TEM investigation of the interface formation in cubic boron nitride containing α-SiAlON composites

Detailed HRTEM/HRSTEM investigations were carried out on the interface between SiAlON and cBN in order to better understand the transformation mechanisms taking place. The interfacial region was found to consist of nano-crystalline hBN grains embedded in an yttrium-containing oxynitride glass. Although dense layers of hBN were observed on the surface of cBN grains, the presence of a very thin yttrium-containing glass phase was found to exist along the boundary interface. Thus hBN layers adjacent to the cBN grains are not formed by direct solid–solid conversion but are instead caused solely by a slow solution-precipitation process. An increase in sintering temperature was found to promote the grain growth of the nanocrystalline hBN, Mrozowski micro-cracking and thickness of the interfacial region which ultimately result in the deterioration of the mechanical properties of these cBN containing composites.