Corrosion protection of carbon fibre reinforced aluminium composite by diamondlike carbon coatings

Abstract

Carbon fibre reinforced aluminium exhibits poor resistance against electrochemical corrosion in 3·5 wt-%NaCl solution. Diamondlike carbon (DLC) coatings provide properties which make them interesting materials for external corrosion protection on metal matrix composites (MMCs). The electrochemical corrosion behaviour of uncoated and DLC coated carbon fibre reinforced aluminium was tested in 3·5 wt-%NaCl solution. It has been found that the pitting potential is shifted significantly in the anodic direction and the corrosion current density is much lower due to the presence of the sealing DLC coating. Additionally, scratch tests and SEM studies were carried out in order to characterise the adhesion of the DLC films on the heterogeneous MMCs. Reliable corrosion protection is connected with sufficient coating durability under loading. In order to ensure sufficient loading capacity of the DLC coating under tribological conditions, wear tests were undertaken which revealed a considerable improvement in wear resistance due to deposition of the DLC coatings.     

Analysis of degradation process during the incorporation of ZrO2:SiO2 ceramic nanostructures into polyurethane coatings for the corrosion protection of carbon steel

Three different molar ratios of ZrO₂:SiO₂ mixed oxides (25:75, 50:50, 75:25) were produced by the sol–gel technique and sintered at different temperatures (400, 600, 800, and 1000 °C) in order to analyze differences in mechanical and electrochemical properties of a wide variety of organic–inorganic hybrid coatings on AISI 1018 commercial carbon steel. For this purpose, 2, 4, and 6 wt% of the obtained ZrO₂:SiO₂ nanoparticles were incorporated to the polymeric matrix under vigorous stirring and spread on metallic substrates to reach between 40 and 55 μm of dry film. Light microscopy, scanning electron microscopy, confocal laser scanning microscopy studies, atomic force microscopy, and nanoindentation tests were used to evaluate morphological, topographical, and mechanical properties; whereas atmospheric corrosion and electrochemical impedance spectroscopy (EIS) were performed using a 3 wt% NaCl medium in continuous immersion for 226 days. The crystallite size of the as-prepared ZrO₂:SiO₂ nanoparticles changed according to the sintering temperature from 4 to 9 nm. It was found that an adequate dispersion and homogeneity was achieved when 2 wt% of sintered ZrO₂:SiO₂ nanoparticles were mechanically mixed with polymer (MDI) to produce hybrid coatings on the metallic substrate. Free-bubble surface and hardness enhancement can be achieved by adding nanostructures assuming fact that the particles are capable of occupying the gas bubble sites. Atmospheric corrosion in the coatings without reinforced particles was more severe than that observed in hybrid coatings, and for these, corrosion was higher according to the increasing zirconia molar ratio. The EIS studies indicated that the synergetic effect between the organic–inorganic phases to seal the surface enhances the barrier properties on this metallic substrate.     

Effect of negative bias voltage on mechanical and electrochemical nature in Ti–W–N coatings

Mechanical and electrochemical surface properties of Si (100) and AISI D3 steel substrates-coated Ti–W–N, deposited by r.f. magnetron sputtering process from a binary (50% Ti, 50% W) target in an Ar/N₂ (90%/10%) mixture, have been studied using nanoindentation, Tafel polarization curves and electrochemical impedance spectroscopy (EIS). The crystallinity of the coatings was analyzed via X-ray diffraction (XRD) and the presence of TiN(111), TiN(200), WN₂(107), and W₂N(220) phases were determined. Depth sensing nanoindentation measurements were used to investigate the elasto-plastic behavior of Ti–W–N coatings. Each group of samples was deposited under the same experimental conditions (power supply, Ar/N₂ gas mixture and substrate temperature), except the d.c. negative bias voltage that varied (0, ?50, and ?100 V) in order to study its effect on the mechanical and electrochemical properties of AISI D3 steel coated with Ti–W–N coatings. The measurements showed that the hardness and elastic modulus increase from 19 to 30 GPa and from 320 to 390 GPa, respectively, as a function of the increasing negative bias voltage. Coating track and coating-substrate debonding have been observed with atomic force microscopy (Asylum Research MFP-3D^®) on the indentation sites. Finally, the corrosion resistance of Ti–W–N coatings in 3.5 wt% NaCl solution was obtained from electrochemical measurements in relation to the increase of the negative bias voltage. The obtained results have shown that at the higher negative bias voltage (?100 V), the steel coated with Ti–W–N coatings presented the lower corrosion resistance. The corrosion resistance of Ti–W–N in 3.5 wt% NaCl solution was studied in relation to the increase of the bias voltage.     

