High-temperature in situ stress monitoring of a co-fired electrolyte for metal-supported solid oxide cells

Improving the robustness of solid oxide cells (SOCs) requires understanding the stress state during the fabrication and operation, as it directly influences failure mechanisms and cell reliability. To determine the stress state, X-ray stress analysis using the cos α method was applied to in situ monitoring of stress distribution on an electrolyte at elevated temperatures under controlled atmospheres. A metal-supported half cell consisting of ferritic stainless steel, yttria-stabilized zirconia (YSZ), and nickel-YSZ was fabricated by tape casting and co-firing and was used for the measurements. At room temperature, circumferential stress showed unexpected distribution from −160 MPa at the center to −20 MPa at the periphery. As the temperature increased under hydrogen, it changed to tensile stress, which saturated at approximately 100 MPa. The observed large temperature dependence was explained by assuming a phase change of the stainless steel from ferrite to austenite near the anode interface due to the diffusion of nickel from the anode. Finite-element calculations explained the temperature dependence of the average stress on the electrolyte. A possible cause for the circumferential stress distribution is also discussed. These results demonstrated the usefulness of in situ stress monitoring in the design of SOCs.