Extreme Hardness Achievements in Binderless Cubic Boron Nitride Tools

Summary, in English

Binderless cubic boron nitride tools are available in two forms: single phase cBN and dual phase wBN/cBN (w is

wurtzite phase). In this work, a novel heat treatment process involving surface heating using a continuous wave

CO2 laser followed by tandem waterjet quenching of the laser beam path was applied to increase the hardness of

both forms of boron nitride. Stress-induced phase transitions and nanometric grain sizes accompanying the rapid

quench heat treatment enabled a hardness increase of 20% in single phase cBN (nominal 60 GPa) and 100% in dual

phase wBN/cBN (nominal 75 GPa) that attest the ability of cBN to reach the hardness of polycrystalline diamond

(65-80 GPa). The effects of laser heat treatment are identified by an examination of the changes in phase and

microstructure by Raman spectroscopy, high resolution scanning electron microscopy and X-ray diffraction.