Microstructure and properties of SiCN-nanocomposites

The densification process via hot pressing and gas pressure sintering, microstructure and the mechanical properties of SiCN-nanocomposites fabricated from different powders produced by plasmasynthesis, pyrolysis of polysilazanes and mixtures of Si3N4 and SiC powders are investigated. The phase transformation during hot pressing of the powder produced by pyrolysis of polysilazanes is completely different of that in the materials produced by the mixture of SiC- and Si3N4-powders or plasmasynthesis. In order to achieve a completely densified material the amount of free carbon content in the initial powder should be less than 1 percent. Additionally a homogeneous green structure and special sintering cycles are necessary. The microstructure is influenced considerably by the powder properties and the densification cycle. Correlations are given between powder properties and densification, microstructure and mechanical properties of the materials. The materials produced show excellent high te mperature bending strength (about 800 MPa at 1400 Cel) and creep resistance.