S. L. Wu, J. C. Chung, P. K. Chu, City University of Hong Kong, Hong Kong, China; X. Liu, City University of Hong Kong, Hong Kong, Hong Kong; R. Y. Chan, J. K. Lam, K. M. Cheung, W. W. Lu, K. D. Luk, K. Yeung, The University of Hong Kong, Hong Kong, Hong Kong; C. L. Chu, Southeast University, Nanjing, China
Electrochemical impedance spectroscopy (EIS) is an effective technique to monitor the corrosion resistance of the protective film on the surface of metals or alloys through the simulation of the experimental EIS spectra by proper equivalent circuits (EC). In this work, the electrochemical behavior of porous NiTi alloys fabricated by capsule-free hot isostatic pressing (CF-HIP) is investigated in simulated body fluids (SBF) by EIS. Two different EC models are proposed to simulate the experimental EIS spectra from different films formed by different surface modification techniques such as chemical treatment and oxygen plasma immersion ion implantation (O-PIII). All the Nyquist plots exhibit a depressed semi-circle in the high frequency region (>1000 Hz), which is believed to be induced by the porous structure of the specimens. The occurrence of peaks in the middle-lower frequency region in the Bode diagrams indicates the presence of the protective surface film. Our EIS results reveal that chemical treatment can significantly improve the corrosion resistance of porous NiTi alloys, and that compared to untreated samples, O-PIII is a more effective technique to enhance the corrosion resistance of porous NiTi alloys.
Summary: Oxygen plasma immersion ion implantation is an effective technique to enhance the corrosion resistance of porous NiTi shape memory alloy.
