Trivalent Chromium Bath Research Articles

Development of Nickel-Chromium Alloy Electroplating and Its Surface Morphology Studies for Automobile Industries

In the electroplating industry, alloy plating is typically one of the most difficult processes. We are showcasing the Ni-Cr (Nickel Chromium) alloy electroplating in our work. Trivalent chromium bath is made in order to resist the hazardous hexavalent chromium, and co-deposition of chromium and nickel is accomplished. Our work is appropriate for industrial electroplating in the automotive industry because Ni-Cr alloy exhibits good corrosion resistance along with features including wear resistance, ductility, and thermal stability. Through the use of SEM (Scanning Electron Microscopy), EDAX (Energy Dispersive X-Ray Analysis), and XRD (X-Ray Diffraction) studies, we are able to clearly observe the surface morphology in this project. These research allow us to observe the Porous behavior surfaces. Figure 1

Influence of nanoparticles concentrations on Cr–C–Al2O3 and Cr–C–SiC nanocomposite coatings electrodeposited from trivalent chromium bath

In the current study, Cr–C–Al2O3 and Cr–C–SiC nanocomposite coatings were electrodeposited on copper substrates using a modified trivalent chromium electroplating bath containing 80 nm Al2O3 and 50 nm SiC powder, respectively. The influence of concentrations of Al2O3 and SiC nanoparticles on the coatings’ crystalline structure, surface morphology, hardness, and corrosion behavior were studied. The crystalline structure, composition, and surface morphology of the coatings were investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and energy-dispersive X-ray spectroscopy (EDX). The corrosion resistance test was carried out by the potentiodynamic polarization method. The microhardness was studied via Vickers Microhardness Test. The incorporation of Al2O3 and SiC nanoparticles into the Cr matrix is critical in enhancing microhardness. From the EDX analysis, it was determined that the highest weight percentage (wt%) of Al2O3 and SiC nanoparticles in the Cr–C– Al2O3 and Cr–C–SiC nanocomposite coatings was deposited from the baths containing 40 g/L Al2O3 and SiC, respectively. Moreover, the Cr–C–Al2O3 and Cr–C–SiC nanocomposite coatings achieved the highest hardness values at concentrations of 40 g/L Al2O3 and 10 g/L SiC, respectively. The addition of nanoparticles enhanced the hardness of the coatings by 17% (Cr–C–Al2O3) and 13% (Cr–C–SiC) compared to the as-plated chromium coating. The study highlights the dispersion hardening effect of the nanoparticles, which effectively strengthens the nanocomposite coatings. However, the incorporation of agglomerated nanoparticles formed surface defects, such as microholes and gaps in the coatings, reducing their corrosion resistance. This was evidenced by a shift in corrosion potential (Ecor) towards more negative values and an increase in the corrosion current density (icor). Notably, increasing the Al2O3 concentration increased particle content and microhardness in the Cr–C–Al2O3 nanocomposite coatings, whereas this effect was not observed for Cr–C–SiC nanocomposite coatings. The hardness of the Cr–C–SiC coatings exhibited a decrease as the nanoparticle concentration increased, primarily due to the poor wettability of SiC particles. This led to the agglomeration of particles and the formation of a defective microstructure. In addition, this study presents a novel approach for the electrodeposition of Cr–C–Al2O3 and Cr–C–SiC nanocomposite coatings, effectively incorporating Al2O3 and SiC nanoparticles into the chromium matrix. The investigation of nanoparticle concentrations and their impact on the crystalline structure, surface morphology, hardness, and corrosion resistance provides valuable insights for the development of nanocomposite coatings with enhanced mechanical and protective properties.

Initial Electrodeposition Behavior of Chromium from Hydrate-Melt Based Trivalent Chromium Baths

Trivalent chromium electrodeposition is expected to substitute the conventional hard chromium electroplating that requires harmful hexavalent chromium. Recently, we revealed that crystalline chromium, which is effective for hard chromium properties, can be electrodeposited from trivalent chromium baths using chloride-based hydrate-melts. Herein, we investigated the initial behavior of the trivalent chromium electrodeposition by in situ analyses using electrochemical quartz crystal microbalance (EQCM) and ex situ characterization of resulting electrodeposits. In the very initial stage of electrolysis, proton reduction proceeds preferentially, resulting in chromium hydroxide precipitation on the electrode due to the local pH increase. Chromium reduction was found to require a few seconds of induction time to start. The transient was interpreted by the Sand equation which also indicated proton depletion near the cathode. In the hydrate-melts, due to the depletion of free water, the high proton mobility due to Grotthuss mechanism is lost, resulting in the suppression of hydrogen evolution after the induction time. This explains why chromium electrodeposits are obtained at extremely high current efficiencies of 60%–80%. Additionally, the proton reduction of the initial electrolysis stage may lead to negative effects, for example, impairing adhesion of chromium electrodeposits.

