MAO/HA Composite Coatings Produced By Microarc Oxidation And Hydrothermal Treatment

The porous oxide film was prepared on the TC4Titanium alloy by using MAO technology, and was treated by hydrothermal method, in which the Ca and P elements in the oxide film were transfered into hydroxyapatite with biological activity. Finally In vitro SBF soaking tests of MAO coating were performed. Effect of the electrolyte component and electrical parameter on MAO coating property was studied; the hydrothermal treatment facters which influence the formation of hydroxyapatite were studied, the cross section photographs after hydrothermal treatment was studied;The performance of MAO coating soaking in SBF fluid was also studied.The results show that:the thickness and roughness of oxide film are increasing when the content of Ca(H2PO2)2increases,and the thickness and roughness of oxide film are increasing first and decreasing finally when the content of Ca(CH3COO)2increases. With the increaseing of current density、impulse duty ratio, the thinkness and roughness of oxide film is increasing. But the thinkness and roughness of oxide film is decreasing with the increasing frequency. Besides, the contents of Ca and P in the oxide film are also correlated to electrical parameter:With the increasing of the current density or impulse duty ratio, Ca and P comparative contents in the coating will both increase and the mole ratio of Ca and P will also both increase. With the increasing of frequency, Ca comparative contents in the coating will decrease, but P comparative contents in the coating will not changed, so the mole ratio of Ca and P will decrease. With the content of additive agent EDTA2Na increaseing, Ca comparative content in the coating will increase significantly, therefore the mole ratio of Ca and P in the coating will increase significantly. When the content of EDTA2Na is10g/L,the Ca comparative content in the coating increase to10.46%, the mole ratio of Ca and P in the coating increase to1.61%.The slippery oxide film with15μm in thickness and～12%in Ca content and～7%in P content when the process parameters are as follows:Ca(H2PO2)2:5g/L,Ca(CH3COO)2:50g/L, EDTA2Na:10g/L, the current density:7A/dm2, impulse duty ratio:50%, frequency:500Hz, the oxidation time:15min.The property anlysis of the above oxide film show that hole is well-distributed in the surface of oxide film, the shape is like crater.The element in the coating is mainly consisted of Ca、P、O、Ti. The coating is mainly made of rutile and brookite TiO2and also a lot of amorphous phase Ca、P compound. All of the hydrothermal time、hydrothermal temperature and the pH of hydrothermal liquid will influence the formation of hydroxyapatite. Hydrothermal temperature have greatly effect on the content of hydroxyapatite formation in the coating. When hydrothermal temperature is less than200℃. A large amount of hydroapatite form on the coating which is rod-shaped. When the hydrothermal temperature exceed200℃, little rod-shaped hydroapatite forms on the coating. Hydrothermal time also have greatly effect on the amount of hydroxyapatite formed on the coating. Only little content of hydroapatite forms on the coating when hydrothermal time is short.When hydrothermal time prolongs, there will be a lot of hydroapatie covering on the surface of the film,but the hydrothermal time should not exceed4hours,or there will be some cracks in the cross section. With pH increasing, The quantity of hydroapatite on the coating become more and more, when pH=12, plentiful hydroapatite can be formed on the coating.When the hydrothermal temperature is160℃, hydrothermal time is4hours, pH=12plentiful hydroapatite can be formed on the coating. When lg/L Ca(CH3COO)2is added in the hydrothermal liquid, there is a lot of alpha-Calcium Phosphate covering on the hydroapatite layer.MAO coating which is rich for Ca and P soaked in SBF fluid shows, there is a lot of calcium phosphate forming on the coating. With time goes on the amount of calcium phosphate become more and more. When soaked at5w, a large mount of calcium phosphate precipitate in the holl of MAO coating. MAO-HA coating soaked in SBF fluid show, hydroapatite will solve first and then a large amount of calcium phosphate precipitate in the holl of MAO-HA coating.