Mechanical properties of Ni-YSZ cermet (Ni 30, 44, 58 vol.%) in SOFC operating conditions in the temperature range of room temperature to 1000°C and in reduction atmospheres, were studied by an in situ four points bending method. Ni30 specimens in the whole testing temperature and Ni44, Ni58 specimens at the temperature lower than 350 °C fractured brittly, and Ni44, Ni58 specimens fractured with plastic deformation at the temperature higher than 350 °C. In the microstructure of three Ni contents, nickel was aggregated and isolated in Ni30 specimens. By contrast, nickel was well distributed in Ni44, 58 specimens. In addition, the yield strength of nickel decreases at the temperatures higher than 300 °C. Hence, observed results suggested being due to the local yield of well distributed nickel in the cermet. Because anode supported type SOFCs employ Ni-YSZ cermet, which nickel content is higher than 44 vol.%, this study suggests that an irreversible deformation occur during SOFC operation due to the plastic deformation of Ni-YSZ cermet.