High-temperature oxidation resistance of hot stamping steel with chromium coating electroplated in trivalent chromium bath

A protective coating is essential for hot stamping steel, which tends to suffer severe oxidation during the manufacturing process to form automotive parts. In this study, chromium (Cr) coating was electroplated on 22MnB5 hot stamping steel in a trivalent Cr bath, and its oxidation resistance during austenitizing was studied. High-speed electroplating was employed, which is in line with the continuous electrogalvanizing process of the steel mill. Experimental results show that the as-electroplated coating was amorphous and composed of Cr, C, and O species. Cracks were present on the Cr coating and their effect on the oxidation resistance was ameliorated when the thickness of the coating was less than 1 μm. Specifically, a compact Cr 2 O 3 layer formed not only on the surface of Cr coating but also in the cracks, which effectively protected the underlying 22MnB5 steel from oxidation during austenitizing at 900℃.

Influence of picoseconds laser irradiation on the properties of black chromium obtained in a trivalent chromium bath

ABSTRACT In this work the influence of picosecond laser (ps) irradiation (PLI) on the properties of black Cr electrodeposited on an SS substrate has been investigated. XPS has shown that black Cr treatment by PLI changes the concentrations of elements on the black Cr coating surface. Furthermore, it diminishes the quantity of CrN compound, while increasing the quantity of metallic chromium (Cro). Full reflectance (RD) of black Cr after treatment with PLI and before treatment in the visible region (300–800 nm) were quite close. Thermal tests at a temperature of 200 oC showed that the adhesion between black Cr treated with PLI and SS is better than that of black chromium not treated with PLI. Thus, such a black Cr absorber may be used in solar water heaters.

Mechanical Behaviour of Hard Chromium Deposited from a Trivalent Chromium Bath

In view of new environmental directives, hexavalent chromium baths can no longer be used to electroplate thick hard chromium deposits. To meet these industrial and environmental challenges, deposits are developed from trivalent chromium electrolytes. Cr(III) coatings are usually studied from the point of view of the use properties and hardness, but their intrinsic properties remain widely unknown. The novelty of this work consists in the mechanical characterisation of these coatings. Properties such as hardness, stiffness, yield strength, and toughness of trivalent chromium deposits are determined by combining instrumented hardness tests, in situ FEG–SEM observations, and finite element simulations. These are explained according to the microstructure of the deposits, which is determined by scanning electron microscopy and X-ray diffraction. Their composition was characterised by glow discharge spectrometry. The structure characterisation deposits showed a more severely fractured coating of trivalent chromium than in the case of hexavalent chromium. Non-post-treated trivalent chromium deposits have a higher hardness (13 ± 1.7 GPa) and yield strength (5 GPa) than hexavalent chromium deposits. However, their stiffness (191 ± 13 GPa) and toughness (1.37 ± 0.13 MPa√m) are lower. Its mechanical behaviour is elastofragile. These differences in mechanical properties can be explained by the amorphous structure of the deposits and their high carbon content.

Wear and corrosion of Co-Cr coatings electrodeposited from a trivalent chromium solution: Effect of heat treatment temperature

