cBN-Al-HfC composites: Sintering behaviors and mechanical properties under high pressure

Cubic boron nitride (cBN) composites, using Al and HfC as the additives, were sintered under static high pressure of 5.0 GPa and at temperatures of 700 °C-1500 °C for 80 s. By analyzing the phase components of the sintered samples through the X-ray diffraction (XRD) analysis, we found that when the temperature increased from 700 °C to 900 °C, cBN reacted with Al and HfC, and produced AlN, AlB2, HfB2 and B2C5N2. Above 1000 °C, AlB2 was not stable. It decomposed and finally generated AlB12. At the meantime, the content of AlN, AlB12, HfB2 and B2C5N2 increased with Al disappearing. The Vickers hardness of the sintered samples increased with increasing the cBN content. The SEM and the abrasion ratio tests revealed that the well-sintered samples with homogeneous microstructure and the best wear resistance could be obtained at 5.0 GPa, 1300 °C for 80 s with the cBN content of 80 wt.%.