Spark plasma sintering and mechanical properties of tantalum carbonitrides Ta2CxNy

Dense tantalum-based carbonitride materials featuring >95 % relative density, TaC, Ta2C1.5N0.5, Ta2CN, Ta2C0.5N1.5 and TaN, were prepared by Spark Plasma Sintering (SPS) at 1873 K with a dwell time of 10 min and a pressure of 50 MPa. Despite the presence of an oxide phase (i.e. 5 vol%) and some W inclusions (i.e. 1 vol%), the mechanical properties of such ultra-high temperature ceramics (UHTC) show promising values. Indeed, the Young's moduli measured by nano-indentation were approx. 600–700 GPa, which is higher than literature values reported for similar UHTC. The hardness values increased from 16.4 ± 0.8 GPa for TaC to 27.9 ± 1.3 GPa for TaN, with an approximately linear trend for the carbonitride samples while the ratio of plastic deformation work over the total indentation work followed the opposite trend.