X-ray reflectivity study of bias graded diamond like carbon film synthesized by ECR plasma

Diamond like carbon (DLC) coatings were deposited on silicon substrates by microwave electron cyclotron resonance (ECR) plasma CVD process using plasma of Ar and CH ₄ gases under the influence of negative d.c. self bias generated on the substrates by application of RF (13·56 MHz) power. The negative bias voltage was varied from ?60 V to ?150 V during deposition of DLC films on Si substrate. Detailed X-ray reflectivity (XRR) study was carried out to find out film properties like surface roughness, thickness and density of the films as a function of variation of negative bias voltage. The study shows that the DLC films constituted of composite layer i.e. the upper sub surface layer followed by denser bottom layer representing the bulk of the film. The upper layer is relatively thinner as compared to the bottom layer. The XRR study was an attempt to substantiate the sub-plantation model for DLC film growth.     

Preparation of layered bioceramic hydroxyapatite/sodium titanate coatings on titanium substrates using a hybrid technique of alkali-heat treatment and electrochemical deposition

Bioceramic hydroxyapatite/sodium titanate coating on sandblasted titanium substrate was fabricated by a three-step process. At first, the sandblasted titanium substrate was coated with a flake-like sodium titanate layer by alkali-heat treatment. In the second step, the alkali-heat treated titanium substrate was hydrothermal treated at 180 °C for 4 h with calcium solutions. In the third step, the hydroxyapatite (HA) coating was deposited onto the hydrothermal treated layer via electrochemical deposition method. The surface topography and roughness of the coatings were determined by field emission scanning electron microscope (FESEM) and a mechanical contact profilometer, respectively. The surface compositions were evaluated by X-ray diffraction (XRD), energy-dispersive X-ray spectrum (EDS), and X-ray photoelectron spectroscopy (XPS). The EDS, XPS, and XRD analysis confirm the presence of element Ca, Ca²⁺, and CaTiO₃ on sodium titanate layer after hydrothermal treatment with Ca(NO₃)₂ solution, respectively. FESEM micrograph shows the rod/needle-shaped crystallites are highly densely packed on the calcium-ion-containing layer with an average size of ~50 nm in diameter. The results indicate that the sodium titanate layer containing Ca²⁺ ions possesses higher ability to induce HA formation compared with the pure sodium titanate layer. It is revealed that surface composition plays an important role in the electrochemical deposition of HA. The calcium-ion-containing layer probably makes the nucleation of HA easy and effectively promotes orientated growth of HA on flake-like sodium titanate surface. The sodium titanate layer possesses a lower corrosion current density and a higher corrosion potential than sandblasted-Ti substrate. The sodium titanate layer should act as a barrier to the release of metal ions from metallic substrate to physiological solutions and thus reducing the electrochemical reaction rate.     

Structural analysis and corrosion studies on an ISO 5832-9 biomedical alloy with TiO2 sol–gel layers

The aim of this study was to demonstrate the relationship between the structural and corrosion properties of an ISO 5832-9 biomedical alloy modified with titanium dioxide (TiO₂) layers. These layers were obtained via the sol–gel method by acid-catalyzed hydrolysis of titanium isopropoxide in isopropanol solution. To obtain TiO₂ layers with different structural properties, the coated samples were annealed at temperatures of 200, 300, 400, 450, 500, 600 and 800 °C for 2 h. For all the prepared samples, accelerated corrosion measurements were performed in Tyrode’s physiological solution using electrochemical methods. The most important corrosion parameters were determined: corrosion potential, polarization resistance, corrosion rate, breakdown and repassivation potentials. Corrosion damage was analyzed using scanning electron microscopy. Structural analysis was carried out for selected TiO₂ coatings annealed at 200, 400, 600 and 800 °C. In addition, the morphology, chemical composition, crystallinity, thickness and density of the deposited TiO₂ layers were determined using suitable electron and X-ray measurement methods. It was shown that the structure and character of interactions between substrate and deposited TiO₂ layers depended on annealing temperature. All the obtained TiO₂ coatings exhibit anticorrosion properties, but these properties are related to the crystalline structure and character of substrate–layer interaction. From the point of view of corrosion, the best TiO₂ sol–gel coatings for stainless steel intended for biomedical applications seem to be those obtained at 400 °C.     

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.     

