Corrosion behavior of Zr-(Nb-)Al-Ni-Cu glassy alloys

The melt-spun glassy Zr_60-xNb_xAl₁₀Ni₁₀Cu₂₀ (x = 0, 5, 10, 15, 20 at%) alloys were found to exhibit a large supercooled liquid region (ΔT_x) exceeding 42 K before crystallization. The largest ΔT_x for the glassy alloys containing Nb reaches as large as 82 K for the Zr₅₅Nb₅Al₁₀Ni₁₀Cu₂₀ alloy. The glass transition temperature (T_g) increases and the ΔT_x value decreases with increasing Nb content. The corrosion behavior of the Zr-(Nb)-Al-Ni-Cu glassy alloys was examined by mass loss (=weight loss) and electrochemical measurements. In 1N HCl solution at 298 K, the addition of Nb for replacing some portion of Zr is effective in improving the corrosion resistance of the investigated Zr-based glassy alloys. The corrosion rate significantly decreases with increasing Nb content. The pitting potential and open circuit potential rise with Nb content. In 3%NaCl solution, the addition of Nb effectively increases the pitting potentials of the glassy alloys. In 1N H₂SO₄ solution, the corrosion rates of the glassy alloys are 10^-4 approx. 10^-3 mm·y^-1 (1 mm·y^-1 = 0.317 pm·s^-1). They are spontaneously passivated and have a wide passive region with significantly low passive current density. The open circuit potential increases with an increase in Nb content.