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Effect of Load Deflection on Corrosion Behavior of NiTi Wire

Institute of Oral Medicine, National Cheng Kung University, Tainan, Taiwan, ROC

View larger version (9K): [in this window] [in a new window]   Figure 1. Typical cyclic potentiodynamic polarization curves of NiTi wires in artificial saliva under three-point bending conditions: (a) pH 5.3; (b) pH 2. unstressed Nitinol wire; stressed Nitinol wire; unstressed Sentalloy wire; • stressed Sentalloy wire. At least 3 specimens were used for corrosion testing. Measurements were performed in de-aerated modified Fusayama artificial saliva at 37°C. The stressed specimens showed higher current density in the passive region, but similar current density in the transpassive region. The corrosion parameters for each group are shown in the Table, and the results indicate that the bending stress had a significant influence on each corrosion parameter (p < 0.01) by one-way analysis of variance (ANOVA).

View larger version (120K): [in this window] [in a new window]   Figure 2. Scanning electron microscopy surface morphologies of NiTi wires before and after potentiodynamic test under bending conditions: (a) as-received Nitinol; (b) as-received Sentalloy; (c) Nitinol, pH 5.3; (d) Sentalloy, pH 5.3; (e) Nitinol, pH 2; (f) Sentalloy, pH 2. Magnification, x100; bar = 500 µm. All data were confirmed with 3 different samples, respectively, for each group.

View larger version (11K): [in this window] [in a new window]   Figure 3. After potentiodynamic tests in pH 2 solution, Auger electron spectroscopic depth-profile chemical composition with sputter time detected on the surfaces of wires. (a) Unstressed Sentalloy specimen (n = 1); (b) stressed Sentalloy specimen (n = 1). A mono-energetic electron beam with energy of 10 KV and current of 100 nA was used in the Auger electron spectroscopic analysis, and the specimens for depth profile examination were milled by argon ion bombardment at 3 KV and 9 mA. Comparison of the results of x-ray photoelectron spectrometry (APPENDIX Fig. 2) and Auger electron spectroscopic analyses revealed that the outermost oxides, which provided the main corrosion resistance for NiTi wires, were mainly TiO2.

Journal of Dental Research, Vol. 86, No. 6, 539-543 (2007)
DOI: 10.1177/154405910708600610


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