# Reconditioning of Diamond Coated Tools and Its Impact on Cutting Performance for CFRP Laminates
## 3 Results and Discussion
### Tool Surface Evaluation
The surface morphologies of the deposited diamond coatings are shown in Figure 5. The diamond surfaces, displayed in Figure 5c,f corresponding to the TLC0 and the TLC1, respectively, showed similar continuous, well-defined faceted textures of randomly oriented diamond grains with an average size of approximately 3 \(\upmu\)m. Contrary, as shown in Figure 5i, the diamond coating deposited on the TLC2 consisted of a combination of small faceted grains in globular agglomerated textures distributed mainly along the cutting edges. This difference between the observed diamond films may be attributed to a high diamond nucleation density as the result of the rougher surface due to a huge amount of pits at the surface, as shown in Figure 5h. As the depth of pits increased with the surface roughness, more diamond particles were embedded within the rough surfaces. This enhanced the nucleation of the diamond crystal and its growth behavior. Therefore, it can be proposed that the WCE2 process detrimentally reconstructed the surfaces, especially in the cutting edge areas, because over-treated surfaces induced the formation of non-uniform diamond films. A similar correlation between the substrate surface roughness and the diamond film morphology has been reported by [PERSON] et al. [17]. In their study, a diamond coating with a combination of small crystal facets in ball-like agglomerates was obtained on rougher samples compared between all pretreated samples. In order to assess the quality of the deposited diamond coatings, Raman spectroscopy was employed. The Raman spectra of the diamond coatings are displayed in Figure 7, adopting the Raman microscope (RAMAN-11, Nanophoton, Osaka, Japan) and a laser with a visible excitation wavelength of 532 nm. It was found that the peak around 1332 cm\({}^{-1}\), indicative of the sp\({}^{3}\) bonding of the diamond, can be visible evidently for all the films [22]. The Raman bands were present as 1337.27 cm\({}^{-1}\), 1337.28 cm\({}^{-1}\), and 1335.38 cm\({}^{-1}\) in CVD0, CVD1, and CVD2 films deposited on the TLC0, the TLC1, and the TLC2, respectively. The wavelengths of these peaks shifted from the value of the natural diamond (1332.4 cm\({}^{-1}\)), indicating the residual stress in the diamond films. From the frequency \(\upsilon\) of the diamond band, the residual stresses in the diamond coatings could be estimated using the method described by [PERSON] et al. in their research [23]:  
\[\sigma\ (\text{GPa})=-0.567\times(\upsilon-\upsilon_{0}), \tag{1}\]  
where \(\upsilon_{0}\) is 1332.4 cm\({}^{-1}\) and the negative corresponds to the compressive stress. According to this method, the residual stresses of the CVD0, CVD1, and CVD2 films were calculated as \(-\)2.761 GPa, \(-\)2.766 GPa, and \(-\)1.689 GPa, respectively. The CVD2 film had the lowest compressive stress value between the compared films, possibly due to the finer B-MCD structure and intergranular relaxation. Furthermore, several visible peaks, characteristic of a diamond coating, can be identified as well. All presented Raman spectra showed two peaks located around 520 cm\({}^{-1}\) and 1250 cm\({}^{-1}\), which is associated with the actual boron incorporation in the lattice [24]. In addition, the broad dominated peaks located around 1500 cm\({}^{-1}\) for the CVD0, CVD1, and CVD2 films revealed the presence of sp\({}^{2}\) graphite (G-peak) phases [22]. The growth G-peak intensity of CVD2 can be associated with an increased non-diamond phase value due to reduced diamond grains.