Characterization of hydroxyapatite/titania composite coatings codeposited by a hydrothermal–electrochemical method on titanium

Hydroxyapatite (HA)/titania (TiO2) composite coatings were successfully prepared in an electrolyte solution contain Ca2+ and H2PO4− ions with added TiO2 particles, between 100 °C and 200 °C in an autoclave through a hydrothermal–electrochemical codeposited method under galvanostatic conditions. The effect of TiO2 additions on the phase composition, microstructure, thermal stability, corrosion behavior and the bonding strength of the HA/TiO2 composite coatings were studied. The results show that the crystallinity of HA in HA/TiO2 composite coatings increased continuously with the electrolyte temperature and became close to stoichiometric HA. The n(Ca)/n(P) ratio for coatings prepared at 200 °C is about 1.67 in accordance with stoichiometric HA. TiO2 particles were imbedded uniformly between HA crystals and the addition of TiO2 reduced the HA crystallite size. After heating at 800 °C, HA in the HA/TiO2 composite coating partially decomposes into β-tri-calcium phosphate (β-TCP) due to the incorporation of TiO2. After heating at 1200 °C, HA tended to react with TiO2 to form CaTiO3, and β-TCP converted to α-tri-calcium phosphate (α-TCP), anatase TiO2 transformed to rutile TiO2. The bonding strength of the HA/TiO2 composite coatings increased with the addition of TiO2, and the bonding strength of the TiO2 reinforced HA increased with increases TiO2 content in the coatings.