Mechanical and tribological properties of dense B4C/graphite composites prepared with nanodiamond as additive

Boron carbide (B 4 C) ceramics have inherent limitations in terms of fracture toughness (<3 MPa·m ½ ) and sinterability. Graphite can improve both sintering and toughening while reducing friction, but it is limited by poor dispersion and weak interfacial bonding strength. To address these issues, we developed an in-situ graphite-toughened B 4 C composite using nanodiamonds (NDs) precursor via spark plasma sintering (SPS). During sintering, NDs transform into graphite, achieving uniform carbon dispersion and producing dense composites (>97 % of the theoretical density) at a moderate sintering temperature of 1800 °C. Through composition optimization, the B 4 C/graphite composite containing 10 wt% graphite achieved an optimal balance among hardness of 27.1 GPa, flexural strength of 457 MPa, fracture toughness of 3.91 MPa·m ½ , and wear rate of 26.7 × 10 −6 mm 3 /(N⋅m). Compared to B 4 C monoliths, the toughness increased by 51 %, and the wear rate decreased by 25 %. The mechanism behind the enhanced toughness primarily stems from crack deflection/bridging, and graphite pull-out effect, while the improved wear resistance is mainly attributed to the lubricating effect formed by exfoliated graphite. Although hardness decreases marginally, composites with graphite content exceeding 5 wt% exhibit improved toughness and wear resistance, demonstrating their potential application in armor and cutting tools. This work provides a scalable in situ toughening strategy that resolves longstanding dispersion and bonding issues in B 4 C composites while balancing hardness, toughness and wear resistance.