Variations of nanotubes on the Ti-Nb-Hf alloys with applied voltages

In this study, variations of nanotubes on the Ti-Nb-Hf alloys with applied voltages in dental applications were studied using different experimental techniques. Cone-shaped nanotubes were formed during the anodization of Ti-29Nb-xHf alloys by varying the applied DC voltage from 10 to 30 V, and from 30 to 10 V. The anodization time was 180 min and the electrolyte was 1 M H3PO4 with 0.8 wt.% NaF. The morphology changes in anodized Ti-29Nb-xHf alloys were analyzed by optical microscopy, field emission scanning electron microscopy and X-ray diffractometer. The microstructures of the Ti-29Nb-xHf alloys changed from needle-like to an equiaxed structure, and with the increasing of Hf content, the β-phase gradually increased with a concomitant decrease in the α″-phase. Cone-shaped nanotubes were formed when the applied voltage was stepped up and the inversed cone-shape nanotube was formed on stepping down the applied voltage. The diameter, cross-section, length, and shape of the nanotube on the Ti-29Nb-xHf alloys can be controlled both by varying the applied voltage and the Hf content.