Microstructure and mechanical properties of TaC ceramics with 1-7.5 mol% Si as sintering aid

Metallic Si as sintering aid was effective in densifying tantalum carbide ceramic (TaC) by spark plasma sintering (SPS) at 1700 degrees C. Full density was reached at 5.0 mol% Si addition (equivalent to 1.088% Si in weight) and above. Enhanced densification of TaC ceramic with Si was associated with decrease in oxygen content from similar to 0.24 wt% in TaC powder to similar to 0.03 wt% in consolidated specimen. Rest of the oxygen species was collected at multigrain conjunctions to form SiO2-based liquid at high temperatures. Upon cooling, Ta, Si, O, and C dissolving in the liquid precipitated minor phases of TaSix and SiC of low concentrations. Microstructure of TaC ceramics was refined by the Si addition, with average grain size decreasing from 11 +/- 8 m at 1.0 mol% Si to 3 +/- 2 m at 7.5 mol% Si addition. Ta solute in SiC and Si solute in TaC were evidenced. TaC ceramic containing 7.5 mol% Si had a relatively good flexural strength and fracture toughness of 646 +/- 51 MPa and 5.0 MPa, respectively.