Electrodeposition from a trivalent chromium bath was employed to obtain the cobalt‑chromium coatings with a thickness of ~25 μm. The effect of heat treatment temperature on characteristics, mechanical properties , and electrochemical behavior of the coatings, were examined. Heat treatment was performed in a wide range of temperatures (200–800 °C). Heat-treating below 400 °C increased the crystallinity of alloy coatings and had a negligible effect on nodular and cracked morphology. Raising the heat-treating temperature changed the X-ray diffraction patterns by thickening the surface oxide films , which consisted of different oxides (e.g., cobalt chromite spinel). The surface nodules were faded out above 700 °C. The heat-treating below 300 °C decreased the hardness and wear resistance of Co-Cr electrodeposits. The 400 °C heat-treated sample had the highest hardness of ~1000 HV, and the best tribological behavior. The weight loss and coefficient of friction of this sample were 24 and ~2 times smaller than the as-deposited coating. The hardness and wear resistance dropped again with further raising the heat-treating temperature. While detachment of coating during sliding occurred at low-temperature heat-treated samples, the abrasion was the main mechanism of material loss at those heat-treated at higher temperatures. According to the corrosion results, the optimum heat-treating temperature that the highest corrosion resistance could be achieved was 300–500 °C. The corrosion current density of 400 °C heat-treated coating was ~3.7 times smaller than the as-deposited Co-Cr film. • The relatively thick Co-Cr coatings were produced from a trivalent chromium bath. • Effect of heat treatment on Co-Cr films' characteristics and properties was studied. • Different types of oxides and morphologies were observed at various temperatures. • The 400 °C heat-treated sample showed the highest hardness and wear resistance. • Optimum heat treatment temperatures for the best corrosion resistance was 300–500 °C.

Microstructure and flow accelerated corrosion resistance of Cr coatings electrodeposited in a trivalent chromium bath

In this study, Cr coatings were electrodeposited on carbon steel substrates by a trivalent Cr salt. The microstructure of the Cr coatings and their flow accelerated corrosion (FAC) resistance in simulated secondary circuit environments (10 MPa and 150 °C) of nuclear power plants were investigated. The results showed that the as-deposited coating was amorphous and crack-free. Annealing at 200 °C resulted in the decrease of Cr (OH) 3 and the increase of Cr and Cr 2 O 3 on the coating surface , which improved the corrosion resistance of the coating. The subsequent FAC test showed that the Cr coatings significantly improved the FAC resistance of the carbon steel substrate. The coating annealed at 200 °C exhibited better FAC resistance. The Cr-rich oxide film formed on the coatings was mainly Cr 2 O 3 , with a small amount of Cr and CrO 2 . Due to the galvanic effects caused by pinhole defects, abnormally grown annular deposits formed on the coating surface. • Uniform and dense Cr coatings were electrodeposited from a trivalent Cr bath. • Annealing at 200 °C reduced Cr(OH) 3 on the coating surface and increased Cr and Cr 2 O 3 . • The Cr-rich oxide film formed in the corrosion was Cr 2 O 3 and a small amount of CrO 2 . • The interface between the coating and the substrate formed Cr-rich corrosion areas.

Electroplating of Thick Hard Chromium Coating from a Trivalent Chromium Bath Containing a Ternary Complexing Agent: A Methodological and Mechanistic Study

Trivalent chromium electroplating is considered a greener alternative to hexavalent chromium electroplating. However, the electrochemical reduction of Cr(III) in aqueous solution is extremely unstable and the thickness of the coating can hardly grow beyond 10 μm, which limits its industrial applications. We herein report a trivalent chromium bath containing a ternary complexing agent, which yields bright and uniform chromium coatings with thickness exceeding 30 μm, as well as high hardness and corrosion resistance. The electroplating behaviors and first principal calculations reveal that the Cr(II) intermediate plays a vital role in sustained electroplating in Cr(III) baths. The composition of complexing agents has a profound effect on the geometry and electron accepting ability of the Cr(II) complex ions. The failure to grow thick Cr coating is attributed to the accumulation of inactive hydroxo-bridged complexes. In the bath with ternary complexing agent, the Cr(II) complex ions are dsp3 or dsp2 hybridized with high electron affinity, which can be readily reduced to metallic Cr. The bath also shows a strong competitive ligand-binding effect that renders Cr(II) to preferentially bind with an organic ligand rather than a hydroxy ligand. Furthermore, the planar geometry of dsp2 hybridization does not favor the formation of hydroxo-bridged complexes because of the steric hindrance effect. The above merits of the ternary complexing agent lead to sustained electroplating, and thick Cr coatings are obtained.

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 %.

