Effect of Current Density on Properties of HA Coatings Fabricated by Hydrothermal-electrochemical Deposition

Ti6Al4V substrates were anodized in aqueous solution containing 0.15mol/L HF+2mol/L H3PO4. After that, hydroxyapatite coatings is deposited on the anodized Ti6Al4V substrates surface by hydrothermal-electrochemical method at a constant current in an electrolyte containing 0.02mol/L CaCl2, 0.012mol/L K2HPO4·3H2O and 0.139mol/L NaCl. The influence of current density on the coating compositions, microstructure, thickness, bioactivity and bonding strength between the coating and substrate was investigated by XRD, SEM, EDS, step profiler and universal testing machine during deposition process. The results indicate that HA coatings can be successfully obtained on anodized Ti6Al4V surface by hydrothermal-electrochemical deposition with different current densities. The coatings appear a layered growth and parts of crystals are characterized by flower-shape. The thickness of the HA coatings increases firstly and then decreases with increasing current density. When the current density is 1.25mA/cm2, the thickness of the HA coatings reaches the maximum 26.4μm,the coating is the most dense and the bonding strength is near 20.0MPa.The simulated body fluid (SBF) immersion test can quickly promote the deposition of calcium phosphate with a maximum diameter of 7-8μm