Microplasma synthesis of Fe-containing coatings on aluminum in homogeneous electrolytes

In this work, we suggest a method for microplasma synthesis of multicomponent iron-containing oxide coatings on the surface of aluminum alloys. For producing the coatings, we use a homogeneous electrolyte that contains iron in the form of its complexes with EDTA⁴⁻ and has a pH value of 9–10. The dynamics of the decrease in the pH value of the electrolyte is studied during microplasma formation of the coatings. The content of iron in the coatings is determined. The morphology, microstructure, and phase composition of the coatings obtained are studied by optical microscopy and X-ray powder diffraction analysis.     

Corrosion protection study of nanocrystalline plasma-electrolytic carbonitriding process for CP-Ti

The effect of various nanocrystalline plasma-electrolytic carbonitriding of a commercially pure titanium in a glycerol bath with various additives, such as carbamide, sodium nitrate, and triethanolamine, was studied. Effects of the bath composition on chemical composition and corrosion resistance of the PEC/N films were examined by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) in Ringer solution. The results showed that the films obtained in solutions with triethanolamine (T-film) had better corrosion resistance. A design of experiment (DOE) technique according to the Taguchi method, was used to optimize the process. The design was constituted of four factors, namely, triethanolamine concentration, electric conductivity of the bath, applied voltage, and duration of the process), each containing three levels. An analysis of the mean of signal-to-noise (S/N) ratio indicated that the corrosion resistance of plasma-electrolytically carbonitrided (commercially pure) Titanium was influenced significantly by the levels in the Taguchi orthogonal array. The optimized coating parameters for corrosion resistance are 1060 g/l for triethanolamine concentration, 360 mS/Cm for electric conductivity of the electrolyte, 260 Volts for applied voltage, and 9 minutes for treatment time. The percentage of contribution for each factor was determined by the analysis of variance (ANOVA). The results showed that the applied voltage is the most significant factor affecting the corrosion resistance of the coatings. Original Russian Text ? M.Kh. Aliev, A. Sabour, P. Taheri, 2008, published in Fizikokhimiya Poverkhnosti i Zashchita Materialov, 2008, Vol. 44, No. 6, pp. 656–660.     

电解质对AZ91D镁合金微弧氧化的影响

在Na2SiO3和NaAlO2为主成膜剂的硅铝复合电解液中,利用交流脉冲电源对AZ91D镁合金进行微弧氧化处理,研究主成膜剂含量的变化对微弧氧化过程及膜层特性的影响规律。利用扫描电镜(SEM)和膜层测厚仪分别研究了膜层的微观形貌和膜层厚度,通过电化学阻抗谱(EIS)测试膜层在3.5%NaCl中性溶液中的耐蚀性能。结果表明,随着主成膜剂含量的增加,微弧氧化过程中起弧电压和终止电压均呈下降的变化趋势,而膜层耐蚀性则基本呈先增大后降低的变化趋势,膜厚的变化趋势与其耐蚀性一致;Na2SiO3含量的变化对膜层内部致密层和外部疏松层的耐蚀性均有影响,而NaAlO2含量的变化则主要影响膜层内部致密层的耐蚀性;适量的主成膜剂含量是获得致密耐蚀膜层的关键。     

Enhancement of Corrosion Resistance of Zinc Coatings Using Green Additives

In the present work, morphology, microstructure, and electrochemical behavior of Zn coatings containing non-toxic additives have been investigated. Zn coatings were electrodeposited over mild steel substrates using Zn sulphate baths containing four different organic additives: sodium gluconate, dextrose, dextrin, and saccharin. All these additives are “green” and can be derived from food contents. Morphological and structural characterization using electron microscopy, x-ray diffraction, and texture co-efficient analysis revealed an appreciable alteration in the morphology and texture of the deposit depending on the type of additive used in the Zn plating bath. All the Zn coatings, however, were nano-crystalline irrespective of the type of additive used. Polarization and electrochemical impedance spectroscopic analysis, used to investigate the effect of the change in microstructure and morphology on corrosion resistance behavior, illustrated an improved corrosion resistance for Zn deposits obtained from plating bath containing additives as compared to the pure Zn coatings.     

