Characterization of the bone-like apatite precipitated on high velocity oxy-fuel (HVOF) sprayed calcium phosphate deposits

Bone-like apatite was precipitated on the surface of thermal sprayed calcium phosphate coatings following in vitro incubation in a simulated body fluid. The coatings were initially deposited on titanium alloy substrates by the high velocity oxy-fuel (HVOF) spray technique. Structural characterization and mechanical evaluation of the precipitated apatite layer were conducted. Results showed that the precipitation rate was directly influenced by the local Ca²⁺ concentration in the vicinity of the coating's surface and that preferential dissolution of certain phases was found to accelerate the precipitation of the bone-like apatite. The dense precipitates exhibited a competitive Young's modulus value of ∼120GPa, which was obtained through nanoindentation. This compared favorably to the calcium phosphate matrix. Differences in microstructure at various locations within the layer resulted in altered Young's modulus and microhardness values. Precipitation mechanism investigation was carried out through a comparative experiment. Chemical analysis showed that the precipitation of bone-like apatite on the calcium phosphate coating was quite conceivably a partial diffusion-controlled process.