# Surface Analysis of 3D (SLM) Co-Cr-W Dental Metallic Materials
## 3 Results and Discussion
### Hardness Analysis
Among  
Figure 7: Scratch test results lateral force (\(\mathrm{F_{x}}\)) (f) distance: (**a**) 25 \(\upmu\)m and (**b**) 50 \(\upmu\)m; coefficient of friction (COF) (**f**) distance: (**c**) 25 \(\upmu\)m and (**d**) 50 \(\upmu\)m; acoustic emission (AE) (**f**) distance: (**e**) 25 \(\upmu\)m and (**f**) 50 \(\upmu\)m.  
biomedical materials, these ones present high hardness and very good wear resistance (300-400 HV) [27,31]. Nevertheless, the wear resistance characteristics of Co-Cr alloys strictly depend on their microstructure and the processes used to obtain/work them. For 3D printed samples, it is important that they behave as per their usual obtained alloy (made by casting) or even better in order to be used for similar applications. The traces made on the surface of the material by scratch tests (Figure 8) present a deformation of the material under the F\({}_{2}\) force with a flattening of semi-melted particles (Figure 8a,b) in the case of the initial surface. Moreover, micro-cracks were observed in the deformed powders on the scratch surface (Figure 8b), and the material was oriented in the scratch direction. The scratch marks decreased as the width of the surface processing increased (Figure 8a,c,e) based on the material response because of the hardening phenomenon, which accompanied the sandblast process. No micro-cracks were observed for the smoother 25 (50) \(\upmu\)m--1 and --2 samples (Figure 8d,f) except at the end of the scratch of the 50 \(\upmu\)m--2 sample, which  
Figure 8: SEM images of the scratch surface of the (**a**) and (**b**) 50 \(\upmu\)m—0, (**c**) and (**d**) 50 \(\upmu\)m—1, and (**e**) and (**f**) 50 \(\upmu\)m—2 for different amplification powers 500\(\times\) and 1000\(\times\). confirms the AE results from Figure 7f. For both sandblasted samples, the scratch marks presented interruptions, caused by the surface profilometry and hardness. Material overlap was observed on the surface of the 50 \(\upmu\)m--2 samples at higher scratch forces (at the end of the test with a force of 20 N). The Vickers microhardness results (HV) (Table 3) show a hardening of the surface with the sandblast process in both samples sets. [PERSON] and others identified microhardness (2 N/15 s) of the Co-Cr-W after different heat treatments between 350 and 550 HV [32]. The hardness values obtained from five different locations highlight the differences between the initial surface and the sandblasted surfaces, especially in the case of the first set of samples (25 \(\upmu\)m--0 (1, 2)). Different values of the micro Vickers hardness on the same surface were observed for all of the samples based on the presence of semi-melted initial particles and different hardened areas. The values obtained recommend these materials for dental applications as metal crowns [33]. On the initial 25 \(\upmu\)m--0 sample, we observed a value much lower than the other four (378 HV), which was probably taken from a semi-melted particle on the surface. In the case of the 25 \(\upmu\)m samples, a high increase in the microhardness was observed with the application of sandblasting, especially for Al\({}_{2}\)O\({}_{3}\)+SiO\({}_{2}\) solicitation, which supplementarily hardens the surface. For samples made of thicker layers (50 \(\upmu\)m), the surface hardening presented smaller differences to the first set (25 \(\upmu\)m), which exhibited average values between the minimum and maximum values. The variation of the microhardness on the material surface confirmed the results obtained from scratch tests. Comparing the results of the hardness for the average values, an almost 23% increase was determined for the first set of samples and 3.5% for the second set.