Crystalline chromium electroplating with high current efficiency using chloride hydrate melt-based trivalent chromium baths

Chromium (Cr) plating using trivalent chromium has been investigated as a replacement for the highly-toxic hexavalent chromium bath. Herein, we report novel chromium plating baths using hydrate-melts. Hydrate-melts have been investigated in recent years as an electrolyte for aqueous Li-ion batteries with a wide electrochemical window, and can be used as an electroplating bath in which the reduction of protons, i.e., bath decomposition, is suppressed. By using a hydrate-melt for electroplating with trivalent chromium, the increase of local pH during electrolysis is suppressed and generation of the electrochemically-inert oligomer of chromium hydroxide can be avoided. Crystalline chromium electrodeposits were successfully obtained from the hydrate-melt-based aqueous baths, which had not been possible with the conventional trivalent chromium process requiring organic coordination agents. Moreover, a current efficiency greater than 80% was achieved. The hydrate-melt-based aqueous bath, with low material cost, is a promising candidate for industrial trivalent chromium plating.

Optimization of Electrochemical Variables of Pulse-Reverse Electroplating in Trivalent Chromium Bath to Enhance the Corrosion Resistance of Chromium Film

Optimization of Electrochemical Variables of Pulse-Reverse Electroplating in Trivalent Chromium Bath to Enhance the Corrosion Resistance of Chromium Film

Hard chromium composite electroplating on high-strength stainless steel from a Cr(III)-ionic liquid solution

A composite chromium coating has been potentiostatically electroplated on high-strength stainless steel substrates from a trivalent chromium bath. The electrolyte solvent consists of 1-butyl-3-methylimidazolium chloride ([Bmim][Cl]) to which water, hexadecyltrimethylammonium bromide (CTAB), poly(diallyldimethylammonium chloride) (PDDA), and Al2O3 particles (≈3–4 μm) were added to improve the ion transport properties, the wettability at the electrolyte–substrate interface, the metallic chromium content, and the microhardness of the coating, respectively. The X-ray photoelectron spectrum of the coating reveals 85% metallic chromium and 15% chromium oxides and chromium hydroxide. Characterization of the coating shows the existence of chromium carbide-type bonds, resulting from the incorporation of carbon atoms into the chromium crystal lattice, leading to a high degree of amorphization of the coating. Optimization of electroplating conditions yielded a uniform chromium composite coating with a Vicker's microhardness of 860 (±10) HV and a thickness of 42 μm (±4), which is comparable to a chromium coating obtained from conventional chromic acid baths.

Improve the mechanical properties and wear resistance of Cr-C thin films by adding Al2O3 particles

In this study, alumina particles with various contents of 5, 10, 15, and 20 g/L in bath are co-deposited within Cr-C matrix by electrodeposition from a trivalent chromium bath. The electrodeposition is performed at a current density of 10, 15, 20 and 25 A/dm2, respectively, for 30 min. The influences of plating parameters including alumina concentration in the plating bath and current density on the volumetric percent of co-deposited particles in coating, deposition rate, morphology, hardness, corrosion resistance and wear behavior of electrodeposited Cr-C/Al2O3 composite coatings are evaluated and compared with that of electrodeposited Cr-C coatings. Our result shows that the codeposited particles percent, a determinant factor governing the hardness, corrosion resistance, and wear resistance of the coating, is influenced by concentration of alumina in bath and the current density. The maximum content of Al2O3 particles of 21.1 vol% is achieved at an Al2O3 concentration of 15 g/L in bath and a current density of 20 A/dm2. An increase of Al2O3 particles content in deposits increases the hardness of the coatings and significantly increases the corrosion as well as the wear resistance of the coatings, whereas the average friction coefficient decreases. The highest hardness approximately at 1075 HV is obtained from the Cr-C/Al2O3 composite coating with Al2O3 content of 21.5 vol%.

MCDM selection of pulse parameters for best tribological performance of Cr–Al2O3 nano-composite co-deposited from trivalent chromium bath

Optimum operating parameters for pulse co-deposition of nano-Al2O3 with Cr from a trivalent chromium bath onto Cu cathode are selected by using “technique for order performance by similarity to ideal solution” (TOPSIS), “VIšekriterijumsko KOmpromisno Rangiranje” (VIKOR), “elimination and choice expressing the reality” (ELECTRE) and “complex proportional assessment” (CORPAS) accompanied with analytic hierarchy processing (AHP) to compare methods for achievement of the best tribological coating performance. Criteria for appropriate selection include wear loss, corrosion resistance, micro-hardness, bath condition and current efficiency. Results ascertain the best Cr–Al2O3 nano-composite coating with 40% duty cycle, 10 Hz current frequency and 1 g/L nano-Al2O3 dispersed into the electrolyte bath. Comparison of the different calculated Speraman's coefficients weighed with the «subjective» analytic hierarchy process indicates more consistent results than «objective» entropy technique. The study clarifies the comparative capability of the weighing and the ranking methods in choosing the best way to make consistent final results independent of the level of knowledge and standpoints of the researchers. Recommendation of subjective rather than objective weighing apparatus to the MCDM researchers is therefore a constructive achievement.

