**1. Introduction**

Nickel matrix composite/nanocomposite coatings have gained a variety of use in many industrial applications where high wear and corrosion performance are required. The applications where these coatings are employed include automotive, aerospace, electronics, petrochemical, nuclear, marine, and many more [1,2]. The incorporation of nanostructured particles into the matrix imparts special characteristics that are not exhibited by the traditional micro-sized composite coatings. The nanocomposite coatings possess improved properties

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such as high hardness, excellent corrosion resistance, thermal stability, wear resistance, and self-lubrication properties [3]. The nanoparticles incorporated into the matrix include those of metal oxides, carbides, nitrides, borides, polymers, and carbon-based materials [4–6].

Electrodeposition is one of the surface modification techniques that are used to fabricate nickel nanocomposite coatings. This technique has several advantages over the other processing methods which include low cost, simplicity of operation, versatility, high production rates, industrial applicability, and few size and shape limitations [7]. However, co-deposition of nanostructured inert particles using electrodeposition has its own challenges. Agglomeration of particles in the electroplating bath, inhomogeneity in the distribution of particles in the matrix, and low content of particles in the coatings are some of the drawbacks associated with this process [8]. These problems compromise the quality of the coatings and result in poor performance during application. Therefore, proper process development and optimization are required to counteract the limitations.

Many researches have been conducted in an attempt to address these limitations. Additions of chemical agents into electrolytic solutions to aid co-deposition of the particles have been found by many researchers to reduce agglomeration of particles and increase their incorpo‐ ration in the matrix. These additives disturb the electrostatic stabilization of the particles and hence promote their suspension in the solution [9]. Pulse current electrodeposition is another method that has been employed to enhance co-deposition and improve uniform distribution of particles. This type of plating has three independent variables for controlling co-deposition as compared to direct current plating which only has one variable [10]. Ultrasonic energy has also been used to improve the inclusion of particles into the metal matrix. It enhances mass transport of particles to the cathode for co-deposition, reduces the thickness of the diffusion layer, and disperses the particles in the electrolyte [11,12].
