Role of Coke in the Passive Properties of Vitallium 2000 CoCrMo Casting Alloy in Simulated Oral Environment

Abstract

The passive behaviors of Vitallium 2000 CoCrMo casting alloy in artificial saliva (AS) and Coke were studied by potentiodynamic polarization, electrochemical impedance spectroscopy, cyclic voltammetry, Mott–Schottky combined with scanning electron microscopy, Auger electron spectroscopy, and x-ray photoelectron spectroscopy surface analysis. The results show that with the increasing content of Coke, the self-corrosion current density of alloy increased sharply, the passive film corrosion resistance showed the best in AS and worst in Coke, and the R_p in Coke is reduced to half of that in AS. The thickness of passive films in AS, AS + Coke, and Coke is about 4.5, 3, and 2.5 nm, respectively. Passive films all exhibit n-type semiconductors; with more defects, the carrier density in Coke is 2.3 times more than that in AS. The Coke inhibits the oxidation of Co, Cr, and Mo, and the Co/Cr rate and Cr⁶⁺ concentration within the passive film increase. Coke weakens the formation process of protected oxides, thus reducing the stability of alloy’s passive film.