Chromium Coatings Research Articles

Design and Structure Analysis of Platinum Titanium Anodes for Hard Chromium Coating on Shock Absorber Piston Rod

Design and Structure Analysis of Platinum Titanium Anodes for Hard Chromium Coating on Shock Absorber Piston Rod

Preparation, characterisation and electrochemical study of crack-free nanocrystalline electrodeposited Co-W alloy coating of high hardness

ABSTRACT In this work, a lustrous metallic grey nanocrystalline Co-W alloy thin coating was successfully fabricated on copper substrates via galvanostatic deposition from an acidic glycine complexing bath. The impacts of various operating conditions e.g. glycine concentrations, applied current, pH and temperature on the cathodic polarisation behaviour, anodic stripping voltammetry, cathodic current efficiency (CCE%), and alloy composition were examined. This gave the opportunity to establish the operating conditions for producing various Co-W alloys. It was found that the W content in the alloy was in the range of 7.7–13.8 wt.% depending on the operating conditions. Moreover, the CCE% of the deposited alloy was characterised by relatively high values (up to 97.0%) in comparison with other baths. The XRD analysis indicates that the Co-W alloy consists of a hexagonal close-packed (hcp) Co lattice crystalline structure of nanosized grains, of average size 15.44 nm, using 25 g L−1 glycine, at 25°C and the highest current density tested.. The microhardness of Co-W alloy coatings is comparable to or even higher than that of hard chromium coatings (∼ 963–1119 kgf mm−2). The Co-W alloy coatings are crack-free as shown from SEM investigations. The glycine bath used for Co-W alloy codeposition is environmentally friendly.

Effect of Process Parameters on Electrodeposited Nanocrystalline Chromium Coatings Investigated by an Orthogonal Experiment

The microporous nanocrystalline chromium coatings were prepared on the H13 steel by electroplating in self-regulating baths. The effects of electroplating parameters including current density, compositions of baths, bath temperature and plating time on the surface quality, thickness of chromium coating and cathode current efficiency were investigated by an orthogonal experiment. Experimental results indicated that the surface quality, thickness of chromium coating and cathode current efficiency can be improved by adjusting these electroplating parameters. Furthermore, bath temperature has the greatest effect on the surface quality of chromium coating, and the high qualified surfaces were only obtained at higher temperatures of 55 and 65°C. Current density was the most significant factor for the thickness of coating and cathode current efficiency. Chromium coating with high surface quality, thickness and cathode current efficiency was obtained at current density 90 A/dm2, CrO3 250 g/L, K2SiF6 10 g/L, SrSO4 1 g/L, bath temperature 65°C and plating time 120 min, which is consisting of pure nanocrystalline chromium with a body-centered cubic structure. And the coating exhibits much higher microhardness and corrosion resistance than for H13 steel.

Effect of Addition of Polyethylene Glycol into Trivalent Chromium Bath on Chromium Coating

Conventionally, chromium is deposited from hexavalent chromium baths containing extremely toxic compounds of Cr (VI). Due to serious health and environmental concerns of Cr (VI), trivalent chromium bath is proposed as a counter approach towards greener and safer chromium plating. In the present work, chromium coatings were electrodeposited onto copper substrate using a modified trivalent chromium electroplating bath with addition of polyethylene glycol (PEG 1500). The effects of PEG on the Cr coating were investigated. The crystalline structure, composition and surface morphology of the deposits were studied by X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX) and scanning electron microscopy (SEM). The surface roughness of the coatings were characterized by atomic force microscopy (AFM). With addition of PEG, the surface roughness of Cr coating decreased by 44.5 % and the corrosion rate decreased by 23.3 % compared to that of without PEG. Meanwhile, the hardness increased by 22.7 %.

Influence of Laser Energy Density on Interfacial Diffusion Bonding and Surface Density of Chromium Coating by Multi-Arc Ion Plating on Zirconium Alloy

