タングステン-コバルト混合粉における炭化タングステンの生成過程

抄録

The carbide formation process in tungsten-cobalt mixed powder was investigated by carburizing of tungsten plates. The carbides are formed uniformly at the whole surface of pure tungsten, where W₂C and WC are formed succesively and the rate-determining stage is the diffusion of carbon in WC.
While in tungsten covered with cobalt, carbides are formed preferentially at the surface of tungsten being in contact with cobalt. Coexisting cobalt with tungsten M₆C(η-W₃Co₃C etc.) and WC are formed by the reaction of W₂C with Co after the formation of W₂C, and then WC is formed by the reaction of M₆C with C. Cobalt is observed in the M₆C layer and at grain boundaries of the WC layer, and it promotes the diffusion of carbon into the inner part of the carbide layer. The rate of carbide forming from tungsten-cobalt mixture deviates from the parabolic law, since the amount of cobalt in the carbide layer increases with the carburizing time and temperature. The rate-determining process of carbide formation in the tungsten-cobalt mixture is the diffusion of carbon in the carbide layer containing cobalt.