AZ31镁合金表面含纳米SiC氟化镁膜层的制备及耐腐蚀性能

为了提高 MgF2 膜层的耐腐蚀性能,利用微弧氧化工艺,通过在 NH4F-EG 电解液中添加纳米 SiC 颗粒,在 AZ31 镁合金表面制备含 SiC 的 MgF2 -SiC 膜层,并探究纳米 SiC 颗粒的浓度对 MgF2 膜层组成、结构和耐腐蚀性能的影响。 采用 SEM、EDS、XRD、XPS 等测试方法对含 SiC 的 MgF2 膜层的微观组织、元素含量和物相组成进行分析,利用电化学工作站对膜层的耐腐蚀性能进行测试。 结果表明:电解液中的纳米 SiC 颗粒成功进入 MgF2 膜层中。 随着电解液中纳米 SiC 浓度的增加,膜层中的 Si、C 元素含量增加,Mg、F 元素含量减少,膜层变得致密平整,孔隙率减少,膜层缺陷得到有效改善,膜层厚度减小;MgF2 膜层的耐腐蚀性能先增大后减小,当电解液中纳米 SiC 的浓度为 5 g / L 时,膜层的耐腐蚀性能最优。 因此,在 NH4F-EG 电解液中添加纳米 SiC 颗粒,可以在 AZ31 镁合金表面制备出含 SiC 的 MgF2 -SiC 膜层, 且耐腐蚀性能优于不含 SiC 的 MgF2 膜层。     

Investigation of corrosion resistance of electrodeposited Ni–W/SiC composite coatings

In this research, Ni–W/SiC composite coatings were electrodeposited from a plating bath containing suspension of SiC particles. The influences of SiC particle concentration in the plating bath on the composition of composite coatings were investigated. The surface morphology and composition of the composite coatings were characterised by scanning electron microscopy, energy dispersive X-ray measurements and X-ray diffraction analysis. The corrosion characteristics of Ni–W/SiC composite coatings were investigated by mass loss and electrochemical measurements, including open circuit potential, electrochemical impedance spectroscopy and potentiodynamic polarisation in a 3·5 wt-%NaCl solution. The results showed that the addition of SiC particle to the deposition bath of Ni–W significantly increased the corrosion resistance. The significant improvement in corrosion resistance observed for Ni–W/SiC composite coatings (17100 Ω cm²) compared to Ni–W (5619 Ω cm²) could have resulted from the microstructural differences.     

Structure and properties of amorphous and nanocrystalline chromium-carbon coatings

Amorphous and nanocrystalline chronium-carbon coatings have higher properties than standard galvanic chromium ones. However, data on these coatings, and their heat-treatment regimes are quite scarce. The present paper concerns the structure, microhardness, ductility, adhesion strength, and resistance to overall and pitting corrosion of amorphous chromium-carbon coatings deposited galvanically by various regimes in an electrolyte based on chromic anhydride with an additive of formic acid. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 10, pp. 7–9, October, 1998.     

Morphology,structure, and composition of coatings at electrodeposition of black nickel

We present the electrolyte composition and the conditions of the electrodeposition with the aim to produce black nickel coatings on the surface of a piece manufactured of steel alloy, including the inner surface of a small diameter hole (3.4–5.0 mm). The method used of the coating production involves the application of two regimes of electrodeposition from one bath containing salts of nickel and zinc, a complexing agent (ammonium thiocyanate), and boric acid. The first regime allows one to produce a fine-grained layer with a high concentration of nickel, and the second one (functional) includes a high concentration of zinc. The produced coatings also contain oxides and sulfides and are amorphous, as the X-ray analysis shows.     

Effect of current density on the pulsed co-electrodeposition of nanocrystalline nickel-copper alloys

Nanocrystalline coatings have become an essential component of single and multilayer electronic packaging, ship building, mining, magnetorestrictive applications, etc. In the current work, nanocrystalline Ni-Cu films were synthesized by pulsed electrode-position using a citrate bath. Cathodic polarization experiments were carried out for optimization of bath composition to co-deposit nanocrystalline Ni-Cu films. Depositions were optimized between the current density range of 0.05–0.25 A·cm⁻² to achieve a uniform equiaxed coating with a target Ni content of greater than 70% owing to their superior corrosion resistance and enhanced hardness.     

Formation of microplasma coatings on high-silicon aluminum alloy and their characteristics

This work presents the results of studying the electrochemical microplasma formation of coatings based on the AK21 alloy of hypereutectic composition in silicate-alkali electrolyte. It is found that the boundary size of primary silicon inclusion in the alloy and additional cathodic surface treatment affect significantly the shape of voltage chronograms and growth dynamics of the coating thickness. It is shown that thick (more than 180 μm) layered coatings with a mosaic inner layer structure formed by fragments on the basis of the aluminum forms (amorphous Al(OH)₃, α-, δ-, γ-Al₂O₃) in the matrix of amorphous SiO₂ are formed on this alloy at all the applied treatment modes and silicon crystal sizes. It is found that the coating inner layer structure is regularly related to the limiting dimensions of primary silicon crystals. In addition, introduction of an additional cathodic component in the high-voltage polarization modes of the electrolytecoating-alloy system yielded a pronounced positive effect in the pattern of inner layer microhardness distribution that also characteristically depends on the limiting dimensions of primary silicon crystals in the initial samples.     

