A new approach to fabrication of gradient WC–Co hardmetals

WC–Co hardmetals with gradient structure comprising neither η-phase nor grain growth inhibitors were produced for the first time by regulating the WC re-crystallisation and carbon content in their near-surface layer and core. Hardmetals with low Co contents in the surface region were obtained by selective carburisation of the near-surface zone of green articles with the original low carbon content and their consequent liquid-phase sintering. The surface region of such gradient hardmetals has a hardness of up 150 Vickers units higher and fracture toughness significantly superior than those of the core. Gradient hardmetals with high Co contents in the surface region were obtained by selective decarburisation of the near-surface zone of green articles with the original high carbon content and their consequent liquid-phase sintering. The new approach for fabrication of gradient WC–Co materials appears to be a unique tool for increasing both the hardmetal hardness and fracture toughness.