**1. Introduction**

It is known that corrosive processes handle many failures and accidents, involving among other drawbacks, environmental damage, and stops in the production with high economic losses. The monitoring and prevention of corrosion processes of materials in industrial plants is a worldwide need, improving the development of new (or advanced) materials, modified surfaces, and engineering processes. The conception of advanced materials is directly linked

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to investigations involving the production, degradation, and, consequently, ways to protect materials. In addition, environmental requirements considering technologies and processes must also be considered.

Functional coatings are so called because they present an additional functionality (such as corrosion protection, improved mechanical resistance or abrasion resistance, and thermal or electrical conductivity/isolation) besides their usual decorative or protection properties. These coatings are generally used to modify the surface of a substrate producing materials with enhanced or even new properties compared to those presented by the substrate itself [1–3]. Thus, depending on the application, several different ceramic, metallic, polymeric, or compo‐ site functional coating/substrate systems with own characteristics can be produced by different techniques [1,2].

The coatings constituted by a metallic matrix containing a second phase of a polymeric, metallic, or ceramic material are called metallic matrix composite coatings (MMC coatings) [4]. The second-phase materials are most commonly added to the metallic matrix as particles or nanowires, whose nature depends on the properties required for the development and application of the MMC coatings, based on the association properties of the particle and the matrix [5]. The materials most used as a second phase in MMC coatings are Al2O3, TiO2, SiO2, Cr2O3, ZrO2, WC, SiC, polystyrene, talc, and MoS2, in sizes ranging from micrometers to nanometers [6–8]. The use of these coatings for corrosion application will be the subject more deeply discussed in this chapter.

MMC coatings containing ceramic nanoparticles are very useful for advanced surface finishing applications, presenting wide application in engineering processes. The dispersion of hard nanoparticles, such as silicon carbide, silica, and alumina, or of nonmetallic nanowires on a metal matrix can yield materials with improved properties, such as hardness, wear and corrosion resistances, self-lubrication, and higher temperature stability, compared to single metal or even alloy metallic coatings [9]. High-pressure valves, drilling and car accessories, engineering and aerospace precision devices, medical, marine, and agriculture devices, mining and nuclear apparatus, microelectronics, corrosion protection for lubrication in sliding electrical contacts, and aircraft systems are some examples of fields in which these coatings are used [10,11].

The literature describes various techniques to produce functional MMC coatings, such as physical vapor deposition (PVD), chemical vapor deposition (CVD), chemical reduction (CR) or electroless process, dip coating, thermal spraying (TS), brush plating (painting) (BP), electrophoretic deposition, and electroplating (electrochemical codeposition). All of these processes aim to achieve coatings with improved uniformity, good reproducibility, high adhesion, high deposition rate, low roughness, and low cost [12–15]. It is important to mention that these features, as well as the coating morphology and microstructure, the incorporated particle size (particle clusters), and the amount of particle in the coating, depend on both the substrate and the deposition process used to produce the MMC coatings, influencing the properties of the coating/substrate system [16–22]. Table 1 presents some examples of MMC coatings produced with different deposition processes and the main results achieved by the researchers. As the present revision concerns about the corrosion resistance of nanocomposite coatings, only the coatings produced on metallic substrates will be considered.


to investigations involving the production, degradation, and, consequently, ways to protect materials. In addition, environmental requirements considering technologies and processes

Functional coatings are so called because they present an additional functionality (such as corrosion protection, improved mechanical resistance or abrasion resistance, and thermal or electrical conductivity/isolation) besides their usual decorative or protection properties. These coatings are generally used to modify the surface of a substrate producing materials with enhanced or even new properties compared to those presented by the substrate itself [1–3]. Thus, depending on the application, several different ceramic, metallic, polymeric, or compo‐ site functional coating/substrate systems with own characteristics can be produced by different

The coatings constituted by a metallic matrix containing a second phase of a polymeric, metallic, or ceramic material are called metallic matrix composite coatings (MMC coatings) [4]. The second-phase materials are most commonly added to the metallic matrix as particles or nanowires, whose nature depends on the properties required for the development and application of the MMC coatings, based on the association properties of the particle and the matrix [5]. The materials most used as a second phase in MMC coatings are Al2O3, TiO2, SiO2, Cr2O3, ZrO2, WC, SiC, polystyrene, talc, and MoS2, in sizes ranging from micrometers to nanometers [6–8]. The use of these coatings for corrosion application will be the subject more

MMC coatings containing ceramic nanoparticles are very useful for advanced surface finishing applications, presenting wide application in engineering processes. The dispersion of hard nanoparticles, such as silicon carbide, silica, and alumina, or of nonmetallic nanowires on a metal matrix can yield materials with improved properties, such as hardness, wear and corrosion resistances, self-lubrication, and higher temperature stability, compared to single metal or even alloy metallic coatings [9]. High-pressure valves, drilling and car accessories, engineering and aerospace precision devices, medical, marine, and agriculture devices, mining and nuclear apparatus, microelectronics, corrosion protection for lubrication in sliding electrical contacts, and aircraft systems are some examples of fields in which these coatings

The literature describes various techniques to produce functional MMC coatings, such as physical vapor deposition (PVD), chemical vapor deposition (CVD), chemical reduction (CR) or electroless process, dip coating, thermal spraying (TS), brush plating (painting) (BP), electrophoretic deposition, and electroplating (electrochemical codeposition). All of these processes aim to achieve coatings with improved uniformity, good reproducibility, high adhesion, high deposition rate, low roughness, and low cost [12–15]. It is important to mention that these features, as well as the coating morphology and microstructure, the incorporated particle size (particle clusters), and the amount of particle in the coating, depend on both the substrate and the deposition process used to produce the MMC coatings, influencing the properties of the coating/substrate system [16–22]. Table 1 presents some examples of MMC coatings produced with different deposition processes and the main results achieved by the researchers. As the present revision concerns about the corrosion resistance of nanocomposite

coatings, only the coatings produced on metallic substrates will be considered.

must also be considered.

148 Electrodeposition of Composite Materials

techniques [1,2].

are used [10,11].

deeply discussed in this chapter.


**Table 1.** Examples of MMC coatings produced by different deposition processes.

Although all of the aforementioned processes may be used to produce functional MMC coatings, the most widely used production method is electrochemical codeposition, also known as electrocodeposition, which consists of incorporating nanoparticles or nanowires (generally nonmetallic ones) intentionally added to the electrolyte to the metallic matrix during the electrodeposition process. This technique has been under investigation for several decades, and some authors have proposed models to explain the codeposition phenomenon of the particles during the formation of a cathodic deposit by electrodeposition [6,8,11,23–25]. This topic is still up to date because the process is more complex than the traditional electrodepo‐ sition and no commercial electrochemical baths have been developed so far for industrial production of these types of composite coatings. The main parameters that affect the process (e.g., solution pH, stirring speed, and current density) were related; however, there is no consensus in the literature concerning their effects in the nanoparticle content in the coating and in the anticorrosive performance of the coating/substrate system [5,6,8,11,12,17,23,26–28]. It is also necessary that the nanoparticles be maintained suspended and dispersed (nonag‐ glomerated) in the electrolyte during the deposition process; otherwise, the precipitation of the nanoparticles occurs and causes the loss of control of the electrochemical codeposition process. Therefore, it is important to present a more fundamental review of the parameters that involve the electrodeposition process of these coatings to obtain a better understanding of the electrochemistry codeposition phenomenon and its consequence on the anticorrosive properties of the composite coatings. Consequently, it will lead to an improvement of the processes for the development of new functional nanocomposite coatings and increase their reliability to prevent corrosion.