Investigation of electrochemical behavior of nitrogen implanted Ti–15Mo–3Nb–3Al alloy in Hank’s solution

Titanium alloy Ti–15–3–3 (Beta-21S) was implanted with nitrogen ions by plasma immersion ion implantation at 700, 750 and 800 °C. Micro Raman and XPS results confirm the formation of nitrides after implantation. Corrosion current density (i_corr) of the treated samples in simulated body fluid (Hank’s solution) is higher than that of the substrate. Treated samples also exhibit lower charge transfer resistance and higher double layer capacitance as compared to that of substrate in electrochemical impedance spectroscopic studies. However, no corrosion related effects are observed after 28 days of immersion in SBF. EDS results show the presence of oxygen after corrosion studies. XPS spectra from the implanted samples show the presence of nitride and oxynitride on the surface and formation of oxide due to corrosion process.     

Corrosion and erosion behavior of iron aluminide (FeAl(Cr)) coating deposited by detonation spray technique

The electrochemical corrosion and erosion behavior of FeAlCr coating was reported in this article. The FeAlCr coatings were deposited by detonation spray coating system (DSC) by utilizing the gas atomized powder with a nominal composition of Fe-12Al-5Cr at two different pulse frequencies on mild steel (MS) substrate. Feedstock and coatings were characterized using XRD, SEM and elemental mapping. Nanoindentation tests using a Berkovich indenter indicate a hardness of 5.5 GPa and 4.9 GPa for the coatings deposited at 3 Hz and 6 Hz respectively as compared to 1.5 GPa of the substrate. Electrochemical corrosion tests were performed on coated samples in 3.5 wt% NaCl and 2 N H₂SO₄ media and are compared with the bulk MS substrate. Detonation pulse frequency significantly influenced the coating microstructure and corrosion performance. The coating deposited at a frequency of 6 Hz exhibited higher resistance against electrochemical corrosion in 3.5 wt% NaCl medium than the coating that was deposited at 3 Hz frequency. Solid particle erosion tests performed at room temperature (25 °C) and an impingement angle of 90° (normal incidence) using Al₂O₃ as the erodent medium demonstrate a higher erosion loss of the coatings than the bulk MS. On the contrary, at a temperature of 400 °C, the coatings exhibited notably better erosion resistance than the MS substrate, illustrating the potential of FeAlCr coatings for high temperature wear-corrosion resistant applications.     

Electrochemical deposition and evaluation of electrically conductive polymer coating on biodegradable magnesium implants for neural applications

In an attempt to develop biodegradable, mechanically strong, biocompatible, and conductive nerve guidance conduits, pure magnesium (Mg) was used as the biodegradable substrate material to provide strength while the conductive polymer, poly(3,4-ethylenedioxythiophene) (PEDOT) was used as a conductive coating material to control Mg degradation and improve cytocompatibility of Mg substrates. This study explored a series of electrochemical deposition conditions to produce a uniform, consistent PEDOT coating on large three-dimensional Mg samples. A concentration of 1 M 3,4-ethylenedioxythiophene in ionic liquid was sufficient for coating Mg samples with a size of 5 × 5 × 0.25 mm. Both cyclic voltammetry (CV) and chronoamperometry coating methods produced adequate coverage and uniform PEDOT coating. Low-cost stainless steel and copper electrodes can be used to deposit PEDOT coatings as effectively as platinum and silver/silver chloride electrodes. Five cycles of CV with the potential ranging from ?0.5 to 2.0 V for 200 s per cycle were used to produce consistent coatings for further evaluation. Scanning electron micrographs showed the micro-porous structure of PEDOT coatings. Energy dispersive X-ray spectroscopy showed the peaks of sulfur, carbon, and oxygen, indicating sufficient PEDOT coating. Adhesion strength of the coating was measured using the tape test following the ASTM-D 3359 standard. The adhesion strength of PEDOT coating was within the classifications of 3B to 4B. Tafel tests of the PEDOT coated Mg showed a corrosion current (I_CORR) of 6.14 × 10^?5 A as compared with I_CORR of 9.08 × 10^?4 A for non-coated Mg. The calculated corrosion rate for the PEDOT coated Mg was 2.64 mm/year, much slower than 38.98 mm/year for the non-coated Mg.     

