**3.1. SiC Particle (SiCP) suspension stability measurements**

The transmission profile (Figure 1a) shows a rapid increase in the transmittance signal from the first scans and remains stable in the 1- to 50-mm range. Additionally, the transmittance signal increased with time, a behavior that is indicative of the formation of a clarifying zone in this region (Figure 1b). Additionally, the backscattering profile (Figure 1c) shows an increase in the backscattering signals as a function of time, which is the characteristic of an increase in particle size. This behavior is related to a phenomenon called differential sedimentation [22]. These results revealed that unstable suspensions of SiCPs were obtained when a surfactant was not used.

Figure 2 shows the typical transmission and backscattering profiles of SiCPs in the electrolytic bath with the surfactant DTAB. The transmission profile (Figure 2a) shows increases with time throughout the length of the vial. This increase is more pronounced in the region from 18 to 50 mm, which indicates the formation of a clarifying zone in this region. Furthermore, in the region from 0 to 48 mm, the transmission signals are less than 10% during the first 13 h of the experiment, indicating that the solution is opaque in this range.

The backscattering profile (Figure 2c) shows a decrease in the signals as a function of time, another indication of differential sedimentation [22,23].

The above results revealed that stable suspensions (less than 10% transmission during the first 13 h) of SiCPs were obtained when DTAB was used as a surfactant.

Electrodeposition of Ni-P/SiC Composite Films with High Hardness http://dx.doi.org/10.5772/61858 127

The electrodeposition current density was selected on the basis of additional tests using a Hull cell. The coatings obtained were of commercial quality, which is suitable for industrial

Crystalline phases were identified by powder X-ray diffraction (XRD) using a Bruker diffrac‐ tometer model D8 Advance (Bragg-Brentano arrangement, Cu rotating anode). The samples

Glow discharge spectrometer (GDS) (Leco, Mod. 850A) was employed to obtain elemental

The coatings hardness value was the average of ten measurements obtained on a Matsuzawa

A reciprocating ball-on-disk tribometer (CSM tribometer instruments) was used to wear tests. All tests were nonlubricated and carried out under dry at 25 °C temperature and relative humidity of 39%. A 3-mm AISI 8620 ball bearing was used as the counter body under a 2-N load at a sliding speed of 1 cm s-1. The friction coefficient of the three wear tests was recorded,

The transmission profile (Figure 1a) shows a rapid increase in the transmittance signal from the first scans and remains stable in the 1- to 50-mm range. Additionally, the transmittance signal increased with time, a behavior that is indicative of the formation of a clarifying zone in this region (Figure 1b). Additionally, the backscattering profile (Figure 1c) shows an increase in the backscattering signals as a function of time, which is the characteristic of an increase in particle size. This behavior is related to a phenomenon called differential sedimentation [22]. These results revealed that unstable suspensions of SiCPs were obtained when a surfactant

Figure 2 shows the typical transmission and backscattering profiles of SiCPs in the electrolytic bath with the surfactant DTAB. The transmission profile (Figure 2a) shows increases with time throughout the length of the vial. This increase is more pronounced in the region from 18 to 50 mm, which indicates the formation of a clarifying zone in this region. Furthermore, in the region from 0 to 48 mm, the transmission signals are less than 10% during the first 13 h of the

The backscattering profile (Figure 2c) shows a decrease in the signals as a function of time,

The above results revealed that stable suspensions (less than 10% transmission during the first

and the wear volume was measured according to the ASTM G99 standard method.

application.

126 Electrodeposition of Composite Materials

**2.3. Morphological and tribological characterization**

were evaluated over the 2θ range from 30° to 95° at a rate of 0.2° s-1.

composition of the coatings as a function of depth into the coatings.

MXT-α7 on the Vickers scale with a load kept at 10 g for 15 s.

**3.1. SiC Particle (SiCP) suspension stability measurements**

experiment, indicating that the solution is opaque in this range.

13 h) of SiCPs were obtained when DTAB was used as a surfactant.

another indication of differential sedimentation [22,23].

**3. Results and discussion**

was not used.

**Figure 1.** (a) Transmission and (b) backscattering profiles typical of an electrolytic bath of Ni-P-SiC with SiC particles (SiCPs) and without the surfactant DTAB. The data are reported as a function of time (0 to 24 h) and sample height (0 to 50 mm).

