Effect of chemical passivation on corrosion behavior and ion release of a commercial chromium-cobalt alloy

The number of ions released as a result of corrosion depends on the alloy chemical composition and microstructure as well as the casting and polishing conditions.2 As a general rule, any dental alloy in the oral environment will be exposed to corrosion due to oral conditions. [...]alloys should possibly be used with minimal ion release and harmful ions. Free ions can cause problems with the restoration function and its destruction, such as breakage of the solder and, from an aesthetic viewpoint, the tarnishing of metal surfaces will deform the restoration.6 However, specific conditions of oral environments such as saliva, dental plaque, bacteria, gastric acid reflux, and so on will affect the corrosion of alloys.5,7 Co-Cr-Mo alloys exhibit better biocompatibility and corrosion resistance than Ni-Cr-based alloys because Co, Cr, and Mo are considered less toxic than Ni and are released at much lower concentrations.8 A few reports are available on the cytotoxicity of Co-Cr-base alloys. Cr-rich passive oxide film, which is highly resistant to acid, contributes to the alloys' biocompatibility.11 Alloys coated with such layers will have lower electrochemical potential.12 Passivation can be achieved by chemical reactions.13 Passive layers will have lower ion conduction, lower solubility, higher abrasion resistance, and higher adhesion.14 The biocompatibility of Co-Cr alloy is associated with high corrosion resistance, resulting from the formation of an internal passive layer on the alloy surface. [...]lack of surface polishing will increase porosity and corrosion, as shown by McGinley et al.20 No study has so far been conducted on the passivation of this alloy. Since this method might be effective in alloy corrosion according to similar previous studies, this study aimed to investigate the effect of chemical passivation on corrosion behavior and ion release of Flexicast Co-Cr alloy.