Characterization of Native Oxide and Passive Film on Austenite/Ferrite Phases of Duplex Stainless Steel Using Synchrotron HAXPEEM

M Långberg,D Lindell,E Lundgren,C Wiemann,A Stierle,A Gloskovskii,U Kivisäkk,F Zhang,Y Matveyev,J Cheng,C Örnek,M Liu,H Noei,J Pan,T F Keller,E Grånäs,S Kulkarni

doi:10.1149/2.0421911jes

Abstract

A new measurement protocol was used for microscopic chemical analysis of surface oxide films with lateral resolution of 1 μm. The native air-formed oxide and an anodic passive film on austenite and ferrite phases of a 25Cr-7Ni super duplex stainless steel were investigated using synchrotron hard X-ray photoemission electron microscopy (HAXPEEM). Pre-deposited Pt-markers, in combination with electron backscattering diffraction mapping (EBSD), allowed analysis of the native oxide on individual grains of the two phases and the passive film formed on the same area after electrochemical polarization of the sample. The results showed a certain difference in the composition of the surface films between the two phases. For the grains with (001) crystallographic face // sample surface, the native oxide film on the ferrite contained more Cr oxide than the austenite. Anodic polarization up to 1000 mV/Ag/AgCl in 1M NaCl solution at room temperature resulted in a growth of the Cr- and Fe-oxides, diminish of Cr-hydroxide, and an increased proportion of Fe3+ species.

Highlights

Many metals spontaneously form oxide films on the surface when exposed to ambient air or aqueous environments
Three different experimental approaches have been reported, aiming to gain local chemical information of the passive films formed on the individual phases: (i) local Auger electron spectroscopy (AES) analysis in combination with ion sputtering, having a spatial resolution up to 5 μm;[13] (ii) selective etching of one of the phases in an acid under potentiostatic control followed by X-ray photoelectron spectroscopy (XPS) measurement on the remaining phase;[14] and (iii) producing the sample material with the chemical composition of the phase of interest, and analyzing the passive film using XPS.[15]
We utilized a new method for non-destructive characterization of the passive film of duplex stainless steel using synchrotron hard X-ray photoemission electron microscopy (HAXPEEM), which can access site-specific chemical information with spatial resolution up to 1 μm and depth information between a few to a few tens of nanometres depending on the energy of the beam.[16]

Summary

Introduction

Many metals spontaneously form oxide films on the surface when exposed to ambient air or aqueous environments. We utilized a new method for non-destructive characterization of the passive film of duplex stainless steel using synchrotron hard X-ray photoemission electron microscopy (HAXPEEM), which can access site-specific chemical information with spatial resolution up to 1 μm and depth information between a few to a few tens of nanometres depending on the energy of the beam.[16] By depositing Pt fiducial markers on the sample surface, regions of interest (ROI) can be selected for HAXPEEM measurement and re-measured after ex-situ electrochemical polarization to investigate the difference between the air-formed film and the anodic passive film.

Results

Conclusion