The chromium coating prepared by multi-arc ion plating on the surface of zirconium alloy is easy to fall off under extremely harsh conditions due to the defects of larger particles, pores and weak adhesion between the coating and the zirconium alloy substrate. Here we apply a new composite process for the fabrication of Cr coating by laser melting multi-arc ion plating technology. The numerical model of temperature field laser melting treatment was established, and based on the analysis of the above temperature field of laser melting treatment, the laser with an energy density of 9 × 104 J/cm2–18 × 104 J/cm2 was selected as the heat source. Laser energy density has a great influence on the diffusion behavior of Cr at the coating-substrate interface. When the energy density of laser is 9 × 104 J/cm2, the laser heat source cannot provide enough energy to melt the surface of the coating, however, the Cr element diffuses slightly at the membrane base interface, forming a Cr diffusion zone of about 4 μm. When the energy density of the laser increases to 13.5 × 104 J/cm2, the Zr element of the substrate diffused to the whole Cr coating, and the original Cr coating disappeared, forming a Zr-Cr diffusion and fusion zone of 30 μm. As the laser preparation process of the coating is a mixed sintering process of liquid phase sintering and solid phase sintering, the coating surface forms a dense zone and a loose zone respectively, resulting in the increase of porosity and particle rate. With the laser energy density increasing gradually, the Zr-Cr fusion zone is formed, and the coating surface particles were gradually refined and the pores were significantly reduced. With the further increase of laser energy density of 18 × 104 J/cm2, the Zr-Cr fusion zone was extended to 60 μm, and the porosity and particle rate were reduced to 0.3% and 0.4% respectively. In addition, the original stratification cracking of the film base at the fracture of the tensile specimen disappears, and the protrusion of the interface is formed. Coatings with dimple fractures were found, which indicates that the coating exhibited ductility and interfacial metallurgical bonding.

The corrosion-resistant Ni-based coatings and their tribological properties

Abstract Ni-based coatings can be successfully applied under abrasive and adhesive conditions as a substitute for environmentally harmful chrome coatings. The research has been carried out for thermally flame sprayed Ni-based coatings with remelting (so-called the two-step process) with the different chemical composition of starting powders. The structure of coatings was evaluated by optical and scanning electron microscopy. Both the three-body abrasive wear test, according to ASTM G65-4 (Dry-Sand Rubber Wheel Test) and dry sliding wear test by the Falex tester, were performed. The results show the influence of the effective chemical composition of the metal powders on improving the properties of the coating. The higher hardness of the coatings leads to a lower tendency for the creation of adhesive bonds, and as a result, leads to a lower tendency to scuffing. A similar trend shows the influence of higher coating hardness on the increasing of abrasive wear resistance.

Mechanical properties, thermal stability and oxidation resistance of TiN/CrN multilayer coatings

Chromium and titanium nitride coatings are well known for their high hardness and good wear resistance. Here, we research the mechanical and thermal properties of TiN/CrN_M1 and _M2 multilayers with bilayer period of ~17.8 and 6.7 nm by means of X-ray diffraction, Transmission electron microscopy, Scanning electron microscopy and Nanoindentation, which combines the advantages of TiN and CrN coatings. The interfacial strengthening arising from coherent interface leads to an increased hardness of ~27.5 GPa for TiN/CrN_M1 and ~29.4 GPa for TiN/CrN_M2, corresponding to ~26.4 Gpa for TiN and ~17.3 GPa for CrN. The TiN insertion layer retards the thermal decomposition process of CrN due to the higher binding energy of Ti–N bond than Cr–N, and thus evinces higher thermal stability of TiN/CrN multilayers. Furthermore, the TiN/CrN multilayers exhibit better oxidation resistance than TiN coatings.

Effect of Electrodeposition Current and Pulse Parameter on Surface Mechanical and Electrochemical Behavior of Ni–W Alloy Coatings

Ni–W alloy coatings have various applications because they are capable of replacing hard chromium coatings due to their corrosion, oxidation, wear, and hardness properties. Moreover, these alloys demonstrate excellent mechanical and thermal stability at high temperatures leading to possible specialized applications of such coatings. In this study, the effect of pulse frequency and current density on the structure and properties of electrodeposited Ni–W coating were investigated. Pulse electro-co-deposition technique was employed to synthesize Ni–W alloy coatings by varying pulse frequency and current density. The deposition process was performed in the newly established deposition bath that does not contain surfactants and stress-relieving agents. The Ni–W-coated samples were evaluated to determine surface mechanical (microhardness and wear) and electrochemical properties. Phase formation, microstructure, and compositional analysis of Ni–W alloy coatings were examined by XRD, SEM, and EDS, respectively. Microstructure examination revealed that morphology of the coating varied with pulsed frequency and current density. An increase in the current density at fixed pulse frequency improved the surface mechanical properties (hardness and wear properties) owing to higher W content, fine, and dense structure of the coating. The maximum hardness (920 HV) and wear resistance were observed in the Ni–W coating that was obtained at the current density of 60 mA cm−2 and frequency of 2 kHz. Electrochemical polarization test and EIS study carried out in 3.5 wt pct NaCl solution reveal that a decrease in corrosion resistance of the coating is due to finer morphology or strained matrix whereas higher W content improves the corrosion resistance.

