Pulsed Electrodeposition of Composite Coatings Based on Zinc–Nickel Alloy

Composite electrochemical coatings (CECs) based on zinc–nickel alloy and modified by carbon nanotubes (CNTs) are obtained by pulsed electrolysis. The microstructure and tribological properties of these CECs are studied. It is found that addition of dispersed CNTs into the electrolyte for zinc–nickel alloy deposition results in a 1.35- to 1.65-fold decrease in the friction coefficient of the formed coatings. The electrochemical corrosion behavior of the zinc–nickel–CNT CECs is studied in 0.5 M H₂SO₄ solution.     

Electrodeposition of Ni–Co alloy films onto titanium substrate

Binary bright Ni–Co alloy films were electrodeposited on titanium in the chloride–sulfate electrolytes.The influences of Co2?concentration, current density, and temperature on the Ni–Co alloy films electrodeposition were investigated. The films were analyzed by scanning electron microscope(SEM), energy dispersive spectroscopy(EDS), and X-ray diffraction(XRD). Cathodic polarization for Ni–Co codeposition was performed on Ti working electrodes. With the increase of Co2?concentration, the Ni content in the films decreases and the current efficiency increases slightly. The Ni content increases with the increase of temperature, while it decreases with the increase of current density to a minimum and then increases. The cathodic reduction peak potential is measured to be-1.34 V. Anomalous deposition is found to occur in the Ni–Co codeposition. The SEM of Ni–Co alloy films shows that hydroxide particles are not present on the surface and fine grain, compact, smooth, and bright Ni–Co alloy films are obtained. The XRD result indicates that the deposited Ni–Co alloy film is Ni-solid solution with a facecentered cubic in structure.     

Electrodeposition of Ni–Co alloys from a deep eutectic solvent

Pure Ni and three Ni–Co alloys films, i.e. Ni–4 wt.%Co, Ni–18 wt.%Co, and Ni–40 wt.%Co, are electrodeposited at room temperature from the choline chloride/ethylene glycol deep eutectic solvent dissolved by nickel or/and cobalt chlorides. Electrodeposition mechanism, microstructure, and corrosion properties of the films are investigated. Surface morphology and chemical composite of the films are significantly dependent on the Ni²⁺ and Co²⁺ concentrations in the electrolytes. Interestingly, it is found that the amount of cobalt in the Ni–Co alloy films is significantly lower than that present in the electrolytes, which indicates an absence of anomalous codeposition process for the non-aqueous electrolytes. However, anomalous codeposition of Ni–Co deposits is frequently observed for the aqueous electrolytes. The Ni–Co alloy films possess face-centered cubic structures and refined grains revealed by X-ray diffractometer and scanning electron microscope. Potentiodynamic polarization measurements show that the Ni film exhibits the noblest corrosion potential and the lowest corrosion current compared with the Ni–Co alloys films. Moreover, the more Co content the Ni–Co films have, the more negative corrosion potential and the higher corrosion current the films exhibit.     

Electrodeposition and corrosion behaviour of nanocrystalline Fe–P coatings

Electrodeposition of alloy coatings is a proven route to corrosion protection of metal substrates but has met some restrictions due to changed European regulations. Iron-phosphorus codeposits appear to be eco-friendly candidates for substitution of hard chromium, and alloys such as Ni–P, Co–Ni etc. The main task in formulating proper electrolytes for Fe–P deposition is the stabilisation of the Fe²⁺ ion to hinder the oxidation to Fe³⁺ by air. In this work glycine was selected as complexing agent for Fe²⁺. Fe–P layers were deposited from a glycine-containing electrolyte at various glycine concentrations, current densities and temperatures. The properties of the layers vary greatly with a change of each applied parameter. Interaction of complex equilibria and pH change due to cathodic hydrogen evolution can lead to electrochemical oscillations which result in multilayer structures of the deposits. The corrosion resistance of Fe–P layers obtained in this work is comparable to industrially used Ni–P coatings.     

Corrosion and Physical-Mechanical Properties of Cr–P–W Alloy Obtained by Electrodeposition from Water–Dimethylformamide Electrolytes

Protection of Metals and Physical Chemistry of Surfaces - Cr–P–W protective coatings are obtained by electrodeposition from water–dimethylformamide solutions based on...     

