Preparation And Characterization Of Degradable Magnesium Based Biofunctional Gradient Materials

with biocompatibility and biodegradability,Magnesium alloy are bone implant materials with great potential for development.However,the lack of mechanical properties of magnesium alloys and excessive corrosion are difficult problems in clinical application at present.Therefore,magnesium alloys need to be processed and surface-modified in order to improve the mechanical properties and controllable degradation of magnesium alloys.Friction stir processing(FSP)can refine the magnesium alloy grains and disperse the second phase uniformly.Hydroxyapatite(HA)and beta-tricalcium phosphate(β-TCP)are important components of bone and have good biocompatibility and osteoinduction.Therefore,the preparation of Mg/HA composites and Mg/β-TCP composites by friction stir processing not only improve the mechanical properties of magnesium alloys but also exert the osteoinductivity of HA andβ-TCP.Pulse reverse current(PRC)electrodeposition was performed on the Mg/HA stirring layer or the Mg/β-TCP stirring layer to prepare a degradable HA coating,and a magnesium-based functionally graded material was obtained to achieve the time sequence of bone repair by the bone implantation device.The microstructure,composition and in vitro degradability of the Mg-based functionally graded materials were studied by means of metallographic microscope,scanning electron microscope and energy spectrum,X-ray diffraction,soaking test and bonding strength test.The influence of friction stir processing parameters and the influence of HA andβ-TCP on the microstructure and properties of Mg-based functionally graded materials were revealed,and the in vitro degradation mechanism of Mg-based functionally graded materials was discussed.The results show that the Mg/HA composites and Mg/β-TCP composites were prepared by HA、β-TCP and Mg-Zn-Y-Nd alloys with multi-pass FSP,and the single-pass composites were obtained.In the agitating layer,the reinforcement body agglomeration phenomenon was serious,but the presence of the reinforcing body makes the grain refinement;with the processing pass increases,the reinforcing body was sheared with the processing process,and was uniformly dispersed in the matrix,when the processing pass was 4 times,HA andβ-TCP were uniformly dispersed in the magnesium alloy.The microhardness of the Mg-based composites prepared by the friction-fed process 4 times at a feeding speed of 25 mm/min was improved.The hardness of the Mg/HA composites and the Mg/β-TCP composite processed areas were 87 HV and 84HV,respectively.Both were well above the homogeneously annealed magnesium alloy with a hardness of 48 HV.The corrosion rates of the two magnesium-based composites were lower than thoseof the homogeneously annealed magnesium alloys.because the magnesium-based composites obtained by the friction stir processing were uniform in structure and fine in grain size,which improves the corrosion resistance.The corrosion resistance of Mg/HA composites prepared by FSP was better than that of Mg/β-TCP composites.The corrosion morphology analysis shows that the two composite materials obtained by friction stir processing form a layer of corrosion products,which effectively prevents alloy corrosion.The prepared coating was electrodeposited on the FSP 1 pass Mg/β-TCP stirring layer and Mg/HA stirring layer,respectively.The coating was prepared at a current density of 0.1mA/cm~2for 5s、15s、1min、and 5min.The change in appearance was flower bud to flower,HA preferentially grows on the surface of the agitation layer where the reinforcements were agglomerated,and the agitation layer of the reinforcement serves as a transition layer to reduce the energy required to form the HA coating,so it preferentially grows on the part.The coating was prepared on the surface of FSP 4 passes of Mg/β-TCP stirring layer and Mg/HA stirring layer respectively by Pulse reverse currentelectrodeposition.The coating was uniformly dense,and the bond strength between the coating and the stirring layer was improved,and the Mg/HA function was improved,The bonding strength of the gradient material was 29.6 MPa,the bonding strength of the Mg/β-TCP functionally graded material was 26.3 MPa,and the bonding strength of the HA coating prepared on the FSP 4 magnesium alloy surface was 23.1 MPa.Analyzing the corrosion rate and corrosion morphology of functionally graded materials,the average corrosion rate after immersed for 336h of Mg/HA functionally graded materials and Mg/β-TCP functionally gradeable materials was 0.028mg/cm~2?h and 0.030mg/cm~2?h,respectively.relative to the friction stir processed composite material,the corrosion rate was significantly reduced,and the corrosion rate of the Mg/HA functionally graded material was the smallest,and the corrosion protection profile analysis showed that the protective period of the coating on the substrate material was 168 h.