Hot Deformation And Degradation Behavior In Vivo And In Vitro Of Medical Magnesium Composites

Mg-Zn alloys have become one of the important research directions in the field of degradable Mg-based composites due to their outstanding biological safety,good mechanical properties and biocompatibility.However,the mechanical properties and corrosion rate of Mg-Zn alloys still cannot meet the clinical use requirements of degradable metal materials.Therefore,the goal of this subject is to obtain excellent mechanical properties and good corrosion resistance,through alloying,adding ceramic particles to prepare composite materials,screw rolling,hot extrusion and surface treatment,etc.,acquiring a degradable Mg-based composites which has a good comprehensive performance.Using advanced material characterization methods and testing techniques,the plastic deformation behavior of magnesium-based composites during hot working was studied,and the effect of screw rolling on the microstructure evolution,mechanical properties and mechanical properties of MgO/Mg-Zn-Ca nanocomposites was explored for the first time.The effect of nano-MgO particles and Na Mg F₃ film on the corrosion behavior of Mg-Zn-Ca alloy were studied in vivo and in vitro.1.The effect of?-TCP on the deformation behavior and microstructure evolution of Mg-Zn-Zr alloy during hot compression were studied,and the effect and mechanism of MgO on the deformation behavior of Mg-Zn-Ca alloy(MZC)under hot compression were also analyzed for the first time.It was found that the addition of ceramic particles refines the microstructure and promotes the process of dynamic recrystallization of the composites.However,the addition of nano-?-TCP ceramic particles improved the stress sensitivity and deformation resistance of the composites,but reduces the plasticity of the composite.On the contrary,the addition of nano-MgO particles not only reduces the stress sensitivity and deformation resistance in the process of hot deformation,but also improves the plasticity of MZC.The maximum power dissipation rates of?-TCP/Mg-Zn-Zr and MgO/Mg-Zn-Ca composites are 37%and 43%,respectively,indicating that the MgO/Mg-Zn-Ca composites have better machinability.Consequently,in the latter parts of this study,x MgO/Mg-Zn-Ca was selected as the research object.2.Bimodal grain structure was observed in the pre-extruded Mg-3Zn-0.2Ca(MZC)and 0.3MgO/Mg-3Zn-0.2Ca(MZCM)(wt.%).After screw rolling,the organization becomes a gradient microstructure from the edge to the center in cross-section,the texture type of the composites changes from(-1100)cylindrical texture to(0001)basal texture,and the texture strength of MZCM is higher than that of MZC,resulting in better ductility of MZCM with elongation of 32.4%.The in vitro immersion test in Hanks'solution prevails that the corrosion rate of immersed MZCM is lower than that of MZC.So the corrosion mechanism of the two materials is different.The potential of second phases are higher than that of the Mg matrix,which will form galvanic corrosion and corrode the Mg matrix preferentially.3.To improve the corrosion resistance,MZC alloy was immersed in Na F solution to obtain a Na Mg F₃ film.Na Mg F₃ film was uniform and dense,the contact angle between the sample surface and water is increased,resulting in the improves of the corrosion resistance of the material.The immersion test in Hanks'solution shows that the Na Mg F₃ film depresses the corrosion rate of MZC to 0.4 mm/y,which satisfies the corrosion rate requirement of Mg alloy for degradable bone repair material,i.e,less than 0.5 mm/y.After 12 weeks of implantation,the Na Mg F₃ coated MZC still has a compressive strength of 164.2 MPa and a maximum compressive strain of 14.1%,which can provide sufficient mechanical support before healing the patient's bone.Therefore,the Na Mg F₃ coated MZC showed an excellent corrosion resistance,stable mechanical properties,osteogenesis and good biocompatibility.