Effect of high-temperature annealing on solid-state reactions in hydroxyapatite/TiO2 films on titanium substrates

Hydroxyapatite (HA) films 0.5 and 1 μm thick with a 0.2-μm TiO₂ underlayer have been grown on titanium by rf magnetron sputtering. After annealing in an argon atmosphere at 900, 950, and 1000°C for 30 and 60 min, the phase composition, elemental composition, and surface morphology of the films have been determined by scanning electron microscopy, X-ray microanalysis, and X-ray diffraction. The surface microstructure of the films is shown to depend on annealing temperature. X-ray microanalysis results indicate that, at HA layer thicknesses of both 1 and 0.5 μm, the Ca/P ratio increases with annealing temperature. In addition, the Ca/P ratio in the films produced under identical conditions depends on the film thickness. X-ray diffraction data indicate the presence of reaction intermediates. A TiO₂ interlayer in the HA/Ti system inhibits titanium oxidation, and the reaction intermediates forming during heat treatment improve the adhesion between the titanium and HA.