Photoelectrochemical investigations on individual ferritic and austenitic grains of a duplex stainless steel oxidized in water vapour

Abstract

This work presents a multiscale photoelectrochemical characterization of oxide layers, and aims mainly at introducing the mesoscopic scale (ca 30 µm). For the first time, photocurrent energy spectra could be recorded on individual ferritic and austenitic grains of a unique 2205 duplex stainless steel sample oxidized for 5 minutes at 650°C under 20% water vapour in nitrogen. These results allowed us to explain contrasting issues in the photoelectrochemical images obtained from the oxidized sample. Moreover, the bandgap energies obtained by fitting these individual mesoscopic photocurrent energy spectra with a novel approach developed in our laboratory, showed that all oxide scales were constituted of Fe₂O₃ and Cr₂O₃ and of an Fe_2-xCr_xO₃ solid solutions, but that the x-value of the latter was different depending on the metallurgic phase of the oxidized substrate. The latter results were shown to be in agreement with those of additional Raman analyses of the oxidized austenitic and ferritic grains.