ZK61S镁合金微弧氧化膜层的结构及耐腐蚀性能

为了提高ZK61S镁合金的耐腐蚀性能,采用微弧氧化方法以不同电压(300,380,450 V)在ZK61S镁合金表面制备氧化膜并进行封孔处理。利用金相显微镜、扫描电镜、X射线衍射仪分析膜层的形貌、结构和组成;通过腐蚀电位试验、中性盐雾腐蚀试验及抗剥落腐蚀试验进行耐腐蚀性能考核。结果表明:微弧氧化呈现疏松多孔形态且均匀覆盖于基材表面,主要由Mg、MgO和Al_2Si_2O_5(OH)4相组成;微弧氧化处理后试样的腐蚀电位显著提升,且380 V所得微弧氧化试板的腐蚀电位达到-881.53 m V,经过408 h的中性盐雾腐蚀试验后的腐蚀速率为0.012g/(m~2·h),耐蚀性能比未进行表面处理的基材提高了88倍;经封孔处理的微弧氧化试板经过456 h的中性盐雾腐蚀试验后腐蚀速率降低到0.003 g/(m~2·h);封孔处理使微弧氧化膜的抗剥落腐蚀性能由微弧氧化后的EB级提升到EA级。     

镁合金表面类金刚石膜的研究进展

类金刚石碳(DLC)膜具有高硬度、低摩擦系数、强化学惰性及生物相容性好等优异性能,镁合金表面制备DLC膜可极大地改善基体的使用性能。综述了采用不同制备技术在镁基体表面获得的多种DLC膜系的抗磨损及耐腐蚀性能,并展望了DLC膜表面改性镁合金的医用前景,指出镁合金表面制备DLC膜是其表面改性技术中具有前景的一个研究方向。     

Schäden wälzbeanspruchter DLC‐Schichten auf Stahlsubstraten unterschiedlicher Härte

Damages of slip‐rolling tested DLC coatings on steel substrates of different hardness Extremely hard diamond coatings on hard SSiC substrates, various hard DLC coatings on 100Cr6 substrates (HRC60) as well as selected DLC coatings on unhardened steel substrates (HRC20) were tested under slip‐rolling conditions. Unadditivated paraffin oil was used as a lubricant. The tests were carried out in an Amsler type twin disc tester at initial maximum pressures of P₀=2.3 GPa according to Hertz. The tests were terminated after n=1.000.000 revolutions (endurance tests: n=10.000.000 revolutions) or if a coherent damaged area of A>1 mm² occurred. The slip‐rolling tests showed that the SSiC had a supportive influence on the diamond coatings which, however, failed due to fractures in the substrate. At least two of the DLC coatings on 100Cr6 substrates (HRC60) withstood the slip‐rolling test for up to n=10.000.000 revolutions with nearly no visible damage. These coatings deposited onto a soft, nitrogen alloyed steel (HRC20) were able to adjust to the deformation of the substrate without major damaged areas (A>1 mm²).     

Room temperature corrosion properties of AZ31 magnesium alloy processed by extrusion and equal channel angular pressing

The electrochemical properties of AZ31 magnesium alloy processed by extrusion and equal channel angular pressing (ECAP) were investigated. The electrochemical properties were evaluated using potentiodynamic tests and electrochemical impedance spectroscopy in corrosion solution of 0.1 M sodium chloride. The electrochemical changes of the sample surface were correlated with microstructure evolution. Material processed by extrusion and subsequently by 8 passes of ECAP shows similar or even inferior corrosion resistance to the extruded material after immersion time up to 96 h. However, corrosion resistance of material after extrusion and ECAP is significantly better than that of the extruded material for immersion time of 168 h. This sudden improvement is caused by different formation and fall off of protective corrosion products. Microstructure after extrusion is inhomogeneous and contains relatively large grains, whereas material after ECAP possesses homogeneous ultrafine-grained (UFG) microstructure. As a result, material after ECAP offers more corrosion nucleation sites, but UFG microstructure causes that only smaller clusters of corrosion products fall off the surface. The easier and faster corrosion protective layer restoration on the surface of UFG material after ECAP leads to enhanced corrosion resistance.     

Hybrid effect of an in situ multilayer Zn–ZnO–Cr2O3 electrodeposited nanocomposite coatings for extended application

Multifunctional composite coatings of Zn?ZnO?Cr₂O₃ were deposited electrolytically on prepared carbon mild steel (CS) from Zn electrolyte, having Zn²⁺ ions and uniformly dispersed nano ZnO?Cr₂O₃ particulates. The corrosion resistance characteristics of the deposited coatings were evaluated using the linear polarization measurement method in 3.65% NaCl. The microstructural properties of the produced multilayered coatings were evaluated by scanning electron microscope (SEM) equipped with an energy dispersive spectrometer (EDS), x-ray diffraction (XRD), and atomic force microscope (AFM). Thermal deformations were observed after 4 h at 250°C and the mechanical response of the coated samples was investigated using a diamond-based Dura Scan microhardness tester and a MTR-300dry abrasive wear tester. From the results, a significant improvement in the corrosion performance of coatings was observed with bath containing less than 2 g/L. The microhardness, thermal stability, and anti-wear properties of Zn?ZnO?Cr₂O₃ shows improved performance against Zn?ZnO coating matrixes, which was attributed to dispersive strengthening effect and grain induced effect of the ZnO/Cr₂O₃ particulate.     

