Sintered polycrystalline compacts in the system diamond-10-50 wt% SiC having 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, and specimens with a Knoop indentation hardness greater 40 GPa were obtained. It was found that small amount of Al addition into the starting diamond-SiC powder was effective to improve relative density and Knoop indentation hardness of the compacts. The formation of graphite was also suppressed by the addition of Al. Microstructure observation by SEM and TEM suggested that Al segregated at the grain boundary and promoted the bonding between grains. Thin microtwins were observed in diamond grains, whereas fine wavy structures with slightly different orientations were observed in SiC grains, with or without Al addition. (C) 2001 Kluwer Academic Publishers. [References: 13]
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