High resolution microscopy study in Cr3C2-doped WC-Co

Microstructure in Cr3C2-doped WC-Co was examined by high-resolution electro n 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 gra in 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 sm all 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 inte rfaces were free from secondary phases or amorphous films. Nano-probe EDS a nalysis revealed that Cr segregated at both WC/Co and WC/WC interfaces in t he Cr3C2 doped WC-Co. The grain growth retardation of carbide grains observ ed in the Cr3C2-doped WC-Co must be closely related to the segregation of C r. On the other hand, an asymmetric tilt Sigma2 grain boundary of WC/WC was observed in the grain orientationof (0001)//(11 (2) over bar0), [1(2)over bar>10]//[(1)over bar>101]. The formation of this coherent boundary results from a small misfit of about 2% in a/c-axis of WC hexagonal lattice struct ure. The segregation of Cr and Co was detected also at this boundary in spi te of high coherent boundary. This would be due to a small distortion of th e grain boundary from an ideal Sigma2 boundary. (C) 2001 Kluwer Academic Pu blishers.