Characteristics and Properties of Chromium Coatings with Diamond Nanoparticles Deposited Directly on Aluminum Alloys

Characteristics and Properties of Chromium Coatings with Diamond Nanoparticles Deposited Directly on Aluminum Alloys

Cobalt/Chromium Carbide Composite Coatings Applied By Brush Plating for Use As an Alternative to Hard Chrome

Due to increased concern for both environmental and worker safety from governments around the world, numerous significant industrial chemicals are being phased out of production processes. One example is the use of hexavalent chromium compounds for the electrodeposition of hard chrome. Electrodeposited chrome is typically used for improved hardness, lubricity, wear resistance, and corrosion resistance. This work will support the use of a metal matrix composite composed of cobalt and chromium carbide particles as an alternative for chrome coatings deposited from hexavalent chromium compounds.Metal matrix composite (MMC) coatings consist of two phases co-deposited during plating: a continuous metal phase such as cobalt and small (<100 µm) particles of another chemical species distributed throughout. The physical qualities of the composite (such as hardness) are strongly dependent on the ratio and distribution of the two constituent phases. The composition of the plating solution and the parameters used during plating both play important roles in the composition and quality of the final deposit.While most research has focused on applying metal matrix composites by tank electroplating methods, this presentation will focus on applying the coating via brush plating. Brush plating is a portable electrodeposition technique where solution is applied to the part by a plating solution saturated sleeve on the anode when contact is made to a localized area. Brush plating operations typically use less masking when plating small areas of a larger part. Less solution is needed because the part does not need to be immersed. And the brushing action allows for faster solution replenishment at the electrode surface.During this presentation, attendees will be shown examples of a matrix material of cobalt co-deposited with either 1 µm or 6 µm chromium carbide particles. Attendees will learn how the concentration of the particle in solution determines the range of particle incorporation; as well as understand how tailoring the plating parameters to the system of particle and matrix is vital to creating a deposit for their specific characteristics.

Application of experimental design for selection of optimal modes of electro-deformation cladding with a flexible tool

Experimental-statistical models of the process of forming composite chromium coatings by electrodeformation cladding with a flexible tool are developed, which allow to determine the parameters of the regimes for obtaining coatings of the required thickness and roughness. Keywords electrodeformation cladding, flexible tool, coating, composite material, experiment planning, noncompositional plan, thickness, roughness. levancev@mail.ru

Effect of Saccharose Concentration and Temperature on the Internal Stress and Corrosion Resistance of Electroplated Chromium Coatings Prepared from Chromium (III) Bath

Effect of Saccharose Concentration and Temperature on the Internal Stress and Corrosion Resistance of Electroplated Chromium Coatings Prepared from Chromium (III) Bath

Effect of pulse current and coating thickness on the microstructure and FCCI resistance of electroplated chromium on HT9 steel cladding

In this study, we examined the interrelations among electroplating parameters, such as pulse current and electroplating duration; structural properties (such as crystalline structure, grain size, micro-cracking, and coating thickness); and physical properties (such as hardness and Fuel and Cladding Chemical Interaction (FCCI) barrier properties) of chromium barriers. Chromium coatings were electroplated onto HT9 steel disks using direct current and pulse current (PC) for different durations to investigate the influence of PC and coating thickness on the resulting microstructure and FCCI resistance. PC and a coating thicker than 20 μm were found to be effective for improving the barrier properties of Cr coatings. Scanning electron microscopy and electron backscatter diffraction analyses revealed sound microstructures without micro-cracking and twofold grain structures including large and small grains near the outer surface and HT9 substrate of the pulse-plated Cr coatings thicker than 20 μm, respectively. These resulted in reduced interdiffusion area and interdiffusion depth in the microstructure of the diffusion-coupled specimens. Heat-treatment of Cr coatings at 650 °C for times ranging from 50 to 1000 h revealed that the grain size increases with increasing heat-treatment time. The measured Vickers hardness of Cr coatings decreased with increasing grain size and resulted in only 42.6% hardness of as-electroplated Cr coatings after 1000 h of heat-treatment.