Electrodeposition Behavior,Physicochemical Properties and Corrosion Resistance of Ni–Co Coating Modified by Gelatin Additive

The effect of gelatin on the microstructure, composition and electroplating mechanism of Ni–Co coating synthesized from sulfate media onto carbon steel substrate was investigated using AFM analysis, SEM/EDS and Electrochemical Quartz Crystal Microbalance (EQCM) coupled with chronopotentiometric measurements. The deposition of gelatin in the coating matrix was found to lower the mass of Ni–Co layers. Moreover, the adsorption of this additive seemed to inhibit the initial nucleation of the Ni–Co electrodeposition, showing homogeneous surface and smaller crystallites. Furthermore, the corrosion performance was studied in 3% NaCl solution by means of potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). After a long immersion into chloride solution, Ni–Co–Gelatin (Ni–Co–Gel) coating showed a good stability and a better corrosion resistance. Therefore, the presence of gelatin additive impacted the crystal size, corrosion resistance and Ni–Co deposits morphology.     

Electrodeposition of high performance multilayer coatings of Zn–Co using triangular current pulses

Abstract

Compositionally modulated alloy (CMA) coatings of Zn–Co were electrodeposited on to mild steel from an acid chloride bath containing thiamine hydrochloride, as an additive. Electroplating was carried out galvanostatically from a single bath containing Zn²⁺ and Co²⁺ ions. Gradual change in composition in each layer was effected by triangular current pulses, cycling between two cathode current densities. Compositionally modulated alloy coatings were developed under different conditions of cyclic cathode current density and number of layers, and their corrosion resistances were evaluated by potentiodynamic polarisation and electrochemical impedance spectroscopy. The formation of multilayer and corrosion mechanism was analysed using scanning electron microscopy. The corrosion resistances of CMA and monolithic alloy coatings were compared with that of the base metal. Compositionally modulated alloy coating at optimal configuration, represented as (Zn–Co)_{2·0/4·0/300}, was found to exhibit ～80 times better corrosion resistance compared with monolithic (Zn–Co)_3·0 alloy, deposited for the same length of time from the same bath. Improved corrosion resistance was attributed to the formation of n-type semiconductor film at the interface, supported by Mott–Schottky plots. Decrease in corrosion resistance at high degree of layering was found, and is due to lower relaxation time for redistribution of solutes in the diffusion double layer, during plating.     

Electrodeposition of gold–indium alloys

The gold–indium alloy system has a number of intermetallic, differently coloured phases, of interest to the jewellery industry, and giving rise to the name blue gold. The present study is aimed at finding out the effect of electrolysis conditions on the morphology, elemental and phase composition of the Au–In alloy coatings from different electrolytes – with cyanide, acetate and glycine – as well as establishing the conditions for formation and observation of spatio-temporal structures on the surface of the electrode, similar to those observed during the electrodeposition of other indium alloys with silver, cobalt and palladium. It was established, that blue coloured matt coatings could be obtained from acetate–citrate electrolytes and the process of electrodeposition of gold–indium alloy from glycine electrolytes is a very promising one because of the possibility to obtain a variety of spatio-temporal structures on the surfaces of the electrode which could allow the comparison with other known cases of electrodeposition of similar structures in many other alloy systems.     

Electrodeposition of zinc–nickel alloy by pulse plating using non-cyanide bath

Abstract

In this study, zinc–nickel electrodeposition was carried out in a sulphamate bath at pH 3–4 by pulse plating and the deposits obtained were characterised by measuring microhardness, surface roughness and by employing SEM, XRD, AFM techniques. The corrosion behaviour of the deposits was evaluated by potentiodynamic polarisation. The deposits obtained by pulse plating have an increased Ni content, thought to be responsible for an improved corrosion resistance.     

Electrodeposition of amorphous Ni–P layers,thermal treatment and corrosion behaviour

The investigation reported comprises an experimental study of the thermal and corrosion properties of electrodeposited nickel-phosphorus amorphous alloy layers. The structure of the species was determined by means of X-ray diffraction spectroscopy. Samples with hypo- and hyper-eutectic compositions were synthesised out of modified classical and customised electrolytic solutions on copper substrates. The composition of the samples was determined via energy dispersive spectroscopy. A short review of the development of the composition of existing plating baths for Ni–P electrodeposition has also been presented. Thermal treatment of the samples has been carried out to crystallise the amorphous structure and to compare the thermal and the corrosion properties of the species with both types of structure. Differential thermal measurements were used to examine the thermal effects in the Ni–P samples obtained. The corrosion parameters of initial as-plated and thermally treated binary Ni–P alloy coatings were determined from Tafel plot analysis.     

