Study On Bioactivity Of Titanium Alloy And Hydroxyapatite Prepared By Biomimetic Growth Method

In this paper, we make surface modification of Ti6Al4V alloy by thermal oxidation and ion inplantation.The results show that: both of these two methods can significantly improve the biological activity of Ti6Al4V alloy.The bioactivity of the oxide layer is higher and the hydroxyapatite coating can grow on it in short time.As the thermal oxidation temperature increases, the surface roughness of the oxide layer increases, the density becomes poorer, and the bonding strength between the coating and Ti6Al4V alloy is smaller. At 900℃, parts of the oxide layer appears off. By the XRD analysis, the rutile TiO₂ in the oxide layer becomes more and more, the bioactivity is better and better.By the alkali treatment, the density of the oxide layer is better and the roughness is smaller. After soaking in SBF soultion, the deposited particles uniformly distribute and are less local aggregation. As the concentration of NaOH increases, the bioactivity of the oxide layer becomes much better. If the concentration of NaOH solution is too large, the pH of the SBF solution changes volatility, the different nucleation of Ca and P and the quality of hydroxyapatite are seriously affected. By plasma based ion implantation, injecting oxygen ions on the Ti6Al4V alloy for 6×10¹⁷/cm² with the voltage of 50kV, we can get a bule TiO₂ film on the surface. After annealing in the air at different temperatures, the surface roughness decreases firstly and then increases. By alkali treatment and soaking in the SBF solution, many black spots rich in Ca and P appear on the surface. As the temperature increases, the bioactivity of the alloy is much better.After soaking in SBF solution for 14days, we can not find the hydroxyapatite ceramic coating on the Ti6Al4V alloy,which treated with ion inplantation. But the ceramic layer rich in Ca and P appears on the surface of Ti6Al4V alloy, after thermal oxidation, alkali treatment and soaking in the SBF solution for 11 days.As the oxidation temperature increases, the cracks firstly decrease and then increase. At 750℃, the cracks are least and the layer becomes off above 800℃. The XRD analysis shows that the ceramic layer is mainly hydroxyapatite, and the crystallinty of the hydroxyapatite increases with the thermal oxidation temperature. The infrared absorption spectra and XPS analysis show that the hydroxyapaitite ceramic layer contains CaCO₃,CaHPO₄ and Ca₃(PO₄)₂, and the Ca/P ratio increases from 1.24 to 1.69 with the oxidation temperature, it is close to the standard value of the pure hydroxyapatite.