Enhanced surface roughness and corrosion resistance of NiTi alloy by anodization in diluted HF solution

NiTi shape memory alloy was anodized in diluted hydrogen fluoride. Surface morphologies and compositions of modified NiTi wires were characterized by using scanning probe microscopy (SPM), field-emission scanning electron microscopy (FESEM) equipped with an energy dispersive spectroscopy (EDS) and x-ray photoelectron spectroscopy (XPS). The formation of oxides with reduced nickel element content was observed on NiTi alloy. In marked contrast to the smooth surface formed in phosphoric acid, an enhanced surface roughness of NiTi alloy was obtained by anodization in a hydrogen fluoride electrolyte. The treated surface was characterized by a nanohardness tester. The corrosion resistance of the treated NiTi alloy was examined in Hank's solution at 37 °C by a potentiodynamic polarization test. The findings indicated that the anodization in HF solution significantly increased the surface roughness and corrosion resistance.