| Compared with clinical medical polymer materials and inorganic non-metallic materials,medical metal materials are widely used due to their excellent strength and hardness,toughness and fatigue resistance.However,common medical metal materials can cause stress shielding after implantation and require secondary surgery to be removed from the body,even release some toxic ions which impair one's health.Compared with widely used biomedical metal materials,the development prospect of magnesium and magnesium alloys is promising in the field of biomedical implant materials because of their good biocompatibility,mechanical properties,and degradability.However,as an implant material,the degradation rate of the magnesium alloy is fast and exceeds the healing rate of damaged bone tissues,which limits the development of magnesium alloys in the field of implant materials.Hydroxyapatite has similar mineral composition,structure to human bone tissues and has excellent biocompatibility,osteoinductive activity and bioactivity.But it has poor brittleness and toughness which limits its application in alternative bone graft materials for load-bearing.In order to combine the advantages of magnesium alloy and hydroxyapatite and improve the corrosion resistance,mechanical properties and biocompatibility of them,HA/ZK61 magnesium alloy composites were prepared by powder metallurgy and hot extrusion with the ZK61 magnesium alloy powder as the matrix and HA powder as the reinforcement.The influence of different contents of HA on the microstructure,mechanical properties,and corrosion properties of composites was studied.The HA/ZK61 magnesium alloy composites with the best overall performance in my studies range was subjected to phytic acid conversion treatment to further improve its corrosion resistance.The HA/ZK61 composites prepared by powder metallurgy and hot extrusion consist of Mg phase and HA phase,and the density decreases with the increase of HA content.The addition of HA increases the hardness and strength of composites.The hardness increases with the increase of the HA content and the maximum hardness value is 92.07 HV.The strength reaches the maximum when the HA content was 20%and the compressive yield strength and compression strength are 173 MPa and 510MPa,respectively.All of them can satisfy the required mechanical strength of human bones.The results of electrochemical experiments show that the corrosion current?22.2?A?of ZK61-10HA composites is about one-fifth that of the as-extruded ZK61alloy and the corrosion potential is slightly increased.The results of the immersion tests for 72 h showed that the ZK61-10HA composite has the lowest weight loss?62.1mg?,the smallest pH change?pH=8.3 after immersion for 72 h?and the least hydrogen evolution?16 m L/cm2?,so ZK61-10HA composite has the best corrosion resistance.The best overall performance material is ZK61-10HA composite.Phytic acid conversion coating was prepared on the surface of ZK61-10HA composite by chemical conversion coating method.The factors including the p H value,temperature,time and concentration of phytic acid were studied on the microscopic structure and corrosion resistance.The degree of the four factors on morphology and corrosion resistance increases in the order of the pH>the temperature>the time>the concentration of phytic acid.The optimum corrosion resistance and the densest microstructure is obtained on the condition of p H 5,60?C,30 min and 5 m L/L.Electrochemical experiments show that the corrosion current after the phytic acid conversion treatment is reduced by about two orders of magnitude,the corrosion potential is increased by about 150mV compared with the untreated ZK61-10HA composite.The immersion test for seven days in simulated body fluid shows that the corrosion resistance of the material after phytic acid conversion treatment was significantly improved,the corrosion rate was stable at 2.4mL·cm-2·d-1,and the pH was stable at about 8.2.The conversion coating composes of phytates,hydroxides and metallic oxide. |
PDF Full Text Request