| Abstract |
| In this work, the growth of nanotubular oxide layers on Ti1-xNix (x=0.49, 0.498, 0.511, 0.522, 0.525) shape memory alloys was investigated. All of the Ti-Ni alloys were fabricated by arc melting process under high vacuum atmosphere. The crystal structure and the growth of the nanotubular oxide layers were investigated by X-ray diffraction (XRD), field-emission scanning electron microscope (FE-SEM) and energy dispersive X-ray spectroscopy attached to a transmission electron microscope (TEM). The electrochemical anodization was carried out at various durations (5 min and 20 min) and applied voltages (20 V, 35 V and 50 V) at room temperature in ethylene glycol containing 0.06 M NH4F and 1.5 wt% H2O. Nanotubular oxide layers were formed on all Ti-Ni alloys by electrochemical anodization, but the morphology of the oxide layers was changed depending on the anodization duration and Ni concentration of the Ti-Ni alloy substrate. In the case of short duration (5 min), the nanotubular oxide layers were formed on all Ti-Ni alloys by electrochemical anodization, however, the morphology of oxide layer was changed from nanotubular structure to nanopore structure with increasing anodization duration. Moreover, it was cleared that the morphology variation of the nanotubular oxide layers was accelerated with increasing Ni concentration, from 49.0 at% to 52.5 at%, which is attributed to the formation of a Ni-rich layer on the Ti-Ni alloy surface by electrochemical anodization. (Received May 30, 2018; Accepted June 30, 2018) |
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| Key Words |
| shape memory alloy, Ti-Ni, nanotubular oxide layer, TiO2, anodization |
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