Abstract
An investigation has been carried out of the surface preparation of Fe-Ni alloys for corrosion and passivity study which often requires the alloy surface having practically the same composition as that of substrate alloy. Ellipsometric measurements of a 50Fe-50Ni alloy show that the surface prepared by electropolishing is optically different from the one prepared by mechanical polishing. ESCA spectroscopic measurements reveal that the electropolished surface layer of 50Fe-50Ni alloy contains no nickel, whereas both nickel and iron is present in the mechanically polished surface layer. Depletion of nickel at the electropolished alloy surface is also shown by anodic passivation and cathodic reduction of the surface. Air-formed oxide films on mechanically polished Fe-Ni alloys can be removed by cathodic reduction in a borate buffer solution of pH 6.45. The optimum current density and time for the cathodic reduction are given for various alloy composition. Mechanical polishing followed by cathodic reduction seems to be preferable to electropolishing followed by cathodic reduction for the alloy surface preparation in passivity study.
