Effects of Hf content and immersion time on electrochemical behavior of biomedical Ti-22Nb-xHf alloys in 0.9% NaCl solution

The aim of this study was to investigate the effects of Hf content and immersion time on the electrochemical corrosion behavior of the Ti-22Nb-xHf (x = 0, 2,4, and 6 at%) alloy samples in 0.9% NaCl solution at 37 degrees C and neutral pH range, utilizing the potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. From the polarization curves, all these alloys exhibited typical passive behavior, which was indicated by a wide passive region without the breakdown of the passive films and low corrosion current densities. In addition, the values of the corrosion current densities and passive current densities decreased with increase in the Hf content. The EIS results, fitted by R-S(Q(P)R(P)) model, exhibited capacitive behavior (high corrosion resistance) with phase angles closed to -80 degrees and high impedance values at low and medium frequencies, indicating the formation of a highly stable film on these alloys in the test solution. The resistance of the passive films improved with increase in the Hf content and immersion time. All these observations suggested a more noble electrochemical behavior of the Ti-22Nb-xHf alloys compared to the Ti-Nb binary alloy.