## 3 Results and Discussion
### Analysis of Surface Topography of the Produced Pockets
#### 3.2.1 Results Regarding Ra and Rz
In general, the surface roughness values were similar to those of the first series of experiments due to the low contribution of the abrasive mass flow rate as a factor regarding surface roughness; in fact, the magnitude of roughness was not significantly altered, as it is mainly regulated by the jet pressure, step  
leads to a higher deviation of surface roughness across the pockets. The highest value of CV was observed for the fourth case, for which the longest exposure time was used, indicating that the pure WJ treatment can have a detrimental effect on the uniformity of surface quality, above the acceptable level of 0.1 or 10%, when improper parameters are employed. An interesting finding is that the use of a higher traverse feed, related to the lowest exposure time, was related to a higher degree of uniformity, although the nominal value of Ra was not improved. Regarding the results presented in Figure 7b, it can be seen that the use of a pure WJ decreased the level of uniformity of the surface roughness, but the use of a higher traverse speed for the post-treatment led to a comparable level of uniformity in respect to the roughing pass. Finally, the relatively higher values of CV for the second series of experiments can be attributed to the lower abrasive mass flow rate, which is related to a lower probability of fracture of the abrasive particles, thus creating a more irregular topography. Apart from Ra, it is important to discuss briefly the findings regarding Rz. Usually, the values of this parameter vary in the same way as the values of Ra and thus, similar conclusions can be expected. However, in the present case, it is important to observe the magnitude of Rz in respect to the variation of the depth of pockets after a pure WJ treatment in order to further explain the findings. In Figure 8, the variation of Rz in respect to different pure WJ treatments for the two different series of experiments is depicted. As can be seen, the use of a pure WJ increased Rz, both for one and two passes. The use of a different speed led to a slight reduction of Rz, especially at the higher traverse feed rate. In the second series of experiments, although the use of two passes led to an almost identical average Rz, the use of three passes showed an indication of improvement. However, the use of a lower traverse rate clearly led to a higher Rz, whereas the use of a higher traverse rate reduced Rz, as was anticipated. In conclusion, despite the considerable variation of Rz values, based on the average values it can be seen that there are many similarities with the variation of Ra and that the value of the total height of the roughness profile is significantly higher than the additional depth of material removed by the pure WJ. The last observation was further investigated by directly analyzing the values of Rp and Rv, as discussed in the following subsection. Figure 7: CV values for Ra for (**a**) the first and (**b**) the second series of experiments. In the case of Rz, the values of CV, as can be seem in Figure 9, exhibit generally higher values than Ra and are less divergent between different treatments. As in the case of Ra, the highest CV value was observed for the case with the lowest traverse feed rate for the first series of experiments, whereas in the second series of experiments, the highest number of passes and the highest traverse feed led to higher degree of uniformity in the Rz values of the produced pocket surface. As a general conclusion, it can be deduced that the surface roughness exhibits rather negligible differences due to the pure WJ treatment for the two different series of experiments studied. The differences between the average values of Ra and Rz indicate that the number of passes or traverse feed rate can yield slight explainable variations but the variability of results indicates that it is not possible to considerably alter the surface roughness by a pure WJ treatment unless different strategies are applied. Figure 8: Rz values for (**a**) the first and (**b**) the second series of experiments.