Preparation of superhard cubic boron nitride sintered from commercially available submicron powders

摘要

Using submicron cubic boron nitride (cBN) powder as a starting material, polycrystalline cBN (PcBN) samples without additives were sintered from 8.0-14.0GPa at 1750°C, and their sintering behaviour and mechanical properties were investigated. Transmission electron microscopy analysis showed that high-density nanotwins could be generated from common submicron cBN grains during high pressure and high temperature treatment. The dislocation glide and (111) mechanical micro-twinning are the main mechanisms that underlie plastic deformation in the sintering process, and this contributes to the grain refinement. A refinement in the grain size (~120 nm), micro-defect (nanotwin and stacking faults), and strong covalent bonding between the grains are crucial for improving the sample mechanical properties. The PcBN sintered at 11.0GPa/1750°C possessed outstanding mechanical properties, including a high Vickers hardness (~72 GPa), fracture toughness (~12.4 MPam~(1/2)), and thermal stability (~1273 °C in air).