Enhanced chloride ion corrosion resistance of Zr-based bulk metallic glasses with cobalt substitution

Zr-based bulk metallic glasses (BMGs) exhibit good mechanical performance and excellent bio-compatibility. However, their high-tech application is limited due to that they are susceptible to chloride ion induced pitting corrosion. Herein, the corrosion behavior and the corresponding mechanism of the Zr65Cu17.5Al7.5Ni10-xCox (x = 0, 2, 4, 6) BMGs in the 3.5% NaCl solution were investigated. The Ni substitution by Co can contribute to significant improvements in the corrosion resistance of the Zr-Cu-Al-Ni BMG. The typical corrosion parameters such as the pitting potential and the pitting overpotential were increased from −199 and 40 mV (x = 0) to −78 and 117 mV (x = 6), respectively. Importantly, the corrosion current density was drastically decreased from 5.8 × 10−6 (x = 0) to 3.2 × 10−7 A/cm2 (x = 6). The electrochemical impedance spectroscopy results demonstrated a distinct increase of the charge transfer resistance from 1.8 × 105 (x = 0) to 8.4 × 105 Ω·cm2 (x = 6). The elemental analysis indicated that the Co substitution could facilitate the formation of stable passivation layer against chloride ion corrosion.