Growth of Oxide Nanotube Arrays on Ti-Ni Alloy

Ti-Ni alloys exhibit unique shape memory effect and superelasticity, which render them a wide range of applications in biomedical fields, such as dental and orthopedic as well as cardiovascular devices. However, it has been reported in-vivo implantation of Ti-Ni alloys caused corrosion after a few months. The corrosion will not only degrade mechanical properties of Ti-Ni alloys but also lead to the release of harmful Ni ion. In order to avoid this problem, many surface treatments have been proposed. In the present study, the growth of oxide layers on Ti-Ni alloys was examined using anodization.Materials examined were Ti-Ni alloys fabricated bya conventional arc melting technique. Anodization of Ti-Ni alloy was carried out in ethylene glycol containing 0.25wt.% NH₄F and 1.5wt.% deionized water. The anodizations were carried out at various voltages at room temperature in a two-electrode configuration with a Ti-Ni alloy as a working electrode and platinum gauze as a counter electrode. After the anodization, the morphology, crystal structure, composition of the substrates and oxide layers formed were characterized.SEM observations revealed that the morphology of resulting oxide layers strongly depended on applied voltage and chemical composition of Ti-Ni alloy. Under optimized conditions it was found that tubular oxide layers could be formed on the substrates.