Electrochemical Characterization of Co-Cr Alloys Manufactured by Casting,CAD/CAM and SLM

Methods: Three groups of specimens were prepared. The CAS group (conventional centrifugal casting/Ducatron, Ugin’dentaire, France) the CAD group (CAD/CAM (Organical, R+K CAD/CAM Technology, Germany) and the SLM group (Phenix System,France), employing V-Comp, Octa-C and ST2724G respectively. The corrosion resistance of the alloys was evaluated by open circuit potential (OCP) and  potentiodynamic anodic scan with a mini cell system (MCS) in a 0.1M lactic acid and 0.1M NaCl solution. A saturated calomel electrode was used as a reference electrode (E_o=241 mVvs.SHE). Acquisition parameters were 10min for OCP and  –1V up to +2V (versus SHE) potential range,10mV/s scan rate and 0.008cm² sampling area. The morphology of tested surfaces was tested in a SEM employing secondary and backscattered electron images. From the generated curves the corrosion potential and pitting potential were calculated.

Results: The CAS group showed the lowest OCP values (-200~-150 mV), while CAD and SLM groups resulted in similar values (-75~20mV). All specimens demonstrated negative hysteresis, during reverse anodic scan denoting that the protective oxide layer can be reversely repaired. All groups tested exhibited similar E_corr values (CAS:-465, CAD:-451 and SLM:-518mV), but the CAD group demonstrated the highest pitting potential (E_pit:651mV), followed by SLM (E_pit:560mV). The CAS group showed no passive region at all. SEM analysis revealed a uniform corrosion pattern in all groups, with deep craters developed on the surface after electrochemical testing.

Conclusions: According to the results of this study the CAD/CAM group presented the best corrosion resistance, followed by selective laser melting. The conventional casting group was the most prone to corrosion.