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.

To achieve lightweight B₄C-based composite ceramics with high electrical conductivities and hardness, B₄C–TiB₂ ceramics were fabricated by reactive spark plasma sintering (SPS) using B₄C, TiC, and amorphous B as raw materials. During the sintering process, fine B₄C–TiB₂ composite particles are firstly in situ synthesized by the reaction between TiC and B. Then, large raw B₄C particles tend to grow at the cost of small B₄C particles. Finally, small TiB₂ grains surround large B₄C grains to create a three-dimensional interconnected intergranular TiB₂ network, which is beneficial for an electro-conductive network and greatly improves the conductivity of the ceramics. The effect of the B₄C particle size on the mechanical and electrical properties of the ceramics was investigated. When the particle size of initial B₄C powders is 10.29 µm, the obtained B₄C–15 vol% TiB₂ composite ceramics exhibit an electrical conductivity as high as 2.79×10⁴ S/m and a density as low as 2.782 g/cm³, together with excellent mechanical properties including flexural strength, Vickers hardness (HV), and fracture toughness (K_IC) of 676 MPa, 28.89 GPa, and 5.28 MPa·m^1/2, respectively.