Study On The Surface Modification And Biocompatibility Of A Ni-free Zr-based Bulk Metallic Glass

In this dissertation, a new bulk metallic glass(BMG)-Zr₆₂Cu₂₀Fe₅Al₁₀Nb₃ was prepared by copper mold casting. The structure and thermal properties of this alloy was characterized by X-ray diffraction (XRD) and differential scanning calorimetry (DSC). Instron mechanical testing system was employed to evaluate its mechanical properties. The in vitro corrosion behavior was investigated in phosphate buffered solution by electrochemical measurements. The cell compatibility was evaluated through cell culture followed by 3-(4,5-dimethylthiazol-2yl)-2,5-diphenyl tetrazolium bromide (MTT) assay. To enhance its bioactivity micro-arc oxidation method was applied to form an oxidation coating containing Ca and P. XRD and energy dispersive X-ray spectroscopy (EDS) were employed to investigate the phase and element composition of the oxidation coating. Surface morphology and roughness were characterized by scanning electron microscopy (SEM) and surface profile meter. Scratch tester was used to measure the bonding strength of the coating.Based on our previous research, a new BMG- Zr₆₂Cu₂₀Fe₅Al₁₀Nb₃ was developed. It was found that this alloy had good glass forming ability and thermal stability, which can be cast into fully amorphous sheet with the size of 70×12×1.5mm. The mechanical test revealed that this alloy exhibits superior strength and plasticity, with the fracture strength and fracture strain of 1683MPa and 9.1% respectively. The Young's modulus was calculated to be 70GPa from the mechanical test. It was found that the passive current density of this alloy is very low, but the passivation region is relatively small. The MTT essay revealed that the cell compatibility of this alloy is nearly as good as the polystyrene, from which the cell culture plate was made.Micro-arc oxidation method was used to enhance the bioactivity of the BMG which is original bioinert. An electrolyte containing Ca(OH)₂,Ethylene diamine tetraacetic acid disodium salt,Na₂SiO₃ and Na₃PO₄ was developed to form an oxidation layer enriched in Ca and P on this alloy by micro-arc oxidation. The oxidized coating mainly contained cubic zirconia and silicon dioxide, and some Ca and P were also incorporated. The Ca content increased with the increase of the oxidation voltage, while the P content decreased with the increase of the voltage. Compared to the original alloy, the Cu content dropped remarkably. A rough and porous surface morphology was obtained by the micro-arc oxidization and there was no distinct interface between the coating and the substrate. The scratch test revealed that the bonding strength of the oxidation coating was very high.