*3.2.4. Hardness/elastic module*

(SCD). In Figure 6, both metallic and composite coatings' hardness and grain size measure‐

**Figure 6.** Hardness (left) and grain size (right) of unalloyed, Ni-45Co, microcomposite and nanocomposite coatings

It is clearly seen that average particle size used in the process also affect the properties under

The particles can create a dispersion-hardening effect so that they hinder the formation of dislocation in the grain, and act as pinning agents. Analogically, they can also hinder grain

Reduction in the size of the particles in the composite coating increase the abrasion resistance. The reason for this case is less delimitation of the particles in the metal matrix. In a study on Cr-Al2O3 composite coatings, researchers indicated the reduction in the wear strength and

Another way to reduce the wear loss of surfaces moving relatively is to decrease the friction coefficient or lubrication. SiC particles create a lubricant film on the surface of Ni-SiC coatings. Because of the lubrication the wear resistance of the composite structure increases up to 2-3

The distribution of the particles and the second phase are important to obtain homogenous coatings. Otherwise, properties can chance locally, regions to regions and can cause the decrease of coatings' lifetime. This would be because of local corrosion attacs and/or wear loss. However, it is hard to obtain a homogenous structure since it can be controlled by agitation of the electrolyte during the co-deposition process. For more details on several agitaton types,

same deposition conditions especially the grain size refinement of the metal matrix.

ments are given, respectively.

68 Electrodeposition of Composite Materials

produced by SCD [21]

*3.2.2. Size of the particles and second phase*

brittleness when the amount of the particles was too big [10].

times of a pure Ni coating. This has been proved by similar studies [10].

growth caused by annealing [8].

*3.2.3. Particle distribution*

revise Section 3.1.5.

The indentation hardness of materials can be measured in several ways by forcing an indenter having specific geometry [22]. The hardness and Young's modulus, two of the most commonly measured mechanical properties of materials, can be determined in an easy and reliable way due to the development of depth-sensing indentation equipment [23].

Furthermore, dynamic indentation method is more beneficial than the conventional Vickers microhardness testing in two aspects. Apart from microhardness the dynamic indentation method can also provide well-defined mechanical parameters such as elastic modulus of the material. Secondly, difficult and inaccurate optical observation and measurement of diagonal length of the indent/impression is no longer required because of the continuous monitoring of the load and depth of an indentation [24].

With the development of the nanoindentation technique, the mechanical properties within a sub-micron or nano scale have been widely discussed. The techniques are expected to be convenient for measurement of the mechanical properties of thin films [14].

The greater hardness values for composite coatings can be attributed to the greater hardness values of the reinforcements. The explaination of this phenomenon is based on the rule of mixture for composite materials. The rule states that the hardness of a composite can be formulated based on the volume fraction and the hardness of each individual component [20].

It is also known that the amount of wear volume (Q) during the wear tests is directly propor‐ tional to the compressive load (W), sliding distance (x) and inversely proportional to the hardness (H). It can be expressed by the Archard Equation (Eq.1) given below, where ko is a non-dimensional wear coefficient that is specific to each material [20].

$$Q = k\_o \frac{W.x}{H} \tag{1}$$

On the contrary, H/E ratio of materials gives an extremely close agreement to their raking in terms of wear behaviour. This is detailed by a similar research [25].

Some of the experimental results are given in Section 4.3 in comparison for in-situ codeposition process. According to these results, one can easily understand the relation between hardness and elastic modulus and also how the second phase particles change these properties.
