Hardness and toughness improvement of SiC‐based ceramics with the addition of (Hf 0.2 Mo 0.2 Ta 0.2 Nb 0.2 Ti 0.2 )B 2

Abstract The influences of different contents ranging 0–15 wt% of high‐entropy boride (HEB) (Hf 0.2 Mo 0.2 Ta 0.2 Nb 0.2 Ti 0.2 )B 2 on the mechanical properties of SiC‐based ceramics using Al 2 O 3 ‐Y 2 O 3 sintering additives sintered by spark plasma sintering process were investigated in this study. The results showed that the introduction of 5 and 10 wt% (Hf 0.2 Mo 0.2 Ta 0.2 Nb 0.2 Ti 0.2 )B 2 could facilitate the densification and the grain growth of SiC‐based ceramics via the mechanism of liquid phase sintering. However, the grain growth of SiC‐based ceramics was inhibited by the grain boundary pinning effect with the addition of 15 wt% (Hf 0.2 Mo 0.2 Ta 0.2 Nb 0.2 Ti 0.2 )B 2 . The SiC‐based ceramics with 15 wt% (Hf 0.2 Mo 0.2 Ta 0.2 Nb 0.2 Ti 0.2 )B 2 showed the enhanced hardness (21.9±0.7 GPa) and high toughness (4.88±0.88 MPa·m 1/2 ) as compared with high‐entropy phase‐free SiC‐based ceramics, which exhibited a hardness of 16.6 GPa and toughness of 3.10 MPa·m 1/2 . The enhancement in mechanical properties was attributed to the addition of higher hardness of HEB phase, crack deflection toughening mechanism, and presence of residual stress due to the mismatch of coefficient of thermal expansion.