Novel rapid discharge sintering technique for damage-free diamond metal matrix composites

The performance of diamond/nickel metal matrix composites (MMCs) produced using a novel microwave plasma technique, rapid discharge sintering (RDS), and conventional tube furnace sintering in argon is compared. The MMCs were sintered at temperatures between 850 and 1050°C in both cases. The RDS treatments were carried out at 20 mbar in plasmas containing hydrogen or hydrogen-nitrogen gases. The addition of nitrogen gas to the hydrogen plasma facilitated a substantial increase in composite firing temperatures. A significant reduction in sintering times, to 10 min from several hours, was achieved using the RDS technique. A further advantage of the RDS treatments was the absence of any diamond graphitisation (as detected by X-ray diffraction), which was reflected in higher sintered densities and flexural strength for RDS than for furnace sintering.