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.