Molybdenum Addition Enhancing the Corrosion Resistance of Ni16Cr Alloy in Aqueous Solution

The influences of Mo on the structures and the electronic properties of passive films on Nil6C Χ Mo ( Χ =0wt.%, 2wt.%, 5wt.%, 8wt.%, 12wt.% and 16wt.%) alloys in pH 1.0 sulfuric acid solution, pH 8.5 borate buffer solution and pH 13 sodium hydroxide solution were investigated using X-ray photoelectron spectroscopy (XPS), potentiodynamic polarization curve, Electrochemical impedance spectroscopy (EIS) and Mott-Schottky plot. The results showed that the addition of Mo can evidently refine the microstructure of Ni16Cr alloy, and the grain size sharply decreased with increasing Mo. Ni16Cr alloy was passivated in pH1 sulfuric acid solution, pH8.5 borate buffer solution and pH13 sodium hydroxide solution, each passive current density decreased and each passive potential region enlarged with the increment of Mo. XPS results showed that the passive films on Ni16CΧMo alloys were mainly composed of the inner Cr 2 s 3 layer and the outer NiO layer with a little amount of Cr 2 S 3 , NiS and NiSO 4 . The resistances and compactness of the passive films on Ni16Cr alloy in the three solutions increased with the increased Mo, which implyed the enhanced protection of the passive film. Mott-Schottky plots revealed that the passive film on Ni16Cr alloy appeared the p-n heterojunction, the defect number of the outer film increased with the increment of Mo, while for the inner film, the defect number decreased with Mo, while the total protection of the passive films to the metal matrix was improved with increasing Mo.