In situ synthesis of polycrystalline cubic boron nitride with high mechanical properties using rod-shaped TiB ₂ crystals as the binder

Polycrystalline cubic boron nitride (PcBN) was sintered in the temperature range of 1050–1650°C under an ultra-high pressure of 5.0 GPa for 20 min using an in situ synthesis method. X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy and energy-dispersive spectrometry were used to study the compositional and morphological changes during the synthetic process. The results showed that rod-shaped TiB2 crystals could be detected at 1150°C, and their quantity increased with sintering temperatures. The TiB2 crystals distributed homogeneously and grew randomly among the cBN grain boundaries and interstitial spaces, ultimately forming an interlocking structure. The PcBN prepared at 1650°C exhibited optimal comprehensive mechanical properties, with a micro-hardness of 44.42 GPa and a flexural strength of 862.5 MPa. Moreover, based on the experimental results, the chemical reaction mechanism and the strengthening mechanisms occurred during the sintering process were also proposed to properly interpret the synthesis of PcBN.