Effect of Nb on the surface composition of FeCrAl alloys after anodic polarization

Abstract

XPS combined with AFM have been used to investigate the surface modifications of nuclear grade FeCrAl-xNb (x= 0, 0.5, 1.0, 1.5 wt.%) alloys, induced by anodic polarization in a simulated primary coolant. Electrochemical tests were performed to study the role of the minor element Nb on the corrosion potential and composition. The optimal content of Nb, obtained after the comparative analysis of the UHV-sputtered surface, native oxide-covered surface and anodic polarized surface, is 0.5 wt.%. This alloy presents a more compact Al-enriched oxide film consistent with a higher corrosion potential at −89 mV. The protectiveness of oxide film against the active dissolution can be improved by Nb addition, but does not increases linearly with Nb content. High resolution XPS analysis details the changes of Nb oxidized states, and provides the stratification of the oxide film containing the (hydr) oxides of Fe, Al and Cr.