Effect of heat treatment on electrochemical behavior of alloy 690 in NaOH solution

Microstructure of alloy 690 solid-solutioned at different temperatures was investigated by SEM. Electrochemical behavior of alloy 690 in NaOH solution was examined by means of potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and localized electrochemical impedance spectroscopy (LEIS). SEM result shows that grain size of alloy 690 solution-treated at 1095°C is larger than that of the alloy treated at 1090°C and 1100°C. Carbides at grain boundaries are observed in the alloy solution-treated at different temperatures. It is shown that the alloy 690 solutioned at 1090°C exhibits the largest corrosion current density in NaOH solution. EIS result indicates that the impedance value of alloy 690 solutioned at 1100°C in NaOH solution is higher than other specimens. LEIS results demonstrate that the surface localized electrochemical impedance spectroscopy of alloy 690 heat treated at different temperatures presents different distribution feature.