Selective leaching and surface properties of TiNiFe shape-memory alloys

This study investigated the selective leaching and surface characteristics of Ti50Ni50-xFex (x = 1, 2, and 3) shape-memory alloys using inductively coupled plasma-mass spectrometry, X-ray diffractometry, electrochemical tests and X-ray photoelectron spectroscopy.According to our results, the concentrations of Ni and Fe ions selectively leached from each specimen were considerably higher than that of Ti ions.Electrochemical tests revealed a gradual deterioration in the corrosion resistance of the Ti50Ni50-xFex SMAs as the Fe content in the alloys was increased.X-ray photoelectron-spectroscopy results indicate that the surface of each specimen is primarily made up of a passive TiO2 film.NiO and Fe2O3 oxides, which also formed on the surfaces of the Ti50Ni50-xFex SMAs, caused a deterioration of the uniformity, undermining the protective effect of the TiO2 films, resulting in a highly selective leaching of the Ni and Fe ions.The Ti50Ni50-xFex SMAs exhibit a number of favourable properties compared to the other SMAs; however, high concentrations of selectively leached Ni and Fe ions may pose a risk in biomedical applications, particularly when used as implant materials.