| Titanium and its alloys are widely used in biomaterials due to their excellent mechanical properties,chemical stability and biocompatibility.However,when titanium alloy is implanted into organisms,it can't directly induce the formation of apatite.At the same time,due to poor wear resistance,it will release harmful metal ions,which will lead to inflammation.In this paper,the elastic modulus of Ti-3Zr-2Sn-3Mo-25Nb(TLM)titanium alloy which compared to TC4 is closer to human bone.Without element Al?V,etc,the new TLM alloy has little toxicity to organisms.In this research,the oxidation coating of TLM alloy obtained from micro-arc oxidation.Under the phosphate electrolyte system,we investigated the effects of five main process parameters:EDTA addition,Ca(CH3COO)2 addition,duty ratio,current density and oxidation time on the basic properties of micro-arc oxidation coatings by single factor method,then we identified a group of parameters.The biological activity,corrosion resistance and wettability of the coatings were analyzed by SBF immersion experiment.The effects of different parameters on the biological activity of the coatings were studied,and another group of technological parameters were determined.Finally,the basic properties and biological activities of the coatings were analyzed comprehensively,and the optimum technological parameters were obtained.The result of the basic process of micro arc oxidation showed that,at the concentration of Ca(CH3COO)2 is 17.62g/L and EDTA is 21.94g/L?the duty ratio is 30%-50%?current density is 8-10A/dm2 and oxidation time is 30-40min,the holes on the surface of the film are suitable in size and uniform in distribution,the thickness of the film reached 35?m,the hardness was about 275 HV,the Ca/P ratio on the surface of the film was closest to 1.67,and the bonding strength between the film and the substrate was 26.5N.There was a high adhesion between coatings and the substrate,reaching 26.5N.In vitro and corrosion resistance tests of the coatings,the process parameters for good biological activities of the coatings were determined.After immersing in SBF,hydroxyapatite was observed on the surface,which indicated that the coatings showed good biological activity,and the Ca/P ratio on the surface had a good influence on the formation of hydroxyapatite.Based on the in vitro analysis,the optimum basic parameters were determined as follows:duty cycle was 40-50%,current density was 10A/dm2,oxidation time was 40-50min.At this time,the coatings presented good biological activities and wettability.The electrochemical corrosion test shows that the coating has higher corrosion resistance than the substrate alloy,the current of the coating is 4.9191±0.0378×10-7A·cm-2.In the electrochemical impedance analysis,the equivalent circuit of TLM alloy and coating were simulated,the resistance value of the inner layer was 9.16×103 M?·cm2,which showed that the corrosion resistance of coating was better.The optimum parameters were obtained by studied of the basic properties and biological activity of the film:duty cycle was 40-50%,current density was 10A/dm2 and oxidation time was 40 min. |
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