The wurtzite phase of boron nitride(wBN)is obtained in large quantities by shock loading graphitic boron nitride(gBN).The sintering of wBN powder at high pressure and temperatures leads to the conversion of wBN to the cubic boron nitride phase(cBN).Compacts with varying amounts of cBN CAN be obtained by controlling the pressure, temperature and time.The wBN-cBN composites with 45-55 % cBN have hardness in the range 30-70 GPa fracture toughness 13-16 MPa m and thermal conductivity 40-50 W m-1 K-1.The composite has a hot hardness of about 20 GPa at 1400 K. The unique combination of high hardness and fracture toughness makes the composite tool capable of machining under interupted conditions.The processing of wBN for cutting tool applications,the characterization of the tools and the performance of the composite tools in the machining of hardened steels(HRC 40-63),high nickel cast iron(BHN 120-160)and Ti-6A1-4V alloy(HV 310)are presented in this pape
