**Figure 7.**

*SEM microstructures of (a) 14-GPa CFPCD, and (b) 16-GPa CFPCD showing fully dense catalyst-free microstructure [19].*

*Applications of Polycrystalline Diamond (PCD) Materials in Oil and Gas Industry DOI: http://dx.doi.org/10.5772/intechopen.107355*

#### **Figure 8.** *The HRTEM showing nanostructure features (substructure) of twin and stacking fault in grains [9].*

Crystallization defects prevent grain alignment during deformation and play a preventive role, which is conducive to its mechanical properties. In addition, during processing, the particles form plastic deformations in the substructure by squeezing the diamond particles, and the hardness is further increased due to the Hall–Petch effect [20].
