Fabricating toughened super-hard B4C composites at lower temperature by transient liquid-phase assisted spark plasma sintering with MoSi2 additives

Toughened, super-hard B4C triplex-particulate composites were densified by spark plasma sintering with MoSi2 additives (5, 10, and 15 vol.%) at temperatures in the range 1750-1850 degrees C at which the reference monolithic B4C ceramics are porous. It is proved that MoSi2 is a reactive sintering additive that promotes densification by transient liquid-phase sintering, thus yielding fully-dense B4C-MoB2-SiC composites at relatively lower temperatures. Specifically, the MoSi2 first reacts at moderate temperatures (< 1150 degrees C) with part of B4C to form MoB2, SiC, and Si. This last is a transient component that eventually melts (at similar to 1400 degrees C), contributing to densification by liquid-phase sintering, and then (at 1500-1700 degrees C) reacts with free C present in the B4C starting powders to form more SiC, after which densification continues by solid-state sintering. It is found that these B4C-MoB2-SiC composites are super-hard (similar to 30 GPa), tough (similar to 3-4 MPa m(1/2)), and fine-grained, a combination that renders them very appealing for structural applications. Finally, research opportunities are discussed for the future microstructural design of a novel family of toughened, ultra-hard/super-hard multi-particulate composites based on B4C plus refractory borides and carbides.