Characterization of microstructure, grain distribution, and tribocorrosion properties of NiTi-based alloy

Hardened 58Ni39Ti3Hf possesses a superior resistance to quenching cracking and spall-type surface fatigue as compared to 60NiTi, which makes it considered as an alternative for this binary intermetallic. Nonetheless, it is still a lack of deep understanding of how the microstructure, grain distribution, and surface properties of 58Ni39Ti3Hf differ from those of 60NiTi. In this work, combined analysis methods of X-ray diffraction (XRD), electron backscatter diffraction (EBSD), and transmission electron microscope (TEM) were conducted to systematically characterize the phase composition, microstructure, and grain distribution. Nanoindentation test was carried out to study the mechanical properties of surface. The growth of passive film in seawater was analyzed using X-ray photoelectron spectroscopy (XPS). Finally, electrochemical impedance spectroscopy (EIS) measurement before, during, and after the tribocorrosion test was performed to evaluate the corrosion resistance of these two alloys when served in different conditions. 58Ni39Ti3Hf was found to have better corrosion and mechanical properties than 60NiTi within the range of this experiment, and the involved mechanism was discussed in detail.