Microstructure and mechanical properties of WC-10Co cemented carbides sintered from nanocrystalline spray conversion processed powders

Abstract

Mechanical properties and microstructure of nanocrystalline WC-10Co cemented carbides were investigated. The nanocrystalline WC-10Co cemented carbide powders were manufactured by reduction and carbonization of the nano-crystalline precursor powders which were prepared by the spray drying process the of solution containing ammonia meta-tungstate (AMT) and cobalt nitrate. The WC powders which diameter were about 100 nm mixed homogeneously with Co binder phase and were sintered at 1375°C under the pressure of 1 mtorr. In order to compare the microstructure and mechanical properties with the nanocrystalline WC-10Co, commercial WC powders with diameters of 0.57-4 μm were mixed with Co powders, and were sintered at the same condition with that of nanocrystalline powders. TaC, Cr3C2 and VC of varying amounts 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, a 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 the WC grain size following the Hall-Petch type relationship. The fracture toughness of WC-10Co cemented carbides increases with increasing the HCP/FCC ratio of Co binder phase by HCP/FCC phase transformation.