Selection and evaluation of heat-resistant alloys for SOFC interconnect applications

Over the past several years, advances in the design and fabrication of planar solid oxide fuel cells (SOFCs) have led to a steady reduction in the temperatures necessary for their operation. Consequently, it appears more realistic now to use low cost heat-resistant alloys for interconnect components in the SOFC stack. However, no specific criteria or inclusive study are available as a reference to help select and evaluate suitable candidates from the hundreds of available heat-resistant alloy compositions, which overall demonstrate oxidation resistance at high temperatures. In this work, composition criteria have been proposed for the preselection of heat-resistant compositions, such as Ni-, Fe-, and Co-based superalloys, Cr-based alloys, and stainless steels. The proposed criteria have been employed to establish a database of heat-resistant alloys at Pacific Northwest National Laboratory, where a systematic approach has been initiated to evaluate and modify and/or develop alloys for SOFC interconnect applications. The preselected compositions are further evaluated by referring in-house studies and reference to published data. It appears that it would be difficult for traditional alloys to fully satisfy the materials requirements for long-term operation at temperatures higher than 700degreesC. However, the applicability can be improved via surface/bulk modification and by the implementation of novel stack designs. (C) 2003 The Electrochemical Society.