Nitinol Case Study

Commercially available superelastic nitinol (55.67% Ni by weight, ASTM 2063) in the form of 1 mm thick mirror surface cold rolled sheets, purchased from HLMET Co. Ltd in China, were stamped into 6.2 mm diameter coins on a computer numerically controlled turret punch press (Amada Arcade, Japan). Prior to surface treatment, coins were washed as previously described [25], to remove any machining contaminant and to reveal the native surface oxide layers prior coating.
Polyphenolic coatings: Samples (n=3 per group) were either treated with pyrogallol (PG) diluted into 100 mM BisTris buffer pH 7.0 with 100 mM MgCl2 at a concentration of 1 mg/ml or with tannic acid (TA) diluted into 100 mM bicine buffer pH 7.8 with 100 mM NaCl at 1 mg/ml [22]. After agitating samples in the

All these measurements were performed on a Gamry potentiostat/galvanostat ZRA Reference 3000 (Gamry Instruments Inc., Warminster, PA), and data were analysed with Gamry Echem 7.03 software (Gamry Instruments Inc., Warminster, PA) and EIS data with Zview 3.4d ( Scribner associates, Inc., NC). An OCP was continuously monitoring for 24 h, and the potential was recorded as function of measuring time every 0.5 s prior potentiodynamic polarisation measurements performed in the potential range from -1 to 1.6 V with a scanning rate of 0.1667 mVs-1. The electrode was immersed in the test solution for 60 minutes prior each test in order to stabilise the system temperature. EIS tests were carried out at OCP with 10 mV of signal amplitude and a frequency interval from 0.01 Hz to 50 kHz. EIS measurements were performed subsequently after 1, 3, 6, 12 and 24 h prior each OCP. The surface morphology of the NiTi samples after the potentiodynamic and EIS measurements was examined by optical and scanning electron microscopy (SEM) equipped with energy dispersive spectrometer