Preparation Of TiO₂-FHA-HA Gradient Coatings On Ti Substract

Preparing hydroxyapatite (HA) bio-coatings on titanium alloy (Ti-6Al-4V) surface is one of hot spots on the study of artificial bone implants, which combines the good mechanical property of titanium alloy and the good biocompatibility of hydroxyapatite. However, as the mechanical property difference between titanium alloy and hydroxyapatite is too big, the bonding strength of the substrate and coating is very hard to approach 20 MPa, and in some friction force area, the coating is very easy to fall off as a result of the stress fatigue. In order to improve the situation, in this study a good bonding strength TiO₂ layer was prepared by micro-arc oxidation pre-treatment on the substrate, then added a fluor-hydroxyapatite (FHA) layer as a transition layer, finally prepared the HA coating as the top layer. The reasons why designed such gradient coating were that F- could promote the apatite mineralization and the crystallization, enhance the binding strength of coating, and compared with HA, FHA had a low dissolution speed in acidic or the corrosive environment, which could extending the planting life of the coating .In this article, fluor-hydroxyapatite (FHA) and hydroxyapatite (HA) gradient bio-coatings were coated on a titanium (Ti) substrate which was prepared by micro-arc oxidation pre-treatment using a sol-gel method. The microstructure, Surface morphologies, phases and chemical compositions of the coatings were analyzed by scanning electron microscopy(SEM), X-ray diffraction(XRD), Fourier infrared absorption spectrometry(FTIR) and energy dispersive spectrometry(EDS),the bonding strength of the coatings was analyzed by nick apparatus. The results showed that the obtained TiO₂-FHA-HA coatings was uniform, dense, and gradient, the apatite coating and the TiO₂ on substrate formed not only the mechanical interaction but also some metallurgical bonding in some microenvironment, and compared with HA coating the gradient coating enhanced bonding strength obviously.This article had studied the influence of sol-gel processing parameter on coating performance the result indicated that: good crystallinity and high purity apatite coatings were obtained if Ca/P of the precursor was strictly controlled to 1.67; the optimum concentration of reactant was 2mol/L P₂O₅-CH₃CH₂OH sol and 4mol/L Ca(NO₃)₂·4H₂O-CH₃CH₂OH sol;the optimum heat treatment temperature of the coating was 500℃.This article further analyzed the factors influencing sol stability and coating uniform, the result indicated that:the sol processed after aging 24 hour could increase its thermal stability ,the adding of complexing agent glycol stabilized the sol, prevented particles reuniting with each other, formed uniform coating. The uniform coatings was obtained if the viscosity of the sol was controlled less than 5 and dragging velocity was controlled within 4¹0cm/min.The dissolvability test was finished cooperating with Fourth Military Medical University. The results indicated dissolution rate of the gradient coatings: TiO₂2-FHA-HA.