# Reconditioning of Diamond Coated Tools and Its Impact on Cutting Performance for CFRP Laminates
## 3 Results and Discussion  
### Tool Surface Evaluation  
Figure 5 displays the substrate surface morphologies obtained by SEM for different stages of the experiment, while Figure 6 shows the resulting surface roughness data of the stages. Surface texture parameter \(S_{a}\), as an arithmetical mean height, based on ISO 25178--\"Surface Texture\", was recorded and averaged from multi-point measurements on the flank surfaces of the drills. The scan size was determined by the optical magnification of the system (100\(\times\)) in a resulting surface area of 129 um \(\times\) 129 um with a profile Gaussian filter \(\lambda_{c}\) of 8 um. Figure 4: Experimental setup for cutting tests ((**a**), machine; (**b**), tested drill; (**c**), carbon-fiber-reinforced plastics (CFRPs) workpiece; (**d**), fixture). Figure 5: Morphologies of the drill flank surface, observed at 6 mm from the drill tip: (**a**) original, as grinded; (**b**) wet-chemical etching 0 (WCE0) of the new drill (TLC0); (**c**) chemical vapor deposition 0 (CVD0) of the TLC0; (**d**) reactive ion beam etching 1 (RIBE1) of the 1 st-time reconditioned drill (TLC1); (**e**) WCE1 of the TLC1; (**f**) CVD1 of the TLC1; (**g**) RIBE2 of the 2 nd-time reconditioned drill (TLC2); (**h**) WCE2 of the TLC2; (**i**) CVD2 of the TLC2. Figure 6: Substrate roughness characteristics by the arithmetical mean height (\(S_{a}\)) of the surface texture. The original drill substrate, as shown in Figure 5a, represented the as-ground surface depicting the directional marks left by the grinding process on the surface of the tool, which also provided a non-uniform texture in terms of the distribution of the WC grains and the Co binder due to the amount of surface damage after the grinding process [21]. These feed marks display an average surface texture roughness of \(S_{a}\) = 0.096 \(\upmu\)m.  
The surface morphology after the WCE0 process, as shown in Figure 5b, revealed a uniform surface with \(S_{a}\) value of 0.151 \(\upmu\)m and some directional surface features. The increase in the roughness after the process is attributed to the WCE, which attacked the WC grains and oxidized the cobalt binder to soluble Co compounds removed during the procedure under applied ultra-sonication [15]. Such a washing action may dislodge weakly bonded WC grains from the surface and create some porous surface textures. Further, Figure 5e shows a uniform surface with a roughness \(S_{a}\) parameter of 0.153 \(\upmu\)m, generated after the WCE1 process of the 1 st reconditioning cycle. However, the surface, produced by the WCE2 process of the 2 nd reconditioning cycle, had a rougher texture with \(S_{a}\) of 0.160 \(\upmu\)m and pitted areas, as shown in Figure 5h. It is possible to propose that an accumulative effect of removing the binder phase in WCE stages led to the formation of randomly distributed, Co-free areas of the substrate with a depth deeper than the WC average grain size. Then, the weakly bonded carbide grains were dislodged by cavitation during an ultrasonic washing action after the chemical etching. As a result, the non-uniform-sized pitted areas appeared on the substrate surfaces after the WCE2 process. Thus, three repeated chemical etching processes over-treated the surface and provided porous textures due to the loss of WC grains and the Co depletion. On the other hand, the RIBE process generated a rather smooth and uniform surface after all decoating cycles. Figure 5d,g shows the morphologies of ion-etched surfaces after the 1 st and 2 nd decoating processes of the tool reconditioning, respectively. The roughness values of the etched surfaces consisted of \(S_{a}\) of 0.085 \(\upmu\)m and 0.087 \(\upmu\)m after the 1 st (RIBE1) and 2 nd (RIBE2) decoatings, respectively. The observed effect of the partial surface integrity regeneration via RIBE can be attributed to the physical sputter etching of the damaged the WC-Co layer by energetic oxygen ions down to the pristine WC-Co.