In situ synthesis and densification of submicrometer-grained B4C-TiB2 composites by pulsed electric current sintering

B₄C composites with 15 and 30 vol% TiB₂ were pulsed electric current sintered from B₄C-TiO₂-carbon black mixtures in vacuum at 2000 °C. Full densification could be realised when applying an optimized loading cycle in which the maximum load is applied after completion of the B₄C-TiB₂ powder synthesis, allowing degassing of volatile species. The influence of the sintering temperature on the phase constitution and microstructure during synthesis and densification was assessed from interrupted sintering cycles. The in situ conversion of TiO₂ to TiB₂ was a complex process in which TiO₂ is initially converted to TiB₂ with B₂O₃ as intermediate product at 1400-1700 °C. At 1900-2000 °C, B₂O₃ reacted with C forming B₄C and CO. The B₄C and TiB₂ grain size in the fully densified 30 vol% TiB₂ composite was 0.97 and 0.63 μm, combining a Vickers hardness of 39.3 GPa, an excellent flexural strength of 865 MPa, and modest fracture toughness of 3.0 MPa m^1/2.