Spark Plasma Sintered Si3N4/TiN Nanocomposites Obtained by a Colloidal Processing Route

Ceramic Si3N4/TiN (22 vol%) nanocomposites have been obtained by Spark Plasma Sintering (SPS). Our colloidal processing route allows obtaining dispersed nanoparticles of TiN smaller than 50 nm avoiding the presence of agglomerates. The nanostructured starting powders were obtained by using a colloidal method where commercial Si3N4 submicrometer particles were coated with anatase TiO2 nanocrystals. A later nitridation process led to the formation of TiN nanoparticles on the surface of Si3N4. A second set of powders was prepared by doping the above defined powders with yttrium and aluminium precursors using also a colloidal method as sources of alumina and yttria. After thermal nitridation and SPS treatment, it has been found that the addition of oxides dopants improves the mechanical performance (K-IC, sigma(f)) but increases the electrical resistivity and significantly reduces the hardness. This is due to the formation of a continuous insulating glassy phase that totally envelops the conductive TiN nanoparticles, avoiding the percolative contact between them. The combination of colloidal processing route and SPS allows the designing of tailor-made free glassy phase Si3N4/TiN nanocomposites with controlled microstructure. The microstructural features and the thermoelectrical and mechanical properties of both kinds of dense SPSed compacts are discussed in this work.