Microstructure and mechanical properties of tantalum carbide ceramics: Effects of Si3N4 as sintering aid

Stoichiometric Tantalum carbide (TaC) ceramics were prepared by reaction spark plasma sintering using 0.333-2.50 mol% Si3N4 as sintering aid. Effects of the Si3N4 addition on densification, microstructure and mechanical properties of the TaC ceramics were investigated. Si3N4 reacted with TaC and tantalum oxides such as Ta2O5 to form a small concentration of tantalum silicides, SiC and SiO2, with significant decrease in oxygen content in the consolidated TaC ceramics. Dense TaC ceramics having relative densities >97% could be obtained at 0.667% Si3N4 addition and above. Average grain size in the consolidated TaC ceramics decreased from 11 µm at 0.333 mol% Si3N4 to 4 µm at 2.50 mol% Si3N4 addition. The Young's modulus, Vickers hardness and flexural strength at room temperature of the TaC ceramic with 2.50 mol% Si3N4 addition was 508 GPa, 15.5 GPa and 605 MPa, respectively. A slight decrease in bending strength was observed at 1200 °C due to oxidation of the samples.