Characterization of Oxidized Ferritic Stainless Steel with Undulated Surfaces for Metallic Interconnects

Abstract

One of the candidates for metallic interconnects of solid oxide fuel cells is a ferritic stainless steel, Crofer22 APU. Ferritic stainless steel Crofer22 APU samples with different roughness were prepared by grinding with SiC grinding papers of various grits, and a polished Crofer22 APU sample was also prepared. The prepared samples were then thermally cycled. The variations of their oxidation behavior with surface roughness and the number of thermal cycles were investigated. After 120 thermal cycles (a total 3000 h of exposure at 800 °C), the polished Crofer22 APU had arelatively flat, continuous Cr2O3 layer (thickness, ~ 1 μm), while the Crofer22 APU ground with 80 grit showed an undulating, continuous Cr2O3 layer (thickness, ~ 2 μm). For the samples that were thermally cycled 4 times (at 800 °C for 100 h total), the area specific resistance (ASR) increased as grit number increased for all measured temperatures (600 – 850 °C). Generally, for the samples that were thermally cycled 20 times, the ASR decreased slowly as the grit number increased. For the samples thermally cycled 40 times, the ASR decreased in general at all the measuring temperatures as the number of grit increased, indicating that the polished Crofer22 APU is better than those with rougher surfaces for the application of Crofer22 APU to an interconnect of SOFC.

Keywords

• fuel cells, oxidation, microstructure, X-ray diffraction, ferritic stainless steel interconnect