Characterization and In Vitro Corrosion Investigations of Thermal Sprayed Hydroxyapatite and Hydroxyapatite-Titania Coatings on Ti Alloy

In the current investigation, hydroxyapatite (HA) powder was mixed with titania (TiO2) in 50:50 wt pct for depositing composite coatings on a Ti-alloy substrate using a thermal-spray coating technique. The coatings were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM)/energy-dispersive X-ray spectroscopy (EDS) analyses. The corrosion behavior of the coatings was studied by electrochemical corrosion testing in simulated human body fluid. After the corrosion testing, the samples were analyzed by XRD and SEM/EDS analyses. HA and TiO2 (rutile) were the main phases observed in the developed coatings. Bulk HA coating was amorphous; however, the addition of TiO2 effectively improved the crystallinity of HA in HA-TiO2 coating. The SEM analysis confirmed the formation of a well-formed HA-TiO2 composite coating. HA coating exhibited higher bond strength (67.8 MPa) compared with HA-TiO2 composite coating (37.6 MPa). The electrochemical study showed a significant improvement in the corrosion resistance of the Ti alloy after the deposition of the coatings.