*2.1.3. Co-deposition of solid lubricant particles*

11

that the former had improved corrosion and oxidation resistance.

**Ni/ZrO2**

**Low ZrO2 content inNi matrix**

**Microcrystalline Ni/C**

**Ni/C**

**Nano crystalline Ni/C**

**High ZrO2 content inNi matrix**

**Ni/Al2O3**

**After annealing at high temperature**

**Nano crystalline Coating**

**Ni/Al2O3**

**Coating made fromDC**

**Coating using PDC**

**Ni/SiC**

Apart from using the conventional electroplating technique (CEP), sediment co-deposition technique (SCD) has gained acceptance for higher level of co-depositing particles in the metal matrix with better dispersion and uniformity. Feng et al. [22] investigated the corrosion resistance and high-temperature oxidation resistance of Ni- Al2O3 nano- composite coatings using SCD technique. The incorporation of the nano-alumina particles in the Ni matrix refined the Ni crystallite and changed the preferential orientation of composite coating. Ni- Al2O3 composite coating produced compared with the one fabricated using CEP technique proved

Fayomi et al. [23] carried out a research on mild steel protection in chloride medium to develop ceramic composite coating that will reduce its susceptibility to corrosion attack. Zn-TiC/TiB composite coating was produced via electro-deposition method. The coatings showed better adhesion strength, improved hardness and enhanced corrosion resistance compared to the

Three different nano- oxides of Al2O3, Cr2O3 and SiO2 have been reinforced in Zn matrix using electro-deposition process to produce composite coating on mild steel [24]. The incorporation of Al2O3, Cr2O3 and SiO2 nanoparticles in the ternary composite showed grain refinement, modified orientation of Zn matrix and good synergetic effect on the corrosion resistance of Znbased coatings. Zn-Cr2O3 nano- composite had the highest micro-hardness while Zn-Al2O3 nano-composite was found to exhibit the highest corrosion resistance coupled with lowest

**After annealing at high temperature**

**Coating using PDC**

**Ni/TiO2**

**Figure 3.** Vickers micro-hardness values for different ranges of particle size in a nickel deposit.

**Microcrystalline Ni/TiO2**

**Nanocrystalline Ni/TiO2**

**Ni/Au**

*2.1.2. Co-deposition of corrosion -resistant particles*

**Microcrystalline Ni/Au**

**Ni/Co/Au**

**Pure Ni**

TiC/TiB -coated mild steel.

wear loss.

**Microcrystalline Ni**

**200**

**400**

**600**

**800**

**Nanocrystalline Ni**

46 Electrodeposition of Composite Materials

Cardinal et., al. investigated characterization and frictional behavior of nano-structured Ni-W-MoS2 composite coatings by pulse plating from an Ni-W electrolyte containing suspended MoS2 particle [30]. MoS2 concentration was varied with the coating composition, morphology, crystalline structure, micro-hardness and frictional behavior. The result obtained indicated that co-deposited lubricant particles strongly influenced the composite Ni-W coating proper‐ ties. As the MoS2 concentration in the coating increases, both the tungsten content and the coating micro-hardness decrease while the average grain size increases. With low MoS2 content, result showed lesser friction coefficients and similar micro-hardness. Therefore, there is a solid lubricant concentration regime where co-deposition of MoS2 particles into Ni-W nanostructure alloys improves the frictional characteristics of the coating with a consistently lower friction coefficient.

Sangeetha used direct current and pulse current methods to incorporate polytetrafluoroethy‐ lene (PTFE) polymer to an optimized Ni-W-BN nano -composite coating deposited on a mild steel substrate [14]. It was observed that the co-deposition of PTFE solid lubricant particles on the Ni-W-BN nano-composite coating resulted in a moderately smooth surface, greater microhardness, a lower friction coefficient, excellent water repellency and enhanced corrosion resistance. The pulse current technique showed enhanced performance over the direct current coating due to uniform and smaller grain deposits.
