## 3 Results and Discussion
### Surface Topography
Interestingly, the surface machined with the 6160 ceramic tool at a cutting speed of \(v_{c}\) = 250 m/min (Figure 3d) shows a lower \(Sa\) parameter value despite the presence of localized high ridges (marked on figure by red circle), compared to the surface machined with the same tool at \(v_{c}\) = 200 m/min (Figure 3c). Additionally, the surface machined with the 6160 tool at \(v_{c}\) = 200 m/min exhibits wide valleys (marked on figure by yellow circle) that are absent on the other surfaces machined at \(f\) = 0.04 mm/rev. This suggests that material removal may have been influenced by the built-up edge on the cutting tool [32]. Figure 2: Surface morphology of Inconel 718 after turning with feed rate \(f\) = 0.025 mm/rev: (**a**) \(v_{c}\) = 80 m/min, carbide insert S205; (**b**) \(v_{c}\) = 200 m/min, carbide insert S205; (**c**) \(v_{c}\) = 200 m/min, ceramic insert 6160; (**d**) \(v_{c}\) = 250 m/min, ceramic insert 6160. Figure 4: Surface morphology of Inconel 718 after turning with feed rate \(f\) = 0.055 mm/rev: (**a**) \(v_{c}\) = 80 m/min, carbide insert S205; (**b**) \(v_{c}\) = 200 m/min, carbide insert S205; (**c**) \(v_{c}\) = 200 m/min, ceramic insert 6160; (**d**) \(v_{c}\) = 250 m/min, ceramic insert 6160. Figure 3: Surface morphology of Inconel 718 after turning with feed rate \(f\) = 0.04 mm/rev: (**a**) \(v_{c}\) = 80 m/min, carbide insert S205; (**b**) \(v_{c}\) = 200 m/min, carbide insert S205; (**c**) \(v_{c}\) = 200 m/min, ceramic insert 6160; (**d**) \(v_{c}\) = 250 m/min, ceramic insert 6160. Figure 4a-d presents the isometric maps of surfaces machined with S205 and 6160 inserts at a feed rate of \(f\) = 0.055 mm/rev. The isometric map obtained after turning with the S205 insert at a cutting speed of \(v_{c}\) = 80 m/min (Figure 4a) clearly differs from the other surfaces machined with the same feed rate. It more closely resembles the isometric map obtained for the lowest tested feed rate, as distinguishing adjacent peaks is more difficult. This effect was likely influenced by the built-up edge (BUE) phenomenon. Interestingly, this surface exhibits the lowest \(Sa\) parameter value, being the only one with \(Sa\) < 0.15 \(\upmu\)m.  
The surface machined with the 6160 insert at a cutting speed of \(v_{c}\) = 250 m/min (Figure 4d) is another example where high peaks were observed (marked on figure by red circle). Analyzing all tested surfaces, it becomes evident that high peaks occur exclusively on surfaces machined with the 6160 insert. However, whether these peaks appear individually or in specific regions, the surface roughness parameter \(Sa\) does not exceed 0.3 \(\upmu\)m.  
The isometric maps of surfaces machined with a feed rate of \(f\) = 0.07 mm/rev show that neither the surfaces machined with S205 inserts nor those machined with 6160 inserts exhibit individual high peaks (Figure 5a-d). The distances between adjacent ridges are evenly distributed. Among the four surfaces, the one machined with the 6160 insert stands out with narrower valleys, making it appear flatter (Figure 5d). A surface with this characteristic is more resistant to wear. [PERSON] et al. [33] defined the \(Sp/Sz\) ratio as the coefficient of emptiness, which reached its lowest value for the surface machined with the 6160 insert at \(f\) = 0.07 mm/rev. Figure 5: Surface morphology of Inconel 718 after turning with feed rate \(f\) = 0.07 mm/rev: (**a**) \(v_{c}\) = 80 m/min, carbide insert S205; (**b**) \(v_{c}\) = 200 m/min, carbide insert S205; (**c**) \(v_{c}\) = 200 m/min, ceramic insert 6160; (**d**) \(v_{c}\) = 250 m/min, ceramic insert 6160.