# Surface Analysis of 3D (SLM) Co-Cr-W Dental Metallic Materials
## 3 Results and Discussion
### Profilometry  
The state of a surface, for two materials placed in contact, is critical for the friction between them based on the specific comportment at the micro-scale of each metallic or non-metallic material. The surface profile is also important for the further deposition of a new material on top of the substrate. The samples presented different profiles of the surface based on the processing mechanism applied (Figure 5). All of the samples exhibited a similar surface, with heights between 0.01 and 20 \(\upmu\)m for most of them, and only a few peaks between 20 and 70 \(\upmu\)m. The average roughness (Ra center line average (CLA)) was between 4.20 (sample 25 \(\upmu\)m--2) and 8.77 \(\upmu\)m (sample 50 \(\upmu\)m--0), which influenced the friction coefficient, microhardness, and the wear resistance of the materials [21]. The average amplitude in the height direction (Rq) was also big for the 50 \(\upmu\)m--0 (11.08 \(\upmu\)m) sample and smallest for the 25 \(\upmu\)m--2 (5.48 \(\upmu\)m) sample, which had the smoothest surface (Table 2). \begin{table}
\begin{tabular}{c c c c c c c} \hline
**Sample/Parameters** & **Rq**\(\upmu\)**m** & **Rq**\(\upmu\)**m** & **Rq**\(\upmu\)**m** & **Rku** & **Rp**\(\upmu\)**m** & **Rv**\(\upmu\)**m** & **RT**\(\upmu\)**m** \\ \hline
25 \(\upmu\)m—0 & 7.16 & 9.73 & 1.57 & 9.06 & 36.65 & 18.30 & 94.53 \\ \hline
25 \(\upmu\)m—1 & 4.73 & 6.39 & 1.11 & 7.09 & 18.21 & 13.12 & 60.16 \\ \hline
25 \(\upmu\)m—2 & 4.20 & 5.48 & 0.90 & 5.69 & 16.62 & 12.35 & 51.64 \\ \hline
50 \(\upmu\)m—0 & 8.77 & 11.08 & 0.28 & 3.27 & 32.10 & 25.59 & 81.45 \\ \hline
50 \(\upmu\)m—1 & 8.00 & 10.05 & 0.07 & 3.05 & 23.61 & 24.54 & 68.82 \\ \hline
50 \(\upmu\)m—2 & 6.11 & 7.96 & 0.19 & 3.82 & 19.82 & 21.38 & 57.44 \\ \hline \end{tabular} Rq, the arithmetic mean deviation of the profile or the average surface roughness; Rq, the mean square deviation of the profile; Rp, the maximum height, Rr, the maximum depth; Rr, the total height of the roughness profile (the difference between the height Zp of the highest peak and the depth of the deepest valley along the entire length of the assessment).  
\end{table} 
Table 2: The main profilometry parameters of the experimental elements. In order to evaluate a surface state in the height direction, two parameters were used: R\({}_{\rm sk}\) and R\({}_{\rm ku}\) (skewness and kurtosis). The value of the R\({}_{\rm sk}\) parameter indicates how a solid material is arranged as a profile of the surface and, in this case, all of the samples presented a positive skewness parameter, that is, the mean of the solid material was mostly below the mean line. The profiles characterized by high peaks, or at which the depression was gentle, had positive skewness parameter values. Another characteristic of a surface is the kurtosis parameter (R\({}_{\rm ku}\)), which depends on the form of the profile. All of the surfaces of the samples had an R\({}_{\rm ku}\) parameter bigger than 3 (except the 50 \(\upmu\)m--1 sample, which was R\({}_{\rm ku}\) = 3.05, meaning that the profile had relatively few high peaks and depressions, such as a platykurtic profile) (Table 2). This is the case of profiles with many high peaks and deep valleys (leptokurtic profile type). The Rp, Rv, and RT parameters confirm that the samples sandblasted with Al\({}_{2}\)O\({}_{3}\) and SiO\({}_{2}\) presented the smoothest surface, and the biggest profile differences were found for the 25 \(\upmu\)m--0 sample, while the smallest was found for the 25 \(\upmu\)m--2 sample (the finest surface). It is known that surfaces with a high roughness (lower quality) have a low fatigue resistance, while surfaces with a low roughness (high quality) have better fatigue resistance, as well as high resistance to corrosion. This does not mean that the over-finishing of surfaces, at the end of which a very low roughness is obtained, will always be beneficial to the normal operation of the parts and will not only generate an unjustified increase in their cost price.