Effect of microstructure on corrosion behaviours of a Ni-based metallic glass

Electrochemical corrosion behaviours of as-spun, as-cast, and relaxed Ni ₅₅Nb ₂₀Ti ₁₀Zr ₈Co ₇ metallic glasses were investigated in 3 mass% NaCl and 1 N H ₂SO ₄ solutions in order to study the effect of different amorphous microstructure. Static immersion tests indicate that the as-spun ribbon possesses the most active state in the NaCl solution at its open circuit potential, followed by the as-cast rod, the relaxed ribbon, and the relaxed rod. While in the H ₂SO ₄ solution, the rod samples are more stable than the ribbons, and the relaxed samples exhibit higher stability than the as-quenched samples. The polarization tests revealed slightly higher passive current density (i _pass) for the ribbons than those of the rods in both electrolytes, although no significant differences in i _pass were found between the relaxed and the as-quenched specimens. It is concluded that electrochemical corrosion behaviours of metallic glasses are related to the amorphous structure, and a decrease in free volume generally favors corrosion resistance.