Chromium Electroplating Research Articles

Properties of nanocrystalline Cr coatings prepared by cathode plasma electrolytic deposition from trivalent chromium electrolyte

Pure Cr coatings were prepared directly from trivalent chromium sulfate electrolyte by cathode plasma electrolytic deposition (CPED). Composition and microstructure of the coatings were investigated by EDS, XRD, SEM and TEM. The deposited Cr coatings are crack-free with the thickness up to approximately 30μm, and exhibit nanocrystalline structure, high hardness, excellent adhesion and corrosion resistance with the stainless steels. The quality of Cr coatings prepared by CPED is improved significantly compared with that prepared by traditional chromium electroplating. It indicates that cathode plasma electrolytic deposition is an effective way to prepare high quality Cr coatings.

PROPIEDADES TOXICOLÓGICAS Y AMBIENTALES DE UN ELECTROLITO BASADO EN CrIII/CLORURO DE COLINA

At present, industrial application of hard chromium electroplating is based on electrolytic baths of sulphuric acid and chromium trioxide solutions in water. Toxicological and environmental properties of this chromium (VI) baths show the convenience of searching for new CrVI free formulations. Research activities have shown that chromium metallic coatings from an ionic liquid (IL) using trivalent chromium salts can be successfully produced. A highly promising CrVI free, bright, thick and hard chromium deposition process has been developed based on an ionic liquid composed of Chromium chloride (CrCl3.6H2O) and Choline chloride (HOC2H4N(CH3)3+Cl?). Jointly with technological properties evaluation, a methodological study on environmental risk analysis and on implications in health & safety for the referred ionic liquid bath has been carried out. With that aim, experimental tests on the basis of toxicological properties, of effects on human health and of environmental effects were conducted. Comparisons of the obtained results with the behaviour of traditional baths used for the same purpose were also accomplished, showing for the ionic liquid formulation a lower toxicity and less environmental risk than for the CrVI formulation.

Experimental Research on Hard and Crack-Free Electrodeposited Chromium Coatings

In order to eliminate cracks in the chromium coating, a novel method named flexible extrusion assisted chromium electroplating was proposed. The bright and crack-free chromium coatings were electrodeposited by using the perturbation and extrusion of hard and insulating particles. The prepared deposits were characterized by scanning electron microscope (SEM) and three-dimensional topography. The testing results showed that the surface was very smooth and there was no micro cracks in the coating. Micro hardness of the electrodeposited layer was also tested. It was confirmed that the chromium coating electrodeposited with rotating cathode in hard particles had high micro hardness as to 850HV and the micro hardness could be controlled by the process parameters. The rule of the micro hardness was concluded by analyzing current density and rotating speed. In addition the results of salt spray test and electrochemical polarization curve showed that the coating deposited by new method had higher corrosion resistance than that by traditional method.

Nickel–tungsten alloy brush plating for engineering applications

Hard coating can improve the surface properties of a material beyond the capability of the substrate. For a long time, coatings such as hard nickel, hard chromium, hard alloys and hard composites have been developed for engineering applications due to the improved wear resistance. A newly-developed nickel–tungsten brush plating process has the potential as an alternative of electroplating of hard chromium for engineering application.The nickel–tungsten solution is based on the ammoniacal citrate bath, which can be conveniently brush plated just as brush plating of other metals or alloys. On the other side, hard chromium cannot be brush plated due to the exposure of hazardous hexavalent chromium exceeding the Occupational Safety and Health Administration (OSHA) limits.The nickel–tungsten alloy coating has been developed for engineering application. It is of nanocrystalline structure (~2nm crystallite size) and demonstrates excellent hardness and wear resistance. The coating is 60% nickel, 40% tungsten by weight. Due to high tungsten content in the alloy, it is thermally stable. Moderately elevated temperatures (200–500°C) do not cause grain size growth and softening as the case of most other hard coatings (such as hard chromium, nickel phosphorus). Actually, the nickel–tungsten alloy coating can be further hardened by exposure to high temperature of 200–500°C for a short period of time. Beyond the hardness and wear properties, the coating has been further characterized by XRD, electronic and optical microscopy, hydrogen embrittlement, salt spray corrosion, tribology, axial fatigue, and other testing.

