High resolution microscopy study in Cr3C2-doped WC-Co

Microstructure in Cr3C2-doped WC-Co was examined by high-resolution electron microscopy (HRTEM) and X-ray energy dispersive spectroscopy (EDS) with a special interest in the segregation of Cr at WC/Co interfaces and WC/WC grain boundaries. The macroscopic morphology of carbide grains in Cr3C2-doped WC-Co was almost the same as that of non-doped one, however, doping of a small amount of Cr3C2 on WC-Co was found to be effective to reduce the grain size of carbide grains. HRTEM study revealed that both WC/Co and WC/WC interfaces were free from secondary phases or amorphous films. Nano-probe EDS analysis revealed that Cr segregated at both WC/Co and WC/WC interfaces in the Cr3C2 doped WC-Co. The grain growth retardation of carbide grains observed in the Cr3C2-doped WC-Co must be closely related to the segregation of Cr. On the other hand, an asymmetric tilt Σ2 grain boundary of WC/WC was observed in the grain orientationof (0001)//(11\(.overline 2 \)0), [1\(.overline 2 \)10]//[\(overline 1\)101]. The formation of this coherent boundary results from a small misfit of about 2% in a/c-axis of WC hexagonal lattice structure. The segregation of Cr and Co was detected also at this boundary in spite of high coherent boundary. This would be due to a small distortion of the grain boundary from an ideal Σ2 boundary.