**8. Fractional factorial design**

increased by decreasing the particle size in Ni/SiC system [21]. Furthermore, the effect of particles in decreasing the friction coefficient is more effective when the particle size is

Generally, increasing the particle concentration in the bath increases the weight percent‐ age of particles in the deposit up to a certain point [9] [22] [23]. That point can be thought like the saturation point. There is a rapid increase in the particle amount in the low particle concentration regions whereas a slight increase occurs in the high concentration regions. The collisions between particles and cathode determine the codeposition of the particles and they are diminished in the high MoS2 concentration region resulting in slight in‐

Coating performance can be developed by the addition of the surfactants like (cetyltrime‐ thylammonium bromide (CTAB), sodyumdodecyl sulfate (SDS), and saccharine [20]. The advantage of adding surfactants is their dispersing effect of particles. Thus the property of the particles will be uniform on the surface. Surfactants adsorb on the particles and favor

Surfactants are indispensable especially for the hydrophobic particles (fluorographite, MoS2) to be dispersed in the electroplating solution. Surfactants like sodium lauryl sulphate enhanced the electrostatic adsorption of suspended particles on cathode surface by increasing their positive charges [25]. Similarly, azobenzene (AZTAB) promoted particle deposition into the nickel matrix by their more positive reduction potential than that of nickel [26]. Another surfactant, cetyl trimethyl ammonium bromide (CTAB) has an advantage of increasing the volume percentage of SiC in the deposit besides homogene‐ ous and non-agglomerated distribution of particles in SiC-nickel composite coatings [27].

Further advantage of the surfactants is suppressing the hydrogen evolution reaction. For example, saccharin which is an anionic surfactant is an effective way to overcome the

The surfactants can be grouped under two main headings which are anionic and cationic surfactants according to their charges. Cationic surfactants increased the particle incorpora‐ tion in the coating [28] [29] [30] [31]. Anionic surfactants may have positive or negative effect on the codeposition efficiency of the particles depending on the particle type and bath solution. For instance, SDS which is an anionic surfactant did not affect the codeposi‐ ton of particles [31]. On the other hand, cationic surfactants have the advantage of adsorbing

crease or decreased particle amount in the growing metal deposit [6].

decreased in Ni-MoS2 system [9].

32 Electrodeposition of Composite Materials

**6. Particle concentration**

**7. Surfactant addition / type**

the distribution of the particles [24].

hydrogen evolution problem [34].

2n-1 fractional factorial design is a statistical design that can be used to identify the effects of n electrodeposition variables on the coating properties with the reasonable number of experi‐ ments. In addition, the interaction effects of the parameters can be analyzed by the help of fractional factorial. The property of the coating in other words the response value in the program is generally taken as the amount of particles in the deposit during composite coatings. For instance, in the study of Hu and Bai [41], phosphorus content in the deposit was taken as the response value and temperature, current density pH, NaH2PO2 H2O concentration of the solution and agitation rate were taken as the electroplating parameters. Another most commonly used response value during composite coating is internal stress. Electroplating parameters were MoS2 particle concentration, temperature, pH, current density and coating thickness where the response value is the internal stress in the study of Saraloglu Guler et. al. [9]. Other response values can be listed as friction coefficient, corrosion resistance, wear resistance, hardness which are the properties obtained by particle addition so increased amount of particle content in the deposit will have a positive effect on these values. The hydrogen evolution reaction must also be considered during this selection. The effects of the electroplating parameters on hydrogen evolution reaction can be studied before the composite deposition in order to determine the current density range where H2 is not simultaneously discharged with Ni plating [12].

Fixed limit values that are said to be low (-1) and high (1) levels are selected for the electro‐ plating parameters in fractional factorial design. Table 1 shows the parameters and their low and high fixed limit values for levels of fractional factorial design.


**Table 1.** The electroplating parameters and the properties of the deposit
