Effects of particle size and additives on phase transformation of cubic BN during the spark plasma sintering

Abstract Cubic boron nitride (cBN) powders with different particle sizes ranging from 250 nm to 6 µm were sintered at temperatures between 800°C and 1450°C under a pressure of 100 MPa using spark plasma sintering (SPS). Elevated sintering temperatures promoted phase transformation from cubic to hexagonal BN phase. It is found that the activation energy for phase transition increased dramatically with cBN particle sizes, ranging from 43 to 739 kJ •mol −1 . Additionally, the addition of various oxide additives (Al 2 O 3 , Y 2 O 3 , ZrO 2 , SiO 2 , and MgO) induced distinct effects on cBN phase transformation during the SPS process. Among these, SiO 2 was observed to retard the transformation due to the separating effect of amorphous SiO 2 , whereas other additives accelerated the transformation by reducing the activation energy of cBN.