Investigation on the preparation and machinability of the B4C/BN nanocomposites by hot-pressing process

The machinable B4C/BN nanocomposites were fabricated by the hot-pressing process using the B4C/BN nanocomposite powders at 1850 °C for 1 h under the pressure of 30 MPa. The nanocomposite powders with the microstructure of micro-sized B4C particles coated with amorphous nano-sized BN particles were prepared by the chemical reaction of H3BO3 and CO(NH2)2 on the surface of B4C particles at high temperature. Then the amorphous BN transformed into the hexagonal-BN (h-BN) after the hot-pressing process at 1850 °C. The microstructure investigations of the B4C/BN nanocomposites sintered samples showed that the nano-sized h-BN particles were homogenously distributed within the matrix grains as well as at the matrix grains boundaries. With the increasing content of h-BN, the relative density of the B4C/BN nanocomposites decreased gradually. The fracture strength and fracture toughness of the B4C/BN nanocomposites decreased gradually, the fracture strength and fracture toughness of the B4C/BN nanocomposites with the h-BN content of 10 wt.% and 20 wt.% achieved high values. The Vickers hardness of the B4C/BN nanocomposites decreased remarkably with the increasing content of h-BN, while the drilling rates and machinability of the B4C/BN nanocomposites increased significantly. The B4C/BN nanocomposites with the h-BN content more than 20 wt.% exhibited excellent machinability.