Calcium phosphate coating of biomedical titanium alloys using metal-organic chemical vapour deposition

Metal-organic chemical vapour deposition was used to fabricate hydroxyapatite (HAp) and α-tricalcium phosphate coatings on the surface of representative biomedical titanium alloys: Ti-29Nb-13Ta-4·6Zr, commercially pure Ti, and Ti-6Al-4V ELI. The effect of the substrate surface roughness, alloy composition and precursor temperature was investigated in relation to the type of calcium phosphate formed and the morphology and thickness of the HAp coating. The surface roughness of substrates mechanically polished by SiC paper was found to vary depending on the type of alloy, whereas the roughness of substrates buff polished using a colloidal SiO₂ suspension was comparable. The type of calcium phosphate formed could be controlled by the precursor temperature. A coarse, granular microstructure was observed on the surface of the thicker HAp coatings formed on the rough polished substrates, while the thinner HAp coatings formed on the smooth polished substrates had a relatively dense and fine grained microstructure.