High pressure sintering of diamond-SiC composite

Sintered polycrystalline compacts in the system diamond-10-50 wt% SiC havin g average grain size of less than 1 mum were prepared at pressure of 6 GPa and temperature between 1400 and 1600 degreesC. Knoop indentation hardness of the compacts increased with diamond content and sintering temperature, a nd specimens with a Knoop indentation hardness greater 40 GPa were obtained . It was found that small amount of Al addition into the starting diamond-S iC powder was effective to improve relative density and Knoop indentation h ardness of the compacts. The formation of graphite was also suppressed by t he addition of Al. Microstructure observation by SEM and TEM suggested that Al segregated at the grain boundary and promoted the bonding between grain s. Thin microtwins were observed in diamond grains, whereas fine wavy struc tures with slightly different orientations were observed in SiC grains, wit h or without Al addition. (C) 2001 Kluwer Academic Publishers.