Electrochemical Corrosion of as-Cast and Annealed Zr48Cu36Al_8Ag_8 BMG in 0.1 M NaCI Solution

摘要

Electrochemical corrosion of as-cast and annealed zirconium-based bulk metallic glass (BMG) Zr4_8Cu36Al_8Ag8 in 0.1 M NaCl solution was investigated in this work. The as-cast specimen, in complete amorphous form, contained null percent of crystal phase (denoted as OC); however, the annealed ones contained 11, 25, 50, 75 and 100 % crystal phase (denoted as 11C, 25C, 50C, 75C and 100C, respectively) determined by the annealing duration of 0C specimen at 471 °C. Through monitoring of open circuit potential (OCP), measurements of direct-current polarization resistance (PR), Tafel plot (TP), cyclic anodic potentiodynamic polarization (CAPD), and electrochemical impedance spectroscopy (EIS), we found that the corrosion behavior of the Zr_(48)Cu36Al_8Ag_8 was determined by the the crystal phase present in the specimens dominated by the annealing durations. The corrosion resistance decreased in the order: 25C> 11C> 0C> 50C> 75C> 100C. This result revealed that the corrosion resistance inclined to be better and reached a maximum with increasing the percentage of the crystal phase from 0 to 25%; however, it decreased with further increasing the crystal phase over 25%. A corrosion mechanism is proposed to rationalize the sequence of corrosion resistance. According to the mechanism, the remained free volume and residual strain energy are responsible for the specimens containing crystal phase less than 25% (i.e., 0C, 11C and 25C); whereas crystal defects such as grain boundaries governed the corrosion of those containing crystal phase more than 25 % (i.e., 50C, 75C and 100C).