A combinatorially developed Zr-Ti-Fe-Al metallic glass with outstanding corrosion resistance for implantable medical devices

Combinatorial Development and In Vitro Characterization of the Quaternary Zr–Ti–X–Y (X–Y = Cu–Ag/Co–Ni) Metallic Glass for Prospective Bioimplants

“…The Bode plot (Figure a) shows the total impedance at the low‐frequency region ( Z mod, f = 0.01 ) of the systems to be 0.13, 0.25, 0.84, and 0.82 MΩ cm −2 , for the 316L SS, cp‐Ti, Zr 50 Ti 32 Cu 13 Ag 5 , and Zr 40 Ti 37 Co 12 Ni 11 , respectively. The higher total impedance demonstrates the formation of a strong barrier against ion dissolution for the MGs than the commonly known biomaterials, which may be attributed to the formation of the strong oxide layer, as previously stated by Khan et al for Zr–Ti–Fe–Al MG. In addition, the Nyquist plot (as shown in Figure b) portrays the charge transfer resistance of the electrode–electrolyte interface.…”

“…The same outcome is also observed in the potentiodynamic polarization curve, which shows no clear potential‐independent dissolution current of 316L SS, and after the potential 0.39 V, the breakdown of the system is detected. The current density versus time curve in the double logarithmic scale (Figure b inset) for the cp‐Ti, Zr 50 Ti 32 Cu 13 Ag 5 , and Zr 40 Ti 37 Co 12 Ni 11 show that the current density deteriorates with time which is said to be the growth of the passive films . The constant slope after a particular time indicates homogeneity in the passive film growth and suggests a denser passive layer .…”

“…The reason behind it can be attributed to the higher range of potential of Zr to form a strong and protective oxide layer, which impedes the chemical attacks . In addition, the capability of the passive layer formation by Ti is also widely known . Thus, the presence of such outstanding oxide former (i.e., Zr and Ti) should provide excellent resistance toward localized corrosion.…”

“…For extracting the quantitative data from the EIS spectra, the curves are analyzed through an equivalent circuit model. Due to the presence of only one time constant in Bode plot (Figure a), the R s (CPE dl R ct ) equivalent circuit model (Figure c) is used to explain the electrochemical behavior of the systems . The R s (CPE dl R ct ) model is used mostly for the systems showing passivation behavior and explains the electrochemistry on the working electrode and electrolyte interface …”

“…The value of α ranges between 0 and 1, where 0 indicates a pure resistor and 1 stands for an ideal capacitor . Moreover, simultaneously ongoing faradic and non‐faradic processes coupled with the phase angle deviation indicate a parallel setting of the CPE dl and R ct in the equivalent circuit, where CPE dl represents the non‐faradic process and R ct represents the faradic process. The corresponding resistance and capacitance values of the equivalent circuit model are listed in Table .…”