| Titanium alloy?Ti6Al4V?has been the ideal material of medical implants owing to its excellent mechanical properties,corrosion resistance and biocompatibility for load bearing orthopaedic applications.However,the bioactivity of titanium alloy is poor.It can only be physical mechanical embedded in bone after implantation,which makes its stability in human's body not high.Therefore,in order to improve its bioactivity as well as its binding capability,it is necessary to modify the surface of titanium alloy.At present,titanium surface modification has been widely studied all over the world.In this paper,Ti6Al4V substrates were anodized in 0.15mol/L HF+2mol/L H3PO4 solution,and then HA coating was deposited on the anodized Ti6Al4V substrate via a hydrothermal-electrochemical method at a constant current.The aim of this work was to investigate the effect of the anodizing voltage and pretreatment time on the morphology,phase,wettability and surface roughness of Ti6Al4V substrates.The results indicated that:?1?A highly ordered amorphous titanium dioxide?TiO2?nanotube arrays were formed on the Ti6Al4V surface after anodic oxidization treatment at different voltage from 5V to 40V,and annealing at450?for 3h caused transformation of anodized TiO2 to anatase TiO2.The pore size of the nanotube increases with the applied voltage increases,until the pretreatment voltage reaches 25V.The internal diameter was approximately 100 nm.The nanotube structure was damaged at a higher voltage than 25V.The contact angle on the surface of Ti6Al4V decreased obviously after anodic oxidization treatment,and the contact angle of the sample at 25V pretreatment had dropped to about 15.5 degree from 50.6degree,which has good wettability.Moreover,the roughness increased with the increase of voltage and was reached about Ra=0.56?m at 25V.?2?When titanium alloy was anodized at 25V for different time?0-45min?,TiO2 porous oxide film was present on the surface.With the increase of the anodization time from 5 min to 30 min,the formed TiO2 layers gradually changed from a nanoporous to a nanotubular structure and the pores size also increased.The sample has a big internal diameter and a smaller contact angle for pretreatment time of 30min.While continuing to increase anodization time,the size of nanotube almost remains the same.The hydrothermal-electrochemical deposition experiment after anodic oxidization pretreatment at 25V for 10min indicated that:The hydroxyapatite coating can be obtained on anodized Ti6Al4V surface after hydrothermal-electrochemical deposition in the electrolyte contained 0.02mol/L CaCl2,0.012mol/L K2HPO4·3H2O and0.139mol/L NaCl.The coating appears a layered growth and HA exhibit rod-like and cotton-like structures.The composition of the HA coating remained relatively unchanged.?1?The HA coating was compact with a small rod-like structure when the deposition temperature was 120?,while the HA grain size increased as the temperature increased from 140?to 200?.The crystallinity of HA increased with temperature increasing,reaching about 75%at 120?.Bonding strength of the HA decreased with the temperature of electrodeposition increasing.The bonding strength of HA coating was about 20.0 MPa when the temperature was maintained at 120?.Meanwhile,the HA coating can induce bone-like apatite after immersed in SBF for 6d,showing that it has excellent biological activity.?2?Changing the current density of hydrothermal-electrochemical deposition,the composition of the HA coating and the grain size remained relatively unchanged.The thickness of coating increased firstly and the decreased with the enhancement of current.While the current was 2.5mA/cm2,the HA coating has the largest thickness of 26.4?m and the binding strength is near to20.0MPa.Biological activity experiments showed that the HA coating has excellent biological activity with a maximum diameter of 7-8?m.?3?The hydroxyapatite coating was successfully obtained when the hydrothermal-electrochemical deposition time is from 0.5 to 3h.When the deposition time is too short,the coating is thin and has a small size.With the time of electrodeposition increasing,the amount of HA coating increases gradually.Nevertheless,when deposition time is too long,the second HA layers become loose,appearing more crack.The bonding strength of HA coating was about 20.0MPa when the electrolyte was maintained at 120?and applied a constant current density of 1.25mA/cm2 for 2h.Meanwhile,the HA coating showed a better bioactivity.The results of the deposition HA coating by hydrothermal-electrochemical method on anodized Ti6Al4V surface at different pretreatment parameters indicated that:?1?HA can be directly deposited on the surface of the substrate at different anodization voltage.The coating appears a layered growth and the amount of rod-like HA increased as oxidation voltage increased.The crystallinity of HA increased with anodic oxidation voltage up to 25V and then decreased.The bond strength between Ti6Al4V substrate and HA coating obviously improved after anodic oxidization pretreatment,and increased with the augment of voltage from 5 to 25V and then decreased slightly when the voltage is higher than 25V.The sample with 25V anodic oxidation pretreatment has better bioactivity.?2?The composition of the HA coating kept unchanged when titanium alloy was anodized at 25V for different oxidization time.The crystallinity of HA increased with anodic oxidation time increasing,reaching about 74%at a time of 30min.Binding strength of the HA increased firstly and the decreased as the pretreatment time increases.The bonding strength was about 20.0MPa when titanium was anodized in 0.15mol/L HF+2mol/L H3PO4 solution at 25V for30min. |
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