Structure And Properties Of Pulsed Laser Deposited Fluoridated Hydroxyapatite Thin Films On TC4Alloy

It is convinced by previous study that titanium alloys coated bioactive apatite films combine metal’s good mechanical properties and bioceramics’good bioactivity together. Besides, incoperating fluorine into hydroxyapatite lattice can evidently improve thermal stability and bring down high dissolution rate of hydroxyapatite films. Inorganic and organic methods were employed in this paper to prepare fluoridated hydroxyapatite（FHA） powder, which was used as raw material to make FHA targets. After that, FHA films were prepared on Ti6A14V（TC4） alloy by pulsed laser deposition method and influence of deposition parameters, fluorine content and follow-up heat treatment on structure and properties of films were investigated.High crystallinity FHA powder without other phase can be prepared by inorganic method, yet thermal stability of it was not so good that the target made of it partially decomposed into whitlockite after sintering. FHA powder made by organic method had a pure phase with fluorine well incoperated into hydroxyapatite structure.With higher pressure, droplets on the films increased, hence the surface became rougher. The Ca/P atomic ratio decreased to get closer to that of hydroxyapatite（1.67） as pressure grew. The phase composition of films transformed from amorphous to high crystallinity as pressure grew.Higher substrate temperature was good for better crystallinity of the film. However, the film deposited at700℃showed partial decomposition of FHA to CaO. As substrate temperature grew from500℃to700℃, density of the film got worse, the Ca/P atomic ratio became higher because of severer ablation of PO₄^3-.A shorter distance between target and substrate helps to obtain thicker film. As target and substrate got closer, droplets on the film and surface roughness of it increases, the Ca/P atomic ratio became higher, crystallinity of the film improved, yet oxidization of the substrate grew severer.Heat treatment of the film could improve crystallinity, but high temperature（600℃） led to decomposition of FHA and cracks in the film. In situ annealing in the deposition chamber can both improve crystallinity and avoid craks, but there was heavy oxidation of the substrate.The particles on the film, surface roughness of the film decreased as the fluorine content grew. The Ca/P atomic ratio and crystallinity of the film got higher with more fluorine.