Variation in the Oxidation Behavior of a Polished Ferritic Stainless Steel with Thermal Cycling

One of the candidates for metallic interconnects of solid oxide fuel cells is a ferritic stainless steel, Crofer22 APU. Crofer22 APU specimens are polished and thermally cycled at 800 ℃ 4, 8, 20, 30, and 40 times, with the periods of maintaining the temperature at 800 ℃ (corresponding to the oxidation times) of 100, 200, 500, 750, and 1,000 h, respectively. The variation in their oxidation behavior with cycling is then investigated. The EDX spectra of the polished Crofer22 APU show that the atomic percentages of the elements Cr, Mn, and Fe decrease, while the atomic percentage of oxygen increases, as the number of thermal cycles, n, increases. XRD patterns of the surfaces for the polished Crofer22 APU samples after thermal cycling show that as the number of thermal cycles increases, the content of the alloy substrate phase decreases and the content of the Cr2O3 phase remains almost constant. The content of (Cr, Mn 3O4 spinel phase increases from n=4 to n=20 and remains almost constant from n=20 to n=40. The slow increase in ASR from n=4 to n=20 is considered to correspond to the formation of the (Cr, Mn)3O4, Cr2O3, and SiO2 phases. The rapid increase in ASR from n=20 to n=40 is considered to occur because the connections between particles become weak due to the expansion and contraction of particles with thermal cycling. (Received July 18, 2013)