Effect of Sintering Temperature on In Situ Synthesis of Polycrystalline Cubic Boron Nitride in cBN-Al-Ti System

Polycrystalline cubic boron nitride(PcBN) was prepared under a high temperature and an ultra -high pressure using an in situ synthesis method. The influence of sintering temperature on composition, micro-structure, relative density, porosity and mechanical property of the PcBN was investigated by means of X-ray diffraction(XRD), field scanning electron microscopy(FSEM) and energy dispersive spectroscopy(EDS). The results show that the composition of PcBN is translated from intermediate phases to stable phases consist of TiB2, h(hexagonal)AlN and TiN when increasing the sintering temperature in the range of 1400-1600 degrees C under ultrahigh pressure of 5. 5GPa. The cBN particles connect with each other by the reaction product. With the increase of the sintering temperature, the length of rod-shaped crystals of strengthening phase TiB2 decreases and the pore in surface reduces. There exist the extraction and fracture mechanism of the rod-shaped crystals in the fracture process. The porosity is prominent reducing and the relative density increases when increasing the sintering temperature. With further increasing the sintering temperature to 1600 degrees C, the PcBN exhibits optimal comprehensive mechanical properties with a micro-hardness of 44. 1GPa and a flexural strength of 859. 3MPa.