Corrosion of Nano-Hydroxyapatite Coating on Titanium Alloy Fabricated by Electrophoretic Deposition

Titanium and its alloys are often used in orthopedic surgery and dentistry due to their excellent corrosion resistance, high mechanical strength and low density. In order to improve their biocompatibility, hydroxyapatite (HAP) is often coated on surface of metallic implants by plasma spraying. However, the plasma-sprayed HAP coatings suffer from various problems such as high degree of porosities, poor bond strength, non-stoichiometric composition and amotphous structure. In the present study, nanocrystalline HAP (n-HAP) coating was fabricated on titanium alloy, Ti-6Al-4V by electrophoretic deposition followed by sintering at 1000 degrees C. Surface morphology, compositions and phases of the n-HAP coating were analyzed by means of optical microscopy and scanning electron microscopy, energy dispersive spectrometry and Xray diffractometry respectively. In addition, the corrosion behavior of the n-HAP coated Ti-6Al-4V in Ringer's solution at 37 degrees C was investigated by means of open-circuit potential measurement and potentiodynamic polarization technique. By X-ray diffractometry analysis, the crystallite size of the sintered n-HAP coating was about 25 nm. The results of electrochemical corrosion studies illustrated that the sintered n-HAP coated Ti-6Al-4V possessed a nobler open circuit potential but a higher corrosion current density due to the presence of micro-cracks and pores in the coating.