Research On Degradability Of Heat Treatment Mg-0.4/1.2Ca-xNd Bone Fixation

In recent years,with the increasing demand for clinical bone fixation materials,the advantages of magnesium alloys as medical materials becomes more and more significant,its modulus of elasticity,density and mechanical properties are similar to human bone compared to traditional bone-implant materials stainless steel and titanium alloys,in addition,it can be degraded in the body to avoid removing it again,however,as bone fixation materials,magnesium alloys eroded too fast in the body resulting in the loss of fixation which the fracture hasn't healed.Therefore,this paper aims to add trace metal elements to pure magnesium,for alloying and heat treatment with respect to slow down biodegradability in simulated body fluid,the microstructure and the change of precipitate have been measured using X-ray diffraction?XRD?,scanning electron microscopy?SEM?and EDS,immerse the as-cast and heat-treated Mg-0.4/1.2Ca-x Nd in simulated body fluid,and looking for better performance alloys by weight loss,pH variation,volume of evolved hydrogen and electrochemical test.Finally,the hemolysis and bone implantation experiental have been studied for alloys that performanced better,the results indicate:?1?The Mg-0.4/12Ca-x Nd?x=0,0.5,1.0,1.5wt.%?alloys were melted in 1100?superalloy melting furnance,and X-ray diffraction results indicated the Mg-0.4/1.2Ca binary alloys including?-Mg and the second phase Mg₂Ca,and the Mg-Ca-Nd ternary alloys mainly consist of?-Mg,Mg₂Ca and Mg₄₁Nd_5.The solid solubility of Ca and Nd element are small in magnesium alloy substrate,that can be present in the form of second phase in the materials.Observing by scanning electron microscopy?SEM?that Mg₂Ca and Mg₄₁Nd₅ mainly distributed on the boundary,and with EDS energy spectrum analyzing,we know that Mg and Ca existed in Mg-0.4/1.2Ca,in addition,Mg-0.4/1.2Ca-xNd alloys consist of Mg,Ca and Nd,the results showed that the Mg-0.4Ca-1Nd and Mg-1.2Ca-0.5Nd alloys were in small grain size,and precipitation phase were uniformly distributed in grain boundary.When Mg-0.4Ca-1Nd and Mg-1.2Ca-0.5Nd alloys after solution treatment,all Mg₄₁Nd₅ and most Mg₂Ca are melted into the?-Mg matrix,while the second phase Mg₂Ca and Mg₄₁Nd₅ precipitated from?-Mg after aging treatment,and the content of second phase increased with aging time increasing,the results indicated that the best aging time of Mg-0.4Ca-1Nd and Mg-1.2Ca-0.5Nd were 12h and4h respectively.?2?The corrosion experiment results of Mg-0.4/1.2Ca-xNd cast alloys showed that the corrosionrateofMg-0.4Ca-1NdandMg-1.2Ca-0.5Ndare0.02mg·cm^-2·h^-1and0.0202mg·cm^-2·h^-1respectively in 120h,which are low.Besides,the change of hydrogen evolution and pH variation are slow,hydrogen evolution are 1.22ml and 2.51ml respectively when the time is 24h.The heat treatment experiments showed that corrosion resistance was good for Mg-0.4Ca-1Nd after 8h solution and 12h aging,Mg-1.2Ca-0.5Nd after 8h solution and 4h aging,the corrosion rates were 0.0119mg·cm^-2·h^-1and 0.0115mg·cm^-2·h^-1respectively in 120h,hydrogen evolution were 0.83ml and 2ml,pH were 8.36 and 8.3 respectively after 24h solution.?3?Electrochemistry test showed that the corrosion current i_corrorr of Mg-0.4Ca-1Nd and Mg-1.2Ca-0.5Nd are 2.453?A and 2.468?A respectively.The result showed the most corrosive when subjecting the Mg-0.4Ca-1Nd and Mg-1.2Ca-0.5Nd alloy to 12h and 4h aging treatment separately.?4?The results of hemolysis experiment showed that the hemolysis rate of pure magnesium is as high as 53.9%over the national standard,but the hemolysis rates of the as-cast and heat-treated Mg-0.4Ca-1Nd and Mg-1.2Ca-0.5Nd alloy samples are in line with the national assessment of the hemolytic rate of medical implant materials,and their values are all below 5%.Bone nails were made by pure Mg and Mg-0.4Ca-1Nd heat treatment alloy and they were implanted in rabbits for two weeks.As a result,we observed that Mg-1.2Ca-0.5Nd alloy after 8h solution and 4h aging?T2?showed an excellent surface morphology by high-power camera,and no inflammations were seen around the material.