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

Abstract

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 30vol% 10–14µm cBN/WC–Co composite (P14V30) exhibited high hardness (18.3GPa, 1200°C) and high fracture toughness (15.6MP·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.