Nanocrystalline high-entropy carbide ceramics with improved mechanical properties

The nanocrystalline (Hf0.25Zr0.25Ta0.25Ti0.25)C high-entropy carbide ceramics were successfully prepared through high-pressure sintering of the self-synthesized nanopowders for the first time. The results showed that the relative density, grain size, hardness, and elastic modulus of all the as-prepared samples increased gradually with the increase of sintering temperatures from 1200 to 1600 degrees C. The as-fabricated samples at 1600 degrees C possessed a relative density of 97.1% and a mean grain size of 98 +/- 35 nm and simultaneously exhibited good comprehensive mechanical properties with Vickers hardness of 25.7 +/- 0.6 GPa and fracture toughness of 4.3 +/- 0.4 MPa center dot m(1/2) at room temperature due to the grain refinement strengthening mechanism and microcrack deflection and bridging toughening mechanism. In addition, they showed a linear decrease in high-temperature Vickers hardness with the increase of the temperature from room temperature to 1000 degrees C, which was determined by the combined effects of the intrinsic softening of HEC-1 ceramics at elevated temperature and the presence of ZrO2 impurity phase at the grain boundaries.

Automated summary

Nanocrystalline (Hf0.25Zr0.25Ta0.25Ti0.25)C high-entropy carbide ceramics were successfully prepared through high-pressure sintering, showing improved mechanical properties at 1600 degrees C. Furthermore, the high-temperature Vickers hardness exhibited a linear decrease, influenced by the ZrO2 impurity phase at grain boundaries and the softening effect at elevated temperatures.