**Figure 2.** (a) Transmission and (c) backscattering profiles typical of an electrolytic bath of Ni with SiCPs and 0.08 mM CTAB. The data are reported as a function of time (0 to 24 h) and sample height (0 to 50 mm).

Figure 3 shows that the values of the thickness of the clarifying layer (∆H) in the upper portion of the aqueous SiCP suspension decreased significantly in the presence of the dispersant and increased over time. The best results were obtained for the highest concentrations of CTAB. During the time period from 0 to 13 h, the ∆H value of the aqueous SiCP suspensions with both 0.08 and 0.10 mM CTAB was only 0.85 mm, whereas for the suspension without surfac‐ tant, ∆H was 48 mm beginning in the first minutes of the experiment. After 20 h, the ∆H value of the aqueous SiCP suspension with 0.08 mM CTAB was only 6.92 mm.

The greater stability of the SiCPs in the suspension with the dispersant is attributed to the modification of the solid surfaces of the SiC particles via the adsorption of CTAB. Because of its spatial structure and hydrophilic functional groups, CTAB can enhance the electrostatic repulsion and steric hindrance between SiC particles.

**Figure 3.** Effect of DTAB dosage on the clarifying-layer thickness (∆H) as a function of time (0 to 24 h).

#### **3.2. Electrodeposition of composite Ni-P-SiC: Influence of the concentration of SiC particles in solution, on the composition of SiC particles in the matrix Ni-P-SiC composites**

#### *3.2.1. Hull cell studies and electrodeposition of Ni-P-SiC composites*

A Hull electrochemical cell was used as a first step to find the suitable values of current density that promote uniform coatings of Ni-P-SiC. Prior to the test, an AISI 1018 steel plate was pickled and activated. For pickling, the steel plate was immersed in a 30% HCl solution for 10 s, immediately washed, and then subsequently activated by its immersion in a 10% HCl solution. Immediately after activation, the AISI 1018 steel plate was submerged in a Hull cell containing solution S (= 0.2 M NaCl + 0.65 M NiSO4⋅6H2O + 0.75 M NiCl2⋅6H2O + 0.1 M H3BO3 + 0.1 M H3PO3) + 0.084 mM DTAB + *x* g mL-1 SiC (*x* = 0.00125, 0.0025, 0.005, 0.01, 0.015, or 0.02) (see Figure 4a). Each test was repeated three times for each given SiC concentration. Tests were performed by applying a current of 1 A for 12 min. Ni plates (99%, Atotech) were used as the anodes.

**Figure 4.** (a) Hull cell containing solution S + 0.084 mM DTAB + 0.02 g mL-1 SiC and the AISI 1018 steel plate electrical‐ ly wired to a power source. (b) Plates with a Ni-P-SiC composite coating obtained after applying 1 A for 12 min.

Figure 4b shows an AISI 1018 steel plate coated with Ni-P-SiC obtained using a solution S + 0.084 mM DTAB + 0.02 g mL-1 SiC solution. It was found that current density (*j*) values between 0.043 and 0.0005 A/cm2 are adequate to obtain coatings with an appearance and adhesion of acceptable quality.

From this result, Ni-P-SiC coatings were obtained from a solution of composition S + 0.084 mM DTAB + *x* g mL-1 SiC (*x* = 0.00125, 0.0025, 0.005, 0.01, 0.015, or 0.02) using 1 cm2 AISI 1018 steel disks as cathodes by applying 0.042 A/cm2 for 10 min. The obtained coatings are shown in Figure 5. Coatings exhibiting metallic luster were obtained when the solution with the highest concentration of SiC (0.02 g mL-1) was used as an electrolyte.

**Figure 5.** Ni-P-SiC coatings obtained by applying a current density of 0.042 A/cm2 for 10 min from an electrolytic bath of S (= 0.2 M NaCl + 0.65 M NiSO4⋅6H2 + 0.75 M NiCl2⋅6H2O + 0.1 M H3BO3 + 0.1 M H3PO3) + 0.084 mM DTAB + *x* g mL-1 SiC, (a) *x* = 0.02, (b) *x* = 0.015, (c) *x* = 0.01.
