Miroslav Balog

The Formation of Two Types of SiC Inclusions in Si3N4/SiC Nanocomposites

Detailed study on the formation of SiC nanoinclusions within the SiC/Si3N4 nanocomposite is presented. Inclusions located within the Si3N4 micrograins are of two different origins. The first category consists of inclusions with the oxygen rich interface between SiC and host Si3N4 grain. The second category of inclusions consists of SiC nanograins without this interface layer. The present study proved that oxygen rich SiC inclusions are created by reduction of SiO2 in the presence of carbon during the liquid phase sintering of the composite.

Hardness Limits of SiC and Si3N4 Ceramic Materials

Nano- and macro-hardness of SiC and Si3N4 based ceramic materials prepared by liquid phase sintering were evaluated. The applied loads were 3.5 mN and 9.81 N, respectively. The measurements showed that the nano-hardness of both ceramics is substantially higher compared to the macro-hardness. The influence of solid solutions and grain boundary composition on the hardness of SiC-based ceramics was studied. The macro-hardness is strongly dependent on the grain boundary composition while the nano-hardness was nearly the same for all tested samples with different Re2O3-AlN additives. In the case of Si3N4 based ceramics the SiC nano-inclusions content was varied. As a source of SiC nanoinclusions and grain boundary phase modifierSiNC polymer precursor has been used. Nano- as well as micro-hardness increased with increasing SiC content. Present paper deals with the explanation of both results.

Nano-Indentation of SiC and Si3N4/SiC Ceramic Materials

The present paper deals with the nano-indentation of SiC-micro and Si3N4/SiCmicro/ nano ceramic materials. The investigated SiC-micro and Si3N4/SiC-micro/nano ceramics were prepared by liquid phase sintering. Liquid phase was formed from different sintering additives (Y2O3, Yb2O3, Sm2O3). In the case of Si3N4/SiC-micro/nano ceramics the SiC nano-grains were created from SiNC amorphous powder. SiNC precursor decomposed to SiC and Si3N4 particles during sintering. The comparison of nano- and macro-hardness of investigated ceramic materials showed that nano-hardness is significantly higher. The indentation modulus correlated with the measured nano-hardness. Remarkable influence of grain boundaries and SiC nano-inclusions on hardness was observed.