Effects of dealloying treatment at low temperature on the surface properties of NiTi alloys

After calculated the dealloying conditions of thermodynamics, a dealloying treatment method is applied to nearly equiatomic NiTi alloy so as to remove the harmful element from NiTi alloys and form a Ni-free titanium oxide layer on the surface. The surface of sample is analyzed by SEM, XRD, XPS and EDX, and then immersed in SBF solution for up to 14 days in order to observe the Ca/P deposition. The results show that the dealloying treatment at low temperature leads to a Ni-free surface layer with a nanometer structure at the depth of 130 nm, and in situ to form a titania surface with a degree of bioactivity and ability to induce Ca/P precipitates combined with hydroxyl (OH^-) groups in the solution simultaneously. As a consequence, the dealloying treatment can increase the biocompatibility of NiTi shape memory alloys for medical applications.