Comparison of chromium poisoning by the ODS alloy Cr5Fe1Y2O 3 and the high chromium ferritic steel Crofer 22 APU

Abstract

The alloys Cr5Fe1Y2O3 and the ferritic steel Crofer 22 APU are typical alloys used as SOFC interconnect materials. Alloy Cr5Fe1Y2O3 is an ODS alloy developed by Plansee, Reutte, Austria, for use at high temperatures. A typical material for medium temperature SOFC is the high chromium ferritic steel Crofer 22 APU supplied by Thyssen Krupp VDM, Germany. The two alloys form different oxide scales which affect chromium poisoning. Chromium vaporization as source and electrochemical degradation describing the poisoning were studied for the two alloys. The dynamics of the chromium deposition at the triple phase boundary (TPB) was studied by a DC two-electrode four-wire method and impedance spectroscopy. Electrical degradation by alloy Cr5Fe1Y2O3 was significantly higher than for Crofer 22 APU. The microstructure of the symmetrical cells was studied after the galvanostatic measurements by scanning and energy filtering transmission electron microscopy (SEM and EFTEM). Significant amounts of chromium were observed at the three-phase-boundary in the functional layer giving insight into the degradation mechanism.