Degradation Behavior Of Biomedical Porous Ti-Mg Composites Prepared By Microwave Sintered

Titanium alloys have been widely applied as the alternative materials for the human body implants due to the excellent corrosion resistance and mechanical properties, while their weakness is the lack of biological activity and the elastic modulus is too large. Magnesium and its alloys possess excellent bioactivity, while they are easy to corrode fastly in the human body fluid environment. Considering both their respective advantages and disadvantages, we attempt to prepare the porous Ti-Mg composites who have close mechanical properties with the human bone tissue,could avoid regular stress shielding of the implants and exhibit significant bioactivity.In this thesis, the Ti-Mg composites were prepared by microwave sintering. Effects of the sintering technological parameters(such as sintering temperature, pressing pressure and Mg contents) and the pore-forming contents and its size on microstructure(the phase composition, porosity, pore size, pore morphology, etc) and mechanical properties(compression strength, elasticity modulus, bending strength and wear resistance) of the porous Ti-Mg composites were investigated. At the same time,the corrosion resistance and degradation behavior of the porous Ti-Mg composites in the SBF solution were also systematicly studied as well as the compression strength of the immersed samples.The results show that the porous Ti-Mg composites are composed of Ti and Mg phases, in which the Mg is evenly distributed over the Ti matrix. The porosity of the porous Ti-Mg composites increases with increasing the sintering temperatures, while the porosity decreases with increasing the pressing pressure. With increasing the Mg contents, the porosity decreases from 30% to 5%. No new phase can be generated as the addition of the pore-forming, while the porosity greatly increases with increasing the contents of the pore-forming. The pore size increases with increasing the size of pore-forming, while the porosity has no obvious change.The compression strength and bending strength of the porous Ti-Mg composites increase with increasing the sintering temperatures. With increasing the pressing pressure, the compression strength, elasticity modulus and bending strength increase first, reaching the maximum values at 450 MPa, and then decrease. With increasing the Mg contents, the compression strength deceases, while the bending strengthincreases. The compression strength, elasticity modulus and bending strength of the porous Ti-Mg composites decrease with increasing the porosity. With increasing the Mg contents, the wear rate increases first, reaching the maximum values at 20%, and then decreases. Addition of pore-forming decreases the wear rate of the porous Ti-Mg composites, and changes the wear mechanism from abrasive wear to adhesive wear.The corrosion resistance of the porous Ti-Mg composites is improved through increasing the sintering temperature. With increasing the pressing pressure, the corrosion resistance increases first, reaching the maximum values at 450 MPa, and then decrease. Mg contents play a negative influence on the corrosion resistance. The porosity of the porous Ti-Mg composites has no obvious effect on the corrosion resistance. When the porous Ti-Mg composites are immersed in the SBF solution, a large amount of Mg degrade first, and then the deposition of HA occurs. Finally, the deposition of HA is dominant. The higher the Mg contents is, the faster degradation rate of Mg is. With prolonging the immersion times, the PH values of the SBF solution gradually increase first, and then change more gently. The compression strength of the porous Ti-Mg composites rapidly decreases after immersed in the SBF solution. As immersed one month,the compression strength keeps a relatively stable value of 150 MPa, decreasing by 45% compared to the original Ti-Mg composite. At the initial of the immersion, a inductive reactance arc appears at the EIS of the porous Ti-Mg composites. The inductive reactance disappears with prolonging the immersion times. Whereafter, a large number of Ca P deposit on the surface of Ti-Mg composites,and the phase angle at high frequency region increases, the maximum value near 75°.