| With the development of medical technology and material science,the requirements of some clinical implant materials are not only limited to the good degradation property in therapeutic periods,but also dissolved ingredients that are beneficial to the human body or can repair the damaged tissue.Hence the degradable composite biomaterials have received more and more attention and research,especially materials based on Mg alloys.The Mg-based alloy is a degradable metal with a good biocompatibility and similar mechanical properties with the human bones,recently,it has received extensive attention in the medical material field.However,the degradation rate of the Mg alloys in the human body environment is too rapid which limits its application.Research on improving the corrosion resistance and degradation resistance of the Mg alloys has become a hot project.Micro-arc oxidation(MAO)technology could fabricate porous ceramic coatings on the valve metals surface,which is beneficial to the improvement of the corrosion resistance and biocompatibility on the Mg alloys.During the MAO process,micropores and microcracks inevitably occurred in the coating,which reduced its corrosion resistance.With the development of MAO surface sealing technology,recently,based on the research of layered double hydroxides(abbreviation in LDHs)composition and structure controllability and ion exchange and other characteristics,it can provide valuable research prospects for preparation of the functional coatings with self-healing,corrosion inhibition and protection functions.In this thesis,the MAO coating was fabricated on the surface of ZK60 Mg alloy,and then the MAO/LDHs composite coating for surface sealing and biological functions was prepared by hydrothermal treatment.And the influence of different concentrations of NaAlO2on the microstructure and phase composition of the MAO coating was studied.Orthogonal experiment was used to study the influence of hydrothermal process parameters(temperature,time,ion concentration)on the growth and corrosion resistance of LDHs coating.X-ray diffractometer(XRD),scanning electron microscope(SEM),energy spectrometer(EDS),Laser confocal microscopy(CLSM),etc.were used to analyze the phase and microstructure of the MAO/LDHs coating;the electrochemical workstation was used to characterize the corrosion resistance of the composite coating;the MAO/LDHs coating prepared by the optimized parameters has been tested the coating ion exchange property.The main content of the research work and the results obtained are as follows:Firstly,the MAO coatings fabricated with different concentrations of NaAlO2,the MAO coating fabricated with 6 g/L NaAlO2 which was considered the best.It was found that this coating had the lowest porosity and roughness,and the coating had a good bonding force with the Mg matrix.The XRD results showed that the increase of the hardness of the MAO coating was related to the hard phase of MgAl2O4 formed in the reaction.Results of the 20-days Hank's solution immersion test showed that the average corrosion rate of the MAO coating fabricated with 6 g/L NaAlO2 was the lowest,which was only 0.09 mg·(cm2·d)-1.Meanwhile,the p H change of the Hank's solution was kept to a minimum.After optimizing the three hydrothermal parameters of ion concentration,temperature and time by simple comparison experiment of univariate and orthogonal experiment,the results showed that under the condition of 0.02 MZn(NO3)2,hydrothermal time are 2 hours and the oven temperature is 120?,the MAO/LDHs coating has the best corrosion resistance in Hank's solution.And the priority of these factors is:time>temperature>concentration.After the hydrothermal reaction with optimized parameters,the dense and uniform LDHs coating is formed on the MAO coating surface,and the defects such as micropores and microcracks on the MAO surface coating can be effectively blocked by LDHs.FT-IR diagrams,characterization of the surface performance and corrosion resistance showed that the MAO/LDHs coating has good ion exchange property.The porosities of the LDHs-Cys and LDHs-Met coating surface were reduced from 7.5%(MAO/LDHs)to 5.6%and 5.9%,respectively;the surface wetting angle were reduced from 82.5°to 70.3°and65.4°,respectively;the Ecorr of the coating after amino acid insertion was higher than the others.The composite coating showed better biocompatibility and corrosion resistance. |
PDF Full Text Request