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

Abstract

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 η 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.