Corrosion properties of oxygen plasma immersion ion implantation treated magnesium

Oxygen plasma immersion ion implantation (PIII) was conducted in magnesium with oxygen doses in the range of 2.5 × 1015 ions cm− 2 up to 2.0 × 1016 ions cm− 2, and the corrosion properties were investigated in neutral phosphate buffer solution (PBS, pH 7.4) and chloride ion enriched PBS (145 mM Cl−, pH 6.4) (PBS(Cl−)). Significantly enhanced corrosion resistance against PBS was achieved on Mg treated with high oxygen doses above 1 × 1016 ions cm− 2. The corrosion current density Icorr of treated Mg was almost five orders less than that of untreated Mg; no intermediate values are obtained for samples with intermediate doses. However, all samples we prepared in this case could not withstand the more aggressive PBS(Cl−). No improvement of corrosion resistance in such solution has been observed even for surfaces implanted at 2.0 × 1016 ions cm− 2. The enhanced corrosion resistance against neutral PBS is ascribed to increased Mg–O bonding states formed on the surface layer of magnesium by the PIII process, as discerned by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) measurements. Further the more homogenous surface morphology, due to the ion bombardment effect, as observed by atomic force microscopy (AFM) may contribute. The Mg–O bondings can be dissolved easily in Cl− enriched and more acidic ambience, as shown with PBS(Cl−).