Chromium Electroplating of Aluminium Alloys Using Electroless Nickel as Underlayer

The growing demand for chromium coated aluminium components especially for the automotive industry is due to their favourable physical properties (density, strength to weight ratio etc.). However, their frequent use under harsh environmental conditions renders them corrosion sensitive and consequently they need to be protected. An approach that has been applied in industry is to directly electroplate nickel onto aluminium substrate prior to a top metallic finish; however, in components with complex geometry, certain areas could become exposed to corrosion attack due to poor surface coverage during plating. In this study, a modified electroless nickel undercoat was applied to pre-treated aluminium alloys prior to duplex nickel and chromium plating with a view to enhance corrosion resistance, improve coating adherence and durability, and overall, to achieve substrate protection. Hexavalent and trivalent chromium were applied to pre-treated Al 1050 and Al 6061 following electroless nickel deposition, and plating performance was assessed by surface and corrosion techniques, while durability was measured by scratch, adhesion and hardness tests. Overall, while chromium plating with an electroless nickel undercoat did not improve corrosion resistance or hardness of the materials, it provided an additional protective layer for the substrate with a potential for longer term durability.

The effect of formic acid concentration on the conductivity and corrosion resistance of chromium carbide coatings electroplated with trivalent chromium

Different concentrations of formic acid were added into a trivalent chromium electroplating solution to produce chromium carbide (CrC) coatings. The influence of the formic acid concentration on chemical composition, microstructure, surface morphology, corrosion resistance, conductivity and carbon content of the resulting CrC coatings was studied. Formic acid was found to increase the carbon content in the coatings so as to form CrC films. These coatings had a nearly amorphous structure containing Cr, Cr2O3, and various CrC compounds with carbon content uniformly distributed throughout the coatings. The carbon content and the conductivity of the CrC layer were correlated with formic acid concentration. For a formic acid concentration of 2M, the CrC layer had the highest carbon content (∼28%), the lowest contact resistance, and the best corrosion resistance along with a corrosion current density of ∼6.4×10−7A/cm2.

Chemometrics applied to functional chromium electroplating by pulse plating techniques

Electrodeposited chromium coatings offer high levels of mechanical and tribological properties that justify their use in many industrial and engineering applications. However, one problem of these functional coatings is their limited corrosion resistance and the low current efficiency of their electrodeposition process. Reverse pulse plating can lead to an improvement in the characteristics of chromium deposits, but the high number of variables involved and the interactions among them make the selection of operating parameters difficult. In this paper, a chemometric approach was used in order to design the experiments and study the effect of pulse plating parameters on the properties of chromium coatings. Multivariate analysis was proposed to establish a relationship among structural and physical characteristics of chromium deposits and to determine the pulse parameters required to achieve certain properties. The results indicated that by reverse pulse electrodeposition, it is possible to obtain crack free chromium coatings, with similar hardness values as those obtained from direct current electrodeposited coatings, but with an improved corrosion resistance.

Wear and Corrosion Resistance of Cr-C Deposits Obtained from a Trivalent Chromium Electroplating Bath with the Addition of Nanosized Al2O3 Powder

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Unusual "chemical" mechanism of carbon co-deposition in Cr-C alloy electrodeposition process from trivalent chromium bath

Kinetics and mechanism of chromium-carbon alloy deposition process were investigated using trivalent chromium electroplating bath containing formic acid and carbamide (urea). The rate of carbon co-deposition process is determined by the rate of chromium electroplating reaction (electrochemical process of Cr-deposition imposes its own kinetics regularities on carbon co-deposition). It was supposed that a part of active chromium ad-atoms generated as a result of Cr(II) ions discharge may interact with adsorbed organic bath constituents by "chemical" mechanism.

