**1. Introduction**

Advanced engineering applications often require multifunctional materials with improved performance capabilities, which are usually difficult to fulfill using single-phase materials [1, 2]. The growing demand for improved material performance has led to the development of numerous nano-structured coatings and nano-composite coatings capable of achieving certain technological goals [3–6]. According to Wu et al. [7], these improved properties observed in

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nano-coatings have increased their range of application. Currently, these materials find application in medicine, aerospace, automotive, dentistry, electronics, and so on [8–12].

The incorporation of these particles during deposition enables the production of a wide range of composite coatings, which significantly improves the coatings' physical and chemical properties, compared to the pure metallic coatings. These properties are however dependent on the volume of particles that are incorporated in the coating during deposition and the uniformity of the distribution. The amount of incorporated particles is a key parameter for the successful application of the coatings, because it largely determines the properties of compo‐ sites such as wear resistance, high-temperature corrosion protection, oxidation resistance, and self-lubrication.

The uniformity of the particle distribution within the metal matrix is strongly influenced by the metal matrix morphological and structural characteristics. As such, the co-deposition of a sufficient amount of non-agglomerated particles should lead to production of harder and more wear-resistant coatings. The concentration of particles suspended in solution ranges from 2 g/ L up to 200 g/L, producing composites with typically 1–10 vol.% of embedded particles [13].

Particle-reinforced nano-composite coatings based on nickel and alumina are being applied in different technological fields with high demands for wear and corrosion resistance [3]. Lekka et al. [14] show that the co-deposition of SiC nano-particles in copper matrix leads to a more noticeable grain refinement, and therefore, the nano-composite deposits presented a very high micro-hardness, 61% higher than pure copper deposits, and an increase of 58% of the abrasion resistance. Future applications of these materials depend on the ability to produce them with controlled composition and properties, using inexpensive and reliable techniques.

Electrodeposition method satisfies some of these requirements because it is an economical and versatile technique compared to other preparation techniques. Electrodeposited nanocomposite coatings are generally obtained by suspending charged ceramic nano-particles in the electrolyte and co-depositing them with the metal. During the electrodeposition process, these insoluble hard particles are suspended in a conventional plating electrolyte and are captured in the growing metal film during deposition. An effective dispersion of inert particles in the electrolyte promotes the adsorption opportunity of inert particles on the cathode and causes a higher volume content of inert particles in the composite coating. The mechanical properties of the composite coating are also promoted by the enhancement of the volume content of inert particles in the coating [15–17].

Two mechanisms have been proposed to describe the process by which ceramic particles are incorporated in the metallic coatings: (1) the first mechanism is known as electrophoresis. The electrophoresis process begins with particles that are well dispersed and are able to move independently in the solvent suspension, and the particles have a surface charge due to electrochemical equilibrium with the solvent. This leads to a migratory attraction of the particles to the deposition electrode [18]. (2) A second mechanism was proposed by Williams and Martin in 1964. In their study, the researchers suggested that the particles were transported to the cathode by a purely mechanical mean due to the agitation of the bath, which leads to entrapment and subsequent embedding of the particles in the growing metal layer [19]. However, the validity of mechanical particle entrapment theory was later challenged by Brandes and Goldthorpe, who suggested that there is some attractive force holding the particles at the cathode long enough to be incorporated by the growing metal layer [20]. Guglielmi proposed a two-step mechanism taking into account electrophoresis and adsorp‐ tion.

In the first step, particles approaching the cathode become loosely adsorbed on the cathode surface [21]. These loosely adsorbed particles are still surrounded by a cloud of adsorbed ions. In the second step, the particles lose this ionic cloud and become strongly adsorbed on the cathode. This step is thought to be of an electrochemical character; that is, it depends on the electrical field at the cathode. Finally, the strongly absorbed particles are occluded by the growing metal layer [1, 22–25]. One method that has been used to reduce particle coagulation is mechanical stirring [26]. If a particle is strongly adsorbed on the cathode, it will be embedded on the growing metal layer by the electrodeposition of free solvated electro-active ions from the plating bath [3, 23].

According to the scientific literature, the factors that affect the coating properties are directly related to the parameter settings during the deposition process, and as such optimization is an important step in coating development. This chapter presents a parametric study of electrodeposited nano-composite coatings for improved abrasive wear resistance using the Taguchi L18 design of experiments (DOEs). The main focus is to evaluate the effects of the coating parameters on its wear resistance, with the objectives being to identify the optimal setting of each parameter and to quantify the contribution of each parameter to the wear resistance of the coating.
