Pulse electric current sintering of cubic boron nitride/tungsten carbide-cobalt (cBN/WC-Co) composites: Effect of cBN particle size and volume fraction on their microstructure and properties

Cubic boron nitride/tungsten carbide-cobalt (cBN/WC-Co) composites were fabricated by pulse electric current sintering (PECS), using Ni-P as sintering additives to promote low temperature densification. The effect of cBN particle size and volume fraction on the densification, microstructure and mechanical properties of WC-Co composites was investigated. There was no phase transformation from cBN to hBN (hexagonal BN) with low-hardness due to low sintering temperature (1100-1200 °C) and short sintering time. Smaller cBN particle led to lower sinter-ability of the composites due to its high specific surface area. The 30 vol% 10-14 µm cBN/WC-Co composite (P14V30) exhibited high hardness (18.3 GPa, 1200 °C) and high fracture toughness (15.6 MP·m1/2, 1000 °C). The high hardness resulted from the homogeneously dispersed cBN particles, which had a good bonding with the WC matrix. Increased fracture toughness was mainly attributed to crack deflection or bridging and pullout of cBN grains.