高温酸化処理を施したNi-Ti形状記憶合金の表面特性と耐食性の評価

概要

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In this study, a mechanically polished Ni-Ti alloy was subjected to isothermal oxidation (TO) in N_2-20vol.%O_2 at temperatures ranging from 300 to 800℃. TO-treated surfaces were then characterized by field emission type scanning electron microscopy (FE-SEM), energy dispersive X-ray spectrometer (EDX), X-ray electron spectroscopy (XPS) and X-ray diffraction (XRD). Electrochemical corrosion tests were also carried out using a three electrochemical cell connected to a computer driven potentiostat. Results showed that Ni-Ti alloy exhibited different oxidation behavior depending on the treatment temperatures. A Ni free layer was observed in the oxide layer for the specimens TO-treated at temperatures 500℃ and above. Specimens TO-treated at temperatures ranging from 300 to 500℃ showed higher corrosion resistance compared to that of the surface finished by polishing. This was because the TO-treatment created a thick oxide layer with an amorphous structure. Specimens TO-treated at above 600℃ showed very low passive current densities, but lower pitting potential. This was because these samples were covered with crystalline oxide. Consequently, the TO-treatment at 500℃ produced a smooth protective nickel free oxide layer, which contributes to good biocompatibility of Ni-Ti implants.
社団法人日本材料学会の論文
2006-10-15