Carbon content dependence of grain growth mode in VC-doped WC–Co hardmetals

• VC-doped WC–Co with various carbon contents was prepared by oil quenching.
• (W,V)Cx grain growth inhibition phase covers WC grains in all samples.
• The coverage depends on the carbon content.
• The above points are discussed in terms of interface energy.

Carbon content dependency of grain growth mechanism and grain growth inhibition mechanism in VC-doped WC–Co hardmetals is investigated. VC-doped WC–Co hardmetals with three different carbon contents were sintered with liquid phase and then rapidly quenched to freeze up the structure at the sintering temperature. In these samples, spatial distributions and atomic scale structures of V-rich phases are investigated using transmission electron microscopy (TEM) and related techniques. In these measurements, doped V is found in liquid phase as solute, in large (W,V)Cx precipitates and in interface segregations. Further detailed observations and discussions are carried out for the (W,V)Cx segregated at the WC grain/Co phase interfaces. These (W,V)Cx phases change their form from planar films to small islands depending on the carbon content. The WC grain/Co phase interfaces are fully covered by planar (W,V)Cx in the sample of low carbon content. On the other hand, the WC grain/Co phase interfaces are partially covered by (W,V)Cx islands in the material of high carbon content. During sintering, the WC grains in this sample grew much faster than those in the sample of low carbon content. These structural differences are discussed in terms of WC grain/(W,V)Cx interface energy.