| Traditional metal implant materials,such as stainless steel,titanium and titanium alloy,have excellent mechanical properties and machinability,which can provide good support at the initial stage of implantation.However,the difference elastic modulus between implant materials and human bone has an adverse effect on bone repair,and these inert implant materials can only be removed by"secondary operation"which results in huge economic burden and psychological pressure on patients.With the gradual change of medical concept,patients wish that the implant materials can be degraded spontaneously in the later stage and the degradation products can be absorbed by the human body.Therefore,biodegradable metals represented by magnesium alloys have gradually become the research focus of biomedical materials.Compared with AZ31 alloy,Mg-RE alloys have the advantages of good processability,high strength and good corrosion resistance,and a small amount of rare earth elements will not affect human health,so Mg-RE alloys can be used as biomedical materials.In this paper,Mg-Gd(Mg-1Zn-1Gd,Mg-1Gd)alloys are chosen as starting material,the preparation and degradation properties of anodized film and Ca-P composite film are studied.The main results are as follows.(1)There are many factors affecting the anodized film formation behavior,and the electrolyte component is one of the most important factors.Therefore,the effects of different oxygen salts on the anodized film formation behavior are firstly studied in this paper.The results of optical microscope and SEM(Scanning Electron Microscope)show that the addition of Na3PO4 can accelerate the growth of anodized film,the addition of Na2Si O3 9H2O seems to have no obvious positive effect on the growth of anodized film.Interestingly,when Na3PO4 and Na2Si O3·9H2O are added together,the growth rate of anodized film is obviously accelerated,and a relatively thick and dense film can completely cover the metal substrate in a short time.The electrochemical characterization shows that the film has better corrosion resistance.(2)Mg-1Zn-1Gd alloy,Mg-1Gd alloy and AZ31 alloy are anodized in order to study the corrosion resistance and degradation mechanism of Mg-Gd alloys after anodizing.SEM results show that the anodized film of Mg-Gd alloys has smaller pore size,denser and thicker after anodizing.The results of XRD(X-ray diffractometer)show that the ratio of crystalline Mg O,Mg2Si O4 and Mg3(PO4)2 in the anodized film of Mg-Gd alloys is higher.Electrochemical tests and immersion tests show that the degradation rate of anodized Mg-Gd alloys is much slower than that of anodized AZ31 alloy,and there is no obvious corrosion pits on the surface of anodized Mg-1Zn-1Gd alloy after immersion tests.The results of SECM(Scanning Electrochemical Microscopy)show that the local corrosion and pitting corrosion of anodized Mg-Gd alloys(especially Mg-1Zn-1Gd alloy)are effectively suppressed,which is supposed to be resulted from the different microstructure,composition and corrosion products of anodized Mg-Gd alloys compared with those of anodized AZ31alloy.(3)In order to further improve the long-term corrosion resistance of Mg-1Zn-1Gd alloy,the anodized sample is subsequently modified by solution treatment,and the effect of Ca/P ratio of the solution on the Ca-P deposition behavior,the morphology,structure and corrosion resistance of film are studied.The SEM results show that the solution treatment can effectively repair the holes and cracks in the anodized film,and the morphology of the Ca-P coating changes significantly with the Ca/P ratio,especially,the samples treated with Ca/P=1.25 solution is denser and thicker.In addition,the results of electrochemical characterization,immersion tests,XRD and SECM show that the samples treated with Ca/P=1.25 solution show the best corrosion resistance during the immersion tests,and the film do not show obvious corrosion,which is related to the denser structure and thicker film,and the repairing effect of degradation product(HA). |
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