Electrochemical corrosion behavior of Cu-20Fe-12Cr alloys with the different grain size in solutions containing chloride ions

Electrochemical corrosion behavior of Cu-20Fe-12Cr alloys prepared by powder metallurgy (PM) and mechanical alloy (MA) with the different grain size was studied in solutions containing chloride ions. The free corrosion potentials move toward negative values and corrosion rates become faster with the increase of chloride ion concentrations for two alloys. Electrochemical impedance spectroscopy (EIS) plots of PMCu-20Fe-12Cr alloy are composed of a capacitive loop and a diffusion tail. Corrosion processes are controlled by diffusion. EIS plots of MACu-20Fe-12Cr alloy in Na2SO4 or 0.02mol.L-1NaCl solution are unable to have characteristics of Warburg impedance. Corrosion processes are controlled by electrochemical reactions. After chloride ion concentrations increase up to 0.05mol.L-1, their EIS plots are composed of double capacitive loops with a straight line induced Warburg resistance between two capacitive loops. The above EIS plots imply the existence of pitting corrosion. The corrosion rates of MACu-20Fe-12Cr alloy become faster than those of PMCu-20Fe-12Cr alloy because the reduction in the grain size of MACu-20Fe-12Cr alloy produces large concentrations of grain boundaries.