Microstructure and mechanical properties of cBN-WC-Co composites used for cutting tools

Composites containing ultrafine tungsten carbide/cobalt (WC-Co) cemented carbides and 30 vol% cubic boron nitride (cBN) were fabricated by spark plasma sintering technique. The effect of cBN particles on the densification behavior, microstructure, and mechanical properties of the composites were investigated. According to SEM observation of microstructure, cBN particles are uniformly distributed and have excellent bonding with the cemented carbide matrix. X-ray diffraction analysis shows that there is no indication of phase transformation from cBN to hBN. The addition of very hard dispersed cBN to the WC-Co promotes an increase of hardness, but a decrease of flexural strength. The density and the hardness of cBN-WC-Co composites increase with the increase of the sintering temperature. However, it has the highest hardness of 2,170 HV at 1,370 °C and then the hardness decreases with the further increase of the sintering temperature.