Corrosion behavior of laser-oxidized NiTi in Hanks' solution

NiTi was surface treated with a pulsed Nd:YAG laser to accomplish oxidation without melting. The oxide layer was characterized by transmission electron microscopy (TEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) to obtain information on the thickness, morphology, and the composition profile. The oxide layer was about 25 nm thick with an average surface roughness (Ra) of about 13 nm. The corrosion behavior of the laser oxidized sample and the untreated sample was studied using electrochemical impedance spectroscopy (EIS) at open-circuit potential and cyclic polarization test in Hanks’ solution at 37°C. EIS results indicated that the polarization resistance of the laser oxidized sample was about 15.8 times that of the untreated sample while cyclic polarization tests similarly recorded reduction of the passive current density for the laser oxidized sample by an order of magnitude.