Control of nanotube shape and morphology on Ti–Nb(Ta)–Zr alloys by varying anodizing potential

• Nanotube formation was controlled by applied potential for two-step anodization.
• The Ti–30Ta–xZr alloys had needle-like microstructures; α′ phase increased with Zr.
• The Ti–30Nb–xZr alloys had a smaller pore size than those of the Ti–30Ta–xZr alloys.
• The Ti–30Nb(Ta)–Zr alloys can have improved corrosion resistance with Zr content.

Different applied potentials have been employed in a two-step anodization process, utilizing a 1 M H3PO4 electrolyte and a solution containing this electrolyte and 0.8 wt.% NaF, to control the shape and morphology of oxide nanotubes on coatings for ternary Ti–30Ta–xZr alloys. The ternary alloys were manufactured using an arc furnace, and corrosion testing was carried out using a potentiostat. The microstructures of the Ti–30Ta–xZr alloys had a needle-like structure, and the lath thickness of the α′ phase increased as the Zr content increased. The microstructures of Ti–30Nb–xZr alloys had equiaxed grains. The Ti–30Nb–xZr alloys showed smaller micropores and nanotubes compared to the Ti–30Ta–xZr alloys. The Ti–Nb(Ta)–Zr alloys tended to have improved corrosion resistance with increasing Zr content.