Mechanical properties, phases and microstructure of ultrafine hardmetals prepared by WC–6.29Co nanocrystalline composite powder

Abstract

WC–6.29Co nanocrystalline composite powder prepared by spray thermal decomposition–continuous reduction and carburization technology was consolidated by spark plasma sintering (SPS), spark plasma sintering with hot isostatic pressing (HIP), vacuum sintering and vacuum sintering with hot isostatic pressing (HIP). The mechanical properties, phases and microstructure of WC–6.29Co hardmetals prepared by different processes were researched. The results show that WC–6.29Co ultrafine cemented carbide consolidated by spark plasma sintering with hot isostatic pressing can reach 99.0% relative density, and transverse rupture strength (TRS) is more than 2740 MPa, Rockwell A hardness (HRA) is more than 93.8, the average grain size is less than 400 nm, and WC–6.29Co ultrafine cemented carbide with excellent properties is achieved. Although specimens consolidated by spark plasma sintering can reach 99.1% relative density, Rockwell A hardness is more than 94, but transverse rupture strength (TRS) is very low. Compared with specimens prepared by spark plasma sintering, there are no eta phases in specimens consolidated by spark plasma sintering with hot isostatic pressing. Furthermore the average grains size of specimens prepared by vacuum sintering or vacuum sintering with hot isostatic pressing is coarser than that of specimens prepared by spark plasma sintering with hot isostatic pressing, but mechanical properties are lower than that of specimens prepared by spark plasma sintering with hot isostatic pressing. Spark plasma sintering with hot isostatic pressing can not only decrease the average grain size of sintered specimens, but also increase mechanical properties of WC–6.29Co ultrafine cemented carbide. The specimens prepared by spark plasma sintering with hot isostatic pressing have better properties than those prepared by spark plasma sintering, vacuum sintering or vacuum sintering with hot isostatic pressing.