Purpose: Ni-Ti alloy has been increasingly applied to dental and medical devices, however, it contains nickel, which is known to have adverse effects on the human body. The purpose of this study was to form a nickel-free surface oxide layer on Ni-Ti alloy by electrolytic treatment for better biocompatibility.

Methods: Ni-49.15Ti (mol%) alloy was used, and the electrolytic treatment was performed in the electrolytes under 50 V for 30 minutes. The electrolytes were composed of lactic acid, water, and glycerol with different compositions. Surface analysis and characterization of Ni-Ti alloy were carried out by means of X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES).

Results: Results indicated that the outmost surface oxide layer was nickel-free when using an electrolyte comprising 7.1% lactic acid, 57.2% water, and 35.7% glycerol by volume. The composition of this nickel-free surface oxide layer was determined as TiO_1.92(OH)_1.35 ∙ 0.43H₂O by XPS, similar to that of unalloyed titanium. The thickness of this nickel-free layer was estimated at 6.4 nm by AES.

Conclusion: The nickel-free surface oxide layer produced on Ni-Ti alloy is considered to improve the biocompatibility of medical and dental devices having shape memory effect and/or super-elasticity.

目的：镍钛合金已越来越多地应用于牙科和医疗设备，但是它含有镍，已知会对人体产生不利影响。这项研究的目的是通过电解处理在Ni-Ti合金上形成无镍的表面氧化物层，以获得更好的生物相容性。

方法：使用Ni-49.15Ti（摩尔％）合金，在50 V的电解液中进行30分钟的电解处理。电解质由乳酸，水和甘油组成不同。Ni-Ti合金的表面分析和表征是通过X射线光电子能谱（XPS）和俄歇电子能谱（AES）进行的。

结果：结果表明，当使用按体积计包含7.1％乳酸，57.2％水和35.7％甘油的电解质时，最外面的表面氧化物层不含镍。通过XPS将该无镍表面氧化物层的组成确定为TiO _1.92（OH）_1.35 ∙0.43H ₂ O，类似于非合金钛。通过AES将该无镍层的厚度估计为6.4nm。

结论：在Ni-Ti合金上生产的无镍表面氧化物层被认为可以改善具有形状记忆效果和/或超弹性的医疗和牙科设备的生物相容性。