Structure and role of the interfacial layers in VC-rich WC-Co cermets

Abstract

The microstructure of WC-Co composites sintered with VC or with a mixture of VC and Cr3C2 is investigated by several techniques in order to understand the grain growth inhibition process. In this work, using the high-resolution transmission electron microscopy and high-resolution energy-filtering electron microscopy, we are able to study on the atomic scale the microstructure and composition of the phases present in the alloys. A thin (VW)C x layer less than 1 nm thick covering all surfaces of WC grains and thin (VW)C x platelets embedded in the WC grains are evidenced. Microsteps are observed at the interface between Co and WC along the ⟨11amp;2macr;0⟩WC directions. Small (VW)C x precipitates lie on the (0001)WC and {10amp;1macr;0} facets of these steps. On the (0001) surface of WC grains, other stacking sequences of the metal planes are sometimes observed and, in particular, the occurrence of the compound (VW)2C is shown. Owing to these observations a grain growth inhibition mechanism is proposed.