Surface characteristics of NiTi alloys modified by dealloying at low temperature

A dealloying treatment method was applied to the surface modification of nearly equiatomic NiTi alloy so as to remove the harmful element of nickel selectively from NiTi alloys and form a Ni-free titanium oxide layer on the surface. Sample surfaces were analyzed by SEM, XRD, AES, FTIR and XPS, and then samples were immersed in SBF solution for 14 d in order to observe the bioactivity. The results show that the dealloying treatment of NiTi alloy at low temperature leads to 400 nm thick Ni-free surface layer that possesses a nanometer grid structure, and titania surface is in situ formed that possesses a degree of bioactivity because of the combination of hydroxyl (OH^-) group in the process of dealloying treatment simultaneously. As-prepared titania layer was changed into anatase after heated at 500°C for 1 h. As a consequence, the dealloying treatment method could improve biocompatibility of NiTi alloys.