Study On Surface Modification Of Medical Rare Earth Magnesium Alloys By High Current Pulsed Electron Beam

Magnesium alloys are considered promising candidates for the next generation of biodegradable medical implants because of their good biocompatibility.But the too fast degradation rate limits its application in biological materials.High current pulsed electron beam?HCPEB?was a surface modification technology developed in recent two decades,and a large number of existing studies have shown that this technology can significantly improve the surface wear resistance and corrosion resistance of various kinds of material.At the same time,fluorinated biomaterials show a better biocompatibility.Therefore,in order to further expand the applications of magnesium alloys in the biological field,HCPEB was applied on the WE43 alloy to study the surface microstructures and properties modification of the WE43 alloy.Meanwhile,a simple chemical conversion technology was used to further treat the HCPEB modified surface with fluoride ions.Transmission electron microscope?TEM?was used to analyze the phase changes in the resolidified layers of HCPEB treated samples.The micromorphology,element distributions and phase compositions of the resolidified layers and fluorine conversion films are characterized by X-ray diffraction?XRD?,X-ray photoelectron spectroscopy?XPS?,and scanning electron microscope and energy spectroscopy?SEM&EDS?.The degradation behavior of the material in simulated body fluid?SBF?,simulated body fluid+10 wt.%bovine serum albumin?SBF+10 wt.%BSA?and DMEM high glucose medium was analyzed by electrochemical workstation and immersion experiments.The results show that the thickness of the resolidified thickness of the layer of the 15pulsed sample is about 13.1?m and the internal precipitated phase particles are uniformly distributed in the layer.There are no obvious impurity ions and defects in the resolidified layer.The electrochemical measurements in the simulated body fluid?SBF?show that the corrosion current density?Icorr?of the 15 pulsed sample(2.66×10^-5 A?cm^-2)reduces by an order of magnitude compared to that of the untreated sample(1.91×10^-4 A?cm^-2),and the polarization resistance?R_p=988.41??cm²?increases by 176.9%compared to that of the untreated sample?R_p=356.95??cm²?.The immersion experiments show that the hydrogen evolution content of the Mg alloy modified in the simulated body fluid?SBF?is significantly lower than that of the matrix sample,and the p H value of the 15 pulsed sample significantly reduces.According to the analysis of the corrosion morphology,it can be known that the modified samples mainly undergo general corrosion,which the matrix samples mainly undergo electrochemical corrosion,which undoubtedly accelerates the corrosion rate of magnesium alloys.This indicates that the surface of the samples treated by HCPEB can effectively improve the corrosion resistance of the Mg alloy.When the samples were fluorinated,electrochemical tests reveal that the fluorinated samples had significantly higher corrosion resistance in SBF than that of the non-fluorinated samples.Meanwhile,when the SBF contains protein,it can reduce the corrosion rate of the magnesium alloy.The immersion experiments in SBF show that the fluorinated films can effectively prevent the magnesium alloy from being corroded by the solution during the initial immersion period.As the immersion time increasing,the corrosion products on the surface of the Mg alloy can also slow down the corrosion rate of the magnesium alloy.The morphology and corrosion resistance of the film prepared on the 15 pulsed sample surface for 15 days is the best.XPS analysis show that the main component of the fluorinated film is Mg F₂.In summary,WE43 Mg alloy treated by HCPEB shows lower corrosion rate than the matrix.At the same time,the resolidfied layer is also conducive to surface fluorination treatment,which further improves the corrosion resistance of magnesium alloys.