Peculiarities of Chromium Coating in Low-Concentrated Electrolytes when Repairing Details

The physical-mechanical properties of chromium coatings from low-concentrated electrolytes with additions of organic substances were studied when comparing with similar ones from standard sulphate electrolyte. It has been established that the properties of chromium coatings from low concentrated electrolytes are superior to those of standard sulphate electrolyte. An additional advantage of low-concentrated electrolytes is less carry-over of chromium anhydrate through ventilation and wash water, which reduces the cost of cleaning them when they are discharged. However, under operating conditions, more frequent adjustment of the composition of such electrolytes is required. The electrolyte is distinguished by a good scattering over the surface of parts and covering power when restored to size on a thickness of 250-300 μm of hydraulic cylinders of agricultural and mining equipment, having a length of up to 4 m and a diameter of up to 0.5 m, an increased current output of up to 24-36 % and up to 3-4 times higher corrosion resistance, micro hardness of up to 1,300 kg / mm2, determined by the conditions of deposition relative to the standard sulfate electrolyte of chromium plating. Chromium coatings from a low-concentration electrolyte with organic additives passed the recommended tests for adhesion, tearing, wear and micro hardness according to GOST methods. Their use at the enterprises of technical service for repair of agricultural parts promises economic advantages in the field of practical application (higher deposition rate and less application time), as well as lower costs for environmental protection.

Corrective Maintenance and Hardening of Agricultural Machinery Parts

The article presents information on the technological characteristics and industrial use of chroming electrolytes. The modern electrochemical technologies of repairing worn-out parts of agricultural machinery are considered. Particular attention is paid to the use of chrome plating methods making possible to increase the durability and reliability of the parts recovered in electrolytes of different composition, allowing to obtain coatings with high physical-mechanical properties that determine their suitability for the operation in the process of use for their intended purpose. The use of self-regulating dilute chroming electrolytes makes possible to increase the productivity of the deposition process of chromium coatings significantly, to obtain high-quality coatings of chromium and iron, and high adhesion to the base material - carbon, alloyed steels, and cast iron. The deposition of metals using reverse, pulsed currents with adjustable anodic-cathodic ratio of amplitude values and its duration allows to influence electro crystallization, control the structure, texture and roughness of the formed precipitate, which makes possible to get with predetermined functional physical and mechanical properties for specific repair conditions and subsequent operation in agricultural machinery. The following modes are recommended for brilliant coatings: when reverse current τ (cat) / τ (an) = 50-70, τ (cat) = 4-7 min, D(cat) = 40-100 А / dm2, D(cat) / D(an) = 3-4, Т = 60-65 ° С; when impulse current D(cat) = 40-100 А / dm2, Т = 60-65 ° С, τ (imp) = 1.5-2.5 min, τ (pauses) = 5-10 sec., impulse ratio 1.07-1.15.

Theoretical Analysis of Chroming Electrolytes and Properties of Chrome Coatings

According to the dynamic characteristics of the electrochemical system, according to V.F. Molchanov, it is possible to optimize the composition of chroming electrolyte and predict the properties of chromium deposits depending on the mode of deposition and the transition time. The possibility of using the transition time for the formation of the cathode surface colloid-dispersion film to study the chemical composition of the chroming solution is considered. The chemical composition can be optimized by the position of the maxima and minima on the polarization curves. An electrochemical cell can be described as a system by a differential equation, the form of which is determined by its internal structure, which varies with electrolysis conditions. The properties of the system are evaluated by a number of factors: the time of the transition process, forcing, attenuation, and the quality factor. This approach is used to develop a low-concentration chroming electrolyte with organic additives. Analytical dependences of chromium yield on current, micro hardness, roughness and deposition rate on deposition conditions are obtained. Chroming on non-stationary modes allows the most effective influence on the structure and physical-mechanical properties of coatings. When changing electrolysis parameters, it is possible to influence the structure and physical-mechanical properties of coatings, to obtain various functional chromium coatings with specified characteristics (adjustable micro hardness in thickness, porosity, internal stresses, corrosion resistance, wear resistance, roughness) from a single electrolyte. The use of a low-concentration electrolyte together with non-stationary deposition modes makes possible to increase the chromium current yield, covering and dissipative ability of the electrolyte, deposition rate, producibility and environmental friendliness of the process, and to reduce hydrogenation. The electrolyte with crystal violet additives has an increased current output (up to 28 %), an extended range of obtaining wear-resistant coatings up to 240 A / dm2, a high deposition rate of up to 2.5 μm / min, an increased micro hardness by 100-300 kg / mm2, reduced toxicity, a decreased absorbed hydrogen level at 500-700 cm3 per 100 grams of chrome coating and internal stresses at 600-950 kg / mm2.