铝材脉冲电镀Pb-WC-CeO_2复合层的电化学性能

为了探究脉冲电镀铝基Pb-WC-CeO2复合镀层的电化学性能,考察了正向脉冲参数(平均电流密度Jm、占空比r及正向脉冲工作时间ton)及温度对镀层在锌电解液中作阳极时的耐蚀性及析氧动力学参数的影响。结果表明:当Jm=120 mA/cm2,r=20%,ton=200 ms、θ=50℃时,Pb-WC-CeO2复合镀层具有较强的耐蚀性;将其用作锌电解的阳极,槽电压最小,能耗小,有最好的电催化活性,且优于直流镀层。     

The influence of chromium on early high temperature corrosion of ferritic alloys under SO2 atmosphere

Comprehensive insights into the early stages of corrosion mechanisms provide fundamental knowledge to further understand and model long time material behaviour. The present work studies the early stages of combined oxidation and sulphidation of ferritic model alloys for time scales up to 250 h at 650°C to observe the influence of chromium during the corrosion under SO₂. Model alloys were used to focus on the reaction of the intended elements: Fe, Cr, S, and O. Pure iron simultaneously forms magnetite and iron-sulphide in an early stage of corrosion, covered by a pure oxide layer after 100 h. Iron with 13 wt-% Cr shows hematite and mixed Fe–Cr-oxides first, before sulphides nucleate in the inner corrosion zone. With increasing ageing time a magnetite layer is observed below the hematite layer. Quantitative phase fractions of all corrosion products observed were determined from cross section images. Characterisation of the Fe13Cr corrosion scale by FIB revealed a highly porous structure in the inner corrosion zone where Cr-rich (Fe, Cr)-sulphides are present, and caused the scale to spall easily.     

Cyclic Oxidation and Hot Corrosion Behavior of Plasma-Sprayed CoCrAlY + WC-Co Coating on Turbine Alloys

Components in energy-producing systems suffer a variety of degradation processes such as oxidation and molten salt-induced corrosion as a consequence of complex multi-component gaseous environment. Coatings provide a composition that will grow the protective scale at high temperatures having long-term stability. Plasma spraying was used to deposit CoCrAlY?+?WC-Co composite coatings on turbine alloys of Hastelloy X and AISI 321. The thermocyclic oxidation behavior of coated alloys was investigated in static air and in molten salt (Na₂SO₄-60%V₂O₅) environment at 700 °C. The thermogravimetric technique was used to approximate the kinetics of oxidation in 50 cycles, each cycle consisting of heating and cooling. X-ray diffraction and SEM/EDAX techniques are used to characterize the oxide scale formed. Coated alloys showed a lower corrosion rate as compared to uncoated alloys. The coatings subjected to oxidation and hot corrosion showed slow scale growth kinetics. Preferential oxidation of Co, Cr, W and its spinel blocks the transport of oxygen and corrosive species into the coating by providing a barrier, thereby making the oxidation rate to reach steady state. As compared to the substrate alloys, coatings show better hot corrosion resistance.     

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.     

封孔处理对等离子喷涂Cr2O3-8TiO2涂层耐腐蚀性能的影响

为了提高等离子喷涂陶瓷涂层的耐腐蚀性能,扩大其应用范围,以环氧树脂和有机硅树脂为封孔剂对等离子喷涂Cr2O3-8TiO2涂层进行了封孔处理,采用盐雾腐蚀和电化学腐蚀方法对封孔涂层和未封孔涂层的耐腐蚀性能进行研究,使用扫描电镜/能谱仪(SEM/EDS)、光学显微镜(OM)观察了腐蚀前后涂层的形貌及成分变化,分析涂层的腐蚀机理.结果表明,240h盐雾腐蚀后未封孔涂层发生剥落失效,而有机硅树脂封孔涂层经1200h盐雾腐蚀表面仍保持完好.封孔涂层的耐腐蚀性明显优于未封孔涂层,有机硅树脂的封孔效果优于环氧树脂.