In situ synthesis and densification of submicrometer-grained B 4C–TiB 2 composites by pulsed electric current sintering

Abstract

B 4C composites with 15 and 30 vol% TiB 2 were pulsed electric current sintered from B 4C–TiO 2–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 B 4C–TiB 2 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 TiO 2 to TiB 2 was a complex process in which TiO 2 is initially converted to TiB 2 with B 2O 3 as intermediate product at 1400–1700 °C. At 1900–2000 °C, B 2O 3 reacted with C forming B 4C and CO. The B 4C and TiB 2 grain size in the fully densified 30 vol% TiB 2 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.