Effects of Temperature on the Properties of Ni–Co–BN (h) Nanocomposite Coating in Jet Electrodeposition

Protection of Metals and Physical Chemistry of Surfaces - Ni–Co–BN (h) nanocomposite coating was prepared by jet electrodeposition (JED) under different temperatures. The surface...     

Cyclic Oxidation of P91 by Thermogravimetry and Investigation of Integrity of Scale by “Transient-Mass-Gain” Method

The growth and degradation of the oxide scale on modified 9Cr–1Mo ferritic steel was studied at 1123 K using a thermogravimetric balance by employing the “transient-mass-gain method” in conjunction with the adaptation of a cyclic-oxidation procedure. The total duration of the oxidation was 1000 h. The experiment revealed that the cracking of the scale was initiated when the average thickness was 72 μm. Spallation occurred when the average thickness was 75 μm. The rate of spallation was found to be enhanced as the scale thickens and attained a higher rate after 90 μm. The rate constants for the different stages of oxidation were found to be different. The specimen was examined by SEM, EDS and XRD. The scale morphology revealed outwardly protruded growth, a uniform adherent oxide layer and a spalled region. Four oxide phases were identified; Cr₂O₃, Fe₂O₃, (FeCr)₂O₃ and FeCr₂O₄. The spall contained more (FeCr)₂O₃ whereas the adherent scale was more FeCr₂O₄.     

Nanocrystalline Fe–C alloys produced by ball milling of iron and graphite

A series of nanocrystalline Fe–C alloys with different carbon concentrations (x_tot) up to 19.4 at.% (4.90 wt.%) are prepared by ball milling. The microstructures of these alloys are characterized by transmission electron microscopy and X-ray diffraction, and partitioning of carbon between grain boundaries and grain interiors is determined by atom probe tomography. It is found that the segregation of carbon to grain boundaries of α-ferrite can significantly reduce its grain size to a few nanometers. When the grain boundaries of ferrite are saturated with carbon, a metastable thermodynamic equilibrium between the matrix and the grain boundaries is approached, inducing a decreasing grain size with increasing x_tot. Eventually the size reaches a lower limit of about 6 nm in alloys with x_tot > 6.19 at.% (1.40 wt.%); a further increase in x_tot leads to the precipitation of carbon as Fe₃C. The observed presence of an amorphous structure in 19.4 at.% C (4.90 wt.%) alloy is ascribed to a deformation-driven amorphization of Fe₃C by severe plastic deformation. By measuring the temperature dependence of the grain size for an alloy with 1.77 at.% C additional evidence is provided for a metastable equilibrium reached in the nanocrystalline alloy.     

Investigation of Si–B–C–N coatings produced by ion sputtering of SiBC target

Using the method of ion sputtering of sintered Si–B–C targets, amorphous Si–B–C–N thin-film coatings with different nitrogen contents have been prepared. The structures of coatings are studied by the methods of X-ray phase analysis, scanning electron microscopy, glow-discharge optical-emission spectroscopy, infrared spectroscopy, and Raman spectroscopy. The mechanical properties of the obtained coatings are determined using the nanoindentation method. To evaluate the oxidation resistance of the coatings, they are annealed in air at temperatures of 1000, 1100, and 1200°C. It is established that coatings of the optimal composition show a hardness of 26 GPa, an elastic modulus of 221 GPa, and an elastic recovery of 65%. The coatings obtained in the medium consisting of Ar and 15% N₂ are oxidation-resistant at temperatures of up to 1200°C owing to the formation of a SiO₂-based protective film on their surface.     

Experimental Investigation of the Phase Equilibria in the Co–V–Sn Ternary System

The phase equilibria of the Co–V–Sn ternary system at the 900 and 1000 °C sections were investigated experimentally by means of electron probe microanalysis and x-ray diffraction analysis. Seven three-phase regions were found in the isothermal section at 900 °C and six triphase regions at 1000 °C. The Heusler-type ternary compound Co₂VSn was confirmed at 900 °C in the composition ranges of 36.7–57.6 at.% Co and 11.8–20.9 at.% Sn, becoming slightly wider at the higher temperature of 1000 °C. Sn dissolves in α(Co), Co₃V, and σ-Co₂V₃ phases with low solubility. V is almost insoluble in liquid, with solubility of less than 0.5 at.%. The solubility of Co in V₃Sn phase increased with temperature, from 4.4 at.% at 900 °C to 11.6 at.% at 1000 °C.     

