Effect of Thermal Cycling on Residual Stress and Curvature of Anode-Supported SOFCs

The residual stress in the electrolyte and the cell curvature of two types of anode-supported SOFC were measured after manufacture, after anode reduction and as a function of thermal cycling between room temperature and 900 degrees C. The simple cells had Ni(O)/YSZ anode supports and 8YSZ electrolytes whereas compensated, cells had an additional 8YSZ layer on the opposite side to counteract bending. The electrolyte residual stress was similar to-600 MPa in both types after fabrication and the curvature of the simple cells was consistent with only elastic bending. On reduction, electrolyte stress decreased to about -450 MPa for simple cells, but remained unchanged for compensated cells. The curvature of the simple cells at this stage was much larger than expected for elastic bending due to considerable plastic deformation during reduction. On thermal cycling the electrolyte stress gradually increased to similar to-610 MPa (30 cycles) and -880 MPa (50 cycles) for simple and compensated cells respectively due to an increase in thermal expansion coefficient of the anode substrate. No evidence of fatigue damage was found. Sealing the cells into Crofer metal frames had only a small effect on electrolyte stress, but the seals failed after 25 cycles.