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

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 m^1/2 respectively; representing an increase of 3.5 GPa (10.5 %), 225 MPa (47.3 %), and 1.72 MPa m^1/2 (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.