Corrosion and wear resistance of AZ31 Mg alloy treated by duplex process of magnetron sputtering and plasma electrolytic oxidation

In order to improve the wear and corrosion resistance of AZ31 magnesium alloy, a magnetron-sputtered Al layer with a thickness of 11 μm was firstly applied on the alloy, and then treated by plasma electrolytic oxidation (PEO) in an aluminate and silicate electrolytes, respectively. The performance of PEO coatings was investigated by dry sliding wear and electrochemical corrosion tests. The aluminate coating exhibits excellent wear resistance under both 10 and 20 N loads. The silicate coating only shows low wear rate under 10 N, but it was destroyed under 20 N. Corrosion tests show that the Al layer after magnetron sputtering treatment alone cannot afford good protection to the Mg substrate. However, the duplex layer of PEO/Al can significantly improve the corrosion resistance of AZ31 alloy. Electrochemical tests show that the aluminate and silicate coatings have corrosion current densities of ∼1.6×10⁻⁶ and ∼1.1×10⁻⁶ A/cm², respectively, which are two orders lower than that of the un-coated AZ31 alloy. However, immersion tests and electrochemical impedance spectroscopy (EIS) show that the aluminate coating exhibits better long-term corrosion protection than silicate coating.     

Plasma-electrolytic oxidation of titanium in Zr(SO<Subscript>4</Subscript>)<Subscript>2</Subscript>-containing electrolyte

It is shown that anodic oxide coatings with a thickness of several to 300 νm can be obtained on titanium by varying the charge spent on (Q). The prevailing phase in the coatings is ZrO₂ in monoclinic and tetragonal modifications. The content of zirconium in the layers is up to 20 at %. Distributions of titanium, zirconium, and oxygen in the cross sections of the coatings are obtained, and the effect of Q on the formation and elementary and phase compositions of the coatings is studied. Tentative experiments clarifying the effects of bipolar anodic-cathodic polarization and electrolyte aging on the composition of coatings are carried out. The coatings are shown to be stable at temperature variations in the range of 20–700°C and to decrease the contact corrosion current at the (titanium + coating)—St3 steel interface by a digit of 10–15 in 3% NaCl.     

Microstructure and Corrosion Resistance of Electrodeposited Ni-Cu-Mo Alloy Coatings

This paper deals with the electrodeposition of Ni-Cu-Mo ternary alloy coatings on low-carbon steel substrate from an aqueous citrate sulfate bath. The structures and microstructure of coatings were characterized by scanning electron microscopy and x-ray diffractometry. The corrosion resistance of coatings was investigated by potentiodynamic polarization (Tafel) and electrochemical impedance spectroscopy techniques. The results show that the Ni-Cu-Mo coatings are mainly composed of fcc-Ni phase and a small amount of NiCu phase. Ni-Cu-Mo coatings exhibit a nodular surface morphology, and the roughness of electroplated coating increases with the increasing of Na₂MoO₄·2H₂O in the bath. The corrosion performance of the coatings is significantly affected by the Mo content of the alloy coating and their surface morphology. The coating prepared in bath containing 40 g/L Na₂MoO₄·2H₂O has the highest corrosion resistance in 3.5 wt.% NaCl solution, while that prepared in bath containing 60 g/L (or more) Na₂MoO₄·2H₂O shows a lower corrosion resistance due to the presence of microcracks on the coating surface.     

Corrosion studies of carbon nanotubes-Zn composite coating

Zn-carbon nanotubes composite coatings were obtained from a sulphate bath containing dispersed carbon nanotubes (CNTs). The electrochemical and weight loss measurements were made to find the corrosion behavior of composite coating. The presence of carbon nanotubes shifts the potential of zinc deposit to more positive values. The composite coatings were porous free and the service life of coating was examined by salt spray test. The electrochemical studies revealed higher resistance of composite coatings to corrosion. The surface morphology was investigated by recording the SEM images of coating before and after corrosion. The mechanism of action against corrosion was established.     

