Nanohydroxyapatite coating on a titanium–niobium alloy by a hydrothermal process

A novel one-step hydrothermal coating process was used to produce nanohydroxyapatite (nano-HA) coating on a titanium–niobium (TiNb) alloy substrate in a newly designed solution containing calcium and phosphate ions. The morphology of the coating was studied using scanning electron microscopy. The phase identification of the coating was carried out using X-ray diffraction, attenuated total reflectance Fourier transform infrared spectroscopy and transmission electron microscopy. The reaction between the surface of TiNb alloy and the solution during the hydrothermal process was studied by Xray photoelectron spectroscopy. Results show that the coating formed on the surface of TiNb alloy was composed of nano-HA particles. During the hydrothermal process, TiO₂ and Nb₂O₅ formed on the TiNb alloy surface and hydrated to Ti(OH)4 and Nb(OH)₅, respectively. Calcium phosphate nucleated and grew into a layer of nano-HA particles on the surface of TiNb alloy under the hydrothermal conditions. The crystallinity of the nano-HA coating was improved with the increase in hydrothermal treatment temperature and time duration. Nano-HA coating with good crystallinity was produced on the TiNb alloy via the hydrothermal process at a temperature of 200 ºC for 12 h.