Novel Rapid Discharge Sintering Technique for Damage Free Diamond MMCs

摘要

This study compares the performance of metal matrix composites (MMC) sintered using a novel microwave plasma processing technique called Rapid Discharge Sintering (RDS) and conventional tube furnace sintering. The MMC composites were prepared from nickel-diamond powder mixtures containing 1 urn nickel and 6-12 μm diamond powders. These mixtures were pressed uni-axially at compaction pressures of 300 MPa. The samples were sintered using both the furnace and RDS treatments at temperatures between 850 and 1050°C. The tube furnace sintering study was carried out in argon gas at atmospheric pressure. 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. The sintered nickel-diamond composites were characterised based on density measurements, flexural strength, SEM and XRD, analysis. A significantly reduction in sintering times were achieved using the RDS technique for which firing process takes 10 minutes, compared with several hours for the tube furnace treatments. A further advantage of the RDS treatments was the absence of any peaks in the XRD spectrum of the sintered composites associated with diamond graphitization. These peaks were observed for the furnace treated composites indicating some graphitization of the diamond during the sintering process.