Hydroxyapatite precipitation on nanotubular films formed on Ti-6Al-4V alloy for biomedical applications

• Hydroxyapatite (HA) precipitation on nanotubular films formed on Ti–6Al–4V alloy was investigated using a variety of experimental methods.
• HA precipitation treatment was carried out using a cyclic voltammetry method after nanotube formation on Ti–6Al–4V alloy.
• Plate-like precipitates were formed on the bulk (not anodized) alloy, and the size of precipitates increased with the number of deposition cycles.
• HA precipitates that formed on the nanotube formed alloy had a mixed plate-like and flower-like morphology with number of deposition cycles.

In this study, hydroxyapatite precipitation on nanotubular film-formed Ti-6Al-4V alloy for biomedical applications has been investigated using a variety of techniques. To prepare the substrate samples for hydroxyapatite (HA) deposition, the starting Ti-6Al-4V alloy was polished and heat-treated for 12 h at 1050 °C in an Ar atmosphere, followed by water-quenching at 0 °C. Nanotube formation on the titanium alloy was performed using anodization with a DC power supply at 30 V for 1 h in 1 M H3PO4 + 0.8 wt.% NaF at 25 °C. Subsequent HA precipitation treatment was carried out by cyclic voltammetry over a potential range of −1.5 V to 0 V using a scanning rate of 100 mV/s in 0.03 M Ca(NO3)2 ∙ 4 H2O + 0.018 M NH4H2PO4 at 80° ± 1 °C. Four different numbers of cycles were employed: 10, 20, 30, and 50. Surface morphology and structure were examined by field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, and Fourier transform infrared spectroscopy.The heat-treated Ti–6Al–4V alloy has a needle-like duplex microstructure containing the martensitic α′ phase and β phase. Plate-like precipitates were formed on bulk Ti–6Al–4V alloy, and the size of these precipitates increased with the number of deposition cycles. The HA precipitates on the nanotube surface showed a mixture of plate-like and flower-like particles with more deposition cycles. The deposited HA phase in the coated layer had an amorphous structure, with particle composition in good agreement with Ca10(PO4)6(OH)2.