One-Step Synthesis of TiO2-Hydroxyapatite Nano-films on NiTi Alloy by Hydrothermal Method

NiTi alloy was subjected to one-step hydrothermal treatment in the concentrated CaHPO4 and Ca(H2PO4)2 solutions for bioactive surface modification. Results show that the treated samples are covered by films composed of fine grains (∼70 nm) and large particles (100∼250 nm). X-ray photoelectron spectroscopy analysis indicates that Ti at the surface presents as TiO2, Ni is not detectable, and Ca and P exist in the form of calcium phosphate. X-ray diffraction peaks of anatase TiO2 and hydroxyapatite are presented for the treated samples. Potentiodynamic polarization test in a Ca-free Hank's balanced solution reveals that the treated sample has a markedly improved corrosion resistance compared with the polished sample. The present work would provide a one-step bioactive surface modification method with easy-operation, relatively low processing temperature and less corrosion, and potentially suitable for biomedical porous NiTi alloy.