Surface modification of NiTi alloy by sol-gel derived porous TiO2 film

Titania films with nano-sized pores were prepared on the NaOH-HCl pretreated NiTi alloy substrate by sol-gel method. A crack-free film is obtained for the sample with a dense inner layer and a porous outside layer (sample TC1+1). The X-ray diffraction shows that the titania films are composed of anatase, and a little Ni4Ti3 phase in the heat treated substrate is also detected. The X-ray photoelectron spectroscopy results indicate that the titania film completely covered the NiTi substrate for sample TC1+1. The sample TC1+1 is hydrophilic with a contact angle about 20 degrees, and UV illumination treatment for 15 min further decreases the contact angle to (9.2 +/- 3.2)degrees. The potentiodynamic polarization test in 0.9% NaCl solution reveals a better corrosion resistance of sample TC1+1 than the polished NiTi sample.