Hydroxyapatite/β-calcium phosphate coatings with a high bonding strength on titanium substrates were prepared by electrodeposited- hydrothermal synthesis and calcination. The phase composition, microstructure and bonding strength of the coatings were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and mechanical testing. It showed that electro-deposition coating phase mainly consisted of dicalcium phosphate dehydrate and hydroxyapatite. A single hydroxyapatite phase coating was obtained after a hydrothermal treatment for four hours in a solution of ammonia with a pH value above 12. After calcination below 700 oC, the phase composition of the coating remained the single hydroxyapatite phase. Then the β calcium phosphate phase appeared when the calcination temperature was above 800 oC. The quantity of β calcium phosphate could be controlled by adjusting the calcination parameters. For the specimens not pre-treated, calcination in air was beneficial to improve the bonding strength below 700 oC. Above 800 oC, the bonding strength decreased obviously because of the appearance of a loose and thick titanium nitride and titanium dioxide transition layer. The highest bonding strength in this study was obtained on the specimens pre-treated in a sodium hydroxide solution and calcined in an argon atmosphere at 900 oC.

Keywords: Calcium phosphate, Hydroxyapatite, Coating, Hydrothermal treatment, Calcination, Bonding strength.