Precipitation of bone-like apatite on plasma electrolytic oxidized Ti-6Al-4V alloy

In this study, precipitation phenomena of bone-like apatite on plasma electrolytic oxidation (PEO)-treated Ti6Al-4V alloys with various electrolyte compositions were studied by using various characterization techniques. A Ti-6Al-4V disk was used as a sample for the PEO treatment, which was performed using pulsed DC power for 3 min at 280 V in an electrolyte solution containing calcium acetate, calcium glycerophosphate, manganese(II) acetate tetrahydrate, magnesium acetate tetrahydrate, strontium acetate hemihydrate, zinc acetate dehydrate, and sodium metasilicate at 25?. The PEO-treated samples were immersed in a simulated body fluid (SBF) solution for 24 h to investigate their bioactivity.The surface morphology, composition, and microstructure of these samples were observed by field emission scanning electron microscopy, energy dispersive X-ray spectrometry, and X-ray diffractometry. The surface of the PEO-treated alloy in the electrolyte containing Ca, P, Mn, Sr, Zn, Mg, and Si ions was covered with precipitates that formed a ring pattern around the pores. Furthermore, Mn was detected in the pores rather than on the surface; this Mn played a role in MnO2 and Mn2O3 formation on the PEO-treated alloy surface. Moreover, on the surface treated in SBF solution after PEO treatment in the electrolyte containing Ca, P, Mn, Sr, Zn, Mg, and Si ions, apatite nucleation occurred in the pores, which coalesced and grew into large precipitates. Fewer number of functional elements, including Mn, were detected on the surface when apatite was precipitated, than that in the case of the non-treated surface in the SBF solution.