Effect of particle size of cubic boron nitride powders on the properties of polycrystalline cubic boron nitride composites

Polycrystalline cubic boron nitride (PcBN) composites were prepared through high-temperature and high-pressure (HTHP) sintering process. Cubic boron nitride (cBN) powders with particle sizes of 0.2, 1, 3, and 8 μm were selected as raw materials, and Al-Co-TiN was employed as a binder. The effect of particle size of initial cBN powders on the microstructure, relative density, flexural strength, microhardness, fracture toughness and abrasive ratio of sintered PcBN composite were systematically studied. The results showed that synthesized products were mostly made of cBN, TiN, AlN, TiB₂ and CoN phases. The mechanical properties of sintered PcBN composites first increased and then decreased with a reduction in the particle size of cBN powders. When the particle size of initial cBN powder was 1 µm, the binder was observed to be evenly distributed around the cBN grains in the sintered product. Moreover, there was a close bonding between cBN grains and the binder in the sintered product when the particle size of initial cBN powders was 1 µm, consequently, the optimal mechanical properties were achieved. The maximum values for relative density, flexural strength, microhardness, fracture toughness and abrasive ratio were 99.1%, 607 MPa, 47.06 GPa, 6.52 MPa·M^1/2 and 7125, respectively.