Preparation And Modification Of The Microwave Sintered Porous Magnesium

Magnesium and its alloys have become the ideal hard tissue replacement materials due to their high specific strength and specific stiffness, the elastic modulus and density closed to the human bone and the degradability. It is beneficial to the transport of the blood and nutrients and the ingrowth of the blood vessels and muscle when the porous structure is introduced into the magnesium. However, both of the strength and corrosion resistance of the magnesium decrease resulted from the porous structure. In this thesis,the porous magnesium was prepared by microwave sintering and the Si C particle reinforcement(Si C/Mg composites) was carried out as well as surface modification through micro-arc oxidation. The effects of technological parameter and pore-forming agent on the surface morphologies, porosities, mircohardness, compression properties,corrosion resistance and degradation properties of the porous magnesium were investigated. The effects of the Si C particle contents and sizes on the mircostructure,phase composition, compression properties, degradation properties and wear resistance of the porous magnesium were studied. Moreover, the effects of electrical parameters on the microstructure and corrosion resistance of the porous magnesium were also researched.The results showed that the porosities increased and the microhardness of the porous magnesium decreased with increasing the sintering temperatures and holding times and decreasing the pressing pressure. With increasing the pore-forming agent contents, the porosities of the porous magnesium increased, while the pore-forming agent sizes had few effects on the porosities of the porous magnesium. With increasing the porosities, both of the compression strength and elastic modulus of the porous magnesium decreased, the corrosion current density increased and the polarization resistance decreased. With increasing the pore diameters, the compression strength of the porous magnesium decreased, while the elastic modulus and corrosion resistance changed little. With increasing the porosities and prolonging the immersion times, the weight loss ratio of the porous magnesium immersed in the SBF solution increased as well as the degradation rate. Moreover, the PH values of the SBF solution increased with increasing the immersion times, while the porosities had few effects on the PH values.The addition of the Si C reinforcement phase had few effects on the microstructure of the porous magnesium. However, with increasing the Si C contents, the compressionstrength of the Si Cp/Mg composites increased first, reaching the maximum at 10%, and then decreased. At the same time, the elastic modulus of Si Cp/Mg composites increased with increasing the Si C contents. Compared to the porous magnesium, the compression strength and elastic modulus of the Si Cp/Mg composites could increase by 47.87% and57.32%, respectively. With increasing the Si C particle size, the compression strength of the Si Cp/Mg composites increased, while the elastic modulus increased first, and then decreased. The Si C contents had little effects on the corrosion resistance of the porous magnesium. All of the friction coefficient, wear volume and wear rate of the Si Cp/Mg composites increased with increasing the Si C contents.Micro-arc oxidation treatment did not change the natural porous structure of porous magnesium. The typical micro-arc oxidized rough and porous ceramic coatings were formed on the surface and pore wall of the porous magnesium after micro-arc oxidation treatment. The thickness of the ceramic coatings was about 1.5~7.8μm. The corrosion resistance of the porous magnesium was improved by more than one order of magnitude after micro-arc oxidation treatment, and the degradation rate and weight loss ratio of the porous magnesium immersed in the SBF solution also decreased.