The conductivity of porous normalNi/ZrO2‐Y2O3 cermets at 1000°C was determined as a function of Ni content between 15 and 50 volume percent (v/o) of total solids for two different zirconia particle sizes (23 and 47 m2/g). Below Ni contents of 30 v/o, ionic conduction through the zirconia phase dominated. At 30 v/o Ni, a greater than three order of magnitude increase in the conductivity was observed, corresponding to a change in mechanism to electronic conduction through the Ni phase. The conductivity of cermets made with a Ni content greater than 30 v/o Ni was found to decrease with increasing temperature between 700° and 1000°C. While the conductivity of the cermets with the larger particle size zirconia was higher by more than a factor of four, all the samples studied had the same activation energy, 5.7±0.1 normalkJ/normalmol . The increase in conductivity with zirconia particle size is attributed to improved Ni particle‐to‐particle contact, resulting from the Ni phase being able to cover more completely the surface of the zirconia matrix where it resides.

at 1000 °C has been measured as a function of the Ni content (15‐50 vol.%) using cermets with two different ZrO2 particle sizes.

Continuous fiber ceramic matrix composites (CFCCs) are currently being developed for a variety of high-temperature applications, including use in advanced heat engines. For such composites, knowledge of porosity distribution and presence of defects is important for optimizing mechanical and thermal behavior of the components. The assessment of porosity and its distribution is also necessary during composite processing to ensure component unifo4ty. To determine the thermal properties of CFCC materials, and particularly for detecting defects and nonuniformities, we have developed an infrared thermal imaging method to provide a "single-shot'' full-field measurement of thermal diffusivity distributions in large components. This method requires that the back surface of a specimen receives a thermal pulse of short duration and that the temperature of the front surface is monitored as a function of time. The system has been used to measure thermal diffusivities of several CFCC materials with known porosity or density values, including SYT.,RAMICm SiC/SiNC composite samples from Dow Corning and SiUSiC and enhanced SiC/SiC samples from DuPont Lanxide Composites, to determine the relationship of thermal diffusivity to component porosity or density.

The room-temperature strength distributims of a sintered and a hot-pressed S i c were examined as-machined, after oxidation at 1370"C, and after oxidation under load at 1370°C. The strengths were observed to be dependent on both the duration of oxidation and the magnitude of the applied load. Processes resulting in both strengthening and weakening behavior were observed to occur, at times simultaneously within the same strength distribution. This dynamic situation indicates that the strength-controlling flaw populations are highly transient in nature.