# Surface Analysis of 3D (SLM) Co-Cr-W Dental Metallic Materials
## 3 Results and Discussion
### Chemical Composition Determination  
The chemical composition of the powders was determined through EDS: Co: 59; Cr: 25; W: 9.5; Mo: 3.50; Si: max. 1; other elements: max. 1.5 (wt%). Except for the presence of oxygen and carbon on the surface, no other elements were identified on the experimental materials after the SLM process (Table 1). The experimental results were obtained as averages of the values determined on five areas of 25 \(\upmu\)m--0 (1, 2) and five areas of 50 \(\upmu\)m--0 (1, 2). A greater oxidized surface was determined on the sample sandblasted only with alumina, while a smaller percentage of O was found on the surface of the sample processed with alumina and silica powders [19]. The growth and quality of a chromium oxide layer are extremely important for the high resistance to corrosion characteristics  
Figure 2: Scanning electron microscopy (SEM) (2D) images of the surface of the 3D printed samples at 1000\(\times\): (a) 25 \(\upmu\)m—0, (b) 25 \(\upmu\)m—1, (c) 25 \(\upmu\)m—2, (d) 50 \(\upmu\)m—0, (e) 50 \(\upmu\)m—1, and (f) 50 \(\upmu\)m—2. of Co-Cr-based alloys. The corrosion of Cr-based materials is based on the growth of a compact Cr oxide film (Cr\({}_{2}\)O\({}_{3}\)) or chromium-rich oxides, which act as a jam between the environment (oxidizing atmosphere) and the alloy. Frequently, the value of the corrosion resistance of these alloys depends on the properties of the Cr oxide formed [20]. After sandblasting with alumina and alumina with silica, the metallic surface was contaminated with alumina and silica parts. On the surface worked with Al\({}_{2}\)O\({}_{3}\)+SiO\({}_{2}\), no more carbon was identified based on the removal of the carbon compounds left behind by the SLM process (Figure 4). The elemental distributions (made with an EDS detector on 25 \(\upmu\)m--0 (1, 2)) of the main elements (Figure 4) determined using the experimental surfaces were in accordance with the chemical composition determinations presented in Table 1. All of the surfaces were covered with oxides and a reduced number of carbon-based compounds. As a general observation in the literature, 3D printed materials typically present a certain oxidation state after the SLM process, and the surface is generally contaminated with particles of alumina and silica during the sandblasting process. A final cleaning stage using alcohol is recommended after the sandblasting operation. \begin{table}
\begin{tabular}{c c c c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Chemical Elements**} & \multicolumn{2}{c}{**Co**} & \multicolumn{2}{c}{**Cr**} & \multicolumn{2}{c}{**W**} & \multicolumn{2}{c}{**Mo**} & \multicolumn{2}{c}{**O**} & \multicolumn{2}{c}{**C**} & \multicolumn{2}{c}{**A1**} & \multicolumn{2}{c}{**Si**} \\ \cline{2-13}  & **wt\%** & **at\%** & **wt\%** & **at\%** & **wt\%** & **at\%** & **wt\%** & **at\%** & **wt\%** & **at\%** & **wt\%** & **at\%** & **wt\%** & **at\%** & **wt\%** & **at\%** \\ \hline
25 (50) \(\upmu\)m—0 & 51.7 & 38.87 & 23.11 & 19.7 & 8.23 & 1.98 & 4.09 & 1.89 & 10.8 & 29.91 & 1.08 & 5.07 & - & - & 1.0 & 2.58 \\ \hline
25 (50) \(\upmu\)m—1 & 49.91 & 34.95 & 21.59 & 17.14 & 7.81 & 1.75 & 4.08 & 1.76 & 12.2 & 31.48 & 2.32 & 7.38 & 1.11 & 1.63 & 0.96 & 2.52 \\ \hline
25 (50) \(\upmu\)m—2 & 46.62 & 35.1 & 23.08 & 19.69 & 7.31 & 1.77 & 4.3 & 1.99 & 9.68 & 26.85 & - & - & 6.02 & 9.9 & 2.98 & 4.71 \\ \hline EDS error & 1.35 & 0.66 & 0.3 & 0.31 & 2.9 & 0.5 & 0.2 & 0.2 & & & & & & \\ \hline \hline \end{tabular} Standard deviation (SD; after 20 replicates of the chemical composition determination on the same 1 mm\({}^{2}\) area): Co: \(\pm\)0.3; Cr: \(\pm\)0.24; W: \(\pm\)0.15; Mo: \(\pm\)0.1; O: \(\pm\)0.2; C: \(\pm\)0.12; Al: \(\pm\)0.1; Si: \(\pm\)0.1.  
\end{table} 
Table 1: Chemical composition results of the experimental surface (average of 10 determinations).