Microstructure, corrosion behavior, and surface mechanical properties of Fe oxide coatings on biomedical ZK60 Mg alloy

The Mg-5.5Zn-0.6Zr (in wt%, ZK60) alloy has been surface modified by dual Fe&O ion implantation and deposition (II&D) under different O-2 fluxes from 0 to 40 sccm. The microstructure is investigated by glancing angle X-ray diffraction, atomic force microscope, and scanning electron microscopy. The results show that the modified layers, with a gradient microstructure of outer deposition region and inner implantation region, are composed of alpha-Fe + Fe&Mg mixture, FeO/Fe-rich oxide + Fe&Mg mixture, and alpha-Fe2O3/Fe-rich oxide + Fe&Mg mixture for 0, 10, and 40 sccm O-2 fluxes, respectively. The electrochemical and immersion tests in 37 degrees C Hank's solution indicate an improvement in corrosion behavior under 0 and 10 sccm O-2 fluxes, but a deterioration in corrosion resistance under 40 sccm O-2 flux. In addition, the nanoindentation tests suggest that the dual Fe&O II&D simultaneously enhances the surface hardness and elastic modulus due to the formation of Fe and its oxide coatings.