Selective leaching and surface properties of Ti50Ni50−xCux (x = 0-20 at.%) shape memory alloys for biomedical applications

This study investigated the selective leaching and surface characteristics of Ti50Ni50 and Ti50Ni50−xCux (x = 5, 10, and 20) shape memory alloys (SMAs) by employing inductively coupled plasma mass spectrometry, electrochemical tests, and X-ray photoelectron spectroscopy. The experimental results revealed that Ti50Ni50−xCux SMAs exhibited corrosion-resistance properties that were more favorable than those of Ti50Ni50 SMAs, whereas the concentrations of the Ni and Cu ions selectively leached from Ti50Ni50−xCux SMAs were considerably higher than those of Ni and Cu ions selectively leached from Ti50Ni50 SMAs. Ti50Ni50−xCux SMAs exhibited higher selective leaching rates of Ni and Cu ions than those of Ti50Ni50 SMAs, because the NiO and Cu2O oxides that formed on the surface caused a deterioration of the uniformity and protection of the passive TiO2 films. Although Ti50Ni50−xCux SMAs exhibited unique properties that are superior to those of TiNi binary SMAs in particular biomedical applications, appropriate surface modifications are necessary to avoid the risk of toxicity caused by the released Ni and Cu ions.