Synthesis and characterization of cubic boron nitride (Al)-Al2O3 composites under high pressure and high temperature conditions

Cubic boron nitride (cBN) (Al)-Al2O3 composites were synthesized by Chinese multi-anvil high pressure apparatus (CHPA) sintering at 5.0 GPa and 1200-1500 & nbsp;C using Al-coated cBN (cBN (Al)) and Al2O3 powders. The effects of Al coating, phase composition, densification, Vickers hardness and thermogravimetry of the composites were investigated. Al coating on cBN powder activated the surface of cBN in the composites and reacted with cBN to produce AlN under high pressure and high temperature (HPHT) environment, which helped to promote the bonding strength of cBN and Al2O3. The hardness of cBN (Al) + 15 vol% Al2O3 is 29.7 GPa when sintered at 5.0 GPa and 1350 degrees C. Compared to cBN-Al2O3 composites, the hardness of cBN (Al)-Al2O3 composites increased by 37.5%. AlN, the reaction product of cBN with Al under HPHT environments, acts as a bridge phase and joins the two phases of cBN and Al2O3 in the form of chemical bonds. This is the intrinsic mechanism of hardness improvement of cBN (Al)-Al2O3 composites.