Processing and properties of nanophase non-oxide ceramics

The present paper describes recent activities in the development of non-oxide nanophase ceramics. Examples on the processing of TiN, TiC, Si3N4, SiC and others will be given. Only a few of the described activities ended up with both high densities (i.e. >95% of the theoretical density (TD)) and grain sizes below 100 nm. A possible reason for the behavior of non-oxide ceramics is the contamination of the surface by oxygen. For SiC, it is shown that the oxide layer on the surface hinders densification. It favors non-densifying sintering mechanisms and hence coarsening of the microstructure. A processing route was developed which effectively reduces the oxide layer. Subsequent Hot Isostatic Pressing (HIP) of these SiC samples led to densities above 97%TD and grain sizes below 100 nm. Finally, a short overview of properties (hardness, fracture toughness, thermal diffusivity, behavior under irradiation) of nanophase non-oxide ceramics will be given. Due to the fact that the manufacture of ceramics with grain size below 100 nm turns out to be difficult also results of samples with slightly larger grain sizes are included.