A comparison of the influence of two alloy pre-treatments and temperature treatments on the formation and composition of zirconium based conversion coating on the AA2024 alloy has been performed. The investigation employed mass changes, atomic force microscopy (AFM), XRD dispersive spectroscopy (EDX), infrared spectroscopy (IR) and electrochemical tests by open circuit potential (OCP) measurements. Pre-treatment using only alkaline etching is called alkaline pre-treatment. When alkaline etching is followed by de-oxidization in a phosphoric acid solution the process is called acidic pre-treatment. Conversion coatings were formed in Pragokor BL. IR analysis revealed the formation of a phosphate on the alloy surface. EDX analysis showed Mg dissolution. The Zr content increased with the temperature of the conversion coating formation. Both pre-treatment methods provided a phosphate layer on the alloy surface.
Hydroxyapatite (HA) coatings were developed on titanium by electrophoretic deposition at various deposition potentials from 30 to 60 V and at a constant deposition time of 5 minutes using the synthetic HA (Ca10(PO4)6(OH)2,) powder in a suspension of dimethyleformamide (DMF, HCON(CH3)2). The electrochemical corrosion behavior of the HA coatings in simulated body fluid (SBF Hanks’ solution) at 37 °C and pH 7.4 was investigated by means of open-circuit potential (OCP) measurement and potentiodynamic polarization tests. The OCP test showed that the values OCP for the coated samples shifted to more noble potential than for uncoated titanium, especially after addition of dispersants. The polarization test revealed that all HA coated specimens had a corrosion resistance higher than that of the substrate, especially after addition of dispersants such as polyvinyl butyral (PVB), polyethylene glycol (PEG) and triethanolamine (TEA) to the suspension. The coating morphology after polarization, characterized by scanning electron microscopy (SEM), showed penetration of electrolyte into the HA coats. Bone bioactivity of the coatings was also studied by immersion of coated specimens in Hanks’ solution for 3 and 7 days. Apatite granules growth on the surface of the HA layers was observed.