Studies on corrosion resistance of Cu-40Ni alloy with different grain size in Cl- media

The corrosion mechanism and corrosion-resistance of Cu-40Ni alloy prepared by conventional casting (CA), mechanical alloy (MA) and hot-pressing processes with the great grain size difference in Cl- media were investigated by PARM273A and M5210 electrochemical apparatus through potentiodynamic polarization method and electrochemical impedance spectroscopy (EIS) technique. Results show that MA and CA Cu-40Ni alloy have similar corrosion law. The corrosion potential of Cu-40Ni alloy moves positively and corrosion rate increases with the increase of Cl- concentration in Na2SO4+NaCl media. Electrochemical impedance spectroscopy (EIS) is composed of double loops. Polarization resistance decreases and at the same time interface capacity increases with the increase of Cl(-)concentration. With the decreasing of grain size, capacitive loop becomes smaller. Because Cl- decreases oxidation-reduction potential by chemical reaction and replaces O-2- in Cu2O and breaks passive oxide films on the alloy surface at the same time, corrosion rate of alloys become higher. Corrosion rate of MA Cu-40Ni alloy is higher than that of CA Cu-40Ni alloy evidently in Na2SO4+NaCl medium.