Corrosion behavior of Ni62Nb33Zr5 bulk metallic glasses after annealing and cryogenic treatments

Abstract

The microstructural evolution and corrosion behavior of Ni62Nb33Zr5 bulk metallic glasses (BMGs) after annealing treatment (AT) at different crystallization temperatures and cryogenic treatment (CT) at −100 ℃ are experimentally investigated. Appropriate AT and CT can both improve the thermal stability and comprehensive corrosion resistance of as-cast BMG in 3.5 wt.% NaCl solution. The annealed and cryo-treated BMGs exhibit one more finite diffusion layer loop in the electrical equivalent circuit than the as-cast BMG, indicating the complexity of the corrosion behavior. Superior corrosion resistance is obtained in the cryo-treated BMG because the high degree of amorphization caused by CT reduces the structural inhomogeneity. Lower Cd and higher Rd values are obtained for the cryo-treated BMG, revealing the formation of a more stable passive film. Among the annealed BMGs, the fully crystallized sample exhibits a higher anti-corrosion performance owing to the existence of Nb-rich oxides in the crystallization products. The passive film is found to be composed mainly of Nb2O5 and ZrO2, demonstrating that Nb and Zr are conducive to reacting with oxygen to form a passive film. Based on the goal of maintaining a fully amorphous phase, appropriate CT causing structural homogeneity of the BMG is a simple and effective means to improve the comprehensive corrosion resistance.

Keywords

• Bulk metallic glass
• Corrosion resistance
• Annealing
• Cryogenic treatment
• Pitting