Shape memory alloys (SMA) show unique thermo-mechanical properties like shape memory effects and pseudoelasticity,which are related to the temperature-dependent austenite-to-martensite phase transformation.Upon phase transformation from a martensite to an austenite for the one-way shape memory effect,starins of up to 10% is recovered,which are accompanied by generation of large work outputs.Therefore SMA is promising materials for actuator and orthodontic devices in various fields.The equiatomic Ni and Ti-based ally is one of SMA which has been widely employed in medical and dental fields such as vascular stents and orthodontic arch wires.Preferable biomedical materials should release no or less toxic products after implantation in the body.It is generally reviewed that NiTi has a good biocompatibility due to the formation of titanium oxide-based film.The oxide film on NiTi seems to protect the bulk material from corrosion and to be a barrier against toxic Ni dissolution.Thus,it is important to know details of behavior during anodic oxidation of SMA,especially,the stability of anodic oxide film under the shape memory performance.
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