**2.1. Factors affecting the coating structure**

In this complex phenomenon, there are many factors that affect the process, consequently the properties and the performance of the material. These factors can be classified in four groups basicly.


The factors are described in Section 3.1 in details for both electrodeposition and electro codeposition techniques.

#### **2.2. Layers and the Properties Related to**

In a coating system four different zones are described by Holleck [3] when protecting materials with coatings. These are:

**•** Substrate;

reactions with the environment take place, which will sooner or later damage functionality by attacking the surface. Because of the atomic structure, the surface of a material or a component is the most vulnerable site for various forms of attacks and, therefore; it might be deemed. These attacks could be present individually or in combination of mechanical, chemical, electrochemical or thermal in nature [1]. The coating processes which maximize the lifetime of the materials can be classified as evaporation, hot metal processes, painting, thermal spraying, and **metallising**. Metallising appears to have particular importance in these main coating processes compared to others. Metallising is devided in two sub-groups, such as

Among the processes concerning the production of nanostructured composites, the electro‐ deposition technique has further demonstrated the following benefits: a smoother surface, a better bonding between particles and a metal, an easier control of the thickness of the coating, appropriacy to automation, availability for obtaining metallic alloys and composite coatings,

It is known that combining the best properties of different materials to obtain one material with excellent properties is the main idea of fabricating composites. **Electrolytic co-deposition**

In the present chapter, entitled **A New Approach: In-situ Codeposition of Composite Coatings,** general information about electrolytic coating and electrolytic codeposition is given and the factors affecting the coating structure, the main layer-property relations are explained in details. The electrolytic codeposition section explains the parameters, such as pH, zeta potential, agitation and etc., affecting this process. Under the section 3, property-performance relations of these coatings are examined. Finally, **in-situ codeposition** is detailed with examples and the experimental findings of our and other research groups are presented.

In this method, a metallic protective layer is applied to a surface as a coating for the component typically carried out in aqueous solution. This process is supported by using an external voltage source generally called rectifier. On the other hand, for electroless deposition, a reduction medium is present in the electrolyte. The latter process is widely used for nonconducting materials' coating such as ceramics and plastics. The electrochemical method (electrocoating, electroplating) is used for deposition onto electrically conducting substrates.

Electrochemical deposition onto an object is achieved by putting a negative charge on it to be deposited and immersing into a solution which contains a salt of the metal. The metallic ions of the salt carry a positive charge are thus attracted to the object providing electrons to reduce the positively charged ions to metallic form when they reach the negatively charged object [1].

**electroless metal coating**, and **electrolytic metal coating**.

and, finally, a possibility to achieve higher microhardness [2].

**technique** seems to be feasible based on the idea determined.

**2. Electrolytic coating**

58 Electrodeposition of Composite Materials


The first layer is substrate where potential hydrogen embrittlement effects are of concern. Commonly, metals are preferable for this layer, steel for engineering application in particular. The second zone is the basis metal interface. In this region adhesion of the coating and diffusion between the coating and substrate takes place. The coating itself is described as the third zone where composition and microstructure determine the properties and factors. The interactions between environment and the coating has to be taken into account in terms of corrosion and/ or wear in the final zone environmental interface.

Obviously, numerous layers are influenced in more than one zone. This phenomenon could be illustrated by the following examples. Firstly, porosity and/or stress in the substrate, rather than just in the coating, can noticeably change coating properties. Secondly, porosity can affect corrosion resistance and mechanical behaviour, such as tensile properties. Another one is hydrogen embrittlement as a factor not only for the substrates (concentrates heavily on steels) but also for some coatings. This is a generic term used to describe a wide variety of fracture phenomena having a common relationship to the presence of hydrogen as a solute element in the alloy or as a gas in the atmosphere [4]. Nickel, aluminium, titanium [5] and even electroless copper coatings [6] exhibit the phenomenon. It explains that any material can weaken by this effect [7].

**Figure 1.** Zones in a coated material

The rest of the zones and the properties affected are clarified in Section 3.2 because these zones are related to the coating itself and the interfaces between coating.
