Corrosion Resistance Of Nickel Coatings Research Articles

Influence of Nickel Powders on Corrosion Resistance of Cold Sprayed Coatings on Al7075 Substrate

The influence of the size and structure of nickel powder grains on the corrosion resistance of nickel coatings on an Al7075 substrate in an acidic chloride solution was investigated. The Ni coating was produced by the cold spraying (CS) method. The surface and microstructure of specimens were observed by a scanning electron microscope (SEM). The corrosion test of the materials was carried out by using the electrochemical method. It has been found that the size of Ni powders has a significant effect on the corrosion resistance of nickel coatings. The porosity of nickel coatings on the Al7075 alloy increases with the increasing size of nickel powders. The corrosion rate of nickel coatings in the chloride environment decreases as the diameter of the nickel powders decreases. On the other hand, the highest corrosion resistance of nickel coatings was obtained using the Ni powders of the irregular spherical or dendritic structure. Moreover, the large particles of nickel powder cause strong residual stress (compared to small grains) in the depth of the nickel coatings.

Corrosion resistance of nickel coatings deposited from low-temperature nickel-plating electrolytes

The corrosion resistance of nickel coatings on a copper substrate, plated from low-temperature electrolytes based on acetates, tartrates, and isobutyrates, was studied by the methods of electrochem ...

Effect of ammonium chloride on microstructure, super-hydrophobicity and corrosion resistance of nickel coatings

Abstract Nickel coatings were prepared at different concentrations of NH 4 Cl as a crystal modifier in the electrodeposition bath. Surface morphology, wettability and the preferred orientation of the coatings were characterized by scanning electron microscopy, optical contact angle meter and X-ray diffractometer (XRD), respectively. The results showed that NH 4 Cl considerably affected the microstructure of the coatings; NH 4 Cl modified surface morphology towards an appropriate micro-nano cones structure. The contact angle of water droplets on the nickel coatings increased over time, eventually approaching a super-hydrophobic surface. Indeed, the super-hydrophobic surface showed a good long-term durability in air. XRD results indicated that NH 4 Cl changed the preferred orientation from (220) to (111) by a complex growth mode. The role of NH 4 Cl was studied by cyclic voltammetry and electrochemical impedance spectroscopy techniques. It was found that NH 4 Cl inhibited the nucleation of nickel deposits by increasing charge transfer resistance. Electrochemical measurements at long-term immersions indicated that the super-hydrophobic nickel coatings greatly enhanced the corrosion resistance of copper substrate in the neutral 3.5 wt.% NaCl solution. The results revealed that super-hydrophobicity considerably increased the polarization resistance from 21 to 272 kΩ · cm 2 . After decay of hydrophobic property, the passive oxide layer played the major role to protect the coatings in the corrosive solution.

Effect of Pulse Electrodeposition on Properties of Nanocrystalline Nickel Coatings

In this work, nanocrystalline nickel coatings were electrodeposited from a Watts bath using direct (DC) and pulsed (PC) current. Effect of deposition conditions on the morphology, hardness, grain size, surface roughness and corrosion resistance of nickel coatings were investigated. Ni films deposited by PC method exhibited greater hardness values and smaller crystallite size compared to those deposited by DC method. A preferential crystallographic orientation or texture was found in the nickel films depending upon the electrodeposition pulse shape, as it is polycrystalline in the DC electrodeposited films, while exhibit <111> crystallographic growth direction for PC method. Corrosion evaluation results showed that the PC electrodeposited nanocrystalline Ni films have higher corrosion resistant compared to those deposited with the DC method in 2 mol/liter NaOH solution.

Corrosion Resistance of Nickel Coatings Obtained by Electrodeposition in a Sulfamate Bath in the Presence of Samarium (III)

Corrosion Resistance of Nickel Coatings Obtained by Electrodeposition in a Sulfamate Bath in the Presence of Samarium (III)

Structure and corrosion resistance of nickel coatings containing tungsten and silicon powders

Ni + W + Si coatings were prepared by nickel deposition from a bath containing a suspension of tungsten and silicon powders. These coatings were obtained at galvanostatic conditions, at the current density of j dep = − 0.100 A cm − 2 and at the temperature of 338 K. For determination of the influence of phase composition and surface morphology of these coatings on changes in the corrosion resistance, these coatings were modified in an argon atmosphere by thermal treatment at 1373 K during 1 h. A scanning electron microscope was used for surface morphology characterization of the coatings. The chemical composition of the coatings was determined by EDS and phase composition investigations were conducted by X-ray diffraction. It was found that the as-deposited coatings consist of a three-phase structure, i.e., nickel, tungsten and silicon. The phase composition for the Ni + W + Si coatings after thermal treatment is markedly different. The main peaks corresponding to Ni and W coexist with the new phases: NiW, NiWSi and a solid solution of W in Ni. Electrochemical corrosion resistance investigations were carried out in 5 M KOH, using potentiodynamic and electrochemical impedance spectroscopy (EIS) methods. On the basis of these investigations it was found that the Ni + W + Si coatings after thermal treatment are more corrosion resistant in alkaline solution than the as-deposited coatings. The reasons for this are a reduction in the amount of free nickel and tungsten, the presence of new phases (in particular polymetallic silicides), and a decrease of the active surface area of the coatings after thermal treatment.

Polarization Characteristics and Corrosion Resistance of Nickel Coatings

The anode-polarization characteristics of four bright and four semi-bright nickel deposits have been determined, in three different electrolytes. In all cases, the semi-bright deposits were more no...