Laser/waterjet heat treatment of polycrystalline cubic/wurtzite boron nitride composite for reaching hardness of polycrystalline diamond

Abstract

We report a heat treatment technique that enabled the hardness of polycrystalline cubic/wurtzite boron nitride composite to reach that of polycrystalline diamond. The process consists of surface heating the composite using a continuous wave laser followed by tandem waterjet quenching of the laser beam path to cause stress-induced phase transitions. Visual examination indicated a change in optical transparency through a color change from black to white. Raman spectroscopy revealed the partial transformation of wBN to cBN and formation of amorphous boron. Vicker's microhardness test showed a dramatic increase in the nominal hardness from 40 to 75 GPa. © 2012 Elsevier B.V.