Surface characterization of multiple coated H11 hot work tool steel by plasma nitriding and hard chromium electroplating processes

Formation of multi-layer coating by plasma nitriding and hard chromium electroplating on the surface of H11 hot work tool steel was investigated. Specimens were coated via a triple process containing plasma nitriding, hard chromium electroplating and plasma nitriding. Surface composition has been studied by X-ray diffraction analysis. The surface morphology and elemental analysis was examined by using scanning electron microscopy. Wear tests were conducted by the use of pin-on-disk method, a cemented tungsten carbide pin and 1000 gF load. Polarization corrosion tests were carried out in distilled water solution containing 3% NaCl. The improvement in hardness distribution after third step is discussed in considering the forward and backward diffusion of nitrogen in the chromium interlayer. Also, the formed phases in the hybrid coating were determined to be CrN + Cr2N + Cr + Fe2–3N + Fe4N. Wear results showed that although the multi-layer coated specimens have higher wear resistance in comparison with the reference specimen, their wear resistance is less than that of two and one layer coated specimens due to micro-ploughing and removal of hard surface nitrides from the surface. By increasing the third step time and temperature, the wear resistance of specimens increases due to higher diffusion of nitrogen in the chromium layer. But polarization results showed that triple coated specimens have the lowest corrosion rate.

Abrasive Wear Behavior of Different Thermal Spray Coatings and Hard Chromium Electroplating on A286 Super Alloy

In cases of decorative and functional applications, chromium results in protection against wear and corrosion combined with chemical resistance and good lubricity. However, pressure to identify alternatives or to improve conventional chromium electroplating mechanical characteristics has increased in recent years, related to the reduction in the fatigue strength of the base material and to environmental requirements (1). In the present study plasma sprayed coatings (aluminum oxide, Co-28Mo-8Cr-2Si, tungsten carbide, chrome carbide) and electrolytic hard chrome coatings abrasive wear properties have been compared. The wear tests were conducted with a Taber abraser, at room temperature.

Monitoring of Urine and Serum Cellular Enzymes in the Chromium Electroplating Workers

Monitoring of Urine and Serum Cellular Enzymes in the Chromium Electroplating Workers

Micromechanical properties and sliding wear behaviour of HVOF-sprayed Fe-based alloy coatings

The tribological performance of two Fe–Cr–Ni–Si–B–C (Colferoloy) alloy coatings manufactured by HVOF thermal spraying was studied by rubber-wheel dry particle abrasion test and ball-on-disk sliding wear tests. The results were compared to those obtained on Ni–Cr–Fe–Si–B–C and Cr3C2–NiCr layers (also manufactured by HVOF-spraying), hard chromium electroplating and bulk tool steel.At room temperature, the sliding wear loss of the Colferoloy coatings against alumina counterpart, caused by a mix of mild abrasion, delamination and tribo-oxidation, was larger than that of Cr3C2–NiCr and tool steel but lower than that of Ni–Cr–Fe–Si–B–C and hard chromium plating. At 400°C and 700°C, Colferoloy coatings mainly suffered abrasive grooving: they were still superior to Ni–Cr–Fe–Si–B–C but inferior to Cr3C2–NiCr. Against steel, Colferoloy coatings, with limited delamination and negligible wear loss, were comparable to Cr3C2–NiCr and superior to Ni–Cr–Fe–Si–B–C, tool steel and electrolytic hard chromium, although they inflicted quite significant wear to the steel counterbody.Colferoloy coatings were therefore validated as alternatives to Ni-based alloys and electroplated chromium under sliding wear conditions, but appeared unsuitable for particle abrasion resistance.The different sliding wear behaviours of HVOF-sprayed coatings could be explained by coupling micro- and nano-hardness to scratch testing, which reflected cracking resistance and plastic deformability.

Investigation Into Rejuvenation of Spent Chromium Plating Solutions by Bipolar Membrane Electrodialysis

Hexavalent chromium electroplating can form decorative or engineered chrome coatings, however it generates serious Cr(VI) contamination. Rejuvenation and reusage of spent chromium plating solutions can powerfully avoid emission of pollutant. Electrodialysis is an effective method to separate impurity cations mixed in spent chrome solutions. In conventional electrodialysis stacks, cations can be deposited on cathodes and current efficiency is decreased. Thus, the bipolar membrane electrodialysis is applied to dispose the cupric (Cu(II)) and ferric (Fe(III)) ions as impurity cations mixed in chrome solutions. Influencing factors on impurity cations removal efficiency were explored including operation conditions, membrane material, and chromium ion concentration in the bipolar membrane electrodialysis system. The results reveal that Cr(VI) concentration is a critical factor on the efficiency of rejuvenation.

