The operating process, versatility and the increasing research interest in optimising the process and products technology in the electroless plating method of metal coating, particularly, the electroless nickel plating of metallic substrates such as mild steel, necessitates the writing of this review. It is also aimed at providing more literature information, both of the past and the present published research in this field. In this paper, electroless nickel plating is introduced. The various nickel plating solutions and baths’ operating parameters; main types of electroless nickel plating; the mechanism involved in the plating process; application of the nickel plating process to iron powders; advantages and disadvantages and the process’s other applications are reviewed. Electroless nickel plating produces an amorphous deposit in the as-plated condition. The deposit is not dependent on current distribution and hence it is almost uniform in thickness. Electroless nickel plating is far more difficult to remove chemically than conventional nickel deposits due to its superior corrosion resistance. The deposit has a good wettability and is generally hard. However, its bath control is more complex than with electroplating. The bath also has lower efficiency and higher operating costs, even without the use of electricity.

Electroless Nickel Plating – A Review

Electrochemical and structural properties of electroless Ni-P-SiC nanocomposite coatings

In this study, a Ni–P–WC nanocomposite coating was prepared by electroless deposition methods, modifying the typical Ni–P coating through the addition of WC nano-particles. The morphology, structure, microhardness and corrosion resistance of the Ni–P–WC coating and conventional Ni–P coating were analyzed by using the optical stereoscopic microscopy (OSM), scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), anodic polarization curve and electrochemical impedance spectroscopy (EIS). It was observed that WC nano-particles and Ni–P deposited homogeneously on the Ni–P matrix, electroless deposited composite coatings exhibit an amorphous structure of the nickel matrix in which crystalline tungsten carbide is incorporated. The microhardness of the coating increased due to the existence of the nano-particles, and it will be improved after heat treatment. According to the results of corrosion testing in the 3.5 wt.% sodium chloride solution, the electroless Ni–P–WC coatings showed significantly improved corrosion resistance due to its special structure, compared to a conventional Ni–P electroless coating, even after 40 days immersion, it also exhibited good corrosion resistance ability.

Development of electroless Ni–P/nano-WC composite coatings and investigation on its properties

Synthesis and properties of electrodeposited Ni–B–CeO2 composite coatings

Properties of electrodeposited Ni–B–Al2O3 composite coatings

To verify the relationship between the properties of composite coatings prepared on Q235 steel and the SiC content of electroless Ni–P–SiC composite coatings, systematic experiments with varied SiC contents and surfactants have been conducted. The experimental results indicated the approximate linear relation between the SiC content and the hardness of composite coatings. With the increasing of SiC content, wear resistance increases correspondingly. In particular, the effect of SiC content on the corrosion resistance of Ni–P–SiC composite coatings immersed in different corrosive solutions (i.e. 5% H2SO4, 20% NaOH and 3.5% NaCl) is explored, followed by a comparative analysis of the corrosion resistance between Ni–P and Ni–P–SiC coatings. Corrosion test indicates that NaOH solution makes no differences in the corrosion resistance between Ni–P coatings and electroless Ni–P–SiC composite coatings, both being uncorroded. Exposed to NaCl solution, the corrosion resistance of electroless Ni–P–SiC composite coatings decreases gradually with the increasing of SiC content in coatings. In H2SO4 solution, the corrosion resistance of coatings increases initially and decreases afterwards with the sustained increasing of SiC content in coatings, and the optimized corrosion resistance is obtained at a SiC content of 9.41 wt.%. Finally, a competent electroless Ni–P–SiC composite plating process producing a high wear resistance and sound corrosion resistance of the coatings is obtained.

Lin Cheng

Papers

The effect of SiC particles added in electroless Ni–P plating solution on the properties of composite coatings