Formation of Carbide Segregations in Nanoscaled Hardmetals

摘要

The use of nanoscaled tungsten carbide (WC) powders allows the production of very fine andnanoscaled hardmetals. These hardmetals show very high hardness values, while keeping a goodfracture toughness. To inhibit grain growth so called grain growth inhibitors (GGI) such as VC andCr_3C_2 are commonly added. In order to keep the grain size below 200 nm higher amounts of GGI thannormally are added. Due to the high amount of GGI carbides often carbide segregations with a size ofup to 20 μm are detected. To limit the size and formation of such segregations different approacheswere studied. It could be shown that the formation is strongly dependent on the carbon content of thehardmetal as well as on the kind and amount of inhibitor used. A mechanism for the formation of V-,Cr- and V-+Cr-rich segregations is proposed.