Corrosion behavior of Cu-Zr-Ti-Nb bulk glassy alloys

Bulk glassy (Cu_0.6Zr_0.3Ti_0.1)_100-xNb_x (x = 0-5 at%) alloys with high thermal stability and good mechanical properties were synthesized and the effects of Nb on the glass formation and corrosion behavior were clarified. As the Nb content increases, the glass transition temperature (T_g) remains constant while the crystallization temperature (T_x) decreases slightly, resulting in a decrease in ΔT_x (= T_x - T_g) from 42 K at 0 at% Nb to 36 K at 5 at% Nb. The maximum diameter for glass formation was 4.0 and 2.0 mm for the 2 at% and 5 at% Nb alloys, respectively. The corrosion rates in various solutions significantly decrease with increasing Nb content. The addition of Nb to the glassy alloys shows higher corrosion potential and lower current density in 1 N HCl and 3% NaCl solutions. In 1 N H₂SO₄ solutions, they are spontaneously passivated in wide passive region and low passive current density range of 10^-2-10^-1 A·m^-2. The XPS results revealed that the Zr was enriched in the surface film by addition of Nb to the Cu-Zr-Ti bulk glassy alloy. It was suggested that the role of Nb is to improve the protectiveness of Zr-rich surface film by decreasing Cu concentration in the surface film.