Location of VC in VC, Cr3C2 codoped WC-Co cermets by HREM and EELS

The microstructure of sintered WC-Co composites doped with VC and Cr3C2 is investigated by several techniques (TEM. HREM, EDXS, EELS) in order to accurately locate the VC phase. Small VC precipitates are frequently found at the junction between two WC grains in the corner of cobalt pockets. Due to the good match between the WC and VC parameters, the VC grains adopt a preferential orientation with regards to WC: (111)(vc)//(0001)(wc) with ((1) over bar 10)(vc)//((1) over bar2 (1) over bar 00(wc). Moreover steps along the (1 1 20)wc directions are observed at the interface between cobalt and WC. Small VC precipitates lying on the (0001)(wc) and {10 (1) over bar0}(wc) facets of the steps are identified. A thin VC layer less than 1 nm thick covering all (0001)(wc) surfaces of WC grains is also pointed out. Some WC grain boundaries contain a thin film of VC phase whereas some high coincidence grain boundaries seem to be free from second phase. (C) 2002 Elsevier Science Ltd. All rights reserved.