Plasma sprayed hydroxyapatite coatings from nanostructured granules

The present study utilized nanostructured hydroxyapatite (HA) granules for plasma-sprayed coating on a titanium alloy (Ti–6Al–4V). The initial nanostructured HA powder was synthesized in aqueous solutions of gelatin. The effect of gelatin solutions of variable concentration on the particles size was investigated. The nanostructured HA particles were formed into the porous granules using a liquid immiscibility effect. Consolidation of these powders at various temperatures was carried out. The phase composition, structure, residual stresses and adhesive bond strengths of the obtained coatings from the developed feedstock were investigated by X-ray diffraction, scanning electron microscopy and mechanical tests. X-ray diffraction showed that all the HA coating is a fully crystalline phase without any decomposition. The coatings exhibited a unique phase construction and a fairly low tensile residual stress. The adhesive bond strength of a HA coating was achieved up to 37 ± 2.2 MPa. Tensile failure analysis has suggested that the failure took place at the coating/substrate interface. It is expected that the developed coatings will have much longer service life as compared to the existing ones.