Some considerations of conductivity and ion species for chromic acid electrodeposition solutions

Measurements of solution conductivity are reported for chromic acid solutions typical of those used in chromium electroplating. Optimum concentrations for conductivity are noted (450 g L−1) and the temperature ranges of ion dominance have been discussed including the use of ion colours in solution. It is concluded that practical solutions normally have trichromate and tetrachromate ions as dominant species.

Novel Chromate Sensor Based on MWCNTs/Nanosilica/Ionic Liouid/Eu Complex/Graphite as a New Nano-Composite and Its Application for Determination of Chromate Ion Concentration in Waste Water of Chromium Electroplating

Novel Chromate Sensor Based on MWCNTs/Nanosilica/Ionic Liouid/Eu Complex/Graphite as a New Nano-Composite and Its Application for Determination of Chromate Ion Concentration in Waste Water of Chromium Electroplating

Polyethylene glycol이 3가크롬 전기도금에 미치는 효과

The effect of organic additives, polyethylene glycol (PEG), on the trivalent chromium electroplating was analysed in the view point of current efficiency, solution stability and metallurgical structure. It was measured that PEG-containing trivalent chromium solution had about 10% higher current efficiency than pure solution and controlled the micro-crack density of electrodeposits. PEG exhibited profound effect on the solution stability by reducing the consumption rate of formic acid which acts as a complexant to lower the activation energy required for electrochemical reduction of trivalent chromium ions. It was also revealed that the formation of chromium carbide layer was facilitated in the presence of polyethylene glycol, which meant easier electrochemical codeposition of chromium and carbon, not single chromium deposition. Trivalent chromium layer formed from PEG-containing solution was amorphous with local nano-crystalline particles, which were prominently developed on the entire surface after non-oxidative heat treatment.

3가크롬 이온의 전착 반응에 용액 산도 및 유기물 첨가제가 미치는 영향 연구

The effect of solution acidity and organic additives, polyethylene glycol (PEG), on the trivalent chromium electroplating was systematically investigated in the view point of electroreduction of trivalent chromium ions and solution stability. It was found that solution acidity controlled at pH 2.5 showed the widest current range for bright electrodeposits in the presence of PEG additives, which reduced the local current intensification at high current densities. Through complex interaction between PEG additives and hydrogen ion, that is, solution acidity, electrode potential was moved in the negative direction in the bulk solution, while it shifted in the positive when electric potential was scanned. In conjunction with electrochemical quartz crystal microbalance (EQCM), it was found that PEG additives had a role in promoting the electron transfer to trivalent chromium ion complexes in bulk solution and their adsorption at the electrode surface as well as interfering with hydrogen ion reduction process below pH 2.5. The PEG additives developed the nodular morphology during electroreduction of trivalent chromium ions with the increase of solution acidity and enhanced its current efficiency by maintaining the consumption of complexant, formic acid, at low speed.

Corrosion Behavior of Different Thermal Spray Coatings and Hard Chromium Electroplating on A286 Super Alloy

Electrodeposited hard chromium (EHC) coatings have been widely used for improving wear characteristics of engineering tools and components. In the electrodeposition processes, in general solutions containing hexavalent chromium have been used. Hexavalent chromium is classified as a carcinogen compound, which causes health risks if used in production, and environmental problems due to the toxic character of the wastes [1]. In the present study plasma sprayed coatings (aluminum oxide, Co-28Mo-8Cr-2Si, tungsten carbide, chrome carbide) and electrolytic hard chrome coatings corrosion resistances have been compared through electrochemical polarization tests and immersion test in 0.1 N HCl aqueous solution.

Electrodeposition of CuSn Alloy from Noncyanide Sulfosuccinate Bath

Recently the regulation of nickel usage because of allergy issues has been strengthened in Europe and other countries. The Cu-Sn alloy (40-55 mass%Sn) is called “speculum alloy” or “white bronze” and has a silvery-white appearance. We developed a noncyanide Cu-Sn alloy plating bath consisting of sulfosuccinic acid, L-methionine and polyoxyethylene-α-naphthol, from which silvery-white Cu-Sn alloy (40-55mass%Sn) were obtained. It is anticipated that the Cu-Sn alloy films will be used as an alternative to nickel undercoating for decorative gold or chromium electroplating.