Sintering of diamond-cemented carbide-composites

Polycrystalline diamonds - composites of diamond and metals (which are generally alloys of cobalt and tungsten) - are manufactured at high temperature and high pressure. Because of their high hardness the composites have better performances in machining wood, non-metals and light metals. Embedding diamonds in cemented carbides without the high temperature-high pressure-synthesis is an interesting way to improve the wear resistance of hard metals. But during common sintering processes a graphitization of the diamond surfaces occurs. To avoid this graphitization process, composites were made with changed binder compositions and densified with fast sintering processes. Composites consisting of 50 vol-% diamond and 50 vol-% cemented carbides (coated diamond powder with grain size 4 to 8 micron, uncoated diamond powder with grain size 6 to 12 micron, cemented carbides with 20 wt-% Fe-Ni-Co- binder and binderless WC without any metallic binder) were sintered via spark plasma sintering and spark plasma consolidation. Diamond composites with binderless WC and with cemented carbide were sintered to full density, while a graphitization of the diamond crystals were nearly prevented.