Low-temperature densification of high-entropy (Ti,Zr,Nb,Ta,Mo)C–Co composites with high hardness and high toughness

In order to prepare high toughness (Ti,Zr,Nb,Ta,Mo)C ceramics at low temperatures while maintaining high hardness, a liquid-phase sintering process combined with Co-based liquid-phase extrusion strategy was adopted in this study. The densification temperature can be lowered to 1350 ℃, which is much lower than the solid-state sintering temperature (~2000 ℃) generally employed for high-entropy carbide ceramics. When sintered at 1550 ℃ and 30 MPa applied pressure, part of the Co-based liquid-phase was squeezed out of the graphite mold, such that only ~3.21 vol% of Co remained in the high-entropy ceramic. Compared to the Co-free solid-state sintered (Ti,Zr,Nb,Ta,Mo)C ceramics, prepared at 2000 ℃ and 35 MPa, the hardness was slightly decreased from 25.06±0.32 to 24.11±0.75 GPa, but the toughness was increased from 2.25±0.22 to 4.07±0.13 MPa·m^1/2. This work provides a new strategy for low-temperature densification of high-entropy carbides with both high hardness and high toughness.