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

Abstract Stoichiometric Tantalum carbide (TaC) ceramics were prepared by reaction spark plasma sintering using 0.333–2.50 mol% Si 3 N 4 as sintering aid. Effects of the Si 3 N 4 addition on densification, microstructure and mechanical properties of the TaC ceramics were investigated. Si 3 N 4 reacted with TaC and tantalum oxides such as Ta 2 O 5 to form a small concentration of tantalum silicides, SiC and SiO 2 , with significant decrease in oxygen content in the consolidated TaC ceramics. Dense TaC ceramics having relative densities >97% could be obtained at 0.667% Si 3 N 4 addition and above. Average grain size in the consolidated TaC ceramics decreased from 11 µm at 0.333 mol% Si 3 N 4 to 4 µm at 2.50 mol% Si 3 N 4 addition. The Young's modulus, Vickers hardness and flexural strength at room temperature of the TaC ceramic with 2.50 mol% Si 3 N 4 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.