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 m1/2.