Abstract: A coarse-grained and two bulk nanocrystalline Ag-25Ni alloys are obtained by powder metallurgy (PM), liquid phase reduction (LPR) and mechanical alloying (MA) methods by means of hot pressing technique. Their corrosion properties were studied in NaCl solutions. The results show that corrosion current densities of three alloys prepared by different processes decrease in the order of LPR Ag-25Ni, PM Ag-25Ni and MA Ag-25Ni. Their electrochemical impedance spectroscopies consist of one capacitive arc and charge transfer resistances increase in the order of LPR Ag-25Ni, PM Ag-25Ni and MA Ag-25Ni. These show that the corrosion rate of nanocrystalline LPR Ag-25Ni alloy becomes faster, while the corrosion rate of nanocrystalline MA Ag-25Ni alloy becomes slower than that of coarse grained Ag-25Ni alloy. The passivation films were formed in 0.3 mol/L NaCl at 0.9 V potential for three Ag-25Ni alloys, and they all were n type semiconductors. The carrier densities decrease in the order of LPR Ag-25Ni, PM Ag-25Ni and MA Ag-25Ni. The passivation properties of MA Ag-25Ni alloy are the best because of the difference in microstructures among three Ag-25Ni alloys. For MA Ag-25Ni alloy, the decrease in the grain size and increase in the solid solubility contribute to its good chemical stability.
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2018, Vol. 32 
