Cr-rich layer at the WC/Co interface in Cr-doped WC-Co cermets:: segregation or metastable carbide?

The effect of Cr on the microstructure of WC-Co alloys after liquid-phase sintering is studied as a function of the C content of the alloy and for two Cr for Co substitution ratio. The distribution of Cr is investigated using X-ray energy dispersive spectrometry. A Cr enrichment at WC/Co interfaces is detected for both C- and W-rich alloys. The observations by high-resolution electron microscopy point out a thin face centred cubic layer at the interface between WC and Co. This layer has grown epitaxially on the surface of the WC grains with two orientation relationships depending on the WC plane. The lattice parameter mismatch is close to 0.2% for the basal plane and less than 3% for the prismatic plane of WC. The composition and crystal structure of this compound correspond to the metastable (Cr,W)C phase that is stabilized by the low energy of the WC/(Cr,W)C interface. (C) 2004 Elsevier B.V. All rights reserved.