## 3 Results and Discussion  
### Pocket Morphology and Average Depth  
In Figure 4a-f, the morphology of the produced pockets for some indicative cases of both series of experiments is depicted. These images were created based on the 3D reconstruction of the pocket surface by the focus variation microscope and allow for a comprehensive qualitative evaluation of the morphology of the created pockets, as they represent the whole pocket area in real color. From the figures relevant to the first series of experiments, it can be seen that the surface of the first pocket seems to lack very deep marks or signs of grooves produced by the movement of the abrasive waterjet, apart from the obvious curvature of the profile near the walls of the pocket. However, there are several flat regions that are separated from the other regions by noticeable lines on most of the pocket surface. On the other hand, the morphology of the pockets treated by a pure WJ is obviously different. The main characteristic of the pockets produced after the four different treatments is the higher irregularity of the surface. From Figure 4b, regarding the third pocket, it was observed that the surface contains numerous shallow circular marks that dominate the surface, probably created either by dislodged embedded particles or by removing material between formerly merged impact sites of abrasives. Although there are other small differences such as the depth of the pockets or some areas with different inclinations, the four pockets that were processed by the pure WJ appear to have the same texture. The same situation also appears in the case of the second series of experiments, with all treated pockets including numerous circular marks on their surface. Despite the fact that the quantitative analysis of the following sections can reveal more details about the differences in the produced texture, it can be concluded that the effect of the pure WJ treatment under the selected conditions definitely alters not only the surface quality of the grooves but also the texture of the surface, probably as the impact of water on the surface can smooth some of the peaks produced by the abrasive, or dislodge some embedded particles, revealing new patterns on the surface. Apart from the discussion of pocket morphology, as part of the general evaluation, the depth of the pockets was measured by CMM and will be briefly discussed afterwards. The average depth of the pockets was evaluated for each different condition and the results are displayed in Figure 5. This information is rather important as the effect of the pure WJ on material removal during the post-process treatment can be determined. The results indicate that the anticipated correlation can be established between the process parameters and the pocket depth, although the amount of removed material is minimal compared to the amount of material removed during the roughing pass. For the first series of experiments, the depth increased when a single pass of pure WJ was carried out and it was further increased by the second subsequent pass. Moreover, the use of a lower traverse feed rate for the WJ produced a higher depth due to a higher exposure time, whereas the use of a much higher speed led to a less noticeable increase in depth. Similar observations can be conducted regarding the results of the second series of experiments, although the depth values are slightly lower due to the lower value of the abrasive mass flow rate. These observations are essential in order to understand the impact of the pure WJ on the surface roughness as the amount of removed material can be correlated with the alteration of existing peaks on the surface, which in turn affects various surface roughness indicators, something that will be discussed afterwards in Section 3.2. It is important to note that given that the differences in average depth are comparable to the Ra and Rz values, the variation of depth will have a prominent impact on the obtained surface quality.