Evaluation of Sintered Powder Metallurgy Fe-Cr Alloys as Metallic Interconnects for Solid Oxide Fuel Cell Applications

Metallic interconnects are key components in planar solid oxide fuel cell (SOFC) stacks. In the present study, we evaluated four Fe-Cr powder metallurgy (PM) alloy specimens, obtained from a domestic manufacturer, at nominal compositions (in wt%) of 5% Fe-95% Cr, 30% Fe-70% Cr, 50% Fe-50% Cr, and 78% Fe-22% Cr. These specimens were tested and evaluated for use in SOFC stack applications. The verification items included coefficient of thermal expansion measurements, high-temperature oxidation resistance and weight gain tests, mechanical strength tests, high-temperature sealant bonding and leakage rate measurements, and high-temperature electrical property (i.e., area-specific resistance) measurements. In addition, the specimens’ microstructures and elemental compositions were observed and analyzed. The test results indicate that the Fe content of the Fe-Cr powder metallurgy alloys influences various properties, while Cr also plays a significant role in high-temperature oxidation resistance. Among the four alloy specimens, the 78Fe-Cr alloy exhibited all of the aforementioned advantages, including a suitable coefficient of thermal expansion of 12.4 × 10−6/°C, excellent high-temperature oxidation resistance, a thermal weight-gain rate of 5.31 × 10−14 g2/cm4·s, a remarkably low high-temperature area-specific resistance of 7.04 mΩ·cm2, and superior bonding and interfacial stability with the GC9 glass–ceramic sealant, achieving a very low leakage rate of 3.47 × 10−6 mbar·l/s/cm. These results indicate that the 78Fe-Cr powder metallurgy alloy performs excellently and is the most promising candidate for metallic interconnects in SOFC stack applications.