Surface characterization of NiTi modified by plasma source ion implantation

This paper reports the novel application of an oxygen ion plasma for surface modification of a shape memory alloy. The surface characterization of oxygen ion implanted Ti-50.7 at% Ni alloy samples was performed with the assistance of Auger electron spectroscopy, X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy techniques (TEM). TEM identified amorphous TiO2 and crystalline phases of Ti11Ni14 and Ti4Ni2O,. XPS results reveal that the surfaces of control samples are covered with predominantly TiO2 and traces of TiO and NiTi, as well as NiO and Ni2O3. At the surface of oxygen-implanted samples, however, only TiO2 and trace amounts of Ni2O3, NiO and NiTi were observed. TiO and NiO exist in much larger range than other oxides, and TiO extends to the oxide-metal interface. These results are especially noteworthy because of their implications for interpreting corrosion, wear, and biocompatibility behavior. (C) 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.