Microstructure, Mechanical and Thermal Properties of Hot-pressed TiB₂ Ceramics with B₄C and Phenolic Resin-Derived Carbon Sintering Additives

TiB₂ is a ceramic material known not only for its excellent thermal and mechanical properties but also for its machinability via electrical discharge machining. However, due to its low sinterability, the high sintering temperature required to achieve a fully densified microstructure restricts the wide application of TiB₂. Here, we used B₄C and phenolic resin-derived C (P.R.-C) as sintering additive to improve sinterability by promoting grain refinement and providing pathways for the release of entrapped gas, thereby achieving a dense microstructure. As a result, the finer microstructure enhanced flexural strength and hardness while reducing thermal conductivity. The residual P.R.-C, present after exceeding the required amount of C for carbothermal reduction, improved the sinterability of TiB₂ by inhibiting grain growth, resulting in enhanced densification. Consequently, the fine-grained microstructure increased flexural strength and hardness, reaching 567.7 MPa and 24.6 GPa at 2.5 wt% P.R.-C. However, the thermal conductivity decreased due to the presence of residual P.R.-C, dropping to 91.6 W.m⁻¹.K⁻¹ at 3.0 wt% P.R.-C. This highlights the possibility for engineering the microstructure, mechanical and thermal properties of TiB₂ by incorporating P.R.-C.