Mechanical properties of WC-10Co cemented carbides sintered from nanocrystalline spray conversion processed powders

摘要

Mechanical properties and microstructures of nanocrystalline WC-10Co cemented carbides were investigated. The nanocrystallineWC-10Co cemented carbide powders were manufactured by reduction and carbonization of the nanocrystalline precursor powders which were prepared by spray drying process of solution containing ammonia meta-tungstate (AMT) and cobalt nitrate. The WC powders were about 100 nm in diameter mixed homogeneously with Co binder phase and were sintered at 1375 deg C under a pressure of 1 mTorr. In order to compare the microstructures and mechanical properties with those of nanocrystalline WC-10Co, commercial WC powders in a diameter range of 0.57-4#mu#m were mixed with Co powders, and were sintered at the same conditions as those of nanocrystalline powders. TaC, Cr_3C_2 and VC of varying amount were added into nanocrystalline WC-10Co cemented carbides as grain growth inhibitors. To investigate the microstructure of Co binder phase in the WC-10Co cemented carbides, Co-W-C alloy was fabricated at the temperature of sintering process for the WC-10Co cemented carbides. The hardness of WC-10Co cemented carbides increased with decreasing WC grain size following a Hall-Petch-type relationship. The fracture toughness of WC-10Co cemented carbides increases with increasing HCP/FCC ratio of Co binder phase by HCP/FCC phase transformation.