Characterization of the Cr-C/Si3N4 Composite Coatings Electroplated from a Trivalent Chromium Bath

Cr-C/Si3N4 composite coatings are obtained by electrodeposition under DC conditions from a trivalent chromium plating bath containing suspended Si3N4 nanoparticles. The influences of plating parameters including Si3N4 concentration in the plating bath and current density on the coating composition, deposition rate, morphology, surface roughness, micro-hardness and wear behavior of electrodeposited Cr-C/Si3N4 composite coatings are evaluated and compared with that of electrodeposited Cr-C coating. Our study reveals that Si3N4 particles can be successfully codeposited and uniformed distributed in the electrodeposited Cr-C matrix. The maximum level of incorporation of Si3N4 particles, about 17.22 vol%, is obtained at a bath loading of 5gL−1 and at a current density of 20A dm−2. Due to enhanced dispersion strengthening effect, the incorporation of Si3N4 particles increases the microhardness of the coatings and significantly increases the wear resistance of the coatings.

A chrome coating from a trivalent chromium bath containing extremely low concentration of Cr<SUP align="right">3+</SUP> ions

In this study, the effects of saccharine on physical and chemical properties of Cr electrodeposition were investigated using electrochemical methods (linear voltammetry and impedance) and surface analysis methods [scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy (SEM-EDS)]. According to voltammetric and EIS measurement results, saccharine shifted Eonset to the negative area, which hinder the evolution of H2 gas and decrease the charge transfer of Cr coating, which increase the efficiency of Cr coating. According to the SEM results, it was found that saccharine increased the number of cracks on the surface. The most important result of this study is that saccharine makes Cr coating possible in the extremely low concentration of Cr3+ ion in a trivalent Cr bath.

３価クロム浴を用いた複合めっきの作製と評価

In this research, composite planting has studied using the improved trivalent chromium bath. It is known that various kinds of particles can be introduced into the chromium layers from trivalent chromium baths, though composite plating is generally difficult by the hexavalent plating bath. So, particles of hexagonal boron nitride or zirconium oxide were added and dispersed into the improved trivalent chromium bath and composite layers were electrodeposited．It was found that the hexagonal boron nitride particles were not composited. However, zirconium oxide particles could be successfully composited. The properties of the composite layers obtained were examined and the number of cracks in the layers decreased than that of the non-composite ones.

401 3価クロム浴の浴組成がめっき被膜に及ぼす効果(OS4-(1),OS4 オーガナイズドセッション≪材料・組織と加工≫)

401 3価クロム浴の浴組成がめっき被膜に及ぼす効果(OS4-(1),OS4 オーガナイズドセッション≪材料・組織と加工≫)

Investigation of the surface composition of electrodeposited black chromium by X-ray photoelectron spectroscopy

The paper reviews black chromium electrodeposited from a trivalent chromium bath containing ZnO as a second main component. The chemical compositions of the top layers of the black chromium coatings were studied by the X-ray photoelectron spectroscopy method. The surface of black chromium was found to be almost entirely covered with organic substances. To gain information on the state of each element in the deposit bulk, the layer-by-layer etching of the black chromium surface with argon gas was used. Analysis of XPS spectra has shown that the top layers of black chromium without zinc are composed of various Cr(III) components, organic substances and metallic Cr, whereas metallic Cr is almost absent in black chromium containing some amount of Zn(II) compounds. The ratios of metal/oxide phases were found to be 10/27 and 2/28 for black chromium without and with zinc, respectively. It has been determined that owing to the presence of ZnO in the Cr(III) bath, the percentage of metallic chromium is substantially reduced in black chromium which is quite important for good solar selective characteristics of the coating.The results confirm some of earlier observations and provide new information on the composition of the near-surface layers.