**3. Results and discussion**

#### **3.1 Coating surface morphology**

**Figures 9** and **10** shows the surface morphology using Field Emission Scanning Electron Microscope (FESEM) of the Ni-CBN coating captured at different magnifications. Both figures depict microstructure with cauliflower pattern. In **Figure 9**, the coating does not display micro-cracked, coarse erection and covers the entire exterior of the substrate. HSS has a high thermal shock resistance, making it resistant to sudden and rapid temperature changes [50]. In addition, HSS can withstand large temperature fluctuations.

**Figure 10** illustrates a micro-crack on the surface layer of the carbide substrate coating due to carbide low thermal resistance. High internal stress levels can cause various problems during coating use, including premature disintegration of the part due to substrate fatigue, fracture formation in the coating, and loss of deposit adhesion [50].

#### **Figure 9.**

*Ni-CBN microstructure on HSS substrate (a) 5000X; (b) 10,000X; and (c) 15,000X.*

*Characterisation and Application of Nickel Cubic Boron Nitride Coating via Electroless Nickel… DOI: http://dx.doi.org/10.5772/intechopen.105364*

Overall, both figures demonstrate rough surface of the coatings. The coating was mainly composed of ceramic CBN powders (white areas), metallic Ni matrix (grey areas), and pores (dark spots). The HSS coating surfaces generally showed a uniform distribution of the ceramic particles compared to the carbide substrate. The carbide substrate shows cracks on the coating surface due to thermal gradient. It is because the roughness of the EN-CBN coatings depends on the roughness of the substrate. It is also due to the growth mechanism of the coating, which forms columns locally perpendicular to the surface. The columns are parallel when the substrate is smooth, and the coating is even softer than the substrate [51].

#### **3.2 Coating elemental composition**

The as-deposited Ni-CBN coatings were subjected to energy dispersive X-ray analysis (EDX) to determine the composition of the co-deposited CBN elements in the EN matrix, as shown in **Table 7** for HSS substrate and **Table 8** for carbide substrate.

The EDX spectrum obtained for the Ni-CBN deposited on the HSS and Carbide substrate is depicted in **Figures 11** and **12**. It displays the peaks corresponding to


#### **Table 7.**

*Elemental composition in weight % of electroless Ni-CBN coating on HSS substrate.*


#### **Table 8.**

*Elemental composition in weight % of electroless Ni-CBN coating on carbide substrate.*

#### **Figure 11.**

*EDX spectrum of as-deposited electroless Ni-CBN coating on HSS substrate.*

### **Figure 12.**

*EDX Spectrum of as-deposited electroless Ni-CBN coating on carbide substrate.*

the CBN, approving the standard deposition of elements in the Ni matrix. There is evidence of significant peak elements of nickel (Ni), boron (B), and phosphorous (P). This proves that metallic nickel and ceramic CBN are exist. The phosphorus element in the composite indicates as one of the most critical elements in the EN hypophosphite-based bath solution [45].
