (CS) with laser technology, is applied to produce hard Ni60 (58–62 HRC) coating on medium carbon steel (AISI 1045 steel) substrate. Different process parameters are investigated to obtain the optimal. The Ni60 coating specimens prepared by SLD process are studied microstructurally using scanning electron microscope (SEM), energy dispersive spectrum (EDS) and X-ray diffraction (XRD). The microstructures of the coatings are compared with those of the coatings produced using laser cladding (LC). The hardness, tribological property and corrosion resistance of the Ni60 coatings produced by SLD and LC with the optimal process parameters are evaluated under Vickers hardness, pin-on-disk wear and electrochemical corrosion tests. It is demonstrated that the Ni60 coating with SLD exhibits some characteristics, such as fine microstructure as cast, stable phases and less dilution; it surpasses the coating produced with conventional LC process in sliding wear resistance; but in 1 mol/L H₂SO₄ solution, the SLD and LC coatings performed similarly in corrosion resistance. This research has proved that SLD technique enables depositing hard Ni60 on steel substrate, which is impossible for CS technique.     

含碳纳米管有机无机复合涂层的制备与防护性能

为了改善铝合金材料的耐腐蚀性能, 研究了以正硅酸乙酯（TEOS）为主要原料, 加入一定量的KH-550, 并引入部分羟基化的多壁碳纳米管（MWCNTs-OH）进行复合, 以冰乙酸为催化剂, 采用溶胶---凝胶法在铝合金基体表面形成复合涂层。腐蚀电化学测试和扫描电镜分析结果表明, MWCNTs-OH的引入能够明显提高涂层的防护性能, 并有效防止涂层开裂。考察了MWCNTs-OH含量和热处理温度对涂层性能的影响。结果表明: MWCNTs-OH质量分数为0.04%、 热处理温度为130℃时制备的涂层性能最佳, 相应的试样在3.5wt%NaCl溶液中的腐蚀电流密度约为3.056×10-8A/cm2, 而同等实验条件下铝合金基体腐蚀电流密度为7.216×10-5A/cm2, 涂层的存在使腐蚀速率降低了3个数量级, 涂层对铝合金基体具有显著的防护效果。      

Corrosion Behavior and Protection Efficiency of 2024Al and SiCp／2024Al Metal Matrix Composite

The corrosion resistance of 2024 Al and SiC particle reinforced 2024 Al metal matrix composite(SiCp/2024Al MMC) in 3.5% NaCl solution was investigated with electrochemical method and immersion test, and the corrosion protection of sulfuric acid anodized coatings on both materials was evaluated by electrochemical impedance spectroscopy.The results showed that the SiCp/2024AlMMC is more susceptible to corrosion than its matrix alloy in 3.5% NaCl.For 2024Al,the anodized coating provides excellent corrosion resistance to 3.5%NaCl.The anodized coating on the SiCp/2024Al provides satisfactory corrosion protection,but it is not as effective as that for 2024Al because the structure of the anodized layer is affected by the SiC particulates.     

Electrochemical behaviour of chromium nitride coatings with various preferred orientations deposited on steel by unbalanced magnetron sputtering

Abstract

Chromium nitride coatings Cr₂N(111) and preferred orientations of CrN(111) and CrN(200) were successfully deposited on AISI 304 stainless steel by an unbalanced magnetron sputtering method. The electrochemical corrosion properties of the deposited films were studied in a 0·5M H₂SO₄ + 1M NaCl aqueous solution at ambient temperature by electrochemical measurements, including the corrosion potential E _corr, linear polarisation, potentiodynamic polarisation and electrochemical impedance spectroscopy. The structural characterisation and surface morphology were investigated using X-ray diffraction, scanning electron microscopy and atomic force microscopy. The experimental results indicated that the CrN(200) coating possesses the best corrosion resistance property, followed by the CrN(111) coating, while the Cr₂N coating has the least resistance among the three types of CrN(111), CrN(200) and Cr₂N(111) coatings. The porosity, corresponding to the ratio of the polarisation resistance of the uncoated and the coated substrates, was higher in the Cr₂N(111) coating than in the other CrN coatings. The CrN(200) coating had a dense microstructure almost without porosity. The void defects of CrN(111) and Cr₂N(111) coatings are responsible for the decrease in corrosion protection.     

Minderung von Reibung und Verschleiß von Bauteilen aus Aluminium mit diamantähnlichen Kohlenstoffschichten (DLC)

Reduction of friction and wear for parts made of aluminium by diamond-like carbon coatings Reduction of friction and wear of machine parts and tools is usually achieved by separating the participating surfaces. This is predominantly done by liquid lubricants. Solid lubricant coatings replace them where hydrodynamic lubrication is not possible or not active. Among the hard and friction reducing layers diamond-like carbon films (DLC) have distinguished themselves as the most interesting representatives. They are deposited on metallic and ceramic parts in a glow discharge of a hydrocarbon gas at temperatures between 150 and 200 °C. Those low deposition temperatures, their very low dry sliding friction coefficient of 0.05 to 0.1, and an elastic recovery of 90 % differentiate them from PVD coatings to a high degree. DLC can also be deposited on light metals with thicknesses of more than 30 μm. For closed films an outstanding protection against corrosion is established. Machining and forming of light metals can be done without cooling lubricants.     

