Formation and corrosion behavior of glassy Ni-Nb-Ti-Zr-Co(-Cu) alloys

Bulk glassy Ni₅₅Nb₂₀Ti₁₀Zr₈Co₇ alloy with a critical diameter of 2 mm was synthesized by copper-mold casting and the glass transition temperature, crystallization temperature and supercooled liquid region are 858 K, 911 K and 52 K, respectively. High corrosion resistance in 1N HCl and H₂SO₄ solutions was recognized for the glassy alloys Ni₅₅Nb₂₀Ti₁₀Zr₈Co₇ together with Ni₅₃Nb₂₀Ti₁₀Zr₈Co₆Cu₃ which possesses higher glass-forming ability. They are spontaneously passivated with low passive current densities of the order of 10^-2 A/m² and their corrosion rate was less than 10^-3 mm/year in the solutions. A small amount addition of Cu (3 at.%) in the Ni-Nb-Ti-Zr-Co glassy alloy system has little effect on corrosion behavior and surface film composition. Niobium-rich passive films form on the glassy Ni-Nb-Ti-Zr-Co(-Cu) alloys, which could be responsible for the high corrosion resistance. © 2006 Elsevier B.V. All rights reserved.