Sintering pure polycrystalline boron carbide bulks with enhanced hardness and toughness under high pressure

Boron carbide ceramics possess high hardness, but they generally are subjected to low toughness due to strong covalent bonds. However, the fabrication of dense and pure polycrystalline boron carbide bulks with excellent mechanical properties by conventional methods remains a significant challenge. Here, the fine-grained and pure polycrystalline boron carbide bulks have been successfully fabricated utilizing submicron-sized boron carbide powder as starting materials under the condition of high pressure (5.5 GPa) and low temperature range (1000–1400 °C). The well-sintered boron carbide bulk recovered at 1000 °C exhibits a mean grain size of 205.2 ± 191.2 nm and relative density of up to ∼97%, and the measured Vickers hardness and fracture toughness achieve 35.0 ± 2.8 GPa and 4.6 ± 0.5 MPa m0.5, respectively. The outstanding trade-off between hardness and toughness demonstrated that the synergistic effect between fine grain size and dislocation, and the interplay between amorphous grain-boundary phases and pores via grain-boundary sliding have critical role in contributing to improve hardness and toughness, respectively. This study has essential implications in sintering fine-grained and pure polycrystalline engineering ceramics and superhard materials, which provide a tuning approach to enhance the mechanical properties.