Electrochemical Corrosion Behavior of Nanocrystalline Bulk Co-45Ni-10Cr Alloy in H2 SO4 Solutions
The Co-45Ni-10Cr alloy powder with conventional size (CS) was prepared by powder metallurgy process,and the Co-45Ni-10Cr alloy powder with nanometer size (NS ) was prepared by mechanical alloying process.The two alloy powders above were hot pressed into the corresponding bulk Co-45Ni-10Cr alloys.The self-corrosion potentials,potentiodynamic polarization curves and electrochemical impedance spectroscopies (EIS) of the two Co-45Ni-10Cr(CS and NS) alloys were tested by an electrochemical workstation with different concentration of H2 SO4 solutions as corrosive media.The corrosion behavior of the conventional and nanometer size bulk Co-45Ni-10Cr alloys and the influence of grain refinement on their corrosion properties were studied.The results show that the higher the concentrations of H2 SO4 solutions are,the more negative the self-corrosion potentials of the two Co-45Ni-10Cr(CS and NS) alloys become and thus the greater the corrosion tendencies are.Meanwhile,the higher the concentrations of H2 SO4 solutions are,the bigger the corrosion current densities and the smaller the charge transfer resistances become and thus the higher the corrosion rates are.In addition,EIS all show the corrosion rate is controlled by an electrochemical process because they only have a single capacitance reactance arc.Compared with the Co-45Ni-10Cr(CS) alloy,the corrosion rate of the Co-45Ni-10Cr(NS) alloy slows down.It is very evident that the corrosion resistance of the Co-45Ni-10Cr bulk alloy is improved after nanocrystallinations.
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