Alloys for ureteral stents must meet strict standards for high corrosion resistance to prevent encrustation and tissue irritation. Yet currently used alloys, such as Ti–6Al–4V, Co–Cr and Ni–Ti, are likely to corrode in urine and inflict some clinical complications. In this study, two new Ti-based alloys: Ti–6Mn–3Mo alloy and TiZrHfNb 0.4 high-entropy alloy, were evaluated for their corrosion and passive-film characteristics in artificial urine at 37 °C using a set of electrochemical tests and surface analyses, with comparison to Ti and Ti–6Al–4V. Results revealed that all evaluated metals showed similar passivating behavior but with appreciable differences in passive film characteristics. The TiZrHfNb 0.4 exhibited the highest corrosion resistance characterized by its high polarization resistance (1891.83 Ω), high impedance magnitude at low frequencies, low donor density (4.30 × 10 19 cm -3 ), broad passive region with most positive pitting potential (1.30 V vs. Ag/AgCl) and stable low potentiostatic current. The lowest corrosion resistance was shown by the Ti–6Mn–3Mo due to early breakdown of passive film, high donor density and high susceptibility to pitting corrosion. This study suggests that the multi-oxide layer formed on TiZrHfNb 0.4 alloy enhances its passive film stability in simulated urinary environment and raises further interest in high-entropy alloys for ureteral stent application.
McLean et al. (Sun,) studied this question.