HREM characterization of VC in doped WC-Co cermets

The microstructure of sintered WC-Co composite doped with VC is investigated by several techniques (TEM, HREM, EDS, 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 <110>vc // <1210>wc. Moreover steps along the <1120>wc directions are observed at the interface between cobalt and WC. Small VC precipitates lying on the (0001)wc facet 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. Most WC grain boundaries contain a thin film of VC phase whereas some high coincidence grain boundaries seem to be free from second phase. (author)