Improved corrosion resistance of CoCrMo alloy with self-passivation ability facilitated by carbon ion implantation

Herein, carbon ion implantation was employed as a method for improving the corrosion resistance of CoCrMo alloy. The structural changes emerging as a result of carbon ion implantation were investigated by using grazing incidence X-ray diffraction (GIXRD) and high-resolution transmission electron microscopy (HRTEM). The corrosion behavior was characterized by electrochemical impedance spectroscopy (EIS) and polarization tests. Following the corrosion test, HRTEM and scanning transmission electron microscopy-energy dispersive spectrometer (STEM-EDS) were employed for the analysis of corrosion related structural and compositional change at the nanometer scale. The results showed that carbon ion implantation promotes surface amorphization in the CoCrMo alloy. In fact, the corrosion resistance of CoCrMo alloy improves significantly, as evidenced by the order of magnitude reduction in corrosion current density (i_corr). The surface amorphization improves the corrosion resistance of CoCrMo alloy through three mechanisms: the amorphous layer formed (i) acts as barrier layer, (ii) suppresses localized corrosion, and (iii) facilitates spontaneous formation of a passive layer (self-passivation).