Improvement of Corrosion Resistance and Reduction of Nickel Release from Dense NiTi Shape Memory Alloys Treated by Water Plasma Immersion Ion Implantation

Dense NiTi shape memory alloys are useful in orthopedic implants due to their super-elastic (SE) and shape memory effect (WE). For instance, in the surgical correction for scoliosis, the use of NiTi allows for Less traumatic gradual correction and overcomes the visco-elastic effects of biological tissues. However, a wider use of the materials is hindered by possible nickel release from these alloys to human tissues. In order to improve the corrosion resistance and depress the nickel release of NiTi alloys, we have performed water plasma immersion ion implantation (PIII). Water Plll was demonstrated to improve the surface bio activity of biomedical titanium metals in our previous experiments. The surface compositions of the NiTi alloys before and after H20-Plll were determined by X-ray photo electron spectroscopy (XPS). Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization were used to investigate the corrosion behaviors and mechanism of the untreated and H20-Plll NiTi alloys in simulated body fluid (SBF) at 37°C. Our results reveal that water Plll can significantly improve the corrosion resistance of NiTi alloys. Independent immersion tests in simulated body fluids demonstrate that the nickel release rate from the H20-Plll NiTi alloys is significantly reduced.