Tuning mechanical and electrical performances of B ₄C–TiB ₂ 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 the 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, electrical properties were also systematically investigated. 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·m1/2, 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·m1/2, together with a decent electrical conductivity of 0.65×10⁴ S/m.