Dependence, on the Cr Content, of the Corrosion Resistance to Fusayama Saliva of Cobalt-Based Dental Alloys, Studied by the Mean of Binary Alloys
Résumé
Cobalt-chromium alloys represent a growing alternative for dental alloys made of noble metals. Superior mechanical strength and the development of a passive layer allow them resisting mastication and aggressiveness of the buccal milieu, respectively. However the Cr content merits to be optimized for achieving fabrication easiness, corrosion resistance and ductility keeping. This work consists in a specific analysis of the dependence of the properties of cobalt-chromium alloys on their Cr contents. To eliminate the possible influences of a maximum of other factors simple binary alloys were initially prepared all according to a precise procedure leading to equi-axed polycrystalline single-phased alloys, chemically homogeneous and with the same mechanical internal states. In parallel with controls in chemical composition, microstructure and hardness, all of them were subjected to electrochemical characterization of corrosion with the same apparatus and the same protocol: Fusayama saliva acidified to pH=2.3, 37±0.5°C, and successive classical electrochemical tests with the same parameters: free potential following up, Stern-Geary method, Tafel method. Results demonstrate that high corrosion resistance thanks to passivation is systematic for Cr content equal or higher than 25wt. %, that 20 wt. %Cr may lead to not reproductible behavior, and lower contents allow high corrosion rates.
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