Exceptional strength-toughness-hardness integrated B4C ceramics with synergistic reinforcement of nano-BN and in-situ ceramic phases

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Boron carbide (B4C) ceramics with enhanced mechanical properties were fabricated by incorporating nano boron nitride (nano-BN), obtained through high-energy ball milling (HEBM) using ZrO2 balls as the medium, and utilizing the spark plasma sintering (SPS) technique. During the densification process of B4C/nano-BN composite powders, an in-situ reaction between the B4C matrix and ZrO2 resulted in the formation of ZrB2 ceramic phases at 1200–1300 °C. Additionally, the rapid sintering densification temperature of composites is reduced to 1500–1700 °C, approximately 80 °C lower than that required for pure B4C ceramics. Notably, while maintaining a high relative density (99.5 %), the Vickers hardness, flexural strength, and fracture toughness of B4C ceramics reinforced with synergistic effects of nano-BN and ZrB2 fabricated at 1750 °C are significantly improved to reach values of 36.8 ± 0.15 GPa, 701 ± 12 MPa, and 5.01 ± 0.13 MPa m1/2 respectively; representing an increase of 3.5 GPa (10.5 %), 225 MPa (47.3 %), and 1.72 MPa m1/2 (52.3 %) compared to pure B4C ceramics alone. The multiple reinforcement mechanisms including pinning effects provided by nano-BN and in-situ formed ZrB2 ceramic phases, B4C/ZrB2 grain boundary pressure and intracrystalline pressure within B4C, interlayer dislocations of nano-BN and turbulent layer of B4C/BN boundaries contribute to energy dissipation during fracture processes, such as crack deflection, bridging, propagation hindrance and branching effect; ultimately resulting in exceptional strength-toughness-hardness integrated B4C-based ceramics.