Investigation of the surface properties of heat treated electroless Ni–P coating

Electroless nickel phosphorus (Ni–P) coatings were synthesised from an acid chloride electrolyte. The synthesised coatings were heat treated at different temperatures, and the surfaces of the heat treated coating were characterised using scanning electron microscopy and X-ray diffraction. Adhesion, wettability, hardness and corrosion behaviour of the coatings were measured. The surface morphology showed the formation of a nano crystalline nickel matrix under heat treated condition. X-ray diffraction analysis of the heat treated samples revealed the recrystallisation of nickel and formation of Ni₃P phase in the coatings. The wettabilty study showed that the as-deposited Ni–P coating is hydrophobic and wettability increases to a maximum of 70.8° contact angle for heat treated temperature of 400°C due to nano crystalline formation. The Rockwell C adhesion test revealed the presence of micro cracks with increase in heat treatment temperature, however the failure is within the acceptability limit. The micro hardness of the Ni–P coating increased with increase in heat treatment temperature. Corrosion potential of the Ni–P coating shifted to a positive potential under heat treated conditions owing to oxidation and precipitation of Ni₃P phase. Decreased corrosion rate and corrosion current density (7.37–0.21?µA?cm^?2) is attributed to heat treatment at 400°C.     

Preparation of an Nanocrystalline Ta-Cu Alloy by Mechanical Alloying

Nanocrystalline alloy wlth graln size of about 10～20nm was prepared by mechanlcal alloying of elemen-tal powders in an imnliscible Ta-Cu system, The structure changes of Ta_70Cu_30 during mechanical alloyingwere monitored by X-ray diffraction. scanning electron microscopy and transmission electron microscopy.High-energy ball milling can efficiently reduce the grain size and considerably increase the Cu solubility in Ta.The significant enhancement of hardness of alloyed powders was also observed.     

Electrodeposition and corrosion resistance of Ni–P–TiN composite coating on AZ91D magnesium alloy

In order to improve the corrosion resistance and microhardness of AZ91D magnesium alloy, TiN nanoparticles were added to fabricate Ni–P–TiN composite coating by electrodeposition. The surface, cross-section morphology and composition were examined using SEM, EDS and XRD, and the corrosion resistance was checked by electrochemical technology. The results indicate that TiN nanoparticles were doped successfully in the Ni–P matrix after a series of complex pretreatments including activation, zinc immersion and pre-electroplating, which enhances the stability of magnesium alloy in electrolyte and the adhesion between magnesium alloy and composite coating. The microhardness of the Ni–P coating increases dramatically by adding TiN nanoparticles and subsequent heat treatment. The corrosion experimental results indicate that the corrosion resistance of Ni–P–TiN composite coating is much higher than that of uncoated AZ91D magnesium alloy and similar with Ni–P coating in short immersion time. However, TiN nanoparticles play a significant role in long-term corrosion resistance of composite coatings.     

Nanocrystalline Ni–3.6 at.% P and its transformation sequence studied by atom-probe field-ion microscopy

The transformation sequence of electroless plated nanocrystalline Ni–3.6 at.% P layers upon different heat treatments is studied by means of differential scanning calorimetry (DSC), X-ray diffraction (XRD) and atom-probe field-ion microscopy (APFIM). APFIM reveals P segregation at the grain boundaries in the as-plated nanocrystalline alloy. DSC shows two heat releases upon isochronic heat treatment. During the first heat release, starting at about 136°C for a heating rate of 20°C/min, structural relaxation occurs first, followed by slight crystal growth and segregation enhancement, as shown by XRD and APFIM. Nucleation of the equilibrium phase Ni₃P starts in the transition to the second heat release. This second heat release, with a sharp onset at 417°C for heating at a rate of 20°C/min, is related to the major part of Ni₃P-phase formation and substantial grain growth. The transformation sequence is compared with the one observed on amorphous Ni–P alloys and discussed in terms of a thermodynamic model.