# On the Detection and Removal of Oxides from Laser-Treated Surfaces
## 3 Results
### Oxide Analysis  
Representative morphologies of the laser-textured steel, W, W-Cu, and Ti alloy substrates are shown in Figures 1-4. These give an idea of the size of the texture features (grooves, dimples) as well as the nature of the various surfaces. The deeper regions of the grooves and dimples are typically smooth, with occasional molten droplets. On the steel substrates treated by the cw laser, the ridges have similar appearances. In contrast, in the dimple pattern textures formed by the ns laser, the upper regions have a more complex morphology and typically contain a significant number of fine particles. These likely originate from ejection from the hollows and redeposition on the top surface. These regions are likely to experience a higher degree of oxidation due to their higher specific surface. Minor differences in morphology obtained from similar laser patterns on different materials can also be observed. Parts of Figures 2-4 also show the surface morphologies after distinct post-treatments; their effects will be discussed in Section 3.3. The results of the EDS analysis on the W-based materials (pure W and W-Cu composite) are shown in Table 1. In addition to the clean and laser-treated samples, another example of an oxidized surface--treated by electric discharge machining (EDM)--is included. One can see a clear distinction between the values obtained on significantly oxidized (LST), moderately oxidized (EDM), and clean (ground) surfaces. Similar results from the steel samples are summarized in Table 2. The overall oxygen content is generally lower, and the difference between the oxidized and clean surfaces is less distinct. Yet, a boundary value between these two may be established. Such a result could be expected in view of the surface morphology, where the steel exhibited much cleaner surfaces than the W-based materials; however, this is a rather indirect indicator. On these materials, XRD measurement was also attempted; however, the oxide amount was found to be below the detection limit. Figure 1: Surface morphology of steel samples textured with a cw laser. (**a**) Lines with a width of 70 \(\upmu\)m and depth of 25 \(\upmu\)m; (**b**) grid of perpendicular lines with a width of 70 \(\upmu\)m and depth of 25 \(\upmu\)m.  
Figure 2: Surface morphology of W samples textured with an ns laser: dimple pattern. (**a**) As-textured; (**b**) heat-treated in hydrogen atmosphere. Figure 4: Surface morphology of Ti alloy samples textured with an ns laser: dimple pattern. (**a**) Regular texturing; (**b**) texturing with nitrogen shielding; (**c**) texturing with subsequent gentle ablation. Figure 3: Surface morphology of W-Cu samples textured with an ns laser: dimple pattern. (**a**) As-textured; (**b**) after laser cleaning with gentle ablation (6 MHz, 30 m/s, 3 passes). The results obtained on the Ti alloy samples after three types of treatment are shown in Table 3. The oxygen content, as determined by EDS with the three variations of laser texturing (regular, with N\({}_{2}\) shielding, and with subsequent laser cleaning by gentle ablation), does not show a significant distinction with respect to the processing variant. However, there are marked differences between the results from the LST surfaces, a clean one (freshly ground) and a significantly oxidized one (long-term storage in open air). The XRD results show similar values for the oxide content in the regular and N\({}_{2}\)-shielded LST samples but a significantly reduced oxide content in the sample treated by gentle ablation. Apparently, in this case, the analytical technique was able to better distinguish between the laser processing variants. There is not a very tight correlation between the EDS and XRD results, which was expected because of the different penetration depths (less than a \(\upmu\)m for electrons and around 20 \(\upmu\)m for X-rays) and the distribution of the oxide in the gauge volume. Still, both techniques show a marked distinction between the clean, moderately oxidized, and heavily oxidized samples.