Scratch resistance and electrochemical corrosion behavior of hydroxyapatite coatings on Ti6Al4V in simulated physiological media

Using an electrochemical process, needle-like hydroxyapatite crystals with Ca/P ratio of 1.67 were synthesized on Ti6Al4V without the formation of any precursor. In vitro dissolution/precipitation process was investigated by immersion of the coated substrate into Hank's solution up to 14 days. Physical and chemical characterizations were performed by scanning electron microscope coupled with energy dispersive X-ray spectroscopy and by X-ray diffraction. In particular, through a sequence of reactions including dissolution, precipitation, and ions exchange during immersion tests, a precipitated bone-like apatite coating homogenous and less porous was formed. Further, the corrosion behavior of the untreated and HA-coated specimens in simulated body fluid was evaluated using potentiodynamic polarization and electrochemical impedance spectroscopy. The results showed that the corrosion rates of the samples with HA layer before and after immersion tests were 72 and 80 % lower than that of the bare titanium alloy. At last, the adhesion of the HA layer was determined through the use of scratch tests. A particular tribological behavior and a strong link to the substrate were revealed.