Processing and characterization of hydroxyapatite coatings on titanium produced by magnetron sputtering

Hydroxyapatite (HA) coatings with different thicknesses were produced on Ti and Si substrates using the radio frequency magnetron sputtering method. The mechanical properties, for example, modulus and hardness, of the coatings were measured using nanoindentation. The measured values of modulus and hardness were close to the upper limit of that reported for bulk HA, indicating a fully dense structure. Interfacial strengths between the HA coatings and substrates were also evaluated using a nanoscratch technique. The HA-Ti interface appeared to be stronger than the HA-Si interface. The microstructures of the HA coating and the HA-Ti interface were examined using high-resolution electron microscopy. Chemical compositions of the HA coating and the HA-Ti interface were also analyzed using x-ray energy dispersive spectrometer and electron energy loss spectroscopy. The results indicated that the strong HA-Ti bonding is associated with an outward diffusion of Ti into HA layer and concomitant formation of TiO2 at or near the interface.