Surface characteristics, nano-indentation and corrosion behavior of Nb implanted NiTi alloy

NiTi shape memory alloy has been modified by Nb implantation with different implantation parameters including incident dose and current. The surface morphology and chemical components are determined by atomic force microscopy (AFM), Auger Electron Spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). The results show that Nb implantation leads to the formation of compact Nb2O5/TiO2 thin film about 30 nm in thickness on the surface of the NiTi alloy and decreases the surface concentration of Ni. A larger incident dose or incident current causes a higher surface roughness and a higher Nb content in the implantation layer of NiTi alloy. The nano-indentation measurements indicate the obvious reduction of both nano-hardness and Youngʹs modulus of the Nb implanted NiTi alloy in the implantation layer and even in deeper NiTi matrix. The results of potentiodynamic polarization test show that the corrosion resistance of NiTi alloy in Hanksʹs solution has been evidently improved by Nb implantation. The NiTi alloy with a moderate implantation parameter of 1.5 × 1017 ions/cm2 and 2 mA exhibits the best corrosion resistance ability.