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

L A Díaz,A Fernández,P Peretyagin,M Morales,C Pecharromán,J S Moya,R Torrecillas,W Solís

doi:10.1155/2016/3170142

Abstract

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 Si3N4submicrometer particles were coated with anatase TiO2nanocrystals. 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 (KIC,σf) 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.

Highlights

Silicon nitride is among the most important ceramic materials for high-temperature applications because of its combination of mechanical properties at room and high temperatures, oxidation resistance, low coefficient of thermal expansion, and low density in comparison to refractory metals [1]
There are important weight losses at low temperatures that correspond to the solvent that is retained on powder surface
In the case of powders doped with Ti precursor, the titanium oxide coating formed on silicon nitride particles after thermal treatment is anatase (Figure 3(b1)) and transforms to titanium nitride (TiN) after nitridation by NH3 gas (Figure 3(b2))

Summary

Introduction

Silicon nitride is among the most important ceramic materials for high-temperature applications because of its combination of mechanical properties at room and high temperatures, oxidation resistance, low coefficient of thermal expansion, and low density in comparison to refractory metals [1]. High performance silicon nitride materials were developed for automotive engine wear parts and as cutting tools In this case, the introduction of titanium nitride (TiN), with a high melting temperature (>3000∘C), good electrical conductivity, and high resistance to corrosion and oxidation, improves the wear resistance in continuous cutting tools [7]. This conductive ceramic has been recently revealed as a possible substitute of plasmonic metals, because of its lower cost, and it is possible to modify the electron density by doping.

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