Effects of added diamond powder on the reaction sintering behaviour of diamond in the graphite-nickel system

Polycrystalline diamond sintered compact was prepared under high pressure and temperature conditions (7 GPa, 1700°C, 10 to 30min) from the starting material with the composition of the system 50 wt% carbon (diamond + graphitized pitch coke (GPC))-50 wt% Ni. The effects of added diamond powder on the microstructure of the sintered compact and reaction sintering behaviour were investigated. The grain size of diamond in the sintered compact decreased remarkably from 20 to 40m to 2 to 3m on addition of 10 to 20 wt% diamond powder (grain size: 1m) to the GPC-Ni system. The grain size can be controlled by that of the added diamond powder. A sufficient supply of carbon from GPC plays an important role in the formation of a covalently bonded compact of diamond. The grain growth of the formed diamond is depressed by the coexistence of diamond powder, which controls the solubility of carbon in the metal-carbon system and also the grain growth process by solution-reprecipitation.