High Hardness and High Toughness Si₃N₄–SiC_w–ZrB₂ Ceramics Prepared by Low-Temperature Hot Pressing

Low-temperature hot pressed Si₃N₄ ceramics show a greater Vickers hardness and a lower fracture toughness, while high-temperature hot pressed Si₃N₄ ceramics show a lower Vickers hardness and a higher fracture toughness. To prepare Si₃N₄ ceramics with a great Vickers hardness and a high fracture toughness, a low-temperature hot pressed Si₃N₄ ceramic was prepared via sintering at 1500 ℃ with 20% SiC whisker (SiC_w, in volume fraction) and 2.5% ZrB₂. The phase composition, relative density, microstructure and mechanical properties of low-temperature hot pressed Si₃N₄ ceramic were investigated, compared with high-temperature hot pressed Si₃N₄ ceramics at 1800 ℃ . The results show that the addition of SiC_w inhibits the densification of Si₃N₄ ceramics sintered at 1500 ℃ , and the relative density decreases from 97.9% to 92.9%, the Vickers hardness decreases from 20.5 GPa to 16.4 GPa, and the fracture toughness increases from 2.9 MPa·m^1/2 to 3.4 MPa·m^1/2. However, the addition of SiC_w and ZrB₂ promotes the phase transition from α-Si₃N₄ to β-Si₃N₄. The relative density of Si₃N₄–SiC_w–ZrB₂ reaches 97.5%, and the Vickers hardness and fracture toughness are 20.7 GPa and 5.1 MPa·m^1/2, respectively. Compared with low-temperature hot pressed Si₃N₄ ceramic, the fracture toughness of Si₃N₄–SiC_w–ZrB₂ ceramic is improved without reducing the Vickers hardness. Compared with high-temperature hot pressed Si₃N₄ ceramic, the hardness is greatly improved. The Si₃N₄–based ceramic with high hardness and toughness prepared via a low-temperature hot pressing with SiC_w and ZrB₂ can have a promising application in ceramic structural parts.