Preparation of high-entropy carbides by different sintering techniques
Dense (Hf-Ta-Nb-Ti-V)C and (Ta-Nb-Ti-V-W)C based high entropy carbides (HEC) where produced by three different sintering techniques: gas pressure sintering or sinter-HIP at 1900 °C and 100 bar Ar, vacuum sintering at 2250 °C and 0.001 bar and SPS/FAST at 2000 °C and 60 MPa pressure. The relative density varied from 97.9% to 100%, with SPS producing 100% dense samples with both compositions. Grain size measurements showed that the (Hf-Ta-Nb-Ti-V)C HEC's had 5-10 times smaller grain size than the (Ta-Nb-Ti-V-W)C samples. Vacuum sintered samples showed the biggest but uniform HEC grain size distribution regardless of compositions. EDS mapping showed the formation of a solid solution with no intermetallic phases or element clustering. X-ray diffraction analysis, showed the formation of single-phase cubic high entropy carbides with a unique lattice parameter for all samples. Hardness measurement revealed that (Hf-Ta-Nb-Ti-V)C samples possess higher hardness values than (Ta-Nb-Ti-V-W)C samples.