Processing and properties of polycrystalline cubic boron nitride reinforced by SiC whiskers

Dense polycrystalline cBN (PcBN)-SiCw composites were fabricated by a two-step method: First, SiO2 was coated on the surface of cubic boron nitride (cBN) particles by the sol-gel method. Then, silicon carbide whisker (SiCw)- coated cBN powder was prepared by carbon thermal reaction between SiO2 and carbon powders at 1500 degrees C for 2 hour. Then, cBN-SiCw complex powders were sintered by high-pressure and high-temperature sintering technology using Al, B, and C as sintering additives. The phase compositions and microstructures of cBN-SiCw composites were investigated by X-ray diffraction and scanning electron microscopy, respectively. It was found that the SiCw and Al3BC3 had been fabricated by in situ reaction, which cannot only promote densification but also improve mechanical properties. The relative density of PcBN composites increased from 96.3% to 99.4% with increasing SiCw contents from 5 to 20 wt%. Meanwhile, the Vickers hardness, fracture toughness and flexural strength of as-obtained composites exhibited a similar trend as that of relative density. The composite contained 20 wt% of SiCw exhibited the highest Vickers hardness and fracture toughness of 42.7 +/- 1.9 GPa and 6.52 +/- 0.21 MPa center dot m(1/2), respectively. At the same time, the flexural strength reached 406 +/- 21 MPa.