Corrosion properties of low carbon CoCrMo and additively manufactured CoCr alloys for dental applications.

Objectives: Additive manufacturing (AM) is being applied to metallic biomaterials and dental alloys, including CoCrMo. CoCrMo mechanical properties and corrosion resistance are vital to the structural integrity of implants and dental appliances. The goal of this work is to assess the resistivity of AM cobalt chromium alloys by comparing them with traditional CoCrMo, regarding electrochemical properties resulting from microstructural and oxide film differences.

Methods: In this work, selective laser melting (SLM), was used to manufacture CoCrMoW. The corrosion characteristics of AM alloy were compared to that of wrought LC CoCrMo (ASTM F-1537) in both phosphate buffered saline (PBS) and PBS with 10 mM HO to simulate increased inflammatory conditions. Anodic polarization and electrochemical impedance spectroscopy (EIS) were performed.

Results: Both alloys were substantially similar in corrosion behavior in both solutions. They exhibited changes with the different solutions. Polarization resistances were statistically lower (R = 1.4 MΩcm (PBS) vs. 0.72 MΩcm (HO), R = 1.86 MΩcm (PBS) vs. 0.55 MΩcm (HO)), and open circuit potentials (OCP's) were statistically higher in 10 mM HO for both alloys (0.20 V (in HO) vs. - 0.09 V in PBS). Chemistry variations were revealed by the corrosion tests indicating that wrought LC CoCrMo retained its casting-based chemical heterogeneity, while AM CoCrMoW had sub-cell structures within the solidified grains.

Significance: As novel production methods like AM arise, it is necessary to understand any microstructural differences that may diminish the corrosion resistance properties. AM CoCrMoW alloys hold significant promise for use in dentistry where complex geometries are required.