Sintering of nano-sized WC-Co powders produced by a gas reduction-carburization process

摘要

Nanocrystalline cemented tungsten carbide has attracted considerable interests for use in cutting tool because of its superior mechanical properties. In this study, nano-sized powders of mixed WC and Co were prepared from attrition-milled oxides by a gas reduction-carburization process. The effects of compacting pressure, heating schedule, additional ball-milling, and the presence of a grain growth inhibitor on the sintering properties of the nano-sized WC-Co powders were examined. The grain size and phases in WC-Co alloy were clearly affected by compacting pressure. Because of the trapped gases and the lower melting point of the cobalt binder, when a compact of nano-sized WC-Co powder was sintered through a heating schedule with holding steps, the sintered alloy maintained the small size of WC grains without any eta phase. In addition, the additional ball-milling improved the microstructure and mechanical properties of the nano-sized WC-Co powder by producing a more uniform distribution of carbon. The addition of VC led to uniformity in microstructure and mechanical properties, even though significant carbon loss occurred.