Effect of heat treatments on the mechanical and tribological properties of electrodeposited Fe–W/Al2O3 composites

In this study, the influence of heat treatment on the mechanical and tribological properties of electrodeposited Fe–W/Al2O3 composite coatings is studied. The properties of the as-deposited and annealed composites are compared with those of electrodeposited hard chromium coatings. The amorphous structure of the Fe–W matrix transforms into a mixed amorphous-crystalline structure upon annealing at 600 °C for 1 h. The observed microstructural transformations result in a substantial increase of both the hardness and the reduced Young's modulus of the Fe–W/Al2O3 composite coatings, reaching values of 16.3 GPa and 191.7 GPa, respectively. The results on the wear resistance studied under dry friction using ball-on-disc sliding tests show that a low wear rate is obtained for both as-deposited and annealed composite coatings, i.e. ~1.5 × 10−6 mm3/Nm. In contrast, the heat treatments are detrimental for both the hardness and wear resistance of hard chromium coatings. As a consequence, the mechanical and wear properties of the electrodeposited Fe–W/Al2O3 composite coatings, especially after annealing, are superior to the properties of hard chromium coatings. Hence, Fe–W/Al2O3 composite coatings can be considered as a valid and sustainable alternative to hard chromium coatings, particularly in applications where these materials may be exposed to high temperatures.

Tribological characterization of electrolytic hard chrome & WC-C0 coatings

Hard chrome plating are commonly used in automobile, aerospace and nuclear industries. Hardness, wear and corrosion resistance of chrome plated component is high. However, there are environmental issues concerning chemical processing. Chrome plating can be replaced by WO-CO coating. The objective of this work is to fabricate both coatings and compare their tribological and mechanical properties. Spray coating is used to fabricate WO-CO layer and conventional route is chosen to fabricate chrome plated specimen. It is observed that WO-CO coating gives much lower coefficient of friction under 20 N, 25 N and 30 N load. The wear rate of the WO-CO coating is less compared to EHC coating.

Synergistic role of carbon nanotube and yttria stabilised zirconia reinforcement on wear and corrosion resistance of Cr-based nano-composite coatings

In the present work, electrodeposited chromium coatings were strengthened with 3 mol% yttria-stabilised zirconia nanoparticles (YSZ) and carbon nanotubes (CNT) to analyse anti-corrosive and wear properties of the coatings. Highest hardness (~24 GPa), minimum scratch wear rate i.e. ~3 × 10−11 m3/Nm and highest corrosion resistance of ~3.9 kΩcm2 was obtained by synergistic incorporation of YSZ and CNT in Cr matrix. This can be linked to high dislocation density ~22 × 1011 cm−2 (Orowan effect) and compressive residual stresses i.e. ~840 MPa (Cr-YSZ-CNT), which tend to seal-up micro-holes and cavities, thereby, restricting the onset of wear and corrosion in the matrix. Addition of inert YSZ nanoparticles imparts chemical stability as well as hardness to the Cr matrix (~11 GPa for Cr-YSZ, ~8.4 GPa for Cr). Further, CNT incorporation, apart from matrix strengthening, results in low COF (~0.12) due to self-lubricating nature of CNTs, which leads to reduced wear rate of ~3.8 × 10−11 m3/Nm (Cr-CNT) with respect to Cr and Cr-YSZ. Thus, barrier protection and corrosion inhibition might be protective mechanisms for Cr-YSZ-CNT coating that make it suitable for engineering and industrial applications in order to protect the vital components exposed to tribological and corrosive media conditions.

Modification of the high-temperature performance of thin chromium coatings deposited on valve steels

ABSTRACTThe influence of yttrium, as well as the thickness of chromium layers sputter-deposited on valve steels (X33CrNiMn23-8, X50CrMnNiNbN21-9, X53CrMnNiN20-8 and X55CrMnNiN20-8) on their oxidation resistance, was studied under isothermal (900°C) and thermal shock conditions (25–900°C). We found out that chromium layers with higher thickness increase oxidation resistance only in the case of valve steels with lower chromium content. On the other hand, a modification made by deposition of small yttrium additions on the surface of coatings significantly increases oxidation resistance of protected steels. This is due to the formation of highly protective chromia scale or chromium-containing spinel oxide phases during oxidation, instead of non-protective iron oxides. Additionally, 100-h corrosion tests were carried out on valves covered by chromium coatings in real working conditions of an internal combustion engine. The obtained positive results strongly support the idea of tailoring a new generation of inexpensive, thin coatings for engine valve protection.