Influence of coating on short steel fiber reinforcements on corrosion behavior of aluminium base short steel fiber reinforced composites

Steel fiber reinforced aluminium composites are attractive materials of high specific strength but exhibit poor resistance against electrochemical corrosion. The study discusses the electrochemical corrosion behavior of uncoated, copper and nickel coated short steel fiber reinforced aluminium and Al–2Mg matrix composites in 1 (N) NaCl solution. Galvanic corrosion between the steel fiber and aluminium governs the corrosion behavior of these composites. It has been observed that open circuit potential (OCP) is shifted to more negative side with copper coating on the fibers and to the more positive side on coating the fibers with nickel. Compared to the uncoated fiber higher corrosion current density indicates corrosion rate was observed for the copper coated fiber reinforced composites where as a lower current density was noted for the nickel coated fiber reinforced composites was observed. Addition of 2 wt% magnesium to aluminium alloy matrix increased the corrosion current density. The corrosion mechanism in these composites is dominated by galvanic cell formation that is evident from the dissolution of Al matrix near the peripheral region of steel fibers.     

Corrosion behavior of plasma sprayed ceramic and metallic coatings on carbon steel in simulated seawater

Al₂O₃, ZrO₂ and Ni60 coatings were produced on carbon steels by plasma spray. Ni60 was used as the bond coat in all the cases. The microstructure of these coatings was analyzed by scanning electron microscopy (SEM). The corrosion behavior of the plasma spray coated samples as well as uncoated samples was evaluated by open circuit potential (OCP) measurements, potentiodynamic polarization tests, and electrochemical impedance spectroscopy (EIS) in simulated seawater. The results showed that Ni60 coating protected carbon steels against the corrosion and plasma spraying ceramic powders on metallic coating improved the corrosion resistance of the coatings further. The corrosion resistance of the Al₂O₃ coating was superior to that of the ZrO₂ coating due to the relatively few defects in Al₂O₃ coating.     

A mussel-inspired delivery system for enhancing self-healing property of epoxy coatings

Dopamine (DA),one type of mussel-inspired biological molecules with adhesive nature and corrosion inhibitor property,are often used to functionalize the surfaces of various materials.Herein,we report the application of polydopamine (PDA) microcapsules as novel nanocontainers for the purpose,loading corrosion inhibitor (benzotriazole) in its shell structure,and then were embedded into epoxy coatings to provide self-healing and anti-corrosion protection for carbon steel.Fast release of benzotriazole in acidic environment caused by local corrosion and the chelating effect of PDA-Fe3+ can synergistically promote the formation of protective film on bare steel surface,which endows coatings with self-healing func-tionality.Electrochemical impedance spectroscopy (EIS),local electrochemical impedance spectroscopy(LEIS),and spray tests were conducted to evaluate the active inhibition and corrosion resistance of the loaded coatings.The scratched coating with incorporation of nanocontainers presented better protection performance,exhibiting increased Ro (oxide layer resistance) and Rct (charge transfer resistance) during initial immersion periods.The EIS tests in long-term immersion were also performed to confirm the anti-corrosion effect of composited coatings.These results demonstrated that benzotriazole-decorated PDA capsules dramatically enhanced the self-healing properties and anti-corrosion performance of epoxy coatings with the synergistic help of PDA and benzotriazole.     

不同等离子源形成的DLC涂层对NiTi合金腐蚀行为的影响

采用等离子浸没离子注入和沉积(PIIID)法分别以C2H2和石墨为等离子源在NiTi合金表面形成DLC涂层来提高该合金的耐腐蚀性.利用Raman光谱和扫描电镜分析膜层结构.利用电化学测试和原子吸收光谱测试涂层前后基体的耐腐蚀性和Ni离子析出.结果表明:采用等离子浸没离子注入和沉积法以乙炔和石墨为等离子源在NiTi合金表面形成均匀致密、结合力良好的DLC涂层.两种涂层都明显地提高了NiTi合金的耐腐蚀性能和有效地抑制了Ni离子的溶出.     

Deposition of diamond like carbon (DLC) and C-N films using ion beam assisted deposition (IBAD) technique and evaluation of their properties

Diamond like carbon films and C-N films were prepared using ion beam assisted deposition technique (IBAD). Tribological properties were studied by subjecting DLC coated films to the accelerated wear tests. These tests indicated a significant improvement in the mechanical surface properties of glass by DLC coating. Better wear features were obtained for thinner DLC coating as compared to the thicker ones. We also studied the optical properties and obtained a band gap of 1·4 eV for these films. An attempt was made to prepare C₃N₄ films by using IBAD. We observed variation in the nitrogen incorporation in the film with the substrate temperature.