Tuning mechanical and electrical performances of B₄C–TiB₂ ceramics in a two-step spark plasma sintering process

B₄C–TiB₂ is an advanced electrically conductive ceramic with excellent mechanical and electrical discharge machinable properties. It is challenging and rewarding to achieve highly conductive and hard B₄C–TiB₂ composites at a minimum content of conductive TiB₂ that has inferior hardness but double specific gravity of the B₄C matrix. A novel strategy was used to construct conductive networks in B₄C‒15 vol% TiB₂ composite ceramics with B₄C, TiC, and amorphous B as raw materials by a two-step spark plasma sintering method. The influences of particle size matching between B₄C and TiC on the conducting of the strategy and the microstructure were discussed based on the selective matrix grain growth mechanism. The mechanical and electrical properties were also systematically investigated. The B₄C–15 vol% TiB₂ composite ceramic prepared from 10.29 µm B₄C and 0.05 µm TiC powders exhibited a perfect three-dimensional interconnected conductive network with a maximum electrical conductivity of 4.25×10⁴ S/m, together with excellent mechanical properties including flexural strength, Vickers hardness, and fracture toughness of 691±58 MPa, 30.30±0.61 GPa, and 5.75±0.32 MPa·m^1/2, respectively, while the composite obtained from 3.12 µm B₄C and 0.8 µm TiC powders had the best mechanical properties including flexural strength, Vickers hardness, and fracture toughness of 827±35 MPa, 32.01±0.51 GPa, and 6.45±0.22 MPa·m^1/2, together with a decent electrical conductivity of 0.65×10⁴ S/m.