Microstructure characteristics and degradation behaviors of medical rare-earth Mg-10.6Gd-0.3Ag-x(Y/Zn) alloys in vitro

Abstract

Due to excellent biological-functionality, unique/suitable elastic-modulus as well as spontaneous degradation behaviors, Mg alloys acted as medical implants have shown enormous potential in surgical operation and bone-fixation fields. Unfortunately, the extreme mass loss and unmarked-fracture could easily induce the implant failure. In the present study, the microstructure characteristics and degradation behaviors of the Mg-10.6Gd-0.3Ag-x(Y/Zn) alloys were investigated through the XRD, TEM, EPMA, XPS, 3D/CLSM and SECM. Results revealed that with the increment of Y/Zn contents, the amount of Mg24(Gd/Y)5 precipitates increased, which were mainly distributed in grains and on grain boundaries. The addition of Zn and Y increased the undercooling and Y had a large mismatch degree with Mg atoms, which could promote the precipitation of second phases. Additionally, the corrosion rates of Mg-10.6Gd-0.3Ag-x(Y/Zn) increased firstly and then reduced. Also, the best corrosion resistance was achieved in the Mg-10.6Gd-0.3Ag-Y-Zn, with the current intensities of 58.49 μA/cm2, attributed to the formation of continuous reticular structure oxide film, which can act as physical barriers and impede the corrosion process.