**4. Particle type**

Another effect of increasing current density from 0.15 to 5 A/dm2 is increasing the internal stress [8] since the stress stems from the residual stresses. However significant effect cannot

current density on the internal stress depends on the electroplating solution composition. Figure 2 shows the effect of changing only one component amount of the solution on the current density dependence of the internal stress [42]. Moreover the effect of the current density

The effect of pH on particle incorporation is dependent on the nature of the particles. For instance, when MoS2 particles are used as the incorporate particles, the effect of pH value on the particle content in deposit was insignificant. Nevertheless it can be concluded that increasing pH decreased the amount of particles present in the coating [6]. However, incor‐ porated particles are significantly decreased when pH is below 2 in Al2O3-Ni coating pair [11]. In addition, decreasing pH is preferred to manage the internal stress. Low pH values, less than 5, are selected to obtain acceptable stress levels [10]. Increase in pH of the solution may lead to discharge of hydroxyl ions instead of nickel dissolution and oxygen evolution [10] resulted in high internal stresses. It is also concluded that the internal stress was increased when the

The effect of the temperature on the particle content in the deposit depends on the type of the particle. There is a small increase in the particle (MoS2) content in coating with increasing the temperature 30, 40, 50 respectively [6]. It was mentioned that the temperature has an insignif‐ icant effect. For instance, no effect of temperature was detected in BaCr2O4-Ni [13] and Al2O3- Ni [14] coating couples. Because, the applied voltage is the main parameter that directly affects the activity of the reaction. In addition, Ni deposits more efficiently with increase in temper‐ ature. On the other hand, the influence of the temperature was reported as positive up to certain point. After that point, the amount of particles decreases with increasing the temperature.

General trend on the effect of the bath temperature on the internal stress is positive, meaning that increasing temperature decreases the internal stress. On the other hand, according to some of the studies the stress is more influenced by the current density regardless of the

Another advantage of the high temperature is the polarization effect. It is known that concen‐ tration polarization is the component of the polarization which is due to the change in the electrolyte concentration that stems from the current flow through the electrode – solution interface. So, the electrochemical cell potential difference deviates from its equilibrium value. Concentration polarization is decreased by increasing temperature because diffusion layer

[9] because the effect of

be detected when the current density increased from 1.2 to 4.8 A/dm2

pH was increased from 2 to 4 in MoS2 – Ni system [12].

thickness gets smaller and ionic diffusion increases.

depends on pH.

**2.2. pH of the bath**

30 Electrodeposition of Composite Materials

**3. Bath temperature**

temperature [10].

It is a common fact that if the amount of the particles in the solution is increased, the particle content in the deposit will also increase up to a certain point. However the type of the particle also acts as an important parameter. Both of the conductive and non-conductive particles have their own advantages against each other. Because conducting particles (molybdenum disul‐ fide, chromium carbide, zirconium diboride, graphite) attracted to the cathode then act as depositing sites which resulted in dendritic growth [15]. Despite the advantage of easily attraction of conducting particles to the cathode, selective deposition on the conducting sites led to increased surface roughness.

On the other hand, non-conductive particles end up with smoother deposit surfaces with low porosity [15].

Mechanical properties can be changed by the type of the incorporated particles. For instance, PTFE in Ni matrix increases wear resistance [16], MoS2 incorporated with Ni decreased the coefficient of friction [9], Al2O3 and SiC dispersed in Cu increased the microhardness of the coatings [17]. Moreover, wear and corrosion resistance can be improved by the addition of silicon carbide nano-particles [18] [19].