Ni-TiO2 nanocomposite coating with high resistance to corrosion and wear

Ni-TiO₂ nanocomposite coatings with various contents of TiO₂ nanoparticles were prepared by electrodeposition in a Ni plating bath containing TiO₂ nanoparticles to be codeposited. The influences of the TiO₂ nanoparticle concentration in the plating bath, the current density and the stirring rate on the composition of nanocomposite coatings were investigated. The composition of coatings was studied by using energy dispersive X-ray system (EDX). The wear behavior of the pure Ni and Ni-TiO₂ nanocomposite coatings were evaluated by a pin-on-disc tribometer. The corrosion performance of coatings in 0.5 M NaCl, 1 M NaOH and 1 M HNO₃ as corrosive solutions was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy methods (EIS). The microhardness and wear resistance of the nanocomposite coatings increase with increasing of TiO₂ nanoparticle content in the coating. With increasing of TiO₂ nanoparticle content in the coating, the polarization resistance increases, the corrosion current decreases and the corrosion potential shifts to more positive values.     

Corrosion study of Ni/Zn compositionally modulated multilayer coatings using electrochemical impedance spectroscopy

Ni/Zn compositionally modulated multilayer (CMM) coatings were deposited using dual bath technique. Coatings corrosion performance was evaluated using electrochemical impedance spectroscopy (EIS) during extended immersion times up to 48 h. The results of electrochemical impedance spectroscopy showed that Ni/Zn CMM coatings had better corrosion resistance compared to that of the zinc single layer coating. The modified corrosion product which is formed on the Ni/Zn CMM coatings during extended exposure times and also a good barrier effect of the nickel layer against aggressive species in these coatings can be two important reasons for high corrosion performance and so protection performance of the Ni/Zn CMM coatings.     

Effect of electrolyte and monomer concentration on anticorrosive properties of poly(N-methylaniline) and poly(N-ethylaniline) coated mild steel

The electrosynthesis of poly(N-methylaniline) (PNMA) and poly(N-ethylaniline) (PNEA) coatings on mild steel in aqueous oxalic acid solutions was carried out by potentiodynamic synthesis technique. The effects of monomer and electrolyte concentrations on electrochemical growth of PNMA and PNEA coatings on mild steel substrates were investigated. Repassivation peak did not appear during electrosynthesis of PNMA and PNEA coatings from solutions containing 0.1 M monomer and 0.1 M electrolyte. The tests for corrosion protection of the polymer coated and uncoated mild steel substrates were done in 3% NaCl solutions by dc polarization and electrochemical impedance spectroscopy (EIS) techniques. Corrosion tests revealed that PNMA and PNEA coatings exhibited effective anti-corrosive properties. The acidity of the polymerization solution was found to influence the anticorrosive behavior of the polymer coating.     

Electrochemical deposition of nanocrystalline zinc on steel substrate from acid zincate bath

Nanocrystalline zinc coatings were deposited from acid zincate bath containing newly synthesized condensation product. The effect of bath constituents, pH, temperature and current density on the deposit nature were investigated through Hull cell experiments. Current efficiency, throwing power, cathodic polarization and corrosion behavior in 3.5 wt.% NaCl were studied under optimum concentration of additives. Salt spray test and electrochemical measurements showed that nanocrystalline zinc coatings have better corrosion resistance than the zinc coatings deposited from a simple acid zincate bath without additive. The surface morphology and thickness (cross section) of the zinc deposits were studied by scanning electron microscopy (SEM). The preferred orientation and average grain size of the zinc electrodeposit were obtained by X-ray diffraction analysis. The particle size was also characterized by TEM analysis. Energy X-ray diffraction (EDX) and FT-IR spectral analysis were carried out to determine the inclusion of addition agent in the deposit. The experimental results indicated that the addition of condensation product of thiamine hydrochloride (THC) and furfural (FFL) leads to a more uniform nanocrystalline deposition with the grain sizes varying from 20-22 nm.     

Electroplating of catalytically active nickel coatings from baths of various anionic compositions

The effect of the nature of bath anions (Cl⁻, SO₄²⁻ and CH₃COO⁻) on the characteristics of the electrochemical plating of nickel coatings, namely, parameters of the cathodic polarization curves, bath stability, and current efficiency, as well as the composition and morphology of deposits and their catalytic activity in the anodic oxidation of hypophosphite ions and cathodic evolution of hydrogen, is studied. The anionic composition of the baths is found to substantially affect not only the kinetics of the deposit growth, but also the properties of the deposit. The differences observed are determined by the complex-forming and buffering properties of the anions.     

Corrosion properties of diffusion coatings under the conditions of cathode protection

Conclusions We have developed a computational-experimental model for determining the parameters of the corrosion process under the conditions of cathode protection, which allowed us to establish that the cathode protection substantially reduces the losses to corrosion in carburized, nitrided, diffusion calorized, and chromized coatings. